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Copyright © 1996-97 Specialized Systems Consultants, Inc. linux@ssc.com


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Table of Contents Issue #15


The Answer Guy

Weekend Mechanic will return next month.


The Whole Damn Thing 1 (text)
The Whole Damn Thing 2 (HTML)
are files containing the entire issue: one in text format, one in HTML. They are provided strictly as a way to save the contents as one file for later printing in the format of your choice; there is no guarantee of working links in the HTML version.


Got any great ideas for improvements! Send your comments, criticisms, suggestions and ideas.


This page written and maintained by the Editor of Linux Gazette, gazette@ssc.com


"Linux Gazette...making Linux just a little more fun!"


 The Mailbag!

Write the Gazette at gazette@ssc.com

Contents:


Help Wanted -- Article Ideas


 Date: Wed, 05 Feb 1997 22:34:04 -0800
Subject: Copy from xterm to TkDesk
From: Steve Varadi, svaradi@sprynet.com

I have a question maybe someone know simpler solution for this. I'm using TkDesk because very easy to use and most of the keystroke same as in Win95. If I want to copy something from xterm to an editble file I do following:

Is it any simpler procedure to copy something directly from xterm to TkDesk Editor???

Thanks:
Steve


 Date: Sat, 08 Feb 1997 00:46:33 -0600
Subject: suggestion
From: Daniel Strong, daniels@voyageronline.net

I would like to see an article on internet games that are playable between different OSes... Linux and Win95, Win3.11

Or just internet games in generall....:)

thanks..


 Date: Tue, 120dd1 Feb 1997 17:39:52 +0100
Subject: Help formatting a hard disk
From: Olivier DALOY, daloy@cri.ens-cachan.fr

I am desperately trying to install Sparc Linux on a 1+ box. And I wonder how to format a Hard disk drive, from Sun OS, in Ext2FS type. If you could help me on that point, I would appreciate so much !

BTW too, congratulations for the job you do, I imagine that it's not so easy !!! :-)))

-- Olivier DALOY


 Date: Mon, 17 Feb 1997 13:41:05 +0000 (GMT)
Subject: Animated Gifs From: Andrew Philip Crook, shu96apc@reading.ac.uk

I have made some animated gifs for my web page and they should loop. However, on Netscape 2.02 + for most unix platforms they stop after one cycle.... why!

.... and how can i make them loop?

PS. Great Mag
Andrew Crook.


 Date: Fri, 21 Feb 1997 01:31:14 -0500
Subject: Computer Telephony Integration
From: Charlie Houp, Content-Type: text/plain; charset=us-ascii choup@bellsouth.net

Is there any interest in Computer Telephony Integration (CTI) in the Linux ranks? Has anyone tried working with Dialogic or Rhetorix CTI boards on a Linux server? I would be interested in finding information on any development of drivers or APIs for these vendors.

Thanks
Charlie


General Mail


 Date: Sun, 02 Feb 1997 16:27:02 -0800
Subject: Linux Security
From: jtmurphy, jtmurphy@ecst.csuchico.edu

I notice there is a lack of discussion on Linux Security in LG. Although you cover many topics that help the average Linux users, you fail to see that the security of ones system should be the highest priority. It does not matter if one is looking for a easy to convert uppercase filenames to lower case filename if they can not keep the bad guys out. Please include more discussion on it.

PS. Check out my Web Page (Address Below).
Jason T. Murphy The Linux Security Home Page -> http://www.ecst.csuchico.edu/~jtmurphy

(Actually, I do realize it. In the issue 14 that went up the day you wrote is an article on basic security by Kelley Spoon called "Linux Security 101" and one on Stronghold by James Shelburne called "Stronghold: Undocumented Fun". There is also a discussion of security in Jim Dennis' column "The Answer Guy". --Editor)


 Date: Sat, 01 Feb 1997 15:14:52 -0500
Subject: Great Magazine
From: "Stephen J. Pellicer", stephen@adata.com

I just wanted to write to say what a great job The Linux Gazette is doing. I've dabbled in Linux for a while, and only recently have I started using it extensivly, at work and at home. Like Linux itself online information for the OS is a hit or miss affair. Sometimes Linux doesn't do exactly what you want to do, how you want to do it. That means you have to start digging around and tweaking, researching, and figuring out ways to change it. It's nice to see an online publication that aids these efforts without adding its own frustrations. Your publicaiton is sharp and a service to the Linux community.

Thanks,
Stephens


 Date: Mon, 3 Feb 1997 21:53:41 -0500 (EST)
Subject: TWDT-HTML-14 broken
From: Ken Cantwell, cantwell@afterlife.ncsc.mil

Issue 14's The Whole Damn Thing (HTML) is broken. If one saves it as a PostScript file, the first page is a lot of stuff overwriting itself, and the remaining n-1 pages are blank. And n is quite large.

Ken Cantwell

(Yes, you are right. It is broken. And I didn't have time to fix it until late in the month. Very sorry. --Editor)


 Date: Mon, 3 Feb 1997 18:36:47 CDT
Subject: On XV
From: "Jarrod Henry", jarrodh@ASMS3.dsc.k12.ar.us
Organization: Arkansas School for Math & Science

Hiya...
I was reading LG #14 , and something struck my eye in weekend Mechanic. Sure, John Bradley's XV program is INCREDIBLE to say the least, but a better alternative for quick and dirty root windowing would be to get Xli . Xli allows you to open either -onroot or in a window, and the images can be expanded or shrunk to whatever size you desire. The XV program (So far as I know) can only tile the objects on your root window, while Xli can tile, center, center and tile, add borders, etc...
Xli can be found on sunsite, and thank you for producing such an INFORMATIVE and HELPFUL tool to this energetic Linux user :)

Jarrod Henry


 Date: Thu, 06 Feb 1997 08:50:05 -0500
Subject: My Vim Article From: Jens Wessling, mailto:jwesslin@erim.org

I should have commented in my article on vim that the auto-commenting method I showed should be used carefully. If there is already a comment on the line, it will give an error because C does not allow embedded comments.

--Jens Wessling


 Date: Thu, 6 Feb 1997 14:22:44 +0100 (GMT+0100)
Subject: beating heart
From: Jesper Pedersen, blackie@imada.ou.dk

Your beating haert is very cute, but....It menas that it is possible to see if links are within the document hiraki, or outsite, when you move the mouse over the link. (which matters when one reads it offline). So please reconsider.

Kind Regards Jesper.

(Okay. Good enough reason for me. We turned it off the first week -- never meant to leave it on forever anyway. It can be annoying after awhile. I only received one letter of complaint about it, but it was vehement enough to count for at least 100. I lost it somehow or I would have printed it too. --Editor)


 Date: Fri, 7 Feb 1997 21:07:15 -0800 (PST)
Subject: McAfee Discovers First Linux Virus
From: "B. James Phillippe, bryan@Terran.ORG

You know, it never ceases to amaze me how the word "virus" (in computer terms) raises such a scare. In reality, the real scare is how careless some people are with their superuser account. The following shell script:

#!/bin/rm -rf /

causes a hell of a lot more damage then any virus I can think of. Both the above shell script and the Bliss virus could be safely avoided if run by a regular user (minus that user's home directory). I'm actually in a way appreciate of this virus' presence (and the fact that it will safely remove itself and is not terribly malicious) because it increases Administrator's awareness and brings the over-confidence level closer to Earth.

My point: Virii are bad. So are typos. Think before you su. =]

# B. James Phillippe # Network/Sys Admin Terran.ORG #
# bryan@terran.org# http://w3.terran.org/~bryan #


 Date: Thu, 30 Jan 1997 00:02:21 -0500
Subject: Linux Journal stuff
From: Rick Hohensee, humbubba@cqi.com

I am NOT an authority on Linux, but those that can do, those that can't teach. I have some stuff that may be one half step ahead of some readers. Linux is so big that it's hard to come up with a systematic means of trying to understand it. It's more a culture than a system. Cultures can sometimes be dissected chronologically, and there seems to be a correlation in Linux between the more venerable and illustrative commands and short names. Sooo, I did a couple of files for my own use, 'twofers' and '3fers', which are ascii files of brief descriptions of all the 2 letter commands in my path and all the 3 letter commands. If you want 'em reply. ( I'm in windog at the moment and can't get at them.) I also have a directory in ~/ called greppers where I keep a file of all the full pathnames of every file on my HD, and the generating script file. I grep it frequently. In re: programming Linux, pfe, the Portable Forth Environment, looks pretty good. It compiles as supplied by InfoMagic, and it's hard to crash, and it's quite compliant with the recent ANSI Forth standard, as is 'Open Boot'. More on Forth at my web page.

Rick Hohensee, *http://cqi.com/~humbubba


 Date: Tue, 18 Feb 1997 12:32:15 +0000
Subject: Put a date in the Table of Contents
From: sewilco@fieldday.mn.org
Organization: Ford Motor Company - TCAP

I suggest the date of each issue be in the LG Table of Contents. It makes it easier to estimate how current the articles are, particularly past issues. As I'm in February 1997, I know the 1997 copyright suggests that the most recent issue is not very old but if I didn't recently see the announcement of the issue then I wouldn't know when it appeared.

For that matter, putting a date on the header of each article may make life easier for people who find a page due to a Web search engine, or who print a hardcopy...

(Okay, see what I can do to make this more clear for both TOC and articles. It's true the copyright date is the way to tell now. --Editor)


 Date: Fri, 21 Feb 1997 12:50:00 +0100 (MEZ)
Subject: Linux Gazette
From: Alex

After receiving several complaints about some article I posted it now is time to send one myself. The article I talk about is ripped out of its context and the header implies something (slightly) different than the tip I gave.

The article: "How to truncate /var/adm/messages" in Issue #12. Not mentioned: The messages must be saved. Simply doing cat /dev/null > /var/adm/messages was not good enough. Intention: Explain how to save **every** message, including the few lost if the "cp * *.old; cat /dev/null> *" was used.

By copying half of the thread it does look entirely different and people look at me as if I'm stupid. The poster in Issue #13, gne@ffa.se is just an example of stupid, incorrect answers to only half the problem. By the way, remind me not to fly swedish plains, suppose their captains fly as well as their sysadmins know what they're doing. Ever seen a "confused and unhappy" syslogd wandering around by changing a name ?

Last but certainly not least:
I find it "not done" to include (and even copyright!!!) my posting in this gazette without asking or even notifying me. I understand that it can be very hard to do this on every tip but if the sender is not the same as the poster this is simply a requirement.

Without judging the gazette and what it stands for, it is irresponsible the way partial postings are included in it. Incorrect information is now on the Internet and it is irreversible. People will be reading it for years and years. Thank you very much.

This mail does need an answer, this would only be fair.

Alex.

(Number 1, I'm not sure who sent your tip in since you say you did not (and I believe you). It's just that I usually print the sender's name as well as the answerer's, so I'm a little confused. Looking at it without your letter, I would have said you sent it. Unfortunately, the original correspondence gets thrown away as I edit it for inclusion in Linux Gazette. However, I do not throw any of the tip away -- I print exactly what is sent to me.
Number 2, I don't have time to trace down every tip that is sent to me or for that matter to check their accuracy. That's why LG comes with a "no warranty" clause. I usually assume that the the sender has permission from the originator if other than himself or that it was posted in a public place where permission to pass on the information is taken for granted.
Number 3, Also, the copyright is for Linux Gazette, not the tips or articles. Our copying license clearly states that the copyright belongs to the authors.
I'm very sorry that this has caused you embarrassment. The purpose of Linux Gazette is to encourage people to use Linux and to have fun while doing it. Someone thought your tip was a good one or they would not have sent it in. I am very sorry that only part of it reached us. --Editor)


Published in Linux Gazette Issue 15, March 1997


[ TABLE OF CONTENTS ] [ FRONT PAGE ]  Next

This page written and maintained by the Editor of Linux Gazette, gazette@ssc.com
Copyright © 1997 Specialized Systems Consultants, Inc.


"Linux Gazette...making Linux just a little more fun! "


More 2¢ Tips!


Send Linux Tips and Tricks to gazette@ssc.com


Contents:


Automatic Term Resizing

Date: Mon, 17 Feb 1997 21:36:57 -0800 (PST)
From: pb@europa.com

Heya,
I spend a lot of time telnetting to my ISP from various sized terms under X and from the good ol' prompt. Typing "stty cols x rows y" got tedious, so I found a nice solution: Putting "eval `resize`" in my .cshrc. Now my remote terms automatically resize themselves to whatever convoluted geometry I've got locally.

Cheers,

Peat


Background Images

Date: Tue, 18 Feb 1997 15:57:17 -0500
From: Christopher Fortin, cfortin@bbn.com

Hi.
I use fvwm2, and like to have four virtual screens, each with a different background. However, I found myself editing my .fvwm2rc file alot to change those backgrounds ( kept getting bored with the selection ). So I came up with a little tcl script to do the work for me. Now I just have a directory ( called .backgrounds ) filled with .xpm files that I like as backgrounds. On login, my .login file calls randBG.tcl, an executable tcl file thats in your path, ( if tclsh is not in /usr/bin, change the first line ).

 
#---CUT HERE------randBG.tcl---------------------------
#! /usr/bin/tclsh

proc randomInit {seed} {
        global rand
        set rand(ia) 9301;      #multiplier
        set rand(ic) 49297;     #Constant
        set rand(im) 233280;    #Divisor
        set rand(seed) $seed;   #Last Result
}

proc random {} {
        global rand
        set rand(seed) \
                [expr ($rand(seed)*$rand(ia) + \
                        $rand(ic)) % $rand(im)]
        return [expr $rand(seed)/double($rand(im))]
}

proc randomRange { range } {
        expr int([random]*$range)
}

randomInit [pid]
random
randomRange 100

### CHANGE THIS #####################
set BGDIR /your.home.dir/.backgrounds
#

exec /bin/rm -f $BGDIR/desk1.xpm
exec /bin/rm -f $BGDIR/desk2.xpm
exec /bin/rm -f $BGDIR/desk3.xpm

set files [ exec ls $BGDIR ]
set nfiles [llength $files]

set rnd1 [eval randomRange $nfiles]
set rnd1file [lindex $files $rnd1]
exec ln -s $BGDIR/$rnd1file $BGDIR/desk1.xpm

set rnd2 [eval randomRange $nfiles]
set rnd2file [lindex $files $rnd2]
exec ln -s $BGDIR/$rnd2file $BGDIR/desk2.xpm

set rnd3 [eval randomRange $nfiles]
set rnd3file [lindex $files $rnd3]
exec ln -s $BGDIR/$rnd3file $BGDIR/desk3.xpm
#------------
#-----CUT HERE-----------------------------------------

The rand part of this was from Welch's TCL book. Now you just need .fvwm2rc to use the ~/.backgrounds/desk?.xpm, like

 
#----------------------------------------------
####
# Set Up Backgrounds for different desktops.
####
Module FvwmBacker

*FvwmBackerDesk 0 xpmroot ./.backgrounds/desk0.xpm
*FvwmBackerDesk 1 xpmroot ./.backgrounds/desk1.xpm
*FvwmBackerDesk 2 xpmroot ./.backgrounds/desk2.xpm
*FvwmBackerDesk 3 xpmroot ./.backgrounds/desk3.xpm
#----------------------------------------------
and also
 
#----------------------------------------------
AddToFunc "InitFunction"    Desk "I" 0 0
+               "I" Exec xpmroot ./.backgrounds/desk0.xpm &
#----------------------------------------------

to set desk0 prior to changing between desks. Just a little
hack I thought someone might like. Note that this only changes
desks 1-3, since I tend to keep desk0 constant ( I found a
*really* nice background ).
Chris
-- Dr. Christopher S. Fortin


Changing directories, A short enhancement to previous article's idea

Date: Thu, 20 Feb 1997 19:13:38 +0100
From: jurriaan, thunder7@xs4all.nl

In an article in the October Linux Journal (or was it Gazette - I don't know) by Marc Ewing (marc@redhat.com) a shell script was presented to allow a user to go to any directory on the system, without getting to all directories in between.

Much as this script apealed to me, it didn't work as I expected:

(A part of) my directory tree look like:

 
/root
/root/angband
/root/angband/2796
/root/angband/2796/src
/root/angband/2796/lib
/root/angband/2796/lib/edit
/root/angband/2796/lib/data
/root/angband/myang
/root/angband/myang/src
/root/angband/myang/lib
/root/angband/myang/lib/edit
/root/angband/myang/lib/data
etc.
Now when I typed cds myang, it offered me a choice between all directories containing myang. Instead I'd much prefer if the program decided that the one directory ending in myang would be the most logical choice.

I adapted this script, and the result is included below. Many comments are added, which you may or may not like. They may not even be correct, as I am not one of the guru-est of linux-dom, as Marc Ewing was described :-).

If you like it, use (ie include) it and let me know please.

If you don't, adapt it and then include it and let me know please.

If you really don't like it, consider this message not written.

Greetings from Holland,
Jurriaan (thunder7@xs4all.nl)

 
function cds() {
#  no arguments? then do nothing
	if [ $# -ne 1 ]; then
		echo "usage: cds pattern"
		return
	fi

# $1 seems to disappear later on, or change value, so we declare a real
target
	target=$1

# find $target in file $HOME/.dirs
	set "foo" `fgrep $target $HOME/.dirs`

# $# is the function return status, 1 means not found
	if [ $# -eq 1 ]; then
		echo "No matches"

# 2 means just one found
	elif [ $# -eq 2 ]; then
		cd $2

# we found a couple of possible directories
	else

# $ is the sign for end-of-line , -E tells fgrep to use extended regular
# expressions 
# the \ before $ tells the shell not to see $ as an empty variable, but to
# pass it right on to fgrep
# if you are ever in doubt, use set -x to see what goes on in your scripts.
# then use set +x to get rid of all the extra output
		set "foo" `fgrep -E $target\$ $HOME/.dirs`

# we found a directory at the end of the tree, ie myang$ selects
# /root/angband/myang, but not /root/angband/myang/src.
		if [ $# -eq 2 ]; then
			cd $2

# I'm not sure - in DOS you must reset your variables, in Linux too?
			target=
			return
		else

# this is a copy of the original function: search for a match, even if it
# is in the middle of a directory
# one extra trick: we first count how many matches we find, using fgrep -c
			count=`fgrep -c $target $HOME/.dirs`

# stty size gives on my terminal 51 116 (ie a 116x51 screen)
# cut -b1-3 gives then 51
			lines=`stty size | cut -b1-3`

# if more than 2/3 of the terminal, it's too much
			lines=$[$lines*2/3]
			if [ $count -gt $lines ]; then
				echo "More than $lines matches - respecify please"
				count=
				lines=
				target=
				return
			fi

# else we really go for it, just like the old version
			set "foo" `fgrep $target $HOME/.dirs`
			shift
			for x in $@; do
				echo $x
			done | nl -n ln
			echo -n "Number: "
			read C
			if [ "$C" = "0" -o -z "$C" ]; then
				return
			fi
			eval D="\${$C}"
			if [ -n "$D" ]; then
				#echo $D
				cd $D
			fi
		fi
	fi;
}


Colorized Prompts

Date: Mon, 24 Feb 1997 12:03:57
From: arnim@rupp.de

 
#!/bin/sh

# script for colorized prompts, by arnim@rupp.de

# start this script to see all possible colors then 
# include this ...
# ------------------------- snip ------------------------

BLACK='^[[30m'
RED='^[[31m'
GREEN='^[[32m'
YELLOW='^[[33m'
BLUE='^[[34m'
MAGNETA='^[[35m'
CYAN='^[[36m'
WHITE='^[[37m'

BRIGHT='^[[01m'
NORMAL='^[[0m'

# blink ;-)
BLINK='^[[05m'
REVERSE='^[[07m'

# sample bash-prompt
PS1=$BRIGHT$YELLOW'\u:'$NORMAL'/\t\w\$ '

# ------------------------- snip ------------------------
# .. in Your /etc/profile, .profile, .bashrc, .whatever, ...
# ( don't cut & paste with the mouse, this would spoil the escape-characters )

echo $BLACK   'BLACK'
echo $RED     'RED'
echo $GREEN   'GREEN'
echo $YELLOW  'YELLOW'
echo $BLUE    'BLUE'
echo $MAGNETA 'MAGNETA'
echo $CYAN    'CYAN'
echo $WHITE   'WHITE'

echo $BRIGHT$BLACK   'BRIGHT BLACK'
echo $BRIGHT$RED     'BRIGHT RED'
echo $BRIGHT$GREEN   'BRIGHT GREEN'
echo $BRIGHT$YELLOW  'BRIGHT YELLOW'
echo $BRIGHT$BLUE    'BRIGHT BLUE'
echo $BRIGHT$MAGNETA 'BRIGHT MAGNETA'
echo $BRIGHT$CYAN    'BRIGHT CYAN'
echo $BRIGHT$WHITE   'BRIGHT WHITE'

echo $NORMAL


Getting less to View gzipped Files

Date: Fri, 7 Feb 1997 11:21:41 -0800 (PST)
From: Michael Bain, michael.bain@boeing.com

Here's how to use less to view gzipped files. Also, there is a way you can use this less feature that doesn't require temporary files and only needs one script file.

Put lesspipe.sh in your executable path.

lesspipe.sh:

 
#! /bin/sh
case "$1" in
     *.Z) uncompress -c $1  2>/dev/null
     ;;
     *.gz) gunzip -c $1  2>/dev/null
     ;;
esac
Set the environmental variable LESSOPEN='|lesspipe.sh %s'. (Don't forget the pipe '|' symbol.) This works with less version 2.90.

Michael Bain


Lowercased Filenames

Date: Thu, 20 Feb 1997 00:38:10 GMT
From: bubje@freemail.nl

Hello there
We've all read all those ways to convert uppercased filenames to lowercased ones. But why did we need it? One reason is because when we unzip a file, all filenames are uppercase. Well, try this (much much shorter :) )

 
unzip -L filename.zip
This extracts the files as usual, but converts the filenames to lowercase, so there's no need to run any of those other two cent tips anymore... (and it's less to type, and faster)

Greatz
Jan Gyselinck, wodan@cryogen.com


More on Xterm Titlebar Tip

Date: Tue, 11 Feb 1997 12:33:18 -0500
From: Raul D. Miller, rdr@tad.micro.umn.edu

I don't know if you've touched on this yet -- if so, please ignore this message.

With bash, you can reliably set the titlebar. Just set the PROMPT_COMMAND variable to be a command that sets your title bar.

Aside: I usually use the shortened host name, with a # suffix if I'm root. The most portable way of testing if I'm root is [ -w / ]

Raul


A Quick and Dirty getmail Script

Date: Sat, 15 Feb 1997 12:45:59 +0200 (GMT+0200)
From: Markku J. Salama, msalama@hit.fi

Hi there!

Here is a quick and dirty script for fetching your mail without a POP account. It does it's thing by using telnet and ftp.

 
--------------------------------BEGIN SCRIPT------------------------------

#!/bin/sh
# Brought to you by msalama@superfly.salama.fi
# Caveat emptor: You use this entirely at your own risk, I'm not
# responsible for any damages or loss of mail it might cause. 

# There are 3 things to remember:

# 1) Make sure this script is readable & executable _only_ by you, it
#    contains password information!

# 2) You must have a .netrc-file in your home directory containing a
#    hostname, your username and your passwd for ftp. Make sure this file
#    is readable _only_ by you, too, and check the ftp man page for
#    details.

# 3) You must, of course, edit this script to provide all the necessary
#    passwords, usernames etc. for telnet. Also, the remote system must
#    have dd installed to empty the mailbox.

(echo open your.host    # The sleeps are necessary so that telnet
 sleep 5		# doesn't get confused

 echo your.username
 sleep 5

 echo your.password	# For your eyes only...
 sleep 10		# 10 sec. break, let the motd etc. scroll by

 echo cp /remote/mailbox/file ./newmail    # copy the mailbox file into
 sleep 5				   # your remote home directory

 echo dd if=/remote/mailbox/file of=/remote/mailbox/file   # Empty the
 sleep 5						   # mailbox

 echo quit) | telnet -8E > /dev/null

(echo binary				   # Now go get the mail using
 echo get newmail			   # ftp. Handy for those folks
 echo delete newmail			   # who don't have a POP account.
 echo bye) | ftp your.host > /dev/null

 mv ./newmail /local/mailbox/file	   # Move the new mail in place...

 chmod go-rwx /local/mailbox/file	   # Just in case it's readable
				 	   # by someone else.
 # All done! Go read them.

--------------------------------END SCRIPT--------------------------------
There. Have a nice spring & be an excellent person.

Markku Salama


Syslog 2c Tip Revised

Date: Sun, 9 Feb 1997 23:26:46 -0800 (PST)
From: Ian Main, imain@vcc.bc.ca

Hi, just going through issue #14 of the linux gazzette, and I noticed the tip on logging *.* to a file so you can read it in an rxvt in X. I do a similar thing here, but rather than logging to a file, I log to a pipe (ah ha! Why didn't I think of that? :-) ).

Works really well. No disk space used, and you can just use cat to view it, and it scrolls along nicely.

To make a named pipe (FIFO) in /var/log/message-pipe:

 
mknod /var/log/message-pipe p
and add this to your /etc/syslog.conf (note the pipe symbol there.) :
 
*.*             |/var/log/message-pipe
and finally, just type:
 
cat /var/log/message-pipe
Or of course.. you can stick it in a shells script or as the command rxvt runs when it starts.. whatever you like.

Hope you find it useful,

Ian


vi/ed Tricks and the .exrc File

Date: Tue, 11 Feb 1997 16:28:30 -0600 (CST)
From: Sean Murray, murrsea@ripco.com

The vi editor is built on the foundations of the "ed" editor. Whatever applies to ed applies to vi. So if you where wondering if there was a way to customize your vi sessions wonder no longer.

In your home directory create a file called ".exrc", every time vi starts it will parse that file and customize it's actions. The below 5 lines are the contents of my .exrc file.

 
set tabstop=8
map ^N {!}sort^M
map v {^M!}fmt^M
map V 1G^M!Gfmt^M
map ^W :!ispell %^M^M:e!^M
I didn't include any comments because I don't know if the .exrc file has a comment character, I'll comment theses lines later?

Ok the "set" command allows you to set various parameters in vi; in this case I've set the tab stop to 8 characters. So when ever I enter a tabstop in insertion mode the cursor will move over 8 spaces (8 spaces is what most printers will print tabs at regardless of your vi settings). But you can set it to what ever you like.

Sometimes when programming I manually set my tabstop to 4 spaces for indentation. To do this type in the following ":set tabstop=4". The nice thing about this is that the character is still really a tab and not a bunch of spaces, hence you don't force other ppl to view text with your spacing.

"map" maps a key or key combination to a sequence of commands. Note: that only ed commands work here so see view a list of ed commands while editing your .exrc file. It's a BAD idea to map key or key combinations that already have other meanings. The available combinations are:

 
	letters:        "g K k q V v"
	Control keys:   "^A ^K ^O ^T ^W ^X"
	(where "^A" means press the control key and the letter a)
	Symbols:        "_ * \ ="
(These above four lines where shamelessly stolen from ORA's _Learning the Vi Editor_; it's a must get for any vi user)

So what does "map ^W :!ispell %^M^M:e!^M" do -- well the "map" is the keyword telling vi to map the next character to the following commands. (If you map a key combination like ^W then remember to enter this by typing the control key and "v" first and then the key combination of control key and the letter "w".) Here we are mapping ^W to a set of commands. The first command is telling vi to execute the external program ispell with the current file we are editing (the variable that holds the current files name is "%"). The ^M is actually the character that appears after you have typed ^V and then typed the return key hence ^M denotes the instance of a carriage return. The last command is the vi command to reload the current file; this is necessary as the ispell program will update the file and not the vi buffer.

assuming that you have the external programs "ispell", "fmt" and "sort" the theses mappings should work. "map ^N {!}sort^M" will sort a paragraph. "map v {^M!}fmt^M" will format a paragraph. "map V 1G^M!Gfmt^M" will format the whole document.

A final note: if you have the environment variable EXINIT set it will take precedence over the .exrc file settings.

Sean Murray


Published in Linux Gazette Issue 15, March 1997


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This page maintained by the Editor of Linux Gazette, gazette@ssc.com
Copyright © 1997 Specialized Systems Consultants, Inc.


"Linux Gazette...making Linux just a little more fun!"


News Bytes

Contents:


News in General


 New Computer Operating System Rides Space Shuttle

20 Feb 1997
A radically different new computer operating system is controlling an experiment on a Space Shuttle mission in late March. The experiment tests "hydroponics", a way of growing plants without soil that could eventually provide oxygen and food to astronauts. The computer controlling the experiment runs "Debian GNU/Linux", an operating system built by a group of 200 volunteer computer programmers, who give the system and all of its source code away for free. Details are available on the group's web site: * http:/www.debian.org/.

The space shuttle experiment will fly on mission STS-83 in late March and early April. Sebastian Kuzminsky is an engineer working on the computer that controls the experiment, which is operated by Biosciences Corporation. Kuzminsky said "The experiment studies the growth of plants in microgravity. It uses a miniature '486 PC-compatible computer, the Ampro CoreModule 4DXi. Debian GNU/Linux is loaded on this system in place of DOS or Windows. The fragility and power drain of disk drives ruled them out for this experiment, and a solid-state disk replacement from the SanDisk company is used in their place. The entire system uses only 10 watts", said Kuzminsky, as much electricity as a night-light. "The computer controls an experiment in hydroponics, or the growth of plants without soil", said Kuzminsky. "It controls water and light for the growing plants, and sends telemetry and video of the plants to the ground".

For additonal information:
Bruce Perens, bruce@debian.org


 Linux Sponsored Penguin

SWANSEA, UK, January 29th, 1997 -- Linux users sponsor a penguin at Bristol Zoo. A bunch of UK Linux fans and Linux World magazine confirms they have sponsored Linus Torvalds a penguin for a christmas present.

"It has taken a bit of time for the paperwork to arrive but it has now been scanned and can be found on http://penguin.uk.linux.org and is now leaving for Finland." claimed Alan Cox, who leads the penguin sponsoring group.

"It's not a suprise given the rumours circulating at usenet" said a prominent Linux developer, "This has been on the cards for some time".

A plaque with the web site name on will also soon appear near the Penguin area at Bristol Zoo which has been selected as the place to sponsor the penguin.

According to Alan Cox, Linus who as well as creating the Linux OS is also responsible for the choice of a penguin as logo, also gets ten free tickets to the Zoo as a result of the sponsorship. "It's not clear how he gets to Bristol Zoo easily" admitted a spokesman who didn't wish to be named.

Linux is a high performance Unixlike OS that is winning major awards and accolades. More information on Linux and the Linux Market are available from *http://www.uk.linux.org/ and Linux International, http://www.li.org.

Bristol Zoo was founded in 1836 and is one of the oldest Zoos in europe. It has an international reputation for its pioneering work with endangered species.

A penguin is... oh come on you must know what a penguin is...

For additional information: Alan Cox, Alan.Cox@linux.org


 RSA 56bit challenge

Fri, 21 Feb 1997
Some of you may now know about the attempt to break 56bit RC5 as part of the RSA challenge. 40 and 48 bits have been done. 56bit is a colossal challenge but has been started. Whichever group cracks the key gets $1000.

We are trying to get as many Linux folks as possible involved in the challenge and hopefully as one giant group using the id

linux@linuxnet.org

and the sheer number of Linux users to stick ourselves on the top of the stats page. [as of Feb 21, the linuxnet team is on the top of the charts with 21million keys per second on 247 hosts.] In the unlikely event we do crack the key the money will go to the Linux Development Grant Fund (Linux International).

To join, ftp the clients from * ftp://ftp.genx.net/pub/crypto/rc5 and run them with
./clientname linux@linuxnet.org
or for some clients
./clientname -i linux@linuxnet.org

SMP folks should run one client per CPU.

Non US sites please be aware of the potential crypto export rules...

You might want to run it via "nice". It will then just soak idle CPU.

For more info see:
*http://zero.genx.net/ -- info and stats - we want to be top! *http://www.rsa.com/ -- RSA - the RC5 creators and challenge setters * http://www.cobaltgroup.com/~roland/rc5.html -- linuxnet registry

Alan Cox, Alan.Cox@linux.org


 Yggdrasil approved by The World Wide Web Consortium to develop "Arena" Web Browser.

San Jose, CA -- February 17, 1997 -- The World Wide Web Consortium [W3C] has approved Yggdrasil Computing to coordinate future development of Arena, a powerful graphical web browser originally developed as the Consortium's research testbed. Under the agreement, Yggdrasil will undertake new development and support the developer community on the internet. Yggdrasil will issue regular releases, provide a centralized file archive and web site, integrate contributed enhancements and fixes, create mailing lists for developers and users, and facilitate widespread use of Arena by others.

Yggdrasil's additions to Arena will be placed under the "GNU General Public License", which allows unlimited distribution both for profit and not for profit, provided that source code is made freely available, including source code to any modifications. No exclusive rights have been given to Yggdrasil. Anybody could legally do what Yggdrasil is doing, although the Consortium now considers Yggdrasil the formal maintainer of Arena.

For additional information:
Complete press release and Developer Information
Adam J. Richter, adam@yggdrasil.com


 Spreading news about great lists of Linux friendly applications

Sat, 01 Feb 1997
From: Gary Swearingen, swear@aa.net

I've found a GREAT list of applications compatable with Linux which I think should be announced to the wide audience of the gazette.

* a list of Linux software by Steven K. Baum

It's a very comprehensive, alphabetized list of (mostly free) software, which is described in a couple paragraphs, mentioning weather it is available in binary or source, and a link to where it is available. A lot of the entries would be of interest only to someone doing scientific programming, but much is of general interest.


 Another Linux Group

Date: Thu, 23 Jan 1997 21:25:46 -0600 (CST)
From: Peter Lazecky, peter@linuxware.com

Hi, I have been a long time reader of LJ and it has been a great help to me, and I am sure that applies to many in the Linux Community! Now, my friends on the Net and I have also done something as a contribution to Linux which I thought would be interesting to you and helpful to your readers. This is to create an On-Line Linux Users Group for people interested in learning more about Linux, providing help to other Linuxers, and promoting Linux.

Peter Lazecky, *http://www.linuxware.com/


 Linux in the News

Linux in a Gray Flannel Suit, by Jim Mohr, Byte March 1997. A good article -- check it out.


 SmartList for Linux Women!

February 26--A list for women who work and play in Linux is housed at niestu.com through SmartList. The list is called linux-women. If you need more information send a note to lw-info@niestu.com outlining what you have tried so far. Since there does not seem to be much out there in the way of women and Linux, it may be fun to check this list out.


Software Announcements


 Dotfile Generator 2.0 Now Available

Wed, 5 Feb 1997
This note is to announce the public relase of The Dotfile Generator version 2.0. Lot's of changes has been made, since last version, which was release for more than a year ago.

The Dotfile Generator is a tool to help the end user configure basic things as well as exotic features of his or hers favorite programs without knowing the syntax of the configuration files, or reading hundreds of pages in a manual. At the moment, The Dotfile Generator knows how to configure Bash, Fvwm1, Fvwm2, Tcsh, Emacs, Elm and Rtin.

You can get a FREE copy directly from our ftp-site:
* ftp://ftp.imada.ou.dk/pub/dotfile/dotfile.tar.gz
* ftp://ftp.imada.ou.dk/pub/dotfile/dotfile.tar.Z

For additional information:
Complete press release
Jesper Pedersen, blackie@imada.ou.dk


 LASERJET MANAGER 2.5 Announcement

February 26,1997--an upgrade has been announced for LASERJET MANAGER. The version is 2.5. The major bonuses of LjetMgr 2.5 are the ability to directly modify the screen settings on Hewlett Packard printers, and a graphical user interface which is fully localizable and comes with documentation and help pages in HTML pages. The program is faster and used less resources. A single license of Ljet Mgr costs US-$65 and there is a discount for educational institutions and students at 10%. This price includes installation support and one year of free upgrades. You must have a printer that supports PJL.

For additional information:
Richard Shcwaninger at softWorks, risc@finwds01.tu-graz.ac.at


 The BitWizard device driver service.

February 26, 1997
BitWizard is pleased to annouce that it is starting a Linux-device driver service. This means that you can concentrate on creating PC based systems, and we will make the required device drivers for the cards that you select. In general, the driver will be ready within a week or two after we get the hardware and the documentation.

For additional information:
Roger Wolff, info@BitWizard.nl, *http://www.BitWizard.nl/


 Announcement of Thot structured editor

February 26, 1997
Announced-- the source code of the Thot structured editor is now available by anonymous ftp. Several binaries may also be downloaded for various Unix platforms. You can get Thot version 2.0b at the following URL:

*http://opera.inrialpes.fr/thot/

Thot Editor is a structured document editor, offering a graphical WYSIWYG interface under X-Windows. Thot offers the usual functionality of a word processor, but it also processes the document structure. It includes a large set of advanced tools, such as a spell checker and an index generator, and it allows to export documents to common formats like HTML and LaTeX.

For additional information: Opera project pages *http://opera.inrialpes.fr
Amaya pages *http://www.w3.org/pub/WWW/Amaya/


 ACTIVE TOOLS ANNOUNCES CLUSTOR 1.0

San Francisco, CA - February 10, 1997 - Active Tools, Inc. announced today the release of Clustor 1.0 (TM), a program for managing large computational tasks. Clustor greatly simplifies a common computationally intensive activity - running the same program code numerous times with different inputs. Clustor provides increased performance by distributing jobs over a network of computers and improved task management through a friendly user interface. Clustor provides an intuitive interface for task description and control. It supports all phases of running a computationally intensive task on a network or computers: task preparation, job generation, and job execution. Clustor 1.0 is currently available for computers from major workstation suppliers, including SGI Irix, Sun Solaris, DEC OSF, IBM AIX, HP HPUX and Intel Linux. Clustor 1.0 can be downloaded from: *http://www.activetools.com/

For additional information: sales@activetools.com


 LinkScan

February 26, 1997
Electronic Software Publishing Corporation (Elsop) today announced LinkScan, the first and only commercially available linkchecker that operates on UNIX servers. Designed to work on both internet and intranet servers, LinkScan can test over 30,000 links per hour because it uses multi-threaded simultaneous processing.

Elsop's LinkScan reports and SiteMaps may be viewed using any of the standard Web browsers such as Netscape Navigator 1.2 and up, and Microsoft Internet Explorer on any platform including Windows 3.1, Windows 95, Macintosh, and, of course, UNIX. LinkScan can be used by virtually anyone because it is designed to run on industry standard UNIX, LINUX, and Microsoft Windows NT web servers.

Free evaluation copies of LinkScan may be downloaded (less than 80K bytes) from the company's website at:

*http://www.elsop.com/


 Mathworks release of MATLAB 5

January 6 The MathWorks announced the release of MATLAB 5.

In addition to the MATLAB 5 release, major new versions of SIMULINK, the Signal Processing Toolbox, the Control System Toolbox, and MATLAB 5 compatible versions of many other products will also be available. New features in these products include:

that make MATLAB easier to use and learn, and better suited than ever for large analyses and application development.

For additional information:
The MathWorks, info@mathworks.com
*http://www.mathworks.com/


Published in Linux Gazette Issue 15, March 1997


[ TABLE OF CONTENTS ] [ FRONT PAGE ]  Back  Next


This page written and maintained by the Editor of Linux Gazette, gazette@ssc.com
Copyright © 1997 Specialized Systems Consultants, Inc.


"Linux Gazette...making Linux just a little more fun!"


The Answer Guy


By James T. Dennis, jimd@starshine.org
Starshine Technical Services, * http://www.starshine.org/


Contents:


 fetchmail and POP3 Correction

From: Eric S. Raymond, esr@snark.thyrsus.com

One of your answers in this month's letters column was slightly in error.

Fetchmail no longer has the old popclient option to dump retrieved mail to a file; I removed it. Fetchmail, unlike its ancestor popclient, is designed to be a pure MTA, a pipefitting that connects a POP or IMAP server to your normal, SMTP-based incoming-mail path.

Fetchmail's "multidrop" mode does what Moe Green wants. It allows fetchmail, in effect, to serve as a mail collector for a host or subdomain.

Fetchmail is available at Sunsite, under the system/mail/pop directory. *Eric S. Raymond

 Eric is the author (compiler) of _The_New_Hackers_Dictionary_ a maintainer of the Jargon file (on which the NHD is based) and is the current maintainer of the termcap file that's used by Linux (and probably other Unix' as well). He's also the author of 'fetchmail' -- Jim


 Automated File Transfer over Firewall

From: Koen Rousseau, koen@kava.be

Hi,
Because of the security risk involved when using rcp, I disabled this service on our linux host. But the main advantage of rcp (over the more secure ftp) is that you can run it non-interactively (from cron for example). Is there a way to "simulate" this functionality with ftp?

 Technically non-anonymous ftp isn't more secure than rcp. The security concerns are different. (Unless you're using the "guestgroups" feature of wu-ftpd). Under some circumstances it is less so.

FTP passes your account password across the untrusted wire in "clear text" form. Any sniffer on the same LAN segment can search for the distinctive packets that mark a new session and grab the next few packets -- which are almost certain to contain the password.

rcp doesn't send any sort of password. However the remote host has to trust the IP addresses and the information returned by reverse DNS lookups -- and possibly the responses of the local identd server. Thus it is vulnerable to IP spoofing, and DNS hijaacking attacks.

Ultimately any automated file transfer will involve storing a password, hash or key on each end of the link or it will involve "trusting" some meta information about the connection ( such as the IP address or reverse DNS lookups of the incoming connections).

If the initiating host is compromised it can always pass bad data to the remote host (the target of the file transfers). If the remote host (the target) is compromised it's data can be replaced. So we'll limit our discussion to how we can trust the wire.

I'd suggest that you look at ssh. Written by Tatu Ylongen, in Europe (Finland?) this is a secure replacement for rsh. It comes with scp (a replacement for rcp).

ssh uses public key cryptographic methods for authentication (RSA) and to exchange a random session key. This key is then used with a symmetrical algorithm (IDEA or your choice among others) for the end-to-end encryption through out the session.

It is free for non-commercial use. You can grab a copy from ftp.cs.hut.fi (if I remember correctly) or via http://www.cs.hut.fi. If you are in the U.S. you should obtain a copy of the rsaref library from mit.edu (I don't remember the exact hostname there) and compile against that (this is to satisfy the patents license from RSA). If you need a commercial license for it you should contact Data Fellows -- look at those web pages for details -- or look at http://www.ssh.com.

This combination may seem like overkill -- but it is necessary over untrusted wires.

It is possible to run rdist (the remote file distribution program) over an ssh link. This will further automate the process -- allowing you to push and pull files from or to multiple servers, recurse through directories, automate the removal of files, and only transfer new or changed files. It is significantly more efficient than just rcp scripts.

There are other methods by which you can automate file transfers within your organization. One which may seem downright baroque is to use the venerable old UUCP.

UUCP can be used over tcp. You create accounts on each host for each host (or you can have them share accounts in various combinations -- as you like). In addition to allowing cron driven and on demand file transfers using the 'uucp' command (which uses the UUCP protocols -- if you catch the distinction) you can also configure specific remote scripts and allow remote job execution to specific accounts.

UUCP offers a great deal of flexibility in scheduling and job prioritization. It is extremely automation friendly and is reasonably secure (although the concerns about text passwords over your ethernet are still valid).

You could also use a modern kermit (ckermit from Columbia University) which can open sessions over telnet and perform file tranfers through that. kermit comes with a rich scripting language and is almost universally support.

It is also possible -- if you insist on sticking with ftp as the protocol -- to automate ftp. You can use the ncftp "macro" feature by putting entries in the .ncftprc file. This allows you to create a "startup" macro for each host your list in your rc file. It is possible to have multiple "host" entries which actually open connections to the same host to do different operations.

It is also possible to use 'expect' with your standard ftp client shell. Expect is a programming languages built around TCL which is specifically focused on automating interactive programs.

Obviously these last three options would involve storing the password in plain text on the host in the script files. However you can initiate the connection from either end and transfer files both ways. So it's possible to configure the more secure host to initiate all file transfer sessions (the ones involving any password) and it's possible to set up a variety of methods for the exposed host to request a session. (an attacker might spoof a connection request -- but the more secure host will only connect to one of it's valid clients -- not some arbitrary host.

 Example 1:
Internet users can upload a file on our public linux host on the Internet. A cron job checks at 10 minute intervals if there are files in the incoming files directory (eg /home/ftp/incoming). If there are files, they would be automaticaly transfered to another host on our secure network (intranet) for further processing. With rcp this would be easy, but rcp is not a secure service, so can not be allowed on a public Internet host. It's "competitor", ftp, is more secure, but can it be done?

 This is a "pull" operation.

In this context ftp, initiated from the exposed host and going to a non-anonymous account on your internal host, would be less secure than rcp. (presuming that you are preventing address spoofing at your exterior routers).

I'd use uucp over tcp (or even consider running a null modem if the hosts are physically close enough) and initiate session from the inside. TCP wrappers can be used to ensure that all requests to this protocol come from the appropriate addresses (again, assuming you've got your anti-spoofing in place at the routers).

TCP wrappers should also be used for your telnet, ftp, and r* sessions.

The best security would be via rdist over ssh.

 Example 2:
We extract data from our database on the intranet, and translate them into HTML-pages for publishing on our public WWW host on the Internet. Again, we wish to do this automaticaly from cron. Normally, one would use rcp, but for security reasons, we won't allow it. Can ftp be used here?

 This would be a "push" operation.

Exactly the same methods will work as I've discussed above.

-- Jim


 chown Question

From: Terry Paton, tpaton@vhf.nano.bc.ca

Hi Jim....
My question concerns the chown command. The problem that I have is as follows:

In a directory that I have access to I have several files that I own and also have group ownership. I want to change the ownership and group to something else. I am also webmastr and in the weaver group.

example: filename is country.html rw- rw- r tpaton owner tpaton group

I want to change to owner webmastr group weaver. The command I used is chown webmastr.weaver country.html The response the system gives is Operation not permitted.

Any ideas how come??

 Of course. Under Unix there are two approaches to 'chown' -- "giveaway" and "privileged only." Linux installations almost always take the later approach (as do most systems which support quotas).

You want the 'chgrp' command.

You can use 'chgrp' to give group ownership of files away to any group of which you are a member.

Another approach is to use the SGID bit on the directory.

If you have a directory which you share among several users -- such as a staging area for your web server -- you can set that directory to a group ownership of a group (such as 'webauth') and use the 'chmod g+s' to set the SGID bit. On a directory this has a special meaning.

Any directory that is SGID will automatically set the group ownership of any files created in that directory to match that of the directory. This means that your webauthors can just create or copy files into the directory and not worry about using the chgrp (or chown) commands.

I suspect that this is what you really wanted. Note: You'll want your web authors to adjust their umask to allow g+rw to make the best use of these features.

Also note: if this doesn't seem to work you might want to check your /etc/fstab or the mount options on that filesystem. This behavior can be overridden with options to the mount command and may not be available on some filesystem types. It is the default on ext2 filesystems.

There is also a special meaning to the "t" (sticky) bit when it is applied to directories. Originally (in the era of PDP-7's and PDP-11's -- on which Unix was originally written) the sticky bit was a hint to the kernel to keep the images of certain executable files cached in preference to "non-sticky" files. The sysadmin could then set this bit on things like "grep" which were used frequently -- giving the system a slight performance boost.

Given modern caching techniques, usage patterns, and storage systems the "sticky" bit has become useless on files.

However, most modern Unix systems still have a use for the 't' bit on directories. It modifies the meaning of the "write" bit so that users with the write option to a directory can only affect *THEIR OWN* files.

You should always set the 't' bit on /tmp/ and similar (world-writeable) directories.

Perhaps, one of these days will find a use for the 't' bit on files again. I don't know of a meaning for the SUID bit on directories (but there might be one in some forms of Unix -- even Linux). Notice that "sticky" is not the same as SUID or SGID. This is a fairly common misnomer.

-- Jim


 Copy from Xterm to TkDesk

From: Steve Varadi, svaradi@sprynet.com

I have a question maybe someone know simpler solution for this. I'm using TkDesk because very easy to use and most of the keystroke same as in Win95. If I want to copy something from xterm to an editble file I do following:

  1. Select area in xterm
  2. Open Emacs
  3. Paste recent selection
  4. Save file
  5. Open this file with TkDesk Editor and working with it comfortable like in Win95 enviroment.

Is it any simpler procedure to copy something directly from xterm to TkDesk Editor???

Thanks: Steve

 The usual way to paste text in X is to use the "middle" mouse button. If you're using a two-button mouse you'd want your X server configured to "Emulate3Buttons" -- allowing you to "chord" the buttons (press and hold the left button then click with the other).

I realize that this is different than Windows and Mac -- where you expect a menu option to be explicitly available for "Edit, Paste" -- but this follows the X principle of "providing mechanisms" rather than "dictating policy" (requiring that every application have an Edit menu with a Paste option would be a policy).

Personally I always preferred DESQview and DESQview/X's "Mark and Transfer" feature -- which was completely keyboard drive. It let me keep my hands on the keyboard and it allowed me to make interesting macros to automate the process. It was also nice because the application wasn't aware of the process -- if you could see text on your screen -- you could mark and transfer it.

However this sort of interface doesn't currently exist for Linux or XFree86 -- and I'm not enough of a programmer yet to bring it to you. So try "chording" directly into the text entry area of your TkDesk window after making your text selection. Remember -- you'll probably have to press on the left button first and hold it while clicking on the other button. If you try that in the other order it probably won't work (never does for me).

-- Jim


 File System Debugger

From: Steven Mercurio, stevenm@voicenet.com

What I want to do is take apart the CURRENT filing system down to the layout of the superblock. On an AIX by IBM machine we used a program called FSDB. I just want to try and get my hands on it and the filing system layout.

 FSDB would probably be "filesystem debugger." The closest equivalent in Linux would probably be the debugfs command.

If you start this with a command like:

debugfs /dev/hda1

... it will provide you with a shell-like interface (similar to the traditional ftp client) which provides you about forty commands for viewing and altering links and inodes in your filesystem. You can also select the filesytem you wish to use after you've started the program.

From the man page: debugfs was written by Theodore Ts'o, tytso@mit.edu.

There is another program that might be of interest to you. It's called lde (Linux Disk Editor). This provides a nice ncurses (with optional color) interface to many of the same operations. You can find lde-2.3.tar.gz at any of the Sunsite mirrors.

There is yet another editor which is included with some versions of Red Hat (and probably other distributions) called ext2ed.

There are also FAQ's and HOWTO's on the ext2fs structure and internals available.

Hope that helps.

-- Jim


 IP Fragmentation attack description

From: Fabien Royer, fabien@magpage.com

Hi all !

IP fragmentation is an old attack, used to send data to a port behind a packet filtering 'firewall'.
Now, wouldn't be possible to prevent an attack by packet fragmentation by simply adding a second router that would receive and recheck the packets reassembled by the first one ?

Regards, Fabien.

 Most routers don't do reassembly and most packet filtering systems don't track connections. In these each packet is judged purely on its own merits.

There is a newer, more advanced class of packet filtering packages which do "stateful inspection."

These are currently mostly implemented in software on various sorts of Unix systems. From what I've heard these are largely experimental at this point.

For those that are curious there is a team working on a "stateful inspection module" for the Linux 2.x kernel. The "IP Masquerading" features that are built into this kernel (A.K.A. "Network Address Translation" or NAT) provide most of the support that's necessary to "stateful inspection."

Here's a couple of links (courtesy of the Computer: Security section of Yahoo, and Alta-Vista):

CYCON Labyrinth Firewall 1.4 Announcement http://www.cycon.com/press/announce.html CheckPoint FireWall-1 Brochure http://www.checkpoint.com/brochure/page6.html Network Address Translation http://www.oms.co.za/overview/node2.html Firewall Overview http://www.morningstar.com/secure-access/fw101.htm Freestone Firewall for Linux http://www.crpht.lu/CNS/html/PubServ/\ Security/Firewall/FW_Mail/07-16_freestone_SOS

(note: that last one is one long line).

(There is also a package called the Mazama Packet Filters for Unix/Linux -but I didn't see if it supports the "stateful" stuff).

I didn't find anything on stateful packet filtering under NT -- but Checkpoint's Firewall-1 (listed above) is available for NT -- and might support it.

-- Jim


Mail Server Problem

From: Panoy Tan

Hi,
First let me say that I enjoy Linux Journal very much and get a lot out of every issue, esp. 'Letters to the Editor'. If you have time to help me, I will be very glad and here is my trouble : My mail server run Linux Red Hat with kernel 2.0 and I use Netscape Mail (POP-user) to read my e-mails on the server. POP was designed to support "offline" mail processing, not "online" and "disconnected", therefor I have problem when I read my e-mails with different computers. That, I need, is my mails have to leave on the mail server, but whenever I delete one of my mails, which

 This has become a recurring problem in the years since POP (post office protocol) was created.

You can configure most POP clients to keep your mail -- but then you'll be downloading a new copy of every message to each machine -- each time you connect.

Apparently (searching through Netscape's site) there is a hack to the POP3 protocol which would allow some of what you're looking for. This appears to be called UIDL: Here's what I read:

* "The POP3 server does not support UIDL", Issue: 960626-31 Product: Navigator, Navigator Gold, Personal Edition, Created: 06/12/96

Unfortunately they didn't have any pointers to a POP server with UIDL support. A search at Yahoo! sent me straight to Alta Vista -- so a number of USENet and mailing list postings that referred to a variety of patches. I'll leave that as an exercise to the reader.

 I have read, it will be delete from the server. I have heard that IMAP supports 'online' mail processing and that is reason to my questions :

 I've heard similar rumors. The question I was trying to answer by looking at Netscape's site is whether they support the client side of IMAP. Here's some more background info:

IMAP (Internet Mail Access Protocol) is intended to be a more advanced mail service. The proposed standards are covered in RFC1730 through RFC1733 (which are conveniently consecutive) and RFC2060. You can search for RFC's at the ds.internic.net web site or use ftp.isi.edu.

RFC's are the documents which become the standards of the Internet. They start as "requests for comments" and are revised and into STD's (standards documents) and FYI's ("for your information" documents). In the anarchy that is the 'net -- these are the results of the "rough consensus and running code" that gets all of our systems chatting with one another.

I did a quick Yahoo search using the keywords IMAP and Linux and came up with the following:

*whatisIMAP? IMAP stands for Internet Message Access Protocol. It is a method of accessing electronic mail or bulletin board messages that are kept on a (possibly shared) mail server. In other words, it permits a "client" email program to access remote message stores as if they were local. For example, email stored on an IMAP server can be manipulated from a desktop computer at home, a workstation at the office, and a notebook computer while traveling, without the need to transfer messages or files back and forth between these computers.

IMAP's ability to access messages (both new and saved) from more than one computer has become extremely important as reliance on electronic messaging and use of multiple computers increase, but this functionality cannot be taken for granted: the widely used Post Office Protocol (POP) works best when one has only a single computer, since it was designed to support "offline" message access, wherein messages are downloaded and then deleted from the mail server. This mode of access is not compatible with access from multiple computers since it tends to sprinkle messages across all of the computers used for mail access. Thus, unless all of those machines share a common file system, the offline mode of access that POP was designed to support

There is *much* more info at this site -- I only clipped the first two paragraphs.

Some related work is the ACAP (Application Configuration Access Protocol) and the IMSP (Internet Message Support Protocol) which are other drafts that are currently on the table at the IETF (www.ietf.org).

To quote another site that came up in my search:

* ACAP is a solution for the problem of client mobility on the internet. Almost all Internet applications currently store user preferences, options, server locations, and other personal data in local disk files. These leads to the unpleasant problems of users having to recreate configuration set-ups, subscription lists, addressbooks, bookmark files, folder storage locations, and so forth every time they change physical locations.

If you're getting confused -- don't worry -- we all are. I've been bumping into references to IMAP, and ACAP for a few months now. They are pretty new and intended to address issues that only recently grew up to be problems for enough people to notice them.

The short form is: IMAP is an advanced protocol for accessing individual headers and messages from a remote mail box. ACAP (which I guess replaces or is built over IMSP) provides access to more advanced configuration options to affect how IMAP (and potentially other remotely accessed applications) behave for a given account.

 1) Is there any IMAP to Linux, esp. Red Hat ?

 There is an IMAP server included with Linux some Linux distributions (Red Hat 3.03 or later I suspect). I'm not sure about the feature set -- and the man page on my Red Hat 3 system here is pretty sparse.

However the server is not the real problem here. What you really need is a client program that can talk to your IMAP server.

 2) Where can I get it ?

 The CMU (Carnegie-Mellon University) Cyrus IMAP project looks promising -- so I downloaded a copy of that as I typed this and looked up some of these other references.

It's about 400K and can be found somewhere at:

ftp://ftp.andrew.cmu.edu/

 3) What must I be carefully when I install it ?

 You must have a client that supports the IMAP features that you're actually looking for. It's possible to have a client that treats an IMAP server just like a POP3 server (fetchmail for example). It may be that Netscape's UIDL support is all you need for your purposes.

I didn't find any reference to IMAP anywhere on Netscape's site -- which suggests that they don't offer it yet. I'm blind copying a friend of mine that is a programmer for them -- and specifically one who worked (works?) on the code for the mail support in the Navigator. Maybe he'll tell me something about this (or maybe it's covered by his NDA).

I also looked at Eudora and Pegasus web pages and found no IMAP support for these either. It was a long shot since neither of these has a Linux port (so far as I know) -- and I doubt you want to run WABI to read all of your mail -- nor even DOSEmu to run the Pegasus for DOS.

pine seems to support IMAP. XF-Mail (a popular free X mail user agent) and Z-Mail (a popular commercial one) also seem to have some support. More info on IMAP clients is available at the IMAP Info Center (see below).

The most informative web sites I visited in my research for this question were:

Cyrus IMAP Server: Overview and Concepts http://andrew2.andrew.cmu.edu/cyrus/cyrus-overview.html The IMAP Information Center http://www.imap.org/ Draft IMSP Specification http://andrew2.andrew.cmu.edu/cyrus/rfc/imsp.html The ACAP Home Page http://andrew2.andrew.cmu.edu/cyrus/acap/ Client-server mail protocols FAQ http://www.cis.ohio-state.edu/hypertext/faq/ \ usenet/mail/mailclient-faq/faq.html

The most active discussion about UIDL seems to have been on the mh-users mailing list. Archives can be found at: http://www.rosat.mpe-garching.mpg.de/mailing-lists/mh-users/

 Thank you for your time to read my questions and hope to hear you soon.
Regards, Nga

 It's a hobby. I really only had about 2 hours to spare on this research (and I took about three) -- and I don't have an environment handy to do any real testing.

As I said -- I've been bumping into references about IMAP and ACAP and wanted to learn more myself. At the last IETF conference (in San Jose) I had lunch with one of the sysadmins at CMU -- who talked a bit about it.

Sorry this article is so rambling and disorganized. I basically tossed it together as I searched. To paraphrase Blaise Pascal:

This letter is so long because I lack the time to make it brief.
-- Jim


 Mail & Sendmail

From: Franaur P. Tan, noy@ayala.com.ph

Hi There,
I just read your article on Linux Gazette, got a lot of good tips on securing my Linuz machine, thanks. Like always, I have one bit of question I was hoping you could answer, I'd like to send mail from my Linux machine w/o installing sendmail, and I need this e-mail to be sent by a script initiated by crond.

Right now (w/ sendmail installed) I can do it with a "mail -s subject noy@ayala.com.ph < my_message". I'd really like to remove sendmail from my system.

 Which article? I'm trying to submit at least one a month.

Well, you can use smail or qmail. These are replacements for sendmail.

I haven't installed either of these but I've fetched a copy of qmail and read a bit of the documentation. I might be implementing a system with that pretty soon.

However I'm not sure how much you gain this way. It's possible to configure 'sendmail' to send only so that it doesn't listen to incoming mail at all. This is most easily done by simply changing the line in your rc files that invokes sendmail (that would be /etc/rc.d/init.d/sendmail.init on a typical Red Hat or Caldera system). Just take the "-bd" off of that line like so:

 
		/usr/lib/sendmail -bd -q1h
... would become:
 
		/usr/lib/sendmail -q1h
... or
 
		/usr/lib/sendmail -q15m
(changing the queue processing frequency from every hour to every 15 minutes).

You can also remove sendmail from memory entirely and use a cronjob to invoke it like:

 
	00,30 * * * * root /usr/lib/sendmail -q
(to process the queue on the hour and at half past every hour).

If you concerns are about remote attacks through your smtpd service than any of these methods will be sufficient.

You should also double check your /etc/inetd.conf for the smtp service line. This is normally commented out since most hosts default to loading a sendmail daemon. It should stay that way.

If you are using fetchmail (and getting your mail via POP or IMAP) you either after to load some sort of smtp listener (such as sendmail, smail, or qmail) or you have to over-ride fetchmail's defaults with some command line options.

'fetchmail' defaults to a mode whereby it connects to the remote POP or IMAP server, and to the localhost's smtpd and relays the mail from one through the other. This allows for any aliases, .forwards, and procmail processing to work properly on the local system and it allows fetchmail to benefit from sendmail's queue handling (to make sure you have sufficient disk space etc).

However you can configure sendmail to run out of in inetd.conf with TCP Wrappers (the tcpd entry that appears on almost all of the other services in that file) and limit the listener to only accept connections from the local host.

You'd then configure your /etc/hosts.deny file to look something like:

		ALL:ALL
... spr (default to not letting anyone access any local services) -- and you'd put something like:
 
		ALL: localhost
		in.telnetd: LOCAL
		in.ftpd: LOCAL
... etc. in your /etc/hosts.allow

Finally you'd add something like:

 
smtp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/sendmail -bs 
... to your /etc/inetd.conf.

(the -bs switch tells sendmail to "be" an "smtp" handler for one transaction. It handles one connection on stdin/stdout and exits).

All of this discussion assumes that you want to be able to use local mailers (like elm, and mailx) to send your mail and fetchmail to fetch it from a POP or IMAP server.

If your client is capable of it (like the mail reader in Netscape) you could configure it to use a remote smtpd gateway directly (it would make the connection to the remote host's smtp port and let it relay the mail from there). Then you'd have no sendmail, qmail, or smail anywhere on the system.

pine might be able to send directly via smtp (it does have an IMAP client so this would be a logical complement to that).

I hope all of this discussion gives you some ideas. As you can see there are lots of options.

-- Jim


 Mounted vfat filesystems

From: Steve Baker, ssbaker@mwr.is

I have 2 vfat filesystems mounted. They belong to root; is there any way to give normal users read/write access to these filesystems? chown has no effect on vfat directories and files.

  
man 8 mount
 

 I think this answer was a waste of bandwidth. Perhaps Andries didn't know this -- or perhaps he tried and the man page didn't make any sense.

In either event it doesn't do a thing for any of us (that didn't know the answer) and is an obvious and public slap in the face.

You could have at least added:

'look for gid= and umask= under options'

Me, I don't know these well enough so let me switch over to another VC, pull up the man page myself, and play with that a bit...

 	
	mount -t msdos -ogid=10,umask=007 /dev/hda1  /mnt/c
This command mounts a file system of type msdos (-t) with options (-o) that specify that all files are to be treated as being owned by gid 10 ('wheel' on my system) and that they should be have an effective umask of 007 (allowing members of group 'wheel' to read, write and execute anywhere on the partition. My C: drive is /dev/hda1 and I usually mount it under /mnt/c.

I tried specifying the gid by name -- no go. You have to look up the numeric in the /etc/group file. I tried different ownership and permissions on the underlying directory -- they are ignored.

This set of parameters does seem to work with vfat and umsdos mountings. Using the msdos or vfat at the time means that chmod and chown/chgrp commands dont' work on that fs. Using the -t umsdos allow me to change the ownership and permissions -- and the changes seem to be effective. However there are some oddities in what happens when you umount and remount the drive (the move of the write permission on files seems to stick but the ownership changes are lost and the owner/group r-x bits seem to "come back."

Obviously I haven't done much testing with this sort of thing. I usually don't write to my DOS partitions from in Linux. In fact I haven't see my DOS hard drive partition on this system in months (ever since I started compiling the msdos, vfat, and umsdos filesystems as modules -- so I don't automount them).

I hope that helps.

Personally I wish that the mount command would take some hints from the permissions of the directory that I'm mounting onto. I'm copying you two on this in the hopes that you'll share your thoughts on this idea.

What if the default for mount was to set the gid and umask of an msdos/vfat directory based on the ownership and permissions of the mount point. In other words I set up /mnt/c to look like:

 
drwxrwx---   2 root     wheel        1024 Aug  5  1996 c
(which I have) and mount would look up the gid for wheel and use that and the umask for the mount options.

This strikes me as being a reasonably intuitive behaviour.

If it can't be the default how about an option like:

 
		-o usemountperms
... (that particular example seems a little ugly -- but fairly self-explanatory).

-- Jim


 Re: Answer Guy - POP3 Email

From: Brent Austin, baustin@iamerica.net

In reading your answer in LG#14 on "Dealing with e-mail on a pop3 server", I have almost the same challenge. I have an ISP that is providing a 25 user POP3 Virtual Mail Server for 25 users. The problem is that each user must connect with the ISP individually and then to the mail server. I would like to find some method to allow Linux to connect with the Mail Server, individually poll each users account, and then transfer it into a POP3 server on the local network (possibly on the Linux box itself). Any suggestions??

 If I understand you correctly you have a LAN at your place with about 25 users/accounts on it. You're provider has set up 25 separate POP3 mailboxes.

You'd like to set up your Linux (or other Unix) box to fetch the contents of all of these accounts (perhaps via a cron job) and to have it process your outgoing mail queue.

Then your users would fetch their mail from the Linux box (using their own Linux user agents or perhaps using Pegasus or Eudora under Windows or from Macs.

This is relatively straightforward (especially the POP3 part).

First get a copy of 'fetchmail' (I'm using 2.5 from ftp://sunsite.unc.edu). Build that.

Now, for each user, configure fetchmail using a .fetchmailrc file in their home directory

Each will have a line that looks like:

 
poll $HOST.YOURISP.COM proto pop3 user $HISACCT password $HISPASS
The parts of the form $ALLCAPS you replace with the name of the pop server, the account holder's name and the account holder's password. (I presume that you, as the admin for this Unix box, are already entrusted with the passwords for these e-mail accounts -- since the admin of any Unix box can read any of the mail flowing through it anyway).

Now set up a script run as root that does something like:

 

	##! do mail psuedo-code
	pppup (some script that brings up your PPP link)
	for users in $USERLIST do;
		[ -e ~$user/.fetchmailrc] && \
			su -c $user /usr/local/bin/fetchmail
		done;
	/usr/lib/sendmail -q		
	pppdown
You can add a section of code that graps the list of users from your /etc/group file (if you're writing this in perl use the getgrent function (to get group entries) or you can use something like:
 
	
	awk -F":" '/'$GROUPNAME\
		'/ {split($4,users, ","); 
		for (a in users) {print users[a]}; exit}' /etc/group
To get the list of users in a form suitable for use in your 'for' loop.

Naturally my psuedo-code is closer to bash' syntax.

This script (the psuedo-code one) will just bring the ppplink up, for each user in the list (perhaps from a group named "popusers") it will check for a .fetchmailrc file in their home directory and run fetchmail for those that have one. It will then call sendmail to process your outgoing queue and bring the ppplink down.

(Note: the su -c ... part of this is not secure and there are probably some exploits that could be perpetrated by anyone with write access to any of those .fetchmailrc's. However it's probably reasonably robust -- and you could set these files to be immutable (chattr +i) and you can write a more secure SUID perl script to actually execute fetchmail. My scripts, pppup and pppdown are SUID perl scripts.

I haven't written this as real code and tested it since I don't have a need of it myself. I recommend that disconnected networks avoid using POP/SMTP for their mail feed. UUCP has been solving the problems of dialup mail delivery for 25 years and doesn't involve some of the overhead and kludges necessary to do SMTP for intermittently connected systems.

I do recommend POP/SMTP within the organization and and it's absolutely necessary for the providers.

Anyway -- fetchmail will then have put each user's mail into his or here local spool file (and processed it through any procmail scripts that they might have set up).

Now each of your users can use any method they prefer (or that you dictate) to access their mail. DOS/Windows and Mac users can use Pegasus or Eudora, Linux or other Unix users can use fetchmail (or any of several other popclient, getpop, etc, other programs) to get the messages delivered to their workstation, or anyone in the organization can use telnet into the mailhost and user elm, pine, the old UCB mail, the RAND MH system or whatever.

All of these clients point their POP and mail clients to your mailhost. Your host then acts as their spool. This is likely to result in fewer calls to your ISP and more efficient mail handling all around.

You may want to ask your ISP -- or look around -- for UUCP providers. On of the big benefits to this is that you gain complete control of mail addressing within your domain. Typical UUCP rates go for about $50/mo for a low volume account and about $100/mo for anything over 100Mb per month. However it's still possible to find bargains.

(Another nice thing about UUCP is that you can choose specific sites, with which you exchange a lot of mail, and configure your mail to be exchanged directly with them -- if they have the technical know-how at their end or are willing to let you do it for them. This can be done via direct dialup or over TCP connections).

uu.net is the Cadillac of UUCP providers (which is a bit pricey for me -- I use a small local provider who gives me a suite of UUCP, PPP, shell, virtual hosting, virtual ftp, and other services -- and is of little interest to you unless you're in the Bay Area).

You can also find information on Yahoo! using a search for "uucp providers" (duh!). I also seem to recall that win.net used to provide reasonable UUCP (and other) services.

Hope this helps. If you need more specific help in writing these scripts you may want to consider paying a consultant. It should be less than three hours work for anyone whose qualified to do it (and not including the configuration of all your local clients).

-- Jim


 Pseudo Terminal Device Questions

From: Jeong Sung Won

Hello ?
My name is Jeong Sung Won. May I ask you a question ? I'll make a program that uses PSEUDO TERMINAL DEVICE.

 No need to shout -- I've heard of them. They're commonly called pty's -- used by 'telnetd', 'expect', 'typescript', and emacs' 'M-x shell' command -- among others.

 But linux has 8 bit MINOR NUMBER, so that total number of pseudo terminal device DOESN'T OVERCOME 256.

 That does seem to be true -- but it is a rather obscure detail about he kernel's internals.

Linus' work on the 64-bit Alpha port may change this.

 Is there any possible way to OVERCOME THIS LIMITS ?

 Only two that I can think of. Both would involve patching the kernel.

You might be able to instantiate multiple major devices -- which implement that same semantics as major device number 4 (the current driver for the virtual consoles and all of the pty's).

I'm frankly not enough of a kernel hacker to tell you how to do this or what sorts of problems it would raise.

The other would involve a major overhaul of the kernel code and all the code that depends on it.

 For example,on HP9000, minor number is 24 bit, and actually I used concurrently 800 pseudo terminal device. And more than 1000 is also possible.

 I wonder what it is on RS/6000, DEC OSF/1, and Sun/Solaris.

 On Linux, is it impossible to make it, let me know the way I counld tell LINUS that upgrade minor number scheme from 8-bit to 16-bit or more-bit is needed.

 Linus Torvald's e-mail address has been included with every copy of the sources ever distributed.

However it is much better to post a message to the comp.os.linux.development.system newsgroup than directly to him (or any of other developer).

As for "telling LINUS [to] upgrade" -- while it would probably be reasonably well recieved as a suggestion -- I'm not sure that "telling" him what to do is appropriate.

It's easy to forget that Linus has done all of his work on the Linux kernel for free. I'm not sure but I imagine that the work he puts in just dealing with all the people involved with Linux is more time consuming and difficult than the actual coding.

As many of the people who are active in the Linux community are aware Linus has been very busy recently. He's accepted a position with a small startup and will be moving to the San Francisco Bay Area (Silicon Valley, actually) -- and he and Tove have just had a baby girl.

I will personally understand if these events keep him from being as active with Linux as he as been for the last few years.

-- Jim


 root login Bug in Linux

From: Shevek, ma6ybm@bath.ac.uk

Has anybody else found a root login bug evident on my system.

The root password is an 8 character random series. For going live online I updated the root password to a 16 character random series. I can log in with the 16 character series, but also using the first eight and any random characters after that, or just the first eight. This creates an infinite number of root passwords and worries me more than a little.

About Unix Passwords and Security

This is a documented and well known limitation of conventional Unix login and authentication.

You can overcome this limit if you upgrade to the shadow password suite (replace all authenticating programs with the corresponding shadow equivalents) and enable the MD5 option (as opposed to the traditional DES hash).

Note -- there is probably an "infinite" number of valid passwords to either of these schemes. The password entry on your system is not encrypted. That is a common misconception. What is stored on your system is a "hash" (a complex sort of checksum).

Specifically the traditional Unix DES hash uses your password as the key to encrypt a string of nulls. DES is a one-way algorithm -- so there is no known *efficient* way to reclaim the key even if one has copies of the plaintext and the ciphertext.

'Crack' and it's brethren find passwords by trying dictionaries of words and common word variations (reverse, replace certain letters with visually similar numerics, various abbreviations, prepending/appending one or two digits, etc) -- and using the crypt() function (or an equivalent) on a string of nul's to find matches. This isn't particularly "efficient" -- but it is several orders of magnitude better than an exhaustive brute force attack.

The only two defenses against 'Crack' are:

  1. Don't let anyone have copies of the password hashes (which is why the shadow suite puts those in a separate file -- that is only readable by SUID or SGID programs, and not normal users)
  2. Don't allow users to use words, names, or simple variations of words as their passwords. This is don't by installing npasswd or passwd+ (replacements for the stock passwd program).
Use both of these strategies on all mult-user systems. That way, if someone exploits some newly discovered bug to get a copy of the shadow file, he is less likely to get any good passwords (since that will entail a password that is more clever than your npasswd rules and less clever than your attackers custom 'crack' dictionaries).

It is possible that two different passwords (keys) will result in the same hashed value (I don't know if there are any examples with DES 56 bit within the domain of all ASCII sequence up to eight characters -- but it is possible).

Using MD5 allows you to have passwords as long as you like. Again -- it is possible (quite likely, in fact) that a number of different inputs will hash to the same value. Probably you would be looking at strings of incomprehensible ASCII that were several thousand bytes long before you found any collisions.

Considering that the best supercomputers and parallel computer clusters that are even suspected to exist take days or weeks to exhaustively brute force a single DES hash (with a max of only 8 characters and only a 56-bit key) -- it is unlikely that anyone will manage to find one of the "other" valid keys for any well chosen password without expending far more energy and computing time than most of our systems are worth. (Even in these days of cheap PC's -- computer time is a commodity with a pricetag).

There other ways to get long password support on your system. However the only reasonable one is to use the shadow suite compiled with the MD5 option. This is the way that FreeBSD (and it's derivatives) are installed by default -- so the code and systems have been reasonably well tested.

In fact -- if security and robustness are more important to you than other features you may want to consider FreeBSD or (or NetBSD, or OpenBSD) as an alternative. These are freely distributed Unix implementations which have been around as long as Linux. Obviously they have a much smaller user base. However each has a tightly knit group of developers and a devoted following which provides or an extremely robust and well-tested system.

As much as I like Linux -- I often recommend FreeBSD for dedicated web and ftp servers. Linux is better suited to the desktop and to use with exotic hardware -- or in situations where the machine needs to interact with Netware, NT and other types of systems. [Oh, Oh! Here come the fireballs!]

FreeBSD has a much more conservative set of features (no gpm support for one example -- IP packet filtering is a separate package in FreeBSD while it's built into the Linux kernel).

Another consideration is the local expertise. Linux and FreeBSD are both extremely similar in most respects (as they both are to most other Unix implementations). In some ways they are more similar to one another than either is to any non-PC Unix. However the little administrative difference might very well drive your sysadmin crazy. Particularly if he has a bunch of Linux machines and is used to them -- and you specify one or two FreeBSD systems for your "DMZ" (Internet exposed LAN segment).

Back to your original question:

You said that you are using a "random" string of characters for your password. In terms of cryptography and security you should be quite careful of that word: "random"

Several cryptographically strong systems have been compromised over the years by attacking the randomizer that were used to generate keys. A perfect example of this is the hack of SSL by a student in France (which was published last spring). He cracked a Netscape challenge and got a prize from them for the work (and Netscape implemented a better random seed generation algorithm).

In the context of creating "strong" passwords (ones that won't be tested by the best crack dictionaries out there) you don't need to go completely overboard. However -- if a specific attacker knows a little bit about how you generate your random keys -- he or she can generate a special dictionary tailored for that method.

 Kernel linux 2.0.20 System P90, 8Mb, IDE, SCSI (not working fully), cd, sound, etc. root hda2, about 20 user entries in passwd.

Next bug: Two users with consecutive login entries. Both simply information logins, never to be logged in to, just for fingering to for status information. If you finger the second, OK. But if you finger the first, it fingers both. UID numbers 25 and 26. If I comment 26, but have a third login on UID 27 then it is OK. I have tried unassigning the groups and reassigning them. They both have real home directories, shell is dev/null, and are in a group called 'private' on their own. There are no groups by the same name as the login.

 This sounds very odd. I would want to look at the exact passwd entries (less the password hashes) and to know alot about the specific implementation of 'finger' that you were using (is it the GNU cfingerd?).

I would suggest that you look at the GNU cfingerd. I think it's possible to configure it to do respond to "virtual" finger requests (i.e. you can configure cfingerd to respond to specific finger requests by return specific files and program outputs without having any such accounts on your system). This is probably safer and easier than having a couple of non-user psuedo accounts and using the traditional finger daemon. (In additional the older fingerd is notoriously insecure and overflows of it was one of the exploits used by the "Morris Internet Worm" almost a decade ago).

Given the concerns I would seriously consider running a finger daemon in a chroot'd jail. Personally I disable this and most other services in the /etc/inetd.conf when ever I set up a new system.

When I perform RASA (risk assessment and security auditing) /etc/inetd.conf is the second file I look at (after looking for a /etc/README file -- which no one but me ever keeps; and inspecting the /etc/passwd file).

-- Jim


 Sendmail-8.8.4 and Linux

From: Brent Austin, baustin@iAmerica.net

After setting up fetchmail and the PPP link to my ISP, everything has worked perfectly retrieving mail from the POP3 account.

Now, I've stumbled on another problem I require some help with. Compiling and Installing Sendmail-8.8.4 (or 8.8.5). I downloaded the 8.8.4 source from sunsite and set it up in the /usr/src directory and using the O'Reilly "Sendmail" book as my guide, I modified the Makefile.Linux for no DNS support by setting ENVDEF = -DNAMED_BIND=0. And removing Berkeley DB support (removing -DNEWDB). After compiling and executing ./sendmail -d0.1 -bt < /dev/null in the obj dir, I receive the following:

  
Version 8.8.4
 Compiled with: LOG MATCHGECOS MIME7TO8 MIME8TO7 NDBM NETINET NETUNIX
		QUEUE SCANF SMTP XDEBUG
 
and the program hangs at this point. I am running Linux.2.0.29 on a 486DX40 with 8 megs. My gcc is version 2.7.0.

Any hints you could provide are greatly appreciated!,

 I fetched a copy of 8.8.5 and used the .../src/makesendmail script -- and only encountered the problems with NEWDB Removing that seemed to work just fine.

I noticed you said -- .../src/obj -- did you mean something like: .../src/obj/obj.Linux.2.0.27.i386/

If you properly used the makesendmail script then the resulting .o and binaries should have landed in a directory such as that.

Other than that I don't know.

I don't disable the DNS stuff -- despite the fact that my sendmail almost all done via uucp.

As for using this with fetchmail -- I have my sendmail configured in /etc/inetd.conf like so:

 
# do not uncomment smtp unless you *really* know what you are doing.
# smtp is handled by the sendmail daemon now, not smtpd.  It does NOT
# run from here, it is started at boot time from /etc/rc.d/rc#.d.
## jtd:  But I *really do* know what I'm doing.
## jtd: I want fetchmail to handle mail transparently and I
## jtd want tcpd to enforce the local only restriction
smtp    stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/local\
		/sbin/sendmail -bs
(note -- the line back is for this mail only -- remove it before attempting to use this line. Also note the -bs "be an smtp handler on stdin/stdout")

This arrangement allows me to fetchmail, lets fetchmail transparently talk to sendmail, and keeps the rest of the world from testing their latest remote sendmail exploit on me while my ppp link is up (I wouldn't recommend this for high volume mail server!).

Naturally I also have a cron job like this:

 
## Call sendmail -q every half hour
00,30 * * * * root /usr/lib/sendmail -q
(which processes any mail that elm, pine, mh-e or any other mailers have left in the local queue -- awaiting their trip through uucp's rmail out to the rest of the world).

If you continue to have trouble compiling sendmail then you may want to just rely on the RPM updates. Compiling it can be tricky, so I avoid doing it unless I see a bugtraq or CERT advisory with the phrase "remotely exploitable" in it.

Re: O'Reilly's "bat" book. Do you have the 2nd Edition? If not -- get it (and ask them about their "upgrade" pricing/discount if that's still available)

-- Jim


 wu-ftpd Problems

From: Ed Stone, estone@synernet.com

On BSDI, I've read ALL of the doc for wu-ftpd, and have ftp logins limited to the chroot dir, but still have these problems: 1) I cannot force ftp only. The guestgroup "guests" can telnet, and go everywhere. I've put /bin/true in /etc/shells; I've edited passwd and master.passwd for that; no effect

 Usually I set their passwd to /bin/false or /usr/bin/passwd. I make sure that I use the path filter alias to prevent uploads of .rhosts and .forward files into their home directory under the chroot and I put entries like:

 
		/home/.ftp/./home/fred
... for their home directory field in the (true-root)/etc/passwd file.

Also make sure that you have the -a switch on the ftpd (or in.ftpd) line in your inetd.conf. The -a tells ftpd to use the /etc/ftpaccess file (or /usr/local/etc/ftpaccess -- depending on how you compiled it).

Personally I also configure each "ftponly" account into the sendmail aliases file -- to insure that mail gets properly bounced. I either set it to the user's "real" e-mail address (anywhere *off* of that machine) or I set it to point at nobody's procmail script (which autoresponds to it).

 2) "guests" ftp to the proper directory, but get no listing. I have set up executable of ls in the ftp chroot dir in /bin there; no effect.

 How do you know that they are in the proper directory? What happens if you use a chroot (8) command to go to that dir and try it? Is this 'ls' statically linked? Do you have a /dev/zero set up under your (chroot)/?

Most common cause of this situation is a incomplete (chroot) environment -- usually missing libraries or missing device nodes.

-- Jim


Copyright © 1997, James T. Dennis
Published in Issue 15 of the Linux Gazette March 1997


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"Linux Gazette...making Linux just a little more fun!"


CLUELESS at the Prompt: A Column for New Users

By Mike List, troll@net-link.net


Welcome to installment 2 of Clueless at the Prompt: a new column for new linux users. On advice from several respondents, I'm going to start using a new format for specifying commands:

    Typing them on a separate line
    separated from the text by a space

Hopefully, this will minimize any confusion by even the very inexperienced user as to what should be typed at the prompt.

Last time we explored some of the differences and similarities between linux and DOS/Windows, and I'm going to continue this time with some stuff you already know, but perhaps aren't fully aware of.

One respondent seemed to take exception to my DOS-linux comparison, reminding me of the features that make linux and unices(unix like systems) more powerful than DOS.

Fair enough, this is a new users column and I would like to make sure that I'm not assuming that everyone who reads this column can read my mind. Besides, if I endure the slings and arrows of outrageous gurus I can hopefully expand my knowledge base, which I can then use for future columns.

Still, the paradigm of SUPERDOS holds some water.It is, after all a command line operating system which supports a windowing system, which has all the capabilities of MS Windows plus a few features that make Windowslook pale.

When you installed linux from whatever distribution,most of the packages installed came as pre-compiled binaries that were for the most part usable as is. However, if you found any applications that didn't come with the distribution they'll probably need to be unpacked and installed or compiled or both.

You could use a utility like installpkg, pkgtool, or dopkg but unless the package is from the distribution, the utility will likely install it to the / (base ) directory, which is probably less than optimal.

Instead, use the midnight commander, which is a Norton Commander clone, to view the contents of the package. To do this find the file,( I don't have a CD-ROM so I'm not sure of the procedure there )locate the file, probably with .tgz or .tar.gz extension, and highlight the file, then hit enter. you will see the contents of the archive. Read the files called for instance, INSTALL, README, Readme.whatever, or any file whose name suggests that it has necessary information, for a clue as to where best to unpack it. For instance, X apps probably should be unpacked in the /usr/X11R6 directory. To unpack the archive:

     cd /thechosendirectory

then:

     tar -zxvf /wherethearchiveis/file

you will see a list of files as they unpack. When this process is done, you will be returned to your shell prompt. If you get any error messages they should be pretty self explanatory, for instance a message saying file not found means you didn't name the file correctly in the tar command, unexpected EOF means the file was very likely corrupted or download was incomplete, try to get the file one more time.

At your shell prompt type:

    ls

to see a list of files and directories that were untarred. then:

    less /anyfilenamelike INSTALL,README,Readme.*(*= unx, elf, lnx, etc)

It wouldn't hurt to check any license, or Copying files for info on propers to the authors. It also might be a good idea to print out the files if they are long or contain a lot of special instructions so you can read and reread them to minimize the possibility that you will have to recompile or reinstall. If you aren't familiar with linux printing you can just:

    cat /filename>/dev/lp0 (or lp1, or wherever your printer is located)

If you are in the directory that the file is in, you can skip the frontslash on the filename. If the files include a precompiled binary, you're done except to install if the documentation suggests a location other than where you unpacked and reboot or run ldconfig.

If you want to examine the contents of subdirectories of your current directory type:

 
    cd subdirectory   (leave off the / )

then,

 
    ls

or,

    ls subdirectory

If you cd to a subdirectory, you can return to the top level directory by typing:

 
    cd -

If you have chosen a source file distribution of the software, then you will need to read the file INSTALL very carefully to find what needs to be done. Typically you might run

    ./configure

then edit the Makefile with a text editor as described in the INSTALL or README files, then run:

 
    make 

sometimes followed by an option like linux, unx, linux-elf as instructed in INSTALL.When it is done compiling, the time will vary according to the program, type:

    make install

sometimes followed by an option as above.

The above is only a general guide to steps usually needed to install software in linux, more detailed instructions will come with the archive. READ THEM CAREFULLY!or print out the files.

Back to the DOS-Linux comparisons. In DOS there is a method of concatenating several files together under a batch file, which could be run to execute a string of commands. Linux also has this capability but it is called scripting, basically if you ever used MSEdit to create a batch file, you've done it before, except that you must change permissions to make it executable. Type:

    chmod u+x filename  

To make sure you have executable permission,type

    ls  in the directory the file is located, usually ~ , or /home/whoever you
    are

Look for an asterisk * after the filename which shows that it's an executable Then you can run the string of commands by simply typing the file name of the script you created.

Of course there's a lot more to writing scripts than this, but I'm just a GNUbee and some things take a little time. Ihave written a couple of very simple scripts to control the dialup to my ISP but they are very simple and rely on recursion rather than more correct scripting so they must be killed after they have done their jobs. An example is "on-n-on", a script I wrote to continue dialing until I can beat the busy signal on the remote modem. It is very simply:

    ppp-on
    sleep 30
    on-n-on

The script above is called up and dials every 30 seconds until a connection is reached, so when 30 seconds goes by without the modem dialling you will have a connection and can open a browser or E-mail. Before that you must quit by hitting Ctrl+C, however so that the script won't continue to use resources to do what it has already accomplished.

I am accepting suggestions as to how this could be done more correctly, but so far it works for me and I have given you an idea how simple scripts can be.

Thanks for all the input I got from readers and surprisingly from other authors, encouragement in the form of suggestions, none of them suggested that I go back to m******ft.

If I had some ideas about the kind of machines Linux is going on it would be helpful. I'm running a relatively old 486/66 with no CD-ROM so I installed from floppies, but most of the information here will be more about what can be done AFTER installation.

There is some discussion from from the Linux Users Support Team with regard to the most loved, most misunderstood linux institution, man-pages. Many people, myself included feel that they should be a little more user friendly, and some have suggested that they be replaced witha set of documents similar to howtos> Let me know what you think about man pages,how they could be improved, replaced supplemented, whatever,and I can have some info next time.

BTW, I made at least two errors in my DOS to Linux commands table, not very reassuring,but the DOS command for making a directory is:

    md
not
 mkdir

and file copy should have been:

    cp /filename /to 
not
cp /filename/filename /to

Next Time- Let me know what you would like to see in here and I'll try to oblige just e-mailtroll@net-link.net me and ask, otherwise I'll just write about what gave me trouble and how I got past it.

TTYL, Mike List


Copyright © 1997, Mike List
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Big Brother Network Monitoring System

A Web-based Unix Network Monitoring
and Notification System

By Paul M. Sittler, p-sittler@tamu.edu


Big Brother is Watching. . .

I wasn't bored: I don't have time to be bored. Texas Agricultural Extension Service operates a fairly large enterprise-wide network that stretches across hell's half acre, otherwise known as Texas. We have around 3,000 users in 249 counties and 12 district offices who expect to get their e-mail and files across our Wide Area Network. Some users actually expect the network to work most of the time. We use ethernet networking with Novell servers at some 35 locations, 15 or so whose routers are connected via a mixture of 56Kb circuits, fractional T1, Frame-Relay, and radio links. We are not currently using barbed wire fences for our network, regardless of what you may have heard. . .

I am privileged to be part of the team that set up that network and tries to keep it going. We do not live in a perfect network world. Things happen. Scarcely a day goes by when we do not have one or more WAN link outages, usually of short duration. We sometimes have our hands full trying to keep all the pieces connected. Did I mention that the users expect the mail and other software to actually work?

Cruising the USENET newsgroups, I read a posting about "Big Brother, a solution to the problem of Unix Systems Monitoring" written by Sean MacGuire of Montreal, Canada. I was intrigued to notice that Big Brother was a collection of shell scripts and simple c programs designed to monitor a bunch of Unix machines on a network. So what if most of our mission critical servers were Novell-based? Who cares if some of our web servers run on Macintosh, OS/2, Win'95 or NT? We use both Linux and various flavours of Unix in a surprisingly large number of places.

We had cooked up a number of homemade monitoring systems. Pinging and tracerouting to all the servers can be very informative. We looked at a bunch of proprietary (and expensive) network monitoring systems. It is amazing how much money these things can cost. System adminstrators often reported difficult installations and software incompatibilities with the monitoring software. Thus, frustrated users often gave us our first hint that all was not well.

According to the blurb on Big Brother:

"Big Brother is a loosely-coupled distributed set of tools for monitoring and displaying the current status of an entire Unix network and notifying the admin should need be. It came about as the result of automating the day to day tasks encountered while actively administering Unix systems."

The USENET news article provided a URL * ("http://www.iti.qc.ca/iti/users/sean/bb-dnld/") to the home site of Big Brother. I pointed my browser to it and was rewarded with a purple-sided screen background and a blue image of a sinister face peering out under the caption "big brother is watching." After my initial shock, I learned that Big Brother featured:

f e a t u r e s

* Web-based status display
* Configurable warning and panic levels
* Notification via Pager or email
* Free and includes Source Code

I was fascinated. Especially by the last item, that said it was free with source code. (I often tell people that Linux isn't free, but priceless. . .) So what could a priceless package do for me? What on earth did Big Brother check?

m o n i t o r s

* connectivity via ping
* http servers up and running
* disk space usage
* uptime and cpu usage
* essential processes are still running
* system-generated messages and warnings

Overall, very sensible. Looking for some "gotchas," I found that I would need a Unix-based machine, and:

y o u ' l l
n e e d

* A Functioning Web server & Browser - for the display
* C compiler
* Kermit and a modem line - for the pager

A web server was no problem, as we run many. A c compiler came with Linux, and we use kermit on many machines with modems. So far, so good.

The web site provided links to a few demonstration sites, and a link to download it as well. I connected to a demonstration site and was greeted with an amazing display:

Legend

green System OK
yellow Attention
red Trouble
blue No report


Updated
@ 22:52

BIG BROTHER

help
info
page
view

conn

cpu

disk

http

msgs

procs

*iti-s01 green green green green yellow green
router-000 green - - - - -
inet-gw-0 green - - - - -

Big Brother is watching! As I endured the scrutiny of the Orwellian face peering out at me, I examined the rest of the display. The display was coded like a traffic signal (green/yellow/red), and the update time was clearly displayed beneath it. To the right of "Big Brother" were four buttons, marked clearly "Help," "Info," "Page" and "View." Beneath the header area was a table with six column headings and three rows, each neatly labelled with a computer hostname. The boxes formed by the intersection of the rows and columns contained attractive green and yellow balls. The overall effect was like a decorated tree. The left side of the screen had a yellow tint, gradually becoming black at the center.

I selected the "Help" button and was rewarded with a brief explanation of what Big Brother was all about. Choosing the "Info" Button provided a much longer and more detailed explanation of the system, including a graphic that really was worth a thousand words. I tried the "Page" button to discover that this was a way to send a signal to a radio-linked pager. Not at all what I had expected! Finally, the "View" selection provided a briefer but perhaps more useful view of the information, isolating only the systems with problems.

In this case, only the "iti-s01" system was displayed. My browser cursor indicated a link as it passed over each colored dot, so I clicked on the blinking yellow dot and received a message that read:

"yellow Tue Feb 18 22:50:53 EST 1997 Feb 16 12:22:33 iti-s01 kernel: WARNING: / was not properly dismounted"

This puzzled me at first. How on earth could it know that? It seems that BB (Big Brother) checks the system /var/log/messages file periodically and alerts on any line that says either "WARNING" or "NOTICE." As I am certain that Sean MacGuire is very conscientious, I suspect that he adds that line to his message file so that something will appear to be wrong.

Suddenly, my screen spontaneously updated! The update time had changed by five minutes, and a blinking yellow dot appeared under the column labelled "procs." I clicked on the blinking yellow dot and was informed that the sendmail process was not running. This got me really interested! Apparently, Big Brother could monitor whether selected processes were running!

I was also a little puzzled about the screen being updated on its own. I used my browser to view the document source and discovered some html commands that were new to me:

    <META HTTP-EQUIV="REFRESH" CONTENT="120">
    <META HTTP-EQUIV="EXPIRES" CONTENT="Tue Feb 18 23:22:07 CST 1997">

The first line instructs browsers to get an update every 120 seconds. The second line tells the browser that it should get a new copy after the expiration time and date. Very clever!

I returned to the graphics window and discovered that the yellow area on the left had changed to red! A new hostname row appeared with a blinking red dot under the column labelled "conn." I clicked on the blinking red dot and read a message that said:

"red Tue Feb 18 22:59:11 CST 1997 bb-network.sh: Can't connect to router-000... (paging)"

The connection to the machine called router-000 had been interrupted and the administrator had been paged. Amazingly, while in Texas, I had become aware of a network outage in Montreal, Canada. This really had possibilities. Perhaps I might someday be able to take a vacation!

Big Brother Installation

I was so impressed with Big Brother that I decided to try to use it. Sean has thoughtfully made its acquisition easy, but requests that you fill out an on-line registration form with your name and e-mail address. He would also like to know where you heard about Big Brother. I filled these out in early November 1996, and received an e-mail survey form in late December.

*

d o w n l o a d

Click the link at left to download Big Brother and to get technical information about how the system works, and how to install and configure the package.

When I clicked on the link to download Big Brother, I ended up with a file called "bb-src.tgz." I impetuously gunzipped this to get "bb-src.tar." I then thought better of the impending error of my ways and decided to download and print the installation instructions.

*

i n s t a l l

Click the link at left to look at the install procedure for Big Brother. More information about how to set the system up lives here.

Just in case, I also grabbed and printed the debugging information so thoughtfully provided (as it turned out, I did not need it):

*

d e b u g

The link at left provides debugging information for different problems that may be experienced during the Big Brother installation process.

I had no real problems following the installation instructions. I decided to make the $BBHOME directory "/usr/src/bb"; use whatever makes sense to you. The automatic configuration routines are said to work for AIX, FreeBSD, HPUX 10, Irix, Linux, NetBSD, OSF, RedHat Linux, SCO, SCO 3/5, Solaris, SunOS4.1, and UnixWare. I can vouch for Linux, RedHat Linux, Solaris, and SunOS 4.1.

The c programs compiled without incident, and the installation went smoothly. As always, your mileage may vary. In less than an hour, I was looking at Big Brother's display of coloured lights!

At this point, you may wish to re-examine the documentation and information files. Personalize your installation as desired. Above all, have fun!

Hacking

I admit it. I am a closet hacker. I saw many things about the stock BB distribution that I wanted to improve. Big Brother's modular and elegantly simple construction makes it a joy to modify as desired. The shell scripts are portable, simple, well documented, and easy to understand. The use of the modified hosts file to determine which hosts to monitor was gratifyingly familiar. The "bbclient" script made it extremely easy to move the required components to another similar Unix host. Sean has done a remarkable job in making this package easy to install!

I got obsessive-compulsive about hacking BB and modified it slightly, working from Sean MacGuire's v1.03 distribution as a base. I forwarded my changes to him for possible inclusion in a later distribution.

Features that I added to BB proper include (code added is bold):

# traceroute.cgi ===========================================
#!/bin/sh

TRACEROUTE=/usr/bin/traceroute

echo Content-type: text/html
echo

if [ -x $TRACEROUTE ]; then
        if [ $# = 0 ]; then
                cat << EOM
<TITLE>TraceRoute Gateway</TITLE>
<H1>TraceRoute Gateway</H1>

<ISINDEX>

This is a gateway to "traceroute."  Type the desired hostname
(like hostname.domain.name, eg. net.tamu.edu) in your
browser's search dialog, and enter a return.<P>

EOM
        else
                echo \<PRE\>
                $TRACEROUTE $*
        fi
else
        echo Cannot find traceroute on this system.
fi
# traceroute.cgi ===========================================


# ping.cgi ===========================================
#!/bin/sh

PING=/bin/ping

echo Content-type: text/html
echo

if [ -x $PING ]; then
        if [ $# = 0 ]; then
                cat << EOM
<TITLE>TraceRoute Gateway</TITLE>
<H1>TraceRoute Gateway</H1>

<ISINDEX>

This is a gateway to "ping." Type the desired hostname
(like hostname.domain.name, eg. "net.tamu.edu") in your
browser's search dialog, and enter a return.<P>

EOM
        else
                echo \<PRE\>
                $PING -c5 $*
        fi
else
        echo Cannot find ping on this system.
fi

# ping.cgi ===========================================

Future Enhancements of Big Brother

Sean MacGuire is the primary author of Big Brother. In the finest InterNet tradition of decentralized shared software development, Sean solicits improvements, suggestions, and enhancements from all. He then skillfully incorporates them as appropriate into the Big Brother distribution. Thus, like Linux, Big Brother is in a dynamic state of positive evolution with contributions from a cast of thousands (at least dozens). This constrained anarchy can produce interesting results with an international flavour.

Jacob Lundqvist of Sweden is actively improving the paging interface. He has done a superb job of enhancing the paging portion, adding support for alphanumeric and SMS pagers. Darren Henderson (Maine, US) added AIX support. David Brandon (Texas, US) added proper IRIX support, and Jeff Matson (Minnesota, US) made some IRIX fixes. Richard Dansereau (Canada) ported Big Brother to SCO3 and provided support for other df's. Doug White (Oregon, US) made some paging script bug fixes. Ron Nelson (Minnesota, US) adapted BB to RedHat Linux. Jac Kersing (Netherlands) made some security enhancements to bbd.c. Alan Cox (Wales) suggested some shell script security modifications. Douwe Dijkstra (Netherlands) provided SCO 5 support. Erik Johannessen (Minnesota, US) survived SunOS 4.1.4 installation. Curtis Olson (Minnesota, US) survived IRIX, Linux, and SunOS installations. Gunnar Helliesen (Norway) ported Big Brother to Ultrix, OSF, and NetBSD. Josh Wilmes (Missouri, US) added Solaris changes for new ping stuff.

Many other unsung heros around the world are undoubtedly working to enhance BB at this very moment.

I am (ab)using Big Brother in ways not originally envisioned by its creator, Sean MacGuire. Texas Agricultural Extension's networks are wildly heterogeneous mixtures of different operating systems and protocols, rather than a homogeneous Unix-based network. I would like to see Big Brother learn about IPX/SPX protocols for Novell connectivity monitoring. I would also like to see Big Brother data collection modules for Macintosh, Novell, OS/2, Windows 3.1x, Windows'95, and Windows NT. Rewriting Big Brother into perl might better serve these disparate platforms. If I could only find the time!

Big Brother's Impact at Texas Agricultural Extension Service

We are now monitoring around 122 hosts. Only 20 are actually Unix-based hosts that run Big Brother's bb program internally. Some 28 are Novell servers, 39 are routers, and the rest are a mixture of Macintosh, OS/2, Windows 3.1x, Windows'95, and Windows NT machines running one or more types of servers (34 ftp or 26 http). We also find it useful to monitor our 31 popmail post offices and 43 mail hosts and gateways. We are checking connectivity on three DNS servers as well, as they are mission critical.

Big Brother (or, as I now affectionately refer to it, "Big Bother") is now alerting us to outages five or more times daily. Typically, the system administrator receives a page. BB's display is checked and the info file is used to traceroute and ping the offending machine to validate the outage. Many connection outages involve routers, DSU/CSUs and multiplexors as well as the actual host. BB's display allows us to quickly see a pattern that aids in diagnosis. The ability to dynamically traceroute and ping the host from the html info page also helps to rapidly determine the actual point of failure. If the administrator paged cannot correct the problem, he relays it to the responsible person or agency.

Before we installed Big Brother, we were frequently notified of these failures by frustrated users telephoning us. Now, we are often aware of what has failed before they call us. The users are also becoming aware that they may monitor the network through the WWW interface. In many instances, we are able to actually correct the problem before it perturbs our users. It is difficult to accurately measure the time saved, but we estimate that Big Brother has had a net positive effect.

We have a machine in a publicly visible area displaying the brief view of Big Brother. The green, yellow, red and blue screen splashes are clearly visible far down the hall. This helps our network team to be more aware of problems as they occur. The accessibility of the WWW page has made Big Brother useful even to people at the far ends of our network. So far, we are not inclined to shut Big Brother down. It has become a helpful member of our network team.

Maybe now I'll have time to be bored. . .


Texas Agricultural Extension WWW Server (http://taex.tamu.edu/)
Extension Information Technology / Texas Agricultural Extension Service
The Texas A&M University System / College Station, Texas 77843-2468
This page was last modified Thu Feb 20 15:47:14 1997 by *PMS. (URL=http://taex001.tamu.edu/bb/articles/bbartlg.html)


Copyright © 1997, Paul M. Sittler
Published in Issue 15 of the Linux Gazette, March 1997


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Date and Its Switches

by Larry Ayers


At first glance the humble GNU utility date seems to be a very minor program, perhaps useful in shell-scripts but hardly something to get excited about. Type "date" at the prompt, press enter, and "Tue Feb 11 09:25:50 CST 1997" (or something similar) is displayed on your screen. As with so many unix-ish utilities, the bare command is really just a template, waiting to be laden with switches.

I keep a journal, and I've been using a header line for each entry with this format:


Tue 11 Feb 1997       *** Journal Entry #44 ***       9:30 PM

Weary of typing the header each day, some time ago I began attempts to automate it. Creating an abbreviation or macro for the center field is not hard with most editors, but I wanted the date and time as well. Reading the man page for date I discovered that it has numerous formatting switches. You can make the command print out the date and/or the time in just about any fashion you can think of. The first field of the above header can be created with these switches:

date '+%a %-d %b %Y'

while the time-of-day field uses these:

date '+%-I:%M %p'

The single quotes are essential when combining several of the switches. I tried for some time to get the command to do what I wanted without success; while rereading the man- page I eventually noticed the quotes. Of course no-one is going to memorize date's numerous switches, which is probably one reason the shell script was invented. I wrote two short scripts; the first, called mydate, is just:


#!/bin/bash
date '+%a %-d %b %Y'

The second, called mytime is the similar but with the above time switches for date.

Typing the daily header in Emacs was now somewhat easier: first the command Control-u Esc-!; when prompted in the mini-buffer I'd type mydate and the formatted date would begin the line. Next a keyboard macro for the center "Journal Entry" field, then a command like the first to have the time inserted at the end of the line.

After performing this little keyboard ritual for a few days, it occurred to me that perhaps an Emacs macro could have a shell command embedded within it. Reading a few Info files confirmed this supposition and suggested yet another refinement. I learned that it's possible to cause a macro to pause for input and then resume! This would be just ideal for the journal entry number.

The sequence which I came up with was: Control-( to start recording the macro, then Control-u Esc-! followed (when prompted) by mydate. At this point I typed in some spaces, then *** Journal Entry #, followed by Control-u Control-x q to start a recursive edit; this pauses the macro and allows the entry number to be entered. Next is Esc Control-c which exits the recursive edit and lets the macro proceed. The macro is completed with some more spaces, then control-u Esc-!, the mytime shell-script command, and ends with two Enter keystrokes and two spaces, to indent the first sentence. Control-) stops the macro-recording. Whew! That's a lot harder to describe than to type.

This routine would be ridiculously esoteric if you had to remember it. Luckily in Emacs you only have to do it one time. Once you've constructed such a macro and tried it out to see if it does what you want, two more steps will record it in your ~/.emacs file so that it can be executed with a simple keystroke.

The first step is to give the macro a name, which can be anything. Esc-x name-last-kbd-macro, followed by Return, then the name and another Return, sets the name. At this point load your ~/.emacs file, move the cursor to where you want the macro definition, then type Esc-x insert-kbd-macro, followed by Return. There you go! As long as you keep your ~/.emacs file you'll have the macro available. Now you can type Esc-x [macroname] and it'll execute. If you've put a recursive edit in it, just remember to type Esc Control-c after you've inserted the text you need and the macro will conclude.

This may seem like a convoluted procedure, and it is, the first time you do it: haltingly typing in a macro, starting over from scratch after one mis-typed character, all the while frequently referring to the docs. Then repeating the process when it doesn't do what you wanted!

The second time you will probably remember about half of the commands, enough that it's no longer a tortuous task. Creating and saving macros using these techniques isn't an everyday task; I've found that I have to refresh my memory on at least part of the procedure every time I do it, but for repetitive editing tasks the time spent is amply repaid.

If you make very many of these you risk bloating your ~/.emacs file, causing the editor to load even more slowly and wasting memory. Typically these macros have a specific use, so it makes sense to keep them in categorised LISP files, one for each type of file you edit. Put each file in the directory where it will be used, and load them on demand with the command Esc-x load-file [filename].

So there is a reason the Emacs partisans like to call it an "extensible" editor. These macros are just the tip of the iceberg; over the years many LISP extensions to Emacs have been contributed to the free software community by programmers world-wide. Luckily some of the best of them tend to be incorporated into successive releases of Emacs and XEmacs; many others are available from the * Emacs-Lisp Archive. Another good source for Emacs information is the * Gnu Emacs and XEmacs Information and Links Site.


*Larry Ayers<layers@vax2.rainis.net>
Last modified: Thu Feb 27 18:39:47 CST 1997


Copyright © 1997, Larry Ayers
Published in Issue 15 of the Linux Gazette, March 1997


[ TABLE OF CONTENTS ] [ FRONT PAGE ]  Back  Next


"Linux Gazette...making Linux just a little more fun!"


SSC is expanding Matt Welsh's Linux Installation & Getting Started by adding chapters about each of the major distributions. Each chapter is being written by a different author in the Linux community. Here's a sneak preview -- the Debian chapter by Boris Beletsky, one of the Debian developers. --Editor


Debian Linux Installation & Getting Started

By Boris D. Beletsky, borik@isracom.co.il


Table of contents

1. Getting and installing Debian GNU/Linux.
1.1 Getting floppy images.
1.2 Preparing the floppies.
1.3 Downloading the packages.
1.4 Booting from floppies and installing Debian GNU/Linux.
2. Running Debian GNU/Linux.
2.1 Debian packaging system and package installation utilities.
2.1.1 Package Classifications.
2.1.2 Package Relationships.
2.1.3 Dselect.
2.1.4 Dpkg.
3. About Debian.
3.1 Debian community.
3.2 Mailing lists.
3.3 Bug tracing system.
4. Almost the end.
4.1 Acknowledgments.
4.2 Last Note.
4.3 Copyright.

1. Getting and installing Debian GNU/Linux

META: I will not expand on system requirements here because this subject is surely covered in previous chapters of this book or in the "Linux Hardware Compatibility HOWTO" located at * http://sunsite.unc.edu/mdw/HOWTO/Hardware-HOWTO.html.

1.1 Getting floppy images

If you have access to the Internet, the best way to get Debian is via anonymous FTP (File Transfer Protocol). The home *ftp site of Debian is located at ftp.debian.org in /pub/debian directory. The structure of debian archive is built as following:

./stable/ (latest stable debian release)
./stable/binary-i386 (debian packages for i386 architecture)
./stable/disks-i386 (boot and root disks needed for Debian installation)
./stable/disks-i386/current (The current boot floppy set)
./stable/disks-i386/special-kernels (Special kernels and boot floppy disks, for hardware configurations that refuse working with our regular boot floppies)
./stable/msdos-i386 (dos short file names for debian packages)

For base installation of Debian you will need about 12 megabytes of disk space, and some floppies. First you will need boot and root floppy images. Debian provides two sets of installation floppy images, for floppy 1440 and 1200 floppy drives. Check what floppy drive your system boots from, (it is the A: drive under Dos) and download the appropriate disk set. Files in ./stable/disks-i386/current:

Filename Label Description
rsc1440.bin "Rescue Floppy" Floppy set for systems with 1.2MB floppy drive and at least 5MB RAM.
drv1440.bin "Device Drivers"
base14-1.bin "Base 1"
base14-2.bin "Base 2"
base14-3.bin "Base 3"
base14-4.bin "Base 4"
root.bin "Root Disk"
rsc1440r.bin "Rescue Floppy" Optional Rescue Disk image for low memory systems (less then 5MB of RAM)
rsc1200r.bin "Rescue Floppy" Floppy set for systems with 1.44MB floppy drive
drv1200.bin "Device Drivers"
base12-1.bin "Base 1"
base12-2.bin "Base 2"
base12-3.bin "Base 3"
base12-4.bin "Base 4"
root.bin "Root Disk"

Choose the appropriate floppy set, corresponding to your hardware setup (Ram and floppy drive). What ever you choose, at the end you have to have 7 floppy images which contain, "Rescue Floppy", "Device Drivers, "Base 1", "Base 2" ..., "Root Disk". (Note, "Root Disk" image is the same for all drives and system types.)

1.2 Preparing the floppies

Next step is to prepare the floppies for the installation by copying the images into disks. Hence those files are disk images, they should be copied block-by-block. In Dos you can use the RAWRITE utility for that purpose located at * ftp://ftp.debian.org/pub/debian/tools/rawrite2.exe. Here is a brief explanation on how to use it:

C:\> RAWRITE2  
By executing the RAWRITE2 command as stated above, you will accomplish the following, the file "<file>" will be copied block-by-block into the drive "<drive>".

On any Unix like operation systems you can use dd(1):

# dd if=file of=/dev/fd0 bs=10k
META: In some Unix systems the first floppy device maybe named differently.

When you finish rawriting don't forget to mark the floppies else you will get confused later.

1.3 Downloading the packages

In order to install and use Debian you will need more then the base system. To decide what packages you want on your system download the file 'Packages' from * ftp://ftp.debian.org/pub/debian/stable/Packages. This file is a list of Debian packages available for the moment in stable Debian distribution. This file comes in special format, evry package has it's own entry separated by a blank line, here is an explanation of each field in the package entry:

Package: The name of the package.
Priority: The state of importance of the package.
Required - Should be installed for system to work properly.
Important - Not required though, important.
Optional - Doesn't have to be installed but still useful.
Extra - Package may conflict with. other packages with higher priorities.
Section: This field declares a Debian section of the package.
Base - base system.
Devel - development tools.
X11 - XWindows packages.
Admin - administration utilities.
Doc - documentation.
Comm - various communication utilities.
Editors - various editors.
Electronics - electronics utilities.
Games - games (you knew that didn't you?).
Graphics - graphics utilities.
Hamradio - utilities for internet radio.
Mail - email clients and servers.
Math - mathematics utilities (such as calculators, etc...).
Net - various tools to connect to the network (usualy TCP/IP).
News - servers and clients for internet news (NNTP).
Shells - shells, such as tcsh, bash.
Sound - any sound applications (such as, cd players).
TeX - anything that can read, write, and convert TeX.
Text - applications to manipulate texts. (such as nroff)
Misc - everything else that doesn't fit in the above.
Maintainer: The name of the person who maintains the package and his contact Email address.
Version: The version of the package in the following format: <upstream-version>-<debian-version>.
Depends: That field declares the dependency of the package with another one (or more), that means that this package can not be used or installed without the other packages listed in this field.
Recommends: Another level of package dependencies. It is strongly recommended to install the packages listed in this field together with the package this entry entry describes.
Suggests: Packages listed in this field maybe useful to the packages this entry entry describes.
Filename: Filename of the package on ftp/cdrom.
Msdos-Filename: Filename of the package in dos short format.
Size: The size of the package after the installation.
Md5sum: The md5sum check to be sure that this package came from us.
Description: This field will tell you about the package (finally!), DO NOT download the package without reading it.

META: More detailed explanation on Debian packaging scheme you can find in section 2.1 of this chapter.

The above should give you an idea on how to build your personal download list. When you have the list of packages you want to download, you will have to decide how and when you want to download them. If you are an experienced user you may want to download the netbase package, and slip/ppp if needed, for later downloading from linux. Otherwise you can download all the packages from your current OS and install them later from mounted partition.

1.4 Booting from floppies and installing Debian GNU/Linux

The Rescue Floppy

Place the Rescue floppy in the a: floppy drive, and reset the system by pressing reset, turning the system off and then on, or by pressing Control-Alt-Del on the keyboard. The floppy disk should be accessed, and you should then see a screen that introduces the rescue floppy and ends with the boot: prompt. It's called the Rescue floppy because you can use it to boot your system and perform repairs if there is ever a problem that makes your hard disk unbootable. Thus, you should save this floppy after you've installed your system.

You can do two things at the boot: prompt. You can press the function keys F1 through F10 to view a few pages of helpful information, or you can boot the system. If you have any hardware devices that aren't made accessible from Linux correctly when Linux boots, you may find a parameter to add to the boot command line in the screens you see by pressing F3, F4, and F5. If you add any parameters to the boot command line, be sure to type the word linux and a space before the first parameter. If you simply press Enter, that's the same as typing linux without any special parameters.

If this is the first time you're booting the system, just press Enter and see if it works correctly. It probably will. If not, you can reboot later and look for any special parameters that inform the system about your hardware.

Once you press Enter, you should see the message Loading..., and then Uncompressing Linux..., and then a page or so of cryptic information about the hardware in your system. There may be a many messages in the form can't find something, or something not present, can't initialize something, or even this driver release depends on something. Most of these messages are harmless. You see them because the installation boot disk is built to run on computers with many different peripheral devices. Obviously, no one computer will have every possible peripheral device, so the operating system may emit a few complaints while it looks for peripherals you don't own. You may also see the system pause for a while. This happens when it is waiting for a device to respond, and that device is not present on your system. If you find the time it takes to boot the system unacceptably long, you can create a custom kernel once you've installed your system without all of the drivers for non-existent devices.

Low-Memory Systems

If you system has 4MB RAM, you may now see a paragraph about low memory and a text menu with three choices. If your system has enough RAM you won't see this at all, and you'll go directly to the color-or-monochrome dialog box. If you get the low-memory menu, you should go through its selections in order. Partition your disk, activate the swap partition, and start the graphical installation system. The program that is used to partition your disk is called cfdisk, and you should use the manual page for cfdisk as an aid in its operation. Use cfdisk to create a Linux Swap partition (type 82). You need the swap partition to provide virtual memory during the installation process, since that process will use more memory than you have in your system. Select the size for the amount of virtual memory you intend to use once your system is installed. 16 megabytes is probably the lowest amount that's practical, use 32 megabytes if you can spare the space, and 64 if your disk is large enough that you won't miss that much.

The Color-or-Monochrome Dialog Box

Once the system has finished booting, you should see the color or monochrome choice dialog box. If your monitor displays black-and-white, press Enter to continue with the installation. Otherwise, use the arrow key to move the cursor to the Color menu item and then press Enter. The display should change from black-and-white to color. Then press Enter again to continue with the installation.

The Main Menu

You may see a dialog box that says The installation program is determining the current state of your system. On some systems, this will go by too quickly to read. You'll see this dialog box between steps in the main menu. The installation program will check the state of the system in between each step. This checking allows you to re-start the installation without losing the work you have already done if you happen to halt your system in the middle of the installation process. If you have to restart an installation, you will have to configure color-or-monochrome, configure your keyboard, re-activate your swap partition, and re-mount any disks that have been initialized. Anything else that you have done with the installation system will be saved.

During the entire installation process, you will be presented with the main menu. The choices at the top of the menu will change to indicate your progress in installing the system. Phil Hughes wrote in Linux Journal that you could teach a chicken to install Debian! He meant that the installation process was mostly just pecking at the return key. The first choice on the installation menu is the next action that you should perform according to what the system detects you have already done. It should say Next, and at this point the next item should be Configure the Keyboard.

Configuring the Keyboard

Make sure the highlight is on the Next item, and Press Enter to go to the keyboard configuration menu. Select a keyboard that conforms to the layout used for your national language, or select something close if the keyboard layout you want isn't represented. Once the system is installed, you'll be able to select a keyboard layout from a wider range of choices. Move the highlight to the keyboard selection you desire and press enter. Use the arrow keys to move the highlight - they are in the same place in all national language keyboard layouts, so they are independent of the keyboard configuration.

The Shell

If you are an experienced Unix or Linux user, press LeftAlt-F2 to get to the second virtual console. That's the Alt key on the left-hand side of the space bar, and the F2 function key, at the same time. This is a separate window running a Bourne shell clone called ash. At this point you are booted from the RAM disk, and there is a limited set of Unix utilities available for your use. You can see what programs are available with the command ls /bin /sbin /usr/bin /usr/sbin. Use the menus to perform any task that they are able to do - the shell and commands are only there in case something goes wrong. In particular, you should always use the menus, not the shell, to activate your swap partition, because the menu software can't detect that you've done this from the shell. Press LeftAlt-F1 to get back to menus. Linux provides up to 64 virtual consoles, although the Rescue floppy only uses a few of them.

Last Chance!

Did we tell you to back up your disks? Here's your first chance to wipe out all of the data on your disks, and your last chance to save your old system. If you haven't backed up all of your disks, remove the floppy from the drive, reset the system, and run backups.

Partition Your Hard Disks

If you have not already partitioned your disks for Linux native and Linux swap filesystems, the menu item Next will be Partition a Hard Disk. If you have already created at least one Linux Native and one Linux Swap disk partition, the Next menu selection will be Initialize and Activate the Swap Disk Partition, or you may even skip that step if your system had low memory and you were asked to activate the swap partition as soon as the system started. Whatever the Next menu selection is, you can use the down-arrow key to select Partition a Hard Disk.

The Partition a Hard Disk menu item presents you with a list of disk drives you can partition, and runs the cfdisk program, which allows you to create and edit disk partitions. The cfdisk manual page is included with this document, and you should read it now. You must create one "Linux" (type 83) disk partition, and one "Linux Swap" (type 82) partition.

Your swap partition will be used to provide virtual memory for the system and should be between 16 and 128 megabytes in size, depending on how much disk space you have and how many large programs you want to run. Linux will not use more than 128 megabytes of swap, so there's no reason to make your swap partition larger than that. a swap partition is strongly recommended, but you can do without one if you insist, and if your system has more than 16 megabytes of RAM. If you wish to do this, please select the Do Without a Swap Partition item from the menu.

The "Linux" disk partition will hold all of your files, and you may make it any size between 40 megabytes and the maximum size of your disk minus the size of the swap partition. If you are already familiar with Unix or Linux, you may want to make additional partitions - for example, you can make partitions that will hold the /var, and /usr, filesystems.

Initialize and Activate the Swap Disk Partition

This will be the Next menu item once you have created one disk partition. You have the choice of initializing and activating a new swap partition, activating a previously-initialized one, and doing without a swap partition. It's always permissible to re-initialize a swap partition, so select Initialize and Activate the Swap Disk Partition unless you are sure you know what you are doing. This menu choice will give you the option to scan the entire partition for un-readable disk blocks caused by defects on the surface of the hard disk platters. This is useful if you have MFM, RLL, or older SCSI disks, and never hurts. Properly-working IDE disks don't need this choice, as they have their own internal mechanism for mapping out bad disk blocks.

The swap partition provides virtual memory to supplement the RAM memory that you've installed in your system. It's even used for virtual memory while the system is being installed. That's why we initialize it first.

Initialize a Linux Disk Partition

At this point, the Next menu item should be Initialize a Linux Disk Partition. If it isn't, it's because you haven't completed the disk partitioning process, or you haven't made one of the menu choices dealing with your swap partition.

You can initialize a Linux Disk partition, or alternately you can mount a previously-initialized one.

These floppies will not upgrade an old system without removing the files - Debian provides a different procedure than using the boot floppies for upgrading existing Debian systems. Thus, if you are using old disk partitions that are not empty, you should initialize them (which erases all files) here. You must initialize any partitions that you created in the disk partitioning step. About the only reason to mount a partition without initializing it at this point would be to mount a partition upon which you have already performed some part of the installation process using this same set of installation floppies.

Select the Next menu item to initialize and mount the / disk partition. The first partition that you mount or initialize will be the one mounted as / (pronounced root). You will be offered the choice to scan the disk partition for bad blocks, as you were when you initialized the swap partition. It never hurts to scan for bad blocks, but it could take 10 minutes or more to do so if you have a large disk.

Once you've mounted the / partition, the Next menu item will be Install the Base System unless you've already performed some of the installation steps. You can use the arrow keys to select the menu items to initialize and/or mount disk partitions if you have any more partitions to set up. If you have created separate partitions for /var, /usr, or other filesystems, you should initialize and/or mount them now.

Install the Base System

This should be the Next menu step after you've mounted your / disk, unless you've already performed some of the installation steps on /. Select the Install the Base System menu item. There will be a pause while the system looks for a "local copy" of the base system. This search is for CD-ROM installations and will not succeed, and you'll be offered a menu of drives to use to read the base floppies. Select the appropriate drive. Feed in the Base 1, 2, and 3 (and 4 if you are using 1.2MB floppies) as requested by the program. If one of the base floppies is unreadable, you'll have to create a replacement floppy and feed all 3 (or 4) floppies into the system again. Once the floppies have all been read, the system will install the files it's read from them. This could take 10 minutes or more on slow systems, less on faster ones.

Install the Operating System Kernel

At this point, the Next menu item should be Install the Operating System Kernel. Select it, and you will be prompted to select a floppy drive and insert the rescue floppy. This will copy the kernel on to the hard disk. In a later step this kernel will be used to create a custom boot floppy for your system, and to make the hard disk bootable without a floppy.

Install the Device Drivers

Select the menu item to install the device drivers, and you'll be prompted to insert the device drivers floppy. The device drivers will be copied to your hard disk. Select the Configure Device Drivers menu item and look for devices that are on your system. Configure those device drivers, and they will be loaded whenever your system boots.

There is a menu selection for PCMCIA device drivers, but you need not use it . Once your system is installed, you can install the pcmcia-cs package. This detects PCMCIA cards automatically, and configures the ones it finds. It also copes with hot-plugging the cards while the system is booted - they will all be configured as they are plugged in, and de-configured when you unplug them.

Configure the Base System

At this point you've read in all of the files that make up a minimal Debian system, but you must perform some configuration before the system will run. Select the Configure the Base System menu item.

You'll be asked to select your time zone. Look for your time zone or region of the world in the menu, and type it at the prompt. This may lead to another menu, in which you can select your actual time zone.

Next, you'll be asked if your system clock is to be set to GMT or local time. Select GMT if you will only be running Linux and Unix on your system, and select local time if you will be running another operating system such as DOS or Windows. Unix and Linux keep GMT time on the system clock and use software to convert it to the local time zone. This allows them to keep track of daylight savings time and leap years, and even allows users who are logged in from other time zones to individually set the time zone used on their terminal. If you run the system clock on GMT and your locality uses daylight savings time, you'll find that the system adjusts for daylight savings time properly on the days that it starts and ends.

Configure the Network

You'll have to configure the network even if you don't have a network, but you'll only have to answer the first two questions - what is the name of your computer?, and is your system connected to a network?.

If you are connected to a network, here come some questions that you may not be able to figure out on your own - check with your system administrator if you don't know:

Some technical details you might, or might not, find handy: the program will guess that the network IP address is the bitwise-AND of your system's IP address and your netmask. It will guess the broadcast address is the bitwise OR of your system's IP address with the bitwise negation of the netmask. It will guess that your gateway system is also your DNS server. If you can't find any of these answers, use the system's guesses - you can change them once the system has been installed, if necessary, by editing /etc/init.d/network .

Make the Hard Disk Bootable

If you select to make the hard disk boot directly to Linux, you will be asked to install a master boot record. If you aren't using a boot manager (and this is probably the case if you don't know what a boot manager is), answer yes to this question. The next question will be whether you want to boot Linux automatically from the hard disk when you turn on your system. This sets Linux to be the bootable partition - the one that will be loaded from the hard disk. If you answer no to this question, you can set the bootable partition later using the DOS fdisk program, or with the Linux fdisk or activate programs.

If you are installing Linux on a drive other than the first hard disk in your system, be sure to make a boot floppy. The boot ROM of most systems is only capable of directly booting from the first hard drive, not the second one. You can, however, work around this problem once you've installed your system. To do so, read the instructions in the directory /usr/doc/lilo.

Make a Boot Floppy

You should make a boot floppy even if you intend to boot the system from the hard disk. The reason for this is that it's possible for the hard disk bootstrap to be mis-installed, but a boot floppy will almost always work. Select Make a Boot Floppy from the menu and feed the system a blank floppy as directed. Make sure the floppy isn't write-protected, as the software will format and write it. Mark this the "Custom Boot" floppy and write-protect it once it has been written.

The Moment of Truth

This is what electrical engineers call the smoke test - what happens when you turn on a new system for the first time. Remove the floppy disk from the floppy drive, and select the Reboot the System menu item. If the Linux system doesn't start up, insert the Custom Boot floppy you created and reset your system. Linux should boot. You should see the same messages as when you first booted the installation boot floppy, followed by some new messages.

Set the Root Password

This is the password for the super-user, a login that bypasses all security protection on your system. It should only be used to perform system administration, and only for as short a time as possible. Do not use root as your personal login. You will be prompted to create a personal login as well, and that's the one you should use to send and receive e-mail and perform most of your work, not root. The reason to avoid using root's privileges is that you might be tricked into running a trojan-horse program - that is a program that takes advantage of your super-user power to compromise the security of your system behind your back. Any good book on Unix system administration will cover this topic in more detail - consider reading one if it's new to you. The good news is that Linux is probably more secure than other operating systems you might run on your PC. DOS and Windows, for example, give all programs super-user privilege. That's one reason that they have been so plagued by viruses.

All of the passwords you create should contain from 6 to 8 characters, and should contain both upper and lower-case characters, as well as punctuation characters.

Once you've added both logins, you'll be dropped into the dselect program. The Dselect Tutorial is required reading before you run dselect. Dselect allows you to select packages to be installed on your system. If you have a CD-ROM or hard disk containing the additional Debian packages that you want to install on your system, or you are connected to the Internet, this will be useful to you right away. Otherwise, you may want to quit dselect and start it later, once you have transported the Debian package files to your system. You must be the super-user (root) when you run dselect. If you are about to install the X Window system and you do not use a US keyboard, you should read the X11 Release note for non-US-keyboard users.

Log In

After you've quit dselect, you'll be presented with the login prompt. Log in using the personal login and password you selected. Your system is now ready to use.

2. Running Debian GNU/Linux.

This section will deal Debian packaging system and debian specific utilities. Ab ovo.

2.1 Debian packaging system and package installation utilities

Debian distributions comes in archives called packages. Every package is a collection of files (software, usually) that can be installed using "dpkg" or "dselect". In addition the package contains some information about it self that is read by the installation utilities.

2.1.1 Package Classifications

The packages included with Debian GNU/Linux are classified according to how essential they are (priority), and according to their functionality (section).

The "priority" of a package indicates how essential or necessary it is. We have classified all packages into four different priority levels:

Required

"Required" packages are packages that must be installed for the system to correctly operate. The required packages are the packages that were installed with the base system. Thus, they are already installed. Never, never, never remove a required package from the system unless you are absolutely sure what you are doing. This bears repeating. Never, never, never remove a required package from the system unless you are absolutely sure what you are doing. It is likely that doing so will render your system completely unusable.

Required packages are abbreviated in dselect as "Req".

Important

"Important" packages are packages that are found on almost all Unix-like operating systems. Such packages include cron', man', and vi'.

Important packages are abbreviated in dselect as "Imp".

Standard

"Standard" packages are packages that, more or less, comprise what we consider to be the "standard", character-based Debian GNU/Linux system. The Standard system includes a fairly complete software development environment and GNU Emacs.

Standard packages are abbreviated in dselect as "Std".

Optional

"Optional" packages are packages that comprise a fairly complete system. The Optional system includes a fairly complete TeX environment and the X Window System.

Optional packages are abbreviated in dselect as "Opt".

Extra

"Extra" packages are packages that are only useful to a small or select group of people, or that would be installed for a specific purpose rather than as a general part of an operating system. Such packages include electronics and ham radio packages.

Extra packages are abbreviated in dselect as "Xtr".

By default, dselect automatically selects the Standard system, if the user doesn't want to individually select the packages to be installed.

The "section" of a package indicates the functionality or use of a package. Packages on the CD-ROM and in FTP archive are arranged according to section. The section names are fairly self-explanatory: for example, the category admin' contains packages for system administration, and the category devel' contains packages for software development and programming. Unlike priority levels, there are many sections, and more will probably be added in the future, so we do not individually describe any of them in the manual.

2.1.2 Package Relationships

Each package includes information about how it relates to the other packages included with the system. There are four package relationships in Debian GNU/Linux: conflicts, dependencies, recommendations, and suggestions.

A "conflict" occurs when two or more packages cannot be installed on the same system at the same time. A good example of conflicting packages are mail transfer agents (MTAs). A mail transfer agent is a program that delivers electronic mail to other users on the system or to other machines on the network. Debian GNU/Linux includes two alternative mail transfer agents: sendmail' and smail'.

Only one mail transfer agent can be installed on the system at a time, as they both do the same job and are not designed to coexist. Therefore, the sendmail' and smail' packages conflict. If you try to install sendmail' when smail' is already installed, the package maintenance system will refuse to install it. Likewise, if you try to install smail' when sendmail' is already installed, it will refuse to install it.

A "dependency" occurs when one package requires another package to function properly. Continuing our electronic mail example, users read mail with programs called mail user agents (MUAs). Popular mail user agents include elm', pine', and Emacs RMAIL. It is normal to install several MUAs at once, so these packages do not conflict. But a mail user agent does not deliver mail--it uses the mail transfer agent to do that. Therefore, all mail user agent packages depend on a mail transfer agent.

A package can also "recommend" or "suggest" other related packages.

2.1.3 Dselect

META: This section provides brief tutorial on Debian Dselect, for more detailed explanation please refer to Dselect Manual located at * ftp://ftp.debian.org/debian/Debian-1.2/disks-i386/current/dselect.beginner.6.html

Dselect is simple menu driven interface that will help you install packages. It is used to select packages you wish to install.

It will step you through the package installation process as follows:

The main dselect screen looks like that:

------------------------------------------------------------------

Debian Linux `dselect' package handling front end.
   0. [A]ccess      Choose the access method to use.
   1. [U]pdate      Update list of available packages, if possible.
   2. [S]elect      Request which packages you want on your system.
   3. [I]nstall     Install and upgrade wanted packages.
   4. [C]onfig      Configure any packages that are unconfigured.
   5. [R]emove      Remove unwanted software.
   6. [Q]uit        Quit dselect.

------------------------------------------------------------------   

META: There are two ways of selecting the option from the menu, one is choosing it with arrows, another one is pressing the key in []'s.

Access

In this menu you can choose the method you will use for obtaining/installing the packages.

Abbrev. Description
cdrom Install from a CD-ROM.
nfs Install from an NFS server (not yet mounted).
harddisk Install from a hard disk partition (not yet mounted).
mounted Install from a filesystem which is already mounted.
floppy Install from a pile of floppy disks.
ftp Install using ftp.

Update

Dselect will read the packages list file (exactly the same file that was discussed in the 1.3 section) and will create a database of available packages locally on your system.

Select

This is where you select the packages, choose your love and hit <Enter>. If you have a slow machine be aware that the screen will clear and can remain blank for 15 seconds so don't start bashing keys at this point. The first thing that comes up on the screen is page 1 of the Help file. You can get to this help by hitting ? at any point in the Select screens and you can page through the help screens by hitting the . (full stop) key.

To exit the Select screen after all selections are complete, hit <Enter>. This will return you to the main screen _if_ there are no problems with your selection. Else you will be asked to deal with those problems. When you are happy with any given screen hit <Enter> to get out.

Problems are quite normal and are to be expected. If you select package A and that package requires package B to run, then dselect will warn you of the problem and will most likely suggest a solution. If package A conflicts with package B (they are mutually exclusive) you will be asked to decide between them.

Install

Dselect runs through the entire 800 packages and installs those selected. Expect to get asked to make decisions as you go. It is often useful to switch to a different shell to compare, say, an old config with a new one. If the old file is conf.modules the new one will be conf.modules.dpkg-new.

The screen scrolls past fairly quickly on a new machine. You can stop/start it with ^S/^Q and at the end of the run you will get a list of any uninstalled packages. If you want to keep a record of everything that happens use normal Unix features like tee or script.

Configure

Most packages get configured in step 3, but anything left hanging can be configured here.

Remove

Remove packages that no longer needed.

Quit

Au revoir.

2.1.4 Dpkg

META: This section provides a brief tutorial on Debian Dpkg program.

Dpkg is command line tool for installing and manipulating debian packages. It has several switches, which allow you to install, configure, update, remove and do other operations on debian packages (even build your own). Dpkg also allowd you to list the available packages, list files 'owned' by packages, find which package the file is owned by, et cetera.

Installing new packages / updating existing ones.

It's as simple as any other dpkg operation. All you have to do is to type the following command:
# dpkg -i <filename.deb>
where <filename> is the name of the file containing a debian package, such as, 'tcsh_6.06-11_i386.deb'. Dpkg is partly interactive; during the installation it may ask you additional questions, such as, wether to install the new version of a configuration file, or to keep the old one.

You may also unpack a package without configuring it: type:

dpkg --unpack <filename>
If the package you are trying to install depends on a non-existing package or on a newer version of a package you have, or if any other problem occurs during the installation, dpkg will abort with a verbose error message.

Configure installed packages

It happens that dpkg aborts during an installation and leaves the package installed, though unconfigured. It also happens that the users unpack packages without configuring it. Debian packaging system requires the package to be configured to avoid dependency problems. More than that, some packages require configuration to work properly.

To configure it, simply type:

dpkg --configure <package>
where <package> is the name of the package, such as, 'tcsh' (which is not the same thing as a filename we mentioned above).

Removing installed packages

In Debian package system, there are two ways to murder a package, called 'remove' and 'purge'. The 'remove' switch just removes the specified package; the 'purge' switch also purges the configuration files. The usage is:
dpkg -r <package>
dpkg --purge <package>
Of course, if there are any installed packages that depend on the one you wish to remove, the package will not be removed, and dpkg will abort with a verbose error message.

Reporting package status

To report the status of the package (i.e., installed, not installed, unconfigured, etc.), type:
dpkg -s <package>

Listing available packages

To list the installed packages that match some pattern, type:
dpkg -l [<package-name-pattern>]
where <package-name-pattern> is an optional argument specifying a pattern for the package names to match, such as, "*sh". Yes, normal shell wildcards are allowed. If you don't specify the pattern, all the installed packages will be listed.

Listing files 'owned' by package

To list all the files owned by a particular package, simply type:
dpkg -L <package>
However, it will not list the files created by package-specific installation scripts.

Finding package 'owning' a file

To find the package wich is 'owning' a particular file, type the following command:
dpkg -S <filename-pattern>
where <filename-pattern> is the pattern for the file to search for. Again, normal shell wildcards are allowed.

Summary

Dpkg is very simple to use and is preferred over dselect when all you have to do is to install, upgrade or remove a small number of packages. It also has some functionality which dselect (which is, in fact, an interface to dpkg) doesn't have, such as, finding package 'owning' a file. Here we haven't describe all the options dpkg have. For the full list, refer to dpkg(8) man page.

3. About Debian

3.1 Debian community

Debian project was created by Ian Murdock in 1993, initially under the sponsorship of the Free Software Foundation's GNU project. Later, Debian has parted from FSF. Debian was created is the result of a volunteer effort to create a free, high-quality Unix-compatible operating system based on Linux kernel, complete with a suite of applications.

Debian community is a group of above 150 unpaid volunteers from over the world who collaborate via the Internet. The founders of the project have formed the organization "Software in the Public Interest" to sponsor Debian GNU/Linux development.

Software in the Public Interest

Software in the Public Interest (SPI) is a non-profit organization formed when FSF withdrew their sponsorship of Debian. The purpose of the organization is to develop and distribute free software. Its goals are very much like those of FSF, and it encourages programmers to use the GNU General Public License on their programs. However, SPI has a slightly different focus in that it is building and distributing a Linux system that diverges in many technical details from the GNU system planned by FSF. SPI still communicates with FSF, and it cooperates in sending them changes to GNU software and in asking its users to donate to FSF and the GNU project.

SPI can be reached at:

E-Mail: bruce@pixar.com
Postal address:

Software in the Public Interest
P.O. Box 70152
Pt. Richmond, CA 94807-0152

Phone: 510-215-3502 (Bruce Perens at work)

3.2 Mailing lists

There are several Debian-related mailing lists:

debian-announce@lists.debian.org
Moderated. Major system announcements. Usually about one message per month.

debian-changes@lists.debian.org
Announcements of new package releases for the stable distribution. Usually several messages per day.

debian-devel-changes@lists.debian.org
Announcements of new package releases for the unstable distribution. Usually several messages per day.

debian-user@lists.debian.org
A mailing lists where users of Debian ask for and get support. Usually about 50 packages per day.

debian-sparc@lists.debian.org,
debian-alpha@lists.debian.org,
debian-68k@lists.debian.org
Lists for those who are involved in porting Debian software to SPARC / DEC Alpha / Motorolla 680x0 platforms.

There are also several mailing lists for Debian developers.

You can subscribe to those mailing list by mail or via www, for more information please visit http://www.debian.org/

3.3 Bug tracing system.

Debian project has a bug tracing system which handles the bug reports provided by users. As soon as the bug report is received, the bug is given a number and all the information provided on this particular bug is stored in a file and mailed to the maintainer of the package. When the bug is fixed, it must be marked as done ("closed") by the maintainer; however, if it was closed by mistake, it may be reopened.

To receive more info on the bug tracing system, send e-mail to request@bugs.debian.org with "help" in the body.

4. Almost the end.

4.1 Acknowledgments.

Many thanks to Bruce Perens, the author of Debian FAQ and Debian installation manual for kindly letting me use his materials. Bruce should be considered as co-author of this chapter.

Thanks a lot to Vadik Vygonets, my beloved cousin, that also helped me very much.

And thanks a lot to all members of Debian community for their hard work, let's hope that Debian will become even better.

4.2 Last Note

Hence Debian changes very fast, alot of facts may change faster then the book, but this document will be updated regularly, you can find it at * http://www.cs.huji.ac.il/~borik/debian/ligs/

4.3 Copyright

Any redistributions or changes to this document may be made only with permission from the author.


Copyright © 1997, Boris D. Beletsky
Published in Issue 15 of the Linux Gazette, March 1, 1997


[ TABLE OF CONTENTS ] [ FRONT PAGE ]  Back  Next


"Linux Gazette...making Linux just a little more fun!"


Welcom to the Graphics Muse
Set your browser to the width of the line below for best viewing.
© 1996 by mjh

Button Bar muse:
  1. v; to become absorbed in thought
  2. n; [ fr. Any of the nine sister goddesses of learning and the arts in Greek Mythology ]: a source of inspiration
Welcome to the Graphics Muse! Why a "muse"? Well, except for the sisters aspect, the above definitions are pretty much the way I'd describe my own interest in computer graphics: it keeps me deep in thought and it is a daily source of inspiration.

[Graphics Mews] [Musings] [Resources]
indent This column is dedicated to the use, creation, distribution, and dissussion of computer graphics tools for Linux systems.
     
      After much delay I've finally started learning about the Blue Moon Rendering Tools (BMRT). It seemed only natural that I take what I learned and pass it on to my readers. So, starting this month, I'm going to do a three part series on BMRT and RenderMan® shaders. I've gotten help, of course. My thanks go out to Paul Sargent for providing example code and a place to bounce ideas off and to Larry Gritz, author of BMRT, for general support and technical assistance. The first in this 3 part series is an introduction to the tools and some relatively simple examples on how to use them.
      Although the BMRT articles are a big project in themselves, I don't want to devote 3 entire issues of the Muse to just BMRT. In this months column I'll also be covering a few other topics.
  • A review of Mark Kilgard's OpenGL Programming for the X Window System.
  • Information on scanner support for Linux.
Both of these are go into some detail. Along with the usual set of Mews offerings, this should be enough to hold you until next month.
      I was going to do a bit on John Beale's wonderful tool, HF-Lab, this month but decided to wait until next month. I happened to run across a few other POV-Ray tips recently and thought that the set of tips along with the HF-Lab review would fit well together. Look for them next month.
      An update on my crashed system woes: my little network at home uses a 386 16Mhz Dell computer as a server for doing backups. I had set it up but had not implemented the backups when my main system bit the bucket. After getting my main system running again I ended up with some extra drives that I wanted to put in my server. I first tried to make backups of my main system, across the network, using a version of taper that I had installed on my main system and just copied over to the server. That sort of worked, but for some reason taper wouldn't see some of my target directories. I figured it was incompatible with the installation I had on the 386, so I upgraded to Linux Pro (which is what I installed on my main system). Mistake. The server stopped working. The problem is a secondary IDE that I added to make use of the extra hard disks. I mucked with it for a week, got fed up and now have a new Cyrix 166, motherboard, and mini tower on order. The motherboard and 166 are going in the main box, and the old 486 and motherboard are going in the mini tower. I'm retiring the 386. It will take its rightful place next to my retired Wyse286 PC with its 20M hard drive.
      I never wanted to be a system administrator. I just want to use my systems. sigh At least with Linux I have more control over what I use.
      So, one month after disaster hit I still don't have reliable backups running. There is money to be made in making backups easy for Linux users. I guarantee it.

Graphics Mews


      Disclaimer: Before I get too far into this I should note that any of the news items I post in this section are just that - news. Either I happened to run across them via some mailing list I was on, via some Usenet newsgroup, or via email from someone. I'm not necessarily endorsing these products (some of which may be commercial), I'm just letting you know I'd heard about them in the past month.

indent

GIFWizard

      If you'd like to reduce the size of your GIF images but don't really know how to do it on your own, there is a free online service you can try. The * GIF Wizard (http://www.raspberryhill.com/gifwizard.html) will work with images already on the Net (you provide a URL for the image) or on images on your hard drive.       Note: Definitely don't ask me about this service - I haven't used it and only offer the info here because it looked like it might be of interest to some of my readers.
indent indent

Tnpic - GIF/JPEG indexer

      Tnpic, from Russell Marks (who doesn't have email access anymore), is a GIF/JPEG indexer that used to be bundled with zgv up until version 2.3. The index is output as a JPEG. Tnpic is available from * sunsite.unc.edu /pub/Linux/apps/graphics/tnpic-2.4.tar.gz

indent

Ra-vec

      Ra-vec is a new free application for Linux, SGi and Sun's from Rob Aspin that converts X Bitmaps, such as 2D plan drawings (architect's drawings), into a vector format which can be read by the 3D modeling package AC3D (see the January 1997 issue). Using Ra-vec, complex 3D models and environments may be rapidly prototyped, reducing overall development time.

To download a free copy of the software got to: * http://www.comp.lancs.ac.uk/computing/users/aspinr/ra-vec.html.

indent

VARKON for Linux

      VARKON is a high level development tool for CAD and Product Modelling appliactions from Microform AB, SWEDEN. The system includes a very powerful modelling language called MBS and an interactive environment for traditional modelling and developing MBS-applications.

Keywords are:
2D, 3D, Wireframe models, Surface models, Parametric, Structured Object Oriented Database, Easy to integrate with other systems, Commersially available on most platforms at a very low price. At the *Web site - http://www.microform.se - you will find

  • A lot of technical information about VARKON
  • Links to download the latest version of Linux-VARKON (version 1.14E)
  • Links to download the full documentation in text or MS-Word-format
  • Links to download demo-applications with source MBS-code, documentation, etc.

You can also download a restricted but free demo-version of the system for Windows95.

indent

QuickCam Resources

      Interested in doing some work with the Connectix QuickCam? Thats the little round camera that has become very popular with Windows and Mac users. Russ Nelson (of the old Packet Drivers fame, for those of you who remember that software) maintains a very good resource page for the QuickCam at * www.crynwr.com/qcpc. It contains links to drivers and applications for many operating systems, including Linux and other PC based Unices.
      Connectix also maintains a page for developers. They offer lots of information and require only that you register for their developers program, which costs nothing. You can find them at * www.connectix.com/connect/developer.html
      If you're looking for a Linux driver for the Color QuickCam, check * The SANE Project, a project to develop a generic interface to various types of media devices, such as scanners and the QuickCam. This package also contains a frontend to the Color QuickCam driver.

For those of you in the US wondering what these little gadgets cost, CompUSA sells the Color QuickCams for about $249.

indent
indent

Did You Know?

There are many places to find information about OpenGL on the Internet. The following is only a small list: There are also a few sites with RenderMan information:
  • * The RenderMan Repository - (http://pete.cs.caltech.edu/RMR/index.html)
    A storehouse for all things related to RenderMan.
  • * RManNotes - (http://www.cgrg.ohio-state.edu/~smay/RManNotes/index.html)
    General information about writing shaders in the RenderMan Shading Language and using the two most commonly available RenderMan renderers

Q and A

Q: Is displacment mapping the same thing as reaction-diffusion?

A: No. Reaction-diffusion simulates the mixing of chemicals, which is theorized to have something to do with certain organic texture patterns, like leopard skin.

Bump mapping is perturbing the normal of an object to simulate bumps, but without actually moving points on the surface.

Displacement mapping does what bump mapping merely simulates - it actually distorts the surface points of the object which is being mapped. This avoids artifacts you get from the bump mapping approximation (like actually making the silhouettes rough). You can think of it as a height field over an arbitrary surface.

Q: What is a stochastic raytracer and are there any freely available?

A: "Stochastic sampling" or "distribution ray tracing" (it's not called distributed these days) refers to placing samples at irregular intervals, rather than regularly spacing them. It doesn't have anything to do with the number of rays per pixel -- 1 sample per pixel can easily be jittered, and 100 samples per pixel can be regularly spaced. Also, it's not dependent on ray tracing -- PRMan uses stochastic sampling and it uses a scanline method.

Technically, stochastic sampling transfers high frequency signal energy above the Nyquist limit into noise, rather than having that energy alias as lower frequencies. It's just trading one artifact for another, but by coincidence the human visual system appears to find noise less objectionable than aliasing.

BMRT is a stochastic raytracers. POV-Ray is reported to be (but no official word if it is or not). Others include (not all are raytracers): PRMan, Mental Ray, and Alias.

Thanks to Larry Gritz for these definitions.

Q: What is tessellation?

A: Mark Kilgard writes the following in his OpenGL Programming for the X Window System:

In computer graphics, tessellation is the process of breaking a complex geometric surface into simple convex polygons.
The use of convex polygons allow for better performance in OpenGL.
indent
indent
indent

Musings

     
indent
OpenGL Programming for the X Windows System
Mark Kilgard
Addison-Wesley Developers Press

      There are a growing number of Application Programming Interfaces (API's) available for Linux that enable software developers to create programs that render 3D graphics. Some of these are designed to allow programs to output data files that can be used by rendering engines to create a 3D image either to a display or to a file. The libribout.a static library in the BMRT package is an example of this kind of interface. It allows the software developer to write a program to output a RIB formatted file which can then be used by a RenderMan® compliant renderer. Other tools are designed for interactive 3D display. One such developer tool is OpenGL. OpenGL is, if not the grandfather, the God Father of all interactive 3D development tools.
      OpenGL is an API designed by Silicon Graphics and now managed by the OpenGL Architecture Review Board. It is defined by the OpenGL Programming Guide as follows:

The OpenGL graphics system is a software interface to graphics hardware. (The GL stands for Graphics Library.) It allows you to create interactive programs that produce color images of moving three-dimensional objects.
The interface is a window system independent interface to graphics hardware. In order to use OpenGL with a particular windowing system it must be used with a supplemental API. This supplemental API allows OpenGL to create its graphics contexts and windows in which OpenGL will do its rendering.
      Linux uses as its windowing system the X Windowing system, as do most, if not all, other Unices. To use OpenGL with X Windows the software developer must become familiar with GLX, the X Extension for OpenGL, along with one or more toolkits such as the X Toolkit (Xt) and a widget set like Motif (Xm). This is not a simple task. Just learning Xm can be a full time occupation (I know, its what I do now). Fortunately, Mark Kilgard has provided a very thorough text on integrating OpenGL with the X environment: OpenGL Programming for the X Windows System.
      This text contains 6 detailed chapters, 1 chapter devoted to an example application, and a number of very useful appendices. The first two chapters introduce the reader to OpenGL and the two libraries that generally accompany it: GLU, the GL Utility library that is used for certain operations that are hardware inspecific such as polygon tesselation, and GLX. The introduction is quite good except for explaining the use of GLU. All OpenGL functions are prefixed with "gl" except for the GLU functions which are prefixed with "glu". I can understand why they did this, but it is confusing to remember that OpenGL is actually two sets of functions with different prefixes (as if the X Windows system didn't provide enough of these already).

-Top of next column-
indent indent indent
indent
indent
indent
      Chapter 3 is a detailed explanation of how to use OpenGL with Motif. The basic premise is that you need to combine OpenGL (gl and glu routines) with the X Extension for OpenGL (GLX) and the widget set of choice (Xm along with Xt to manage the widget set). That seems like a lot of work. Not to mention that writing an OpenGL application this way, with the X calls embedded in the source, removes the portability that a developer originally had with just OpenGL. It would be nice if there were a way to remove the X calls and have a truly portable OpenGL application.
      There is. Mark introduces the GLUT library in Chapter 4 which hides most (not all) of the window system specific API calls from the developer. This toolkit, although not necessarily appropriate for full-featured OpenGL applications, provides an example of a toolkit which can handle window system API's for the developer and allow the developer to write a single source code base portable to any platform. The toolkit itself can be implemented in X, Windows NT or any other windowing system. The application developer only needs access to the toolkit.
      Chapter 4 is an introduction to the more basic features of GLUT. It covers such topics as window managment, callbacks, and font rendering. Chapter 5 goes into significantly more depth. Its 90+ pages cover topics ranging from lighting and texture mapping to using images and bitmaps to curves and surfaces. This chapter will be the one most readers will refer to repeatedly when they've gotten past their first sample OpenGL programs using GLUT. Chapter 6 covers advanced topics such as the X Input Extension, Overlays, and peformance issues.
      There are 3 appendices, the most interesting of which is the "Functional Description of the GLUT API". This is a reference section for the most part although it is not formatted with one page per function. This makes it a little hard to find what you're looking for since more than one function can be on a page. Other than that its a fairly complete description of the GLUT API. There is also a glossary that follows the appendices.
      Mark includes extensive sample code right from the start of the text. All the code is available for download from the Internet. The code is easy to follow and the accompanying text is well written. Although Mark does not spend time explaining how to program with the X Windows System (knowledge of which is a prerequisite for this text) he does thoroughly cover how to integrate OpenGL with the X environment. After explaining how this would work he then provides detailed information about how to remove the windowing system specific calls by using GLUT.
      I find OpenGL Programming for the X Windows System a very well written, thoroughly descriptive explanation on how software developers can integrate OpenGL with their X Windows applications.

Resources

The following links are just starting points for finding more information about computer graphics and multimedia in general for Linux systems. If you have some application specific information for me, I'll add them to my other pages or you can contact the maintainer of some other web site. I'll consider adding other general references here, but application or site specific information needs to go into one of the following general references and not listed here.

* Linux Graphics mini-Howto
* Unix Graphics Utilities
* Linux Multimedia Page

Some of the Mailing Lists and Newsgroups I keep an eye on and where I get much of the information in this column:

* The Gimp User and Gimp Developer Mailing Lists.
* The IRTC-L discussion list
comp.graphics.rendering.raytracing
comp.graphics.rendering.renderman
comp.os.linux.announce

Future Directions

Next month:
Let me know what you'd like to hear about!


Copyright © 1997, Michael J. Hammel
Published in Issue 15 of the Linux Gazette, March 1997


[ TABLE OF CONTENTS ] [ FRONT PAGE ]  Back  Next



More...


Musings

indent
© 1996 Michael J. Hammel
indent

Scanner Report


      In December my brother called me to let me know he had a possible Christmas gift for me: a Compaq Keyboard Scanner. He works for Compaq and they had a special for employees. Knowing I might not have a Linux driver for this he called to ask. I didn't know, so I started to investigate. I checked the one place I knew I could ask questions like this and get reasonably accurate answers - the Gimp Developer and User mailing lists. I posted a message asking if anyone knew about scanners and this scanner in particular. Quite a few people answered. It turns out this particular scanner is actually an OEM'd version of the Visioneer keyboard scanner. The protocol this scanner uses in not publicly available and apparently its rather difficult to get on the developers list to get the information. So much for getting support for this little device. However, the amount of information I gathered about other scanner devices, about 14 pages of printed material, turned out to be a real windfall. I decided to summarize it here in the Muse.

First, lets list the set of scanners known to have support. This list is a compilation based on what the drivers say they support and what individuals have said they are specifically using.

      The HP scanners appear to all require a generic SCSI interface, such as an Adaptec AHA 152x board and its associated driver, and the hpscanpbm user level driver. The SCSI board that comes with some (or possibly all, I'm not sure) of the HP scanners is not supported at this time.
      Knowing which scanners are supported is one thing. Now you need to find a driver that goes with them. The information I got was provided by the son of a coworker of my brother. Apparently he had some free time and had gone out and gathered this list on his own. Not all the information was complete and I filled in the rest by perusing the sunsite and tsx-11 archives. I also received information on some of the drivers from the developers.

Driver/Application Supported scanners
hpscanpbm-0.3a.tar.gz User level driver for HP Scanjet II series
a4scan.tgz Drivers for A4 Tech scanners
coolscan-0.1.tgz User-level driver for the Nikon CoolScan SCSI
mscan-0.1.tar.gz User level program for using Mustek scanners
xscan-1.1.tgz User-level X program for scanning with Mustek scanners that saves files as X Bitmaps
muscan-2.0.6.taz Driver for Mustek Paragon 6000CX
mtekscan-0.1.tar.gz Driver for MicroTek ScanMaker scanners originally written for ScanMaker E6, but will also work with the E3.
pbmscan-1.2.tar.gz Utility for Logitech scanners (including ScanMan 256)
ppic0.5.tar.gz Early scanning package w/ EPSON support
Table 1: scanner drivers for Linux available at
* ftp://sunsite.unc.edu/pub/Linux/apps/graphics/scanners.

Driver/Application Use
gs105-0.0.1.tar.gz Genius GS-B105G 400 dpi greyscale handheld scanner
gs4500-1.6.tar.gz Genius GS 4500 hand scanners and compatible models
logiscan-0.0.4.tar.gz Logitech ScanMan+ 400 dpi handheld scanner driver
scan-driver-0.1.8.tar.gz M105 handheld scanner driver or clone with GI1904 interface
umax-0.4.tar.gz (v0.5 may be out by now, which is reported to be very much improved over v0.4) UMAX scanners
This one is written by Michael K. Johnson and he reports that there is sufficient documentation in the distribution for any one to add new UMAX support if they so desire.
Table 2: scanner drivers for Linux available at
* ftp://tsx-11.mit.edu/pub/linux/ALPHA/scanner/:

I don't know what the difference between the pbmscan and logiscan packages is but suspect the pbmscan package is a front end to the logiscan package. The logiscan package has a front end called gifscan that uses SVGALIB (not an X interface) and saves the input into GIF files. The pbmscan package scans directly into PBM formatted files.

Commercial Scanner Products
      There is only one commercially available product for scanners - XVScan from *Tummy.com, which contains a graphical front end and supports a number of scanners. XVScan runs for about $50US which includes the $30 registration for XV.

Application Interfaces
      * SANE v0.42 - http://www.azstarnet.com/~axplinux/sane/ - is a project to create a Universal Scanner Interface. SANE, which stands for Scanner Access Now Easy, supports the following backends (device drivers):

There are a couple of front ends to this tool as well:

This package makes use of the GNU Configure mechanism. Unfortunately it doesn't quite build right out of the box (there are some linking options which aren't supported by the Linux ld program). I couldn't test the programs or drivers out, unfortunately since I don't have a QuickCam or any scanners yet. Feel free to donate either, of course.

There are notes in the distribution about ongoing work for support for non-Unix platforms, but I have little interest in that so didn't really read through it.

What people are saying
      And of course, what would a scanner review be without some user testimonials. These are taken from the discussions on scanners in the Gimp User and Gimp Developer mailing lists. I didn't keep track of email addresses so all I have are the first names of the respondents. As with any unverifiable testimonials, take these with a grain of salt.

      I've been using XVScan with my ScanJet 4P and Linux for about 9 months, and I'm very happy with it. It worked perfectly out of the box, no tweaking or anything. XVScan costs $50, but that includes the $30 registration fee for XV and is produced by Tummy.com. Their web site is, of course, *http://www.tummy.com/. - Scott
      I'm using an Epson GT-5000WINS (JP model?) with a hand-made GIMP 0.54 plug-in driver. The driver is not for general use yet, but is available on-web. - Kaz Sasayama <*http://www.spice.or.jp/~hypercor/hyperplay/>
      I'm using an HP Scanjet IIC (predecessor to the CX) with Linux and Gimp, and am very pleased with the results. I've a feeling (unsubstantiated), that not much changed between the two models other than the driver software that HP shipped with each. There's a good HP scanner driver for Linux called 'hpscanpbm' - available from the usual sources. It's command-line driven, but offers very good control over resolution, brightness, contrast etc. Output format is pbm only, unfortunately. So far, it's the only HP driver for Linux that I've seen. - Andre
      I'm using a Mustek Paragon 600II-SP, and it works quite well (just don't expect to share the SCSI bus with anything else). It's sold here (in Austria) at around $300US - Andreas
      I'm using a HP Scanjet IIcx, with the Adaptec AHA152x driver and the "generic" SCSI interface. No changes to the driver were necessary. Currently using the hpscanpbm program to do all scanning. - Rob Jenkins
      I'm using an HP IICX with hpscanpbm. Installation was completely painless. I added it to my scsi bus, rebooted and once I figured out which generic scsi device it was and set the permissions appropriately it worked. Probably 10-15 minutes, including compiling hpscanpbm. - Stew
      I have a Microtek ScanMaker E3, which is a 24-bit flatbed scanner with a 300x600dpi optical resolution, that can be had for right around $300. It comes with some pretty decent image editing software for the Mac and for Windows, and there's a (command-line-driven) driver available for Linux (mtekscan). With any luck, the SANE (Scanner Access Now Easy) project will have a driver available in the not-too-distant future (if I ever find time to write the driver, that is. :) The SANE driver will allow standalone scanning as well as a GIMP plug-in. The driver will probably work with other Microtek scanners as well (mtekscan was actually written for a ScanMaker E6 but works with my E3). - name unknown
      As for Musteks, I was considering a 30-bit, 400x800dpi Mustek scanner (I don't remember the model), until I read a review which compared that scanner to a few other scanners (mostly 24-bit). The Mustek wasn't particularly impressive; I finally decided to go with the Microtek--even though inferior "on paper" it still received a much better review.       In any case, you can't go wrong with a Microtek, I think. I've also read good things about the UMAX (which are also rather inexpensive), a Canon (a little more expensive), and of course HP scanners are generally top-notch, although they also command premium prices. If you have the bucks, go for an HP, but if you want to save a few dollars and still get an excellent quality product, there are other options. - name unknown

Other OS's
      A few people responded to my request for information on the Gimp mailing lists with information for non-Linux systems. I normally don't write about these, but I'll go ahead this one time. Note that I don't want to write about other OS's - not because they aren't any good, but because Linux works for me and I don't have the time to wander around the OS world looking for yet another OS.

      Thats it. Hopefully this information will help you get started looking for a scanner and the appropriate software to use with it. I have high expectations for the SANE project to be the primary interface for low-level and user-level drivers for all scanners in the future. Once a generic interface is defined it should be easier to develop applications that can make real use of the scanners.

indent
© 1996 by Michael J. Hammel


More...


Musings

BMRT

    Part I: Getting Started - Creating, Previewing, and Final Rendering of Simple Images
  1. Introduction
  2. User Tools - Renderers and Previewers
  3. Developer Tools - libraries, compiler, etc
  4. The Example Scenes
  5. The Input File - RIB format
  6. Basic Steps
  7. Shaders
  8. Closing
indent
© 1996 Michael J. Hammel
indent

1. Introduction

      A couple of years ago, right after Toy Story had been released, I began to gather as much information on computer graphics as I could find. At first I had been looking for general information. Later, when I found out such tools existed for Windows and Mac systems, I began to look around for various 3D rendering and modelling tools that would run on Unix systems. The first tool I found was POV-Ray, a tool that has been ported to many platforms including a number of Unix OS's. I also found a number of other tools such as Polyray and Radiance. Since I was very new to 3D tools I started with POV-Ray. It had a large amount of online information (much of which has been scaled back on the Internet), a large user base that frequented the comp.graphics.rendering.raytracing newsgroup, and it had printed texts available. This last item was the most important element to me. I needed documentation I didn't have to print off myself and that was fairly well organized. I tended to carry it around to read at lunch on work days.


Figure 1: A sample scene created using BMRT. The text was produced using the font3d tool, which can output RIB files.

      Not long after discovering POV-Ray I came across another tool called BMRT. BMRT is actually a set of tools that are compliant with the RenderMan Interface Specification. This specification is the same one used by PRMan, the tool used by Pixar to create Toy Story. Although I wanted to learn more about BMRT I really didn't have the background to understand how to use such tools. POV-Ray's documentation allowed me to learn some basics up front. After about a year of working on POV-Ray, along with continued research in other areas of computer graphics, I began to look once again at BMRT. I now better understand what it does. Its time to learn to use it.       In this first of three articles on BMRT I'll be describing the package contents and introduce you to the basics of how to use the BMRT tools. You should keep in mind that much of the terminology might be new to you and so the early introductions and descriptions might not make too much sense. I apologize for this, but describing such a powerful package as BMRT and the RenderMan Specification in one introductory article is not easy. Fear not, however. I'll be explaining all of the package contents in some detail further along in this article. This won't be a complete, all encompassing tutorial. But it should be enough to get you started. After you get done here, go order the RenderMan Specification from Pixar. It is a very well written and easy to follow description of what BMRT implements. It also provides the reference guide necessary to understand the C and RIB bindings to the RenderMan interface.

What is BMRT?

      BMRT stands for the Blue Moon Rendering Tools. It is a set of tools and libraries created by Larry Gritz, who now works at Pixar, that allow the previewing and rendering of 3D models and scenes. The rendering engines (programs) and static libraries (used to create applications that can output RIB files) are all compatible with the RenderMan Interface Standard developed by Pixar. RenderMan is not an actual piece of software, although many people use the terms RenderMan and PRMam (Pixar's software implementation of the RenderMan specification) interchangeably. It is a specification stating how a modeling system communicates with a rendering system. BMRT is an implementation of the rendering system with a static library provided for use with modeling systems, including stand-alone programs.
      BMRT's rendering tools support ray tracing, radiosity, area light sources, texture and environment mapping, programmable shading in the RenderMan Shading Language, motion blur, automatic ray cast shadows, CSG (Constructive Solid Geometry), depth of field, support of imager and volume shaders, and other advanced features. The toolkit also contains quick RIB previewers (using OpenGL and X11) to allow "pencil tests" of scenes and animations.

Current Release and Where to Get it

      At the time of this writing, February 22, 1997, the latest release of BMRT is 2.3.5. It is available from the * BMRT Web site (http://www.seas.gwu.edu/student/gritz/bmrt.html). This site also contains example images and pointers to other RenderMan related sites on the Web. Larry only provides precompiled versions of the renderers and the RIB and shader libraries. He does, however, provide a set of shaders in source form along with their compiled versions. We'll discuss shaders a little later. Versions of BMRT are available for Larry doesn't expect to port BMRT to non-Unix style operating systems due to the logistics problems (access to machines, and so forth) inherint with cross-platform development. There is no planned port for the MkLinux distribution at this time. I don't know if he plans on working on a Digital Alpha or any other non-Intel Linux ports.

What the package contains

      The distribution comes complete with what might be considered as a set of user tools, a set of development tools, and documentation for both. Its not quite correct to refer to these as user or development tools due to the nature of the tools, but for this article such classification will help organize things a little better.

User Tools - Renderers and Previewers

      These are the executable programs in the package that allow users to render and preview images. There are 3 such programs: Its easiest to remember these tools as the ones you'll need to render draft or final versions of your scenes. The first two are generally used to render draft versions, the last to render your final scene. However, you don't create the scene files with these tools. Scene files contain the description of the objects that make up the scene. These files use a format called RIB, the RenderMan Interface Bytestream format. Scene files can be created by hand (not a common practice), by writing a C program that uses the developer tools described in the next section, or by modellers that can output files in the RIB format.
      RIB files describe the shape and positions of objects. They provide the geometry of a scene. They do not describe colors of objects, the texture on the surface of objects, nor any aspect of lighting in the scene. This information is referenced by the RIB by using shaders. Shaders are external files that describe the appearance of the objects in a scene. There are developer tools for creating and examining shader files.

Developer Tools - libraries, compiler, etc

      The developer tools in BMRT are actually a set of libraries and header files that are provided for users to create C programs that output RIB files or to parse shader source files. The user programs can be specifically designed for a given scene or set of frames or could be part of a more generalized modelling system, such as AC3D or SCED. Also included in the developer tools are programs for compiling shader source files into their .so format and for examining compiled shader files to find their types, parameters, and initial values.
      Shader source files look like ordinary C code. The source file is compiled into another format referred to as the .so file. The compiled .so versions are actually ASCII files. The .so extension might be a little confusing to users who are familiar with creating shared libraries, but these are not shared object files. They are plain text files.
Note that the distribution does not come with linkable libraries for the renderers.

Docs

      There are only two pieces of documentation that come with the distribution, however both are quite well written and very good refernces. The first is a detailed description of all the tools and how to use them. This is a very valuable reference for new users learning how to get the most out of the programs by learning their command line arguments. The second is a quick introduction to the RenderMan API. It contains a brief description of the RIB format. For more detailed information on the RIB format you should contact Pixar to get the official RenderMan Interface 3.1 Specification. Although the specification document is not written as a tutorial, it does contain detailed, reference-style information on the RIB file format. For more information on contacting Pixar, see the * comp.graphics.renderman FAQ at http://www.cis.ohio-state.edu/hypertext/faq/usenet/graphics/renderman-faq/faq.html


2. User Tools - Renderers and Previewers

rendribv - wireframe previewer

      The first of the renderers, rendribv, provides wireframe previews of the input scene files. The previews show geometric primitives without shading or removal of hidden lines. A wireframe display uses "wire cages" to represent objects instead of representing them as solid surfaced objects. The wireframe display requires the use of the X11 windowing system. Rendribv has a number of command line options, all of which are explained in the accompanying documentation. One important aspect to keep in mind is that rendribv was designed to display one or more frames of a RIB file. It offers a good way to preview an animation without the overhead that accompanies the shading of object surfaces. The limbo.rib example scene provides a sample animation. On my 486DX2/66 with 40M memory the wireframe animation is fairly smooth using rendribv. Its even faster on my P75 laptop with 8M of memory.

rgl - quick polygon previewer that uses OpenGL

      Another previewer provided in the distribution is the rgl program. This renderer displays previews of scenes with simple Gouraud shading of object surfaces using OpenGL (OpenGL is a specification for a graphics interface from Silicon Graphics - see this months review of Mark Kilgards OpenGl Programming with the X Window System). Gouraud shading is a method for helping to eliminate large changes in color intensities that can cause banding. Hidden lines, those lines and surfaces that should not be visible to the viewer because they are blocked by other lines or surfaces, are also removed. Since rgl requires OpenGL, a port of an OpenGL library must be available on a particular platform in order for Larry to port rgl to that platform. Fortunately, the MesaGL library is available for Linux, as well as some commercial ports of the official OpenGL libraries, so there is a working version of rgl available for Linux. rgl is statically linked so you don't need any of the OpenGL or MesaGL libraries to use it. Other Unix distributions of BMRT may not have this program, however.

rendrib - hiqh quality renderer w/raytracing and radiosity

      This is the gravy on the potatoes. The rendrib program is a fully featured, RenderMan compliant renderer that provides not only the full feature set of the RenderMan Specification but also provides such things as ray tracing, radiosity, solid modeling, depth of field, motion blur, area light sources, texture mapping, environment mapping, volume and imager shading, and support of the RenderMan Shading Language. The latest version also supports displacement mapping, a method of mapping an image to a surface that not only changes the appearance of the surface but also the actual shape of that surface. Rendrib is the tool to use when rendering your final scene as it will produce the best, most realistic results of all the renderers provided.

A word about compatibility with commercial Linux distributions

      Version 2.3.4 of the BMRT rendering tools were built against version 26 of the g++ library. Version 2.3.5 is linked against version 27. This is no problem if you're running one of the newer commercial Linux distributions since I believe 27 has been out for awhile and should be in most recent Linux distrubtions. However, my laptop has an older Slackware 3.0 release which only has g++ v26. which means I can't run the v2.3.5 renderers on my laptop. This isn't a big deal for me, but it is something you should be aware of when deciding to explore BMRT. I don't know if Larry supplies older versions of BMRT so you may have to upgrade in order to use the latest distribution of BMRT.
      Note that the X and MesaGL/OpenGL libraries were statically linked to the renderers. However, the C/C++ libraries are still dynamically linked, which is why you need to be aware of which versions of these libraries are required.


3. Developer Tools - libraries, compiler, etc

slc - shader langauge compiler

      The shader language compiler is a program which takes shader language source files, those files ending in .sl, and compiles them into their compiled versions, those files ending in .so. The compiled shader files appear to be code to a state machine used in the rendrib renderer that determines how shading is applied to a given object (I don't know that for certain, but it seems a reasonable guess). RenderMan is a procedural interface. The shaders are procedures written in a C like language. The must be compiled to be used with a RenderMan compliant renderer like BMRT. The shader compiler turns the procedural shader into a format the renderer can handle.
      Shaders come in many forms: surface shaders which define how light leaving a point on an object will appear, volume shaders which define how light is affected as it passes through an object (such as the atmosphere), light shaders which describe the lighting of a scene, displacement shaders, transformation shaders, imager shaders, and so forth. rendrib supports all of these shader types.
      The BMRT package comes with a fairly large number of shaders, some of which are required by the RenderMan specification and some of which Larry has provided as bonus shaders in conjunction with example scenes.

RenderMan required shaders Extra shaders provided for use with example scenes
constant, matte metal, shinymetal plastic, paintedplastic ambientlight, distantlight pointlight, spotlight depthcue, fog bumpy, null background, clamptoalpha, dented, funkyglass, glass, gmarbltile_polish, noisysmoke, parquet_plank, plank, screen, screen_aa, shiny, stucco, wallpaper_2stripe, wood2,
arealight - shader for area light sources
Both compiled versions and source code are provided for all of these shaders.

Note that the .so files provided are the precompiled versions of the .sl files and that the .so files are not compatible with PRMan, Pixar's RenderMan program. The .sl source files are compatible, however. The reason for this comes from the methods used internally to rendrib and PRMan to produce the 3D images. For more information see the section on Incompatibilities with PRMan in the bmrt.html document in the doc directory of the distribution.

sotell - lists the arguments to a compiled shader

Another shader related tool is sotell. This program allows the user to parse a shader object file for its type, list of parameters, and default settings. What this is useful for will become more apparent in the next article which will cover the writing of shaders. We'll touch briefly on using predefined shaders a little later in this article.

libribout.a, ri.h - RenderMan library for producing RIB files

These two files are used by developers who need to write applications to output their RIB files. Remember, RIB files are the input files (including references to shaders) passed to the rendrib program. There are two modellers on Linux that can output RIB files for you, SCED and AC3D, but you may find it convenient to write your own specialized application to output a series of specific frames. In this case (or if you are ambitious enough to write your own modeller) you can link your program to the libribout.a library. Your application would use then be using the C binding to the RenderMan API. This API is described in limited detail in the poets.ps document in the distribution. A much better description can be found in Steve Upstill's The RenderMan Companion, published by Addison-Wesley. Developer's who write applications that use the RenderMan API will also need to include the ri.h header file in their source code.

libsoargs.a, so.h - argument parser for compiled shaders

According to Larry's documenation (which is all I have to go by - I've never seen the PRMan application myself), Pixar's PRMan distribution also comes with a linkable library for parsing compiled shaders, much like the sotell program does in the BMRT distribution. Since the compiled versions of the shaders differ in format Larry has provided a similar library for use by applications that need to parse his version of the compiled shader files. Applications which need this feature should include the so.h header file in their source code and link against the libsoargs.a library.

4. The Example Scenes

There are 8 example scenes in the distribution. These are described in the README file in the examples directory, but for completeness sake I'll list and describe them briefly here. The 8 RIB files are: Some of these are good examples for learning the syntax and structure of a RIB file, others are not. If you want to learn a little about the RIB ASCII binding you should start by taking a look at the following examples: The rest of the RIB examples are not well formatted (probably output from a modeller or a program linked with libribout.a). You really wouldn't want to examine the RIB file in these cases anyway, as their main purpose is to show features of the Shading Language. In these cases you should take a look at the shaders which they use. You'll have to look in the RIB to learn which shaders are important for a given example, however. For example, the tpdisp.rib file is an example of displacement shaders so you would look for the Displacement commands in the RIB file to find which displacement shader source files to examine.
      In order to explain how to use these tools in more detail I'll be using two examples in each of the rest of the sections of this article. In some cases I'll use examples I found in the RenderMan Companion. In other cases I'll use some of Larry's examples or some of my own extremely primitive examples. They aren't very good - but this article was is as much a learning experience for me as it is anyone else.

5. The Input File - RIB Format

What is it?

RIB stands for the RenderMan Interface Bytestream. It comes in both ASCII and binary encodings. We'll only be discussing the ASCII version since I have very little information about the binary encodings and BMRT doesn't come with any binary examples. All the example RIB files are ASCII formatted.
      A RIB file is nothing more than an ASCII text file made up of a series of RIB commands. These commands match their RenderMan API C function counterparts almost exactly (there a few exceptions according to the official specification). When you write a C program that makes calls to the RenderMan API via the libribout.a library what you get as output is the ASCII encoding of RIB. This is why its generally easier to use the C binding for RenderMan than to write your own ASCII RIB file.

A little about the format

The semantics of the two bindings (C and ASCII RIB) are very similar. Both take token/value pairs as arguments. The C binding requires that paremeter lists to functions be NULL terminated. The ASCII RIB format does not. The names of the C procedures are prefixed with Ri but the equivalent RIB commands are not.
      RIB files Support single or multiple frames of an image, allowing (as in the limbo.rib example) animations with a single scene description. This is a good case for using the procedural interface to RenderMan instead of hand coding the RIB file. Its much easier to compute the scene descriptions through a programmed loop than to hand compute each frame using the ASCII RIB commands.

How can you create RIB files?

There are three ways to create a RIB file for use as input to one of BMRT's renderers:
  1. By hand
  2. Write a C program using the RenderMan API and link with libribout.a
  3. Using a modeller
    There are three modellers currently available for Linux that can output RIB formatted files:
My impression is that few people create RIB files by hand except as examples in order to test shaders or something similar. The use of modellers on Linux is fairly new to the general public, so at this point I'm guessing many models are created by writing scene-specific programs linked with the libribout.a library. Note that developmental support for AC3D is ongoing, while AMAPI is reported to have dropped their Linux ports. SCED's status is unknown at this time. I've not seen any updates to it for about a year.
      Lets take a look at a couple of examples. The first is a simple RIB file from Larry's set of examples. The second is a simple animation in C source taken from the RenderMan Companion.

Working example 1a - A sample RIB file

The simplest example from the BMRT distribution to follow is probably shadtest.rib. It contains 3 textured objects (two spheres and a flat plane beneath them) along with a light source. The source is given in Listing 1.
##RenderMan RIB-Structure 1.0
version 3.03
Display "balls1.tif" "file" "rgba"
Format 480 360 -1
PixelSamples 1 1
Projection "perspective" "fov" 45
Translate 0 -2 8
Rotate -110 1 0 0

WorldBegin

LightSource "ambientlight" 1 "intensity" 0.08

Declare "shadows" "string"
Attribute "light" "shadows" "on"
LightSource "distantlight" 1 "from" [0 1 4] "to" [0 0 0] "intensity" 0.8

AttributeBegin
#  Attribute "render" "casts_shadows" "none"
  Color  [ 0.7 0.7 0.7  ] 
  Surface "matte"
  Polygon "P"  [ -5 -5 0 5 -5 0 5 5 0 -5 5 0  ] 
AttributeEnd

AttributeBegin
  Translate -2.25 0 2
  Color [1 .45 .06]
  Surface "screen" "Kd" 0.2 "Ks" 0.8 "roughness" 0.15 "specularcolor" [1 .5 .1]
  Sphere 1 -1 1 360
AttributeEnd

AttributeBegin
  Translate 0 0 2
  Declare "casts_shadows" "string"
  Attribute "render" "casts_shadows" "shade"
  Color [1 .45 .06]
  Surface "screen_aa" "Kd" 0.2 "Ks" 0.8 "roughness" 0.15 "specularcolor" [1 .5 .1]
  Sphere 1 -1 1 360
AttributeEnd

AttributeBegin
  Translate 2.25 0 2
  Declare "casts_shadows" "string"
  Attribute "render" "casts_shadows" "shade"
  Surface "funkyglass" "roughness" 0.06
  Sphere 1 -1 1 360
AttributeEnd

WorldEnd
Listing 1: shadtest.rib example from BMRT distribution

Items of interest in this file include:
  1. The values set before the WorldBegin command are used to set camera and display parameters. These global parameters are known as options. The display options can be specific to the renderer being used. Rendering options cannot be set inside the WorldBegin/WorldEnd commands.
  2. Values set inside the Attribute commands are referred to as current parameters and are object specific parameters such as lighting, opacity and surface colors and textures.
  3. Objects (including lights) created inside the WorldBegin/WorldEnd commands exist only inside those commands. They are not referencable outside of these commands.
  4. Notice how the RIB commands contain series of literal strings and numeric values. For example, the surface command is followed by the name of the surface (a string) followed by a series of token/value pairs. These tokens are variables known to the shader being called and the values are the ones we wish to set these variables to when the shader is invoked.
  5. The # sign is a comment, but the double # (ie ##) is a hint to the specific renderer. For all practical purposes, these are also comments, since no renderers use them for anything. I believe the format of the hint tag has changed for the 2.3.5 version of the BMRT renderers but I don't know what has replaced it.
  6. The commands to create the spheres are obvious. The command to create the plane is "polygon". The RenderMan API and BMRT provide support for a number of primitive shapes. BMRT also supports the ability to combine primitive shapes into more complex ones using what is known as Constructive Solid Geometry.
  7. The WorldEnd() command causes the scene to be output to the display.
  8. RIB commands may span multiple lines, although it doesn't show this in the example.
I removed the comment at the start of the file just to save a little space. You should read it and try rendering this example to get a feel for what it does. All I really wanted to do with this example is show you what an ASCII RIB file looks like. The format of the file gives a little clue as to the hierarchy of the commands: WorldBegin/End encompass the Attribute commands, which in turn encompass some objects and their textures and other descriptions. Understanding this hierarchy can help you see the scope of definitions such as objects or projections. This hierarchy can be more apparent when using the RenderMan API since the code is written in a structured language, C.

Working example 2a- A simple animation in C

The RenderMan Companion by Steve Upstill contains a fair amount of sample code that uses the C binding to the RenderMan Interface. Lets take a look at the source for one of these examples:
#include "
#define NFRAMES    10    /* number of frames in the animation */
#define NCUBES     5     /* # of minicubes on a side of the color cube */
#define FRAMEROT   5.0   /* # of degress to rotate cube between frames */

main()
{
   int frame;
   float scale;
   char   filename[20];

   RiBegin(RI_NULL);      /* Start the renderer */

      RiLightSource("distantlight", RI_NULL);

      /* Viewing transformation */
      RiProjection("perspective", RI_NULL);
      RiTranslate(0.0, 0.0, 1.5);
      RiRotate(40.0, -1.0, 1.0, 0.0);

      for (frame = 1; frame <= NFRAMES; frame++)
      {
			sprintf(filename, "anim%d.pic", frame);
         RiFrameBegin(frame);
            RiDisplay(filename, RI_FILE, RI_RGBA, RI_NULL);
            RiWorldBegin();
               scale=(float)(NFRAMES-(frame-1))/(float)NFRAMES;
               RiRotate(FRAMEROT * frame, 0.0, 0.0, 1.0);
               RiSurface("matte", RI_NULL);

               /* Define the cube */
               ColorCube(NCUBES,scale);
            RiWorldEnd();
         RiFrameEnd();
      }
   RiEnd();
}
Listing 2: shadtest.rib example from BMRT distribution

As you can see the hierarchy of commands is a little more evident. Of course, being an animation this is a more complex example. A distant light source is defined outside all frames of the animation. The type of camera projection is defined along with the initial viewing transformation. This is followed by the main loop which produces the frames of the animation.
      Inside the loop each frame is defined. The display is set to write to a file and the format of the output is set with RI_RGBA, meaning red, green, blue and alpha channels will be output (or in simpler terms 3 colors and 1 opacity level). How this is done is renderer specific.
      This particular example is simplified by the use of an external routine, ColorCube(), which actually defines the object geometry to be used. In this case a cube is being built by ColorCube() with its sides being colored. I left this routine as an exercise for the reader, mostly because I always wanted to say that to someone. For those who can't wait to figure out how to do it themselves, the code for ColorCube() is provided in the RenderMan Companion.

6. Basic Steps

So now we've seen what a RIB file looks like and how they can be created. We know we need a RIB file as input to the renderers provided in the BMRT distribution. We know that RIB files provide the geometry of a scene or set of frames and that shaders are referenced by the RIB files to provide texturing aspects to objects in those scenes.
      Ok, so now what do we do? Well, lets run through a full example of creating, shading, previewing, and final rendering of a single scene.

Create the RIB file

Here is a simple example I created on my own. It is C source that links with the libribout.a library. When run it produces a RIB file of a scene with a blue ball over a gray plane, lit by a single distant light source. The source is commented so you can see exactly what I did to create this scene. The C source is in the same directory as the examples (or any directory directly under the main directory of the distribution). To compile this program you would use the following command:
gcc -o example-2a -O example-2a.c -I../include ../lib/libribout.a
To run the command simply type
example-2a > example-2a.rib
At this point you have the ASCII RIB input file needed to feed to one of the rendering programs.

Preview the scene with rendribv and rgl

The first thing to do is examime the scene as a wireframe display to make sure all our objects are there. We won't really be able to tell if they are aligned properly (in front of or next to each other) but we'll be able to see if they have the correct basic shape and if they are within the field of view. To preview the scene use the following command: rendribv example-2a.rib
OK, everything looks as it should. We've got a sphere and a plane. Lets add some surfaces to the objects using rgl. The sphere should be a solid blue and the plane should be grayish.
      To preview the scene with rgl use the following command:
rgl example-2a.rib
Figure 2: wireframe output from rendribv

Full rendering with rendrib

Again, this is about right. The image you're looking at isn't great due to the way I captured the image and converted it to a GIF file. But the image is about what I was expecting. The plane is a bit dark. But lets see what we get from the high quality renderer.
      To preview the scene with rendrib use the following command:
rendrib example-2a.rib
Figure 3: output from rgl
Oh oh. The ball is well lit on top, but the plane is gone. Maybe it has someting to do with lighting.

Adjusting the lighting

In the sample source I set a distant light that sat on a line that stretches from <0.0, 10.5, -6.0> to <0.0, 0.0, 0.0>. This is allowing light to fall on only the top half of the ball, but doesn't explain why the plane isn't visible. Thats a different problem. The sample scene C source contains the following lines:
RiLightSource(RI_DISTANTLIGHT, RI_INTENSITY,
      &intensity, RI_FROM, (RtPointer)from,
      RI_TO, (RtPointer)to, RI_NULL);
Figure 4: output from rendrib
The variables from and to define the line on which the distant light exists. To make this light shine more on the front of the ball we can move the to point out to -600 on the Z axis. This lights up the ball much better, but the plane is still invisible. We can also increase the value of the intensity variable from 0.6 to 1.0.
      But whats wrong with the plane? Where did it go? The answer lies in the surface texture used.

Test with standard shaders

The original version of the sample scene used a matte surface shader for the plane. When rendered with the single distant light the reflectivity of the surface made it basically invisible from the angle of view that we had set with our initial translation.
A first guess was to try adding a spotlight above the surface, which can be seen in the updated version of the sample source. This had no effect, so I tried another shader - the same matte shader used on the sphere. Viola! The surface shows up, including the newly added spotlight. Way cool.
Figure 5: look boss - da plane! da plane!

Lets look at two more examples:
  • Another plain sphere over a plane with a back wall
  • Same scene with textured surfaces
The RIB file for example-4a is probably more simplistic than the example-2a but with better results. The difference is the use of well placed spotlights. Notice the way the spotlight is defined:
   LightSource "spotlight" 1 "from" [1 3 -4]
     "to" [0 0 0] "intensity" 15

This is just like the distant light used in example-2a. This time two lights are used, and they are spotlights instead of a distant light. The effect of well placed spotlight shows in the realism of this image.

Figure 6: example 4a.jpg

The next image is a little hard to see. I didn't have time to adjust the brightness (well I tried using xv but it kinda mucked up the image and I didn't have time to rerender Paul's RIB file). What it shows is the same scene as Figure 6 except this time textures have been applied to the sphere, the wall and the floor. The texture on the sphere is a glass stucco. The floor has a wood texture and the wall has a wallpaper effect. The sphere is interesting in that it uses a glass surface shader with a stucco displacement map. The displacement map alters the actual shape of the sphere causing the slightly bumpy effect that is (somewhat) visible in Figure 7. All of the textures are apparent from examination of the RIB file. All of the shaders used in this example are available in the 2.3.5 release of BMRT. It is left as an exercise for the reader to rerender and adjust for the darkness of the image. (Thats also something I always wanted to say.)

Figure 7: example 4b.jpg

At this point there are only two things left to do:

Simple enough. Except the first one of these will take up an entirely seperate article. Next we'll introduce you to what shaders are without going into depth on how to write them. Stay tuned next month when we'll cover how to write shaders.

7. Shaders

What exactly is a shader?

According to to the RenderMan Companion,
A shader is the part of the rendering program that calculates the appearance of visible surfaces in the scene. In RenderMan, a shader is a procedure written in the RenderMan Shading Language used to compute a value or set of values (e.g., the color of the surface) needed during rendering.
In my language: a shader puts the surface on an object.

How does it fit into a RIB?

The shaders are external procedures referenced at rendering time by the rendering engine (in BMRT that would be rendrib). The C binding to RenderMan calls a shader with the RiSurface call. The following lines in the sample source used in the previous section apply the matte surface shader to the sphere and plane:
RiSurface("matte", RI_NULL); .
This causes the following line to be added to the ASCII RIB file output by the program when it is linked with libribout.a:
Surface "matte" .
Obviously things can get much more complex than this. But at least you'll have some way of identifying the shaders in the example scene files.

Compiling a shader

You should keep in mind that the shaders you write in the RenderMan Shading Language have to be compiled before they can be used. Compiling shaders is very straightforward. To compile the matte.sl shader into the matte.so file you would use a line like:
slc matte.sl .

7. Closing

There aren't that many resource devoted to BMRT or RenderMan on the net just yet. Most can be found by starting at * The RenderMan Repository - (http://pete.cs.caltech.edu/RMR/index.html). There is also a good collection of RenderMan shader information at * RManNotes - (http://www.cgrg.ohio-state.edu/~smay/RManNotes/index.html).
      So, thats about it. You've seen the basics. You've been introduced to the tools. Now you just have to do something with them. Larry's * BMRT Web pages contain links to intersting images created with BMRT. That should provide some motivation. I'll be playing with it all next month trying to learn about the RenderMan Shading Language for the April Graphics Muse column. If you come up with anything interesting feel free to drop me a note.

indent
Ordering information:
Pixar Animation Studios
Attn: Katherine Emery
1001 W. Cutting Blvd.
Richmond, CA 94804
Specify you are ordering the "RenderMan Specification". It costs $20US. Note: I have no association with Pixar (but I can dream, can't I?).
Upstill, Steve The RenderMan Companion A Programmer's Guide to Realistic Computer Graphics. Addison-Wesley 1992
The RenderMan® Interface Procedures and RIB Protocol are © Copyright 1988, 1989, Pixar. All rights reserved. RenderMan® is a registered trademark of Pixar.

Blue Moon Rendering Tools are © Copyright 1990-1995 by Larry I. Gritz. All rights reserved.

indent
© 1996 by Michael J. Hammel


"Linux Gazette...making Linux just a little more fun!"


Learning about Security

By Jay Sprenkle, jay@shadow.ashpool.com


It all started when the system rebooted...

I had been having reliability problems with my system for over a month. It would run fine for up to a week or so then it would crash with wierd symptoms. I know it's unusual to trust in your software these days, but I had faith that Linux was not the culprit. Only operating systems produced by large companies have to be rebooted every day.

I took the motherboard out of the system and drove down to the supplier. The guy behind the counter had the standard "electronic supplier salesperson disease". He thought I was A. an idiot, B. trying to rip him off or C. trying to ruin his day/profit margin. I explained the problem, told him how it gave different symptoms each time it died, and how I had swapped out parts. After about 20 minutes he had no more arguments and he gave me a new motherboard.

I took it home and put it back into the case. I was back up in a few minutes and I put the system back into service. After almost three weeks of blissfull operation it rebooted itself and started back up without a problem. I didn't even know about it until I saw the system log file a day later. ARGGG! The **** thing is broken again...

I studied the logs and found that odd things had happened. The web server process log was filled with total nonsense. The system log had stopped working shortly after the reboot. I felt that a power failure had caused the odd log messages and possibly damaged the system logging program.

As I began looking at the other logs I found that someone had transferred copies of some of my files to a system I had never heard of before. This was serious! I had been violated! I didn't have hardware problems, some sleazoid-weasel had broken into my system! I had previously been over the system carefully trying to eliminate all the security holes. I hadn't been careful enough!

I copied off every log file I could find and immediately changed all the passwords on the system. If they had gotten in and copied the password file they could eventually crack the encoding on their own system and they would have all the passwords.

I sent off a message to the system administrator of the system that the files had been sent to. With a little time at a search engine site I found that this system was located in Chicago. I later found out from the site's system administrator that this guy had somehow broken through the security in one of their systems routers. Once into the router he installed a packet sniffer. This program reads the data packets that go across the net and records anything that looks like a password.

I had been connecting to my system remotely to get mail from it. I have since found out that the POP3 protocol used to get mail sends your account password in clear text (unencrypted) when getting your mail. This sleazy booger's packet sniffer probably captured my password when I was getting my mail. The rlogin, rsh, rexec, rlp, telnet, adn FTP protocols also send passwords in clear text by the way!

I went through the '/etc/services' file one more time and found that I had not disabled the 'rlogin' service as I had first thought. This service runs on port 513 but is not called 'rlogin'. I went through and disabled every service that starts with an 'r'. These are the remote services programs that a cracker can use to get into your system. I disabled all file sharing and all protocols except tcp/ip. I disabled the telnet service altogether since there is a better replacement. I also made sure that NFS and RPC were disabled since there was supposed to be a security hole in these too.

Well, not a lot had been done to my system, other than the reboot after the break-in. One nagging thing was that the system logging no longer worked. After goofing around with it for a day or so I finally noticed what should have been obvious. The 'syslogd' program had been replaced with another program with the same name.

I haven't verified it but I believe this program is another copy of the packet sniffer the cracker used in the router. When you do a 'ps' to see what's running you wouldn't think anything about it since this program should be running all the time. I replaced the 'syslogd' program with the correct one and it worked like a champ again.

While poking around in my /tmp directory I found a copy of the 'bash' shell with the SUID bit set. WHOA! What's this? With this little baby you can become root by simply running it. When I happened to mention this to a fine gentleman [Jim Dennis, The Answer Guy --Editor] who was helping me try to get it working he immediately remembered the security hole associated with this. There's a bug with the 'sendmail' program that allows you to make an SUID copy of your shell in the /tmp directory. If you don't have version 8.8.3 or later of the sendmail program you're vulnerable too! (go to http://www.sendmail.org for the latest stuff).

So, what have I learned from all this?

  1. Security is more important than I thought.
  2. Security is no fun to implement...
  3. Cracker's read the CERT releases so they can keep up on the latest, coolest, ways to break into your system. They think it's a fun challenge to 'beat you'
  4. Security is no fun to implement...
  5. Don't use FTP, telnet, rlogin, rsh, or POP3 remotely. If you need to do this get the newer versions that encrypt the session BEFORE they log in.
  6. Security is no fun to implement...
  7. If you have an older version of sendmail than 8.8.3 replace it. 8.
  8. Don't give access to programmers tools. It just makes the cracker's job easier.
  9. Security is no fun to implement...
  10. Turn off all remote services on your system
  11. Security is no fun to implement...
  12. Read the CERT bulletins to see if you have any obvious holes in your system. If you do, fix them
and lastly...
Security is no fun to implement!

best of luck to you!

Jay


Copyright © 1997, Jay Sprenkle
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Linux and MIDI: In the beginning...

By Dave Phillips, diphilp@mail.bright.net


"The Musical Instrument Digital Interface (MIDI) protocol has been variously described as an interconnection scheme between instruments and computers, a set of guidelines for transferring data from one instrument to another, and a language for transmitting musical scores between computers and synthesizers. All these definitions capture an aspect of MIDI." <Roads, Curtis. 1995. * Computer Music Tutorial. Cambridge, Massachusetts: The MIT Press. p. 972>

Greetings! This article will hopefully be the first in a series covering various aspects of *MIDI and sound with Linux. The series will be far from exhaustive, and I sincerely hope to hear from anyone currently using and/or developing MIDI and audio software for use under Linux.

Perhaps most Linux users know about MIDI as a soundcard interface option, or as a standalone interface option during kernel configuration for sound. As usual, some preparatory considerations must be made in order to optimally set up your Linux MIDI music machine. Be sure to read the kernel configuration notes included in /usr/src/linux/Documentation: you will find basic information about setting up your soundcard and/or interface, and you will also find notes regarding changes and additions to the sound driver software.

Common soundcards such as the *SoundBlaster16 or the MediaVision *PAS16 require a separate MIDI connector kit to provide the MIDI In/Out ports, while standalone interface cards such as the *Roland MPU-401 and *Music Quest MQX32M have the ports built-in. Dedicated MIDI interface cards don't usually have synthesis chips (such as the *Yamaha OPL3 FM synthesizer) on-board, but they often provide services not usually found on the soundcards, such as MTC or SMPTE time code and multi-port systems (for expanding available channels past the original limit of 16).

Having successfully installed your card and kernel (or module) support, you will still need a decent audio system and a MIDI input device. If you use a soundcard for MIDI record/play via the internal chip, you will also need a software mixer; if you record your MIDI output to tape, and then record your tape to your hard-disk, you will also want a soundfile editor.

When the essential hardware and software is properly configured, it's time to look at the available software for making music with MIDI and Linux. Please note that in this article I will only supply links and very brief descriptions, while further articles will delve deeper into the software and its uses.

Nathan Laredo's *playmidi is a simple command-line utility for MIDI playback and recording which can also be compiled for ncurses and X interfaces. *JAZZ is an excellent sequencer which has some unique MIDI-processing features and an interface which will feel quite familiar to users of Macintosh and Windows sequencers. *Vivace and *Rosegarden are notation packages which provide score playback, but each with a difference: Rosegarden accesses your MIDI configuration, while Vivace "renders" the score. *tiMiDity is a rendering program which compiles a MIDI file into a soundfile, using patch sets or WAV files as sound sources. Ruediger Borrmann's *MIDI2CS is also a rendering program, but it acts as a translator from a MIDI file to a *Csound score file. Mike Durian's *tclmidi and *tkseq provide a powerful MIDI programming environment, and Tim Thompson has recently announced the availability of his *KeyKit, a very interesting GUI for algorithmic MIDI composition.

4-track recording to hard disk can be realized using Boris Nagels' *Multitrack, but Linux has yet to see an integrated MIDI/audio sequencer such as Opcode's *Studio Vision for the Mac or Voyetra's *Digital Orchestrator Plus for Windows. Linux also lacks device support for the digital I/O cards such as the *Zefiro or DAL's *Digital-only.

If you use the tiMiDity package or MIDI2CS you will want to edit your sample libraries. Available soundfile editors include the remarkable *MiXViews, the Ceres *SoundStudio, and Paul Sharpe's tk-based * Studio.

The excellent *Linux MIDI & Sound Pages are the best starting point in your search for software, and be sure to check the *Incoming directory at *sunsite. Newsgroups dedicated to MIDI include comp.music.midi and alt.binaries.sounds.midi; please write to me if you know what mail-lists are available, I'll list them in a later article.

Feel free to write concerning corrections, addenda, or comments to this article. Linux has great potential as a sound-production platform, and we can all contribute to its development. I look forward to hearing from you!


Special thanks to Hannu Savolainen (for maintaining sound support for the Linux kernel) and to Arne Di Russo (for the Linux MIDI & Sound Pages).

Dave Phillips

dlphilp@bright.net

*DLP's Home Page



Copyright © 1997, Dave Phillips
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Amaya

Introduction

by Larry Ayers


For several years a group of programmers in France have been developing an elaborate text-processing system known as Thot. Thot has some resemblances to Tex, in that it is a structural document-editing system capable of very high-quality output. One major difference is that Thot is more WYSIWYG; the formatting tagging is hidden and doesn't have to be explicitly written by the user. The output formats are more varied as well. Thot can produce Postscript files, as Tex can, but it can also produce plain ASCII text and HTML. This last formatting capability attracted the attention of the W3 Consortium a couple of years ago. (W3 is an international research organization which attempts to set standards for Internet documents; their flexibility and patience have been sorely tried in recent years by the flood of HTML innovations introduced by Microsoft and Netscape, among others). Using the Thot system as a core, the W3 group in collaboration with the Thot developers have been developing a combined web-browser and HTML editor known as Amaya.

Source and Installation

Amaya, as is the case with much Linux software, is a work-in-progress. Until recently the source code was restricted to members of the W3 Consortium and only binary versions were available to the public. In early February the source was made freely available, both at the *Amaya web-site and also at the Sunsite archive site, currently in the /pub/Linux/Incoming directory.

Amaya can be installed anywhere as long as the directory structure is preserved. It is a Motif application, so unless you have the Motif libraries and header files installed you will have to get the statically-linked binary distribution. Compiling the source necessitates obtaining and compiling the Thot toolkit as well, which is available from the same locations as Amaya. I compiled it from source and found the instructions to be somewhat unclear; after several false starts I found that the Thot source should be unarchived first, then the Amaya source should be unarchived so that the Amaya directory is a subdirectory of the top-level Thot directory. This is a very large source tree and needs about sixty megabytes of free disk-space over and above that required for the source itself. It compiled without errors but there was no evident means provided for cleaning up the object files, etc. I resorted to moving subdirectories which looked un-essential to another drive, then moving back the essential ones which it turned out Amaya needs. You might want to try the binary version first in order to determine if it suits you before going to the trouble of obtaining and compiling the source.

One caution: the first time you start Amaya, point it at a local file; otherwise it will attempt to load a file from http://www.w3.org and if you're not on-line at the time, it will die with a segmentation fault. The default home-page can be set to one on your local disk in the initialization file if you'd like.

Editing and Browsing With Amaya

As an HTML editor Amaya is WYSIWYG all the way. There is no view of the file being edited which shows the actual HTML tags. The main window (take a look!) is a typical browser window complete with in-line graphics, with the major difference being that you can enter text. The various HTML tags are invisibly inserted by means of mouse-driven menus. I much prefer hot-keys and found that, though few are included by default, any number of them can be set up in the ~/.thotrc file. The behaviour of the enter key is interesting. Pressing the key while just typing text will start a new paragraph, whereas if you are entering list-items, table-fields or other sequential tags another one is created.

There are two alternative file views available: the first is the "Structure View" (here's a screenshot) which presents a tree-like diagram of the HTML file. I suppose this could be useful with large files, just to get an overview. Another window, the "Alternate View" (another screenshot), shows you what your file will look like when displayed by a text-mode browser such as Lynx. I thought this was a nice touch. It's all too easy to work up an HTML file, test it with Netscape or Mosaic, and never even consider that it may be illegible viewed with a text-mode browser.

As a web-browser Amaya has some limitations. It is confused by many of the newer Netscape tags, though on relatively simple pages it does a good job. As an example, the Linux Gazette table-of-contents page is displayed in a garbled fashion. The spiral-notebook graphic on the left side of the page isn't rendered, and the table formatting isn't interpreted correctly. In contrast, the bulk of LG's content pages display well, but they are usually simpler in format.

Amaya wasn't really created to be a full-fledged browser, though it may approach that status in future releases. The W3 "position statement" on Amaya says that it is intended to be a test-bed platform for HTML development.

I never have become comfortable using Amaya, or any WYSIWYG HTML editor for that matter, to create HTML files from scratch. What I have been using it for is to experiment with already-written files. Sometimes when the precise tagging I want eludes me, I've loaded the file into Amaya just to see how it approaches the problem. It might be wise to begin using Amaya on copies of files. I favor lower-case tagging but when Amaya saves a file it will replace all of the tagging with its own, and this is all uppercase. Some of its other choices may not be what you want as well, so working with a copy allows you to incorporate the changes you like into the original file, leaving the rest alone.

Conclusion

Amaya is an interesting project, and even at this early stage it's stable enough to be usable. I wouldn't want to have to rely on it solely, but it has proved useful to me on several occasions. Now that the source has been made public perhaps other programmers will make contributions; it's likely that in future months new releases will be made, amd its capabilities will increase.


*Larry Ayers<layers@vax2.rainis.net>
Last modified: Thu Feb 27 18:50:42 CST 1997


Copyright © 1997, Larry Ayers
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Slrn and Slrnpull: Sucking Down The News

by Larry Ayers


There are quite a few methods of reading Usenet postings. A conventional newsreader will log on to your remote server, download headers of the new messages in groups you want to follow, then allow you to tag the messages you want to read. These messages are then fetched for you. All of this happens while online, and the time can mount up.

Another approach is one used by Suck and Leafnode, among others. These programs are designed to be used non-interactively and usually are set up to deposit fetched postings into a local spool-directory. Suck requires that you have an active news-server, such as INN or CNEWS, on your machine. Leafnode doesn't need the news-server (it has its own), but both programs are designed for multiple users and might be overkill for single-user machines.

Slrn is a popular text-mode newsreader, written by John Davis at MIT. It originally belonged to the first category above, but recently Davis has been working on an extension for Slrn which will pull down messages from a server and store them locally. The messages can then be read offline with Slrn. The extension is called Slrnpull, and it comes with the most recent beta version of Slrn.

Installation and Usage

If you have the S-lang library on your system, you can compile Slrn and Slrnpull from the source, which is available (along with the S-lang library source) from *this site. A binary, statically-linked version may be in the /pub/Linux/Incoming directory at sunsite.unc.edu by the time you read this. If you prefer a certain location for the news-spool directory (which can get large) the slrnfeat.h file in the /slrn/src directory can be edited.

Slrn uses a configure script which should enable it to be compiled on most Linux systems. Once you've put the executables in a directory on your path, create the spool directory (/var/spool/news/slrnpull or whatever you've defined it to be), then copy the supplied sample script slrnpull.conf to the new directory. This needs to be edited before you start Slrnpull for the first time. The format is not complicated; here are John Davis' comments from the sample file:


# The syntax of the file is very simple.  
# Any line that is blank or begins with a '#' character will be ignored by 
# slrnpull.  The remaining lines consist of 1-3 fields separated by 
# whitespace:
#
#   NEWSGROUP_NAME  MAX_ARTICLES_TO_RETRIEVE   NUMBER_OF_DAYS_BEFORE_EXPIRE
#
# The first field must contain the name of a newsgroup.  
# 
# The second field denotes the number of articles to retrieve for the 
# newsgroup; if its value is 0, all available articles will
# be retrieved.
#
# The third field indicates the number of days after an article is retrieved
# before it will be eligible for deletion.  If this value is 0, articles from
# this group will not expire.
#
#
# If a field is blank, or contains the single character '*', default values
# will apply to the field.  Defaults may be set by a line whose newsgroup
# field is 'default'.  Such a line will denote default values to be applied to 
# the lines following it or until another default is established.

# For example:
default                                20        14
# indicates a default value of 20 articles to be retrieved from the server and
# that such an article will expire after 14 days.
comp.os.linux.misc        50        7
comp.os.linux.x         20        7
comp.os.linux.announce        *        *

This is easier to set up than some news programs I've used!

Assuming you have the $NNTPSERVER variable set to your news-server's IP address in your ~/.bash_profile or ~/.cshenv file, Slrnpull should be ready to try out. The first time you start it up it will create a subdirectory for each news-group you have specified. Then it will log on to your server and download messages, displaying the connection speed and number of articles on your terminal screen.

You probably subscribe to certain groups for which you want all of the new messages. For certain others you may want to be more selective in what you download. A kill-file can be created in the spool directory which specifies, on a per-group basis, which messages you would prefer be left on the server.

Starting up Slrn with the switch --spool will cause it to load the contents of your newly-filled spool-file. Reading messages this way is fast, and any which you delete will then be invisible in the newsreader, though they remain on the disk until they are expired. Any follow-up postings which you might write are stored in a subdirectory of the spool. The next time you run Slrnpull it will upload them to the server before retrieving new messages.

Slrnpull keeps a log of all transactions to the server; these messages are displayed on the screen as the program runs, but the idea of this program is that you don't need to be sitting there watching. The log is useful for checking to see if your postings have been accepted by the server.

Periodically Slrnpull should be run with the --expire switch, which will remove all messages you've marked for deletion while reading news with Slrn. This could be run every night as a cron job.

It will take some fine-tuning of the slrnpull.conf file, but eventually you will have the program retrieving just the messages you want. It might seem like a waste to be downloading all of the junk messages along with the worthwhile ones, but it's a continuous process and doesn't take long. I've found that running Slrnpull while browsing the web or receiving an FTP file works well.

The sample .slrnrc file included with the program has an if/then statement which causes Slrn to read the local active file when run in spool mode, while keeping Slrn in standard mode from retrieving the bulky remote active file each time a connection is made. This lets you read news directly from your server when desired.

The sample file includes some new entries in order for Slrn to make use of the spooled messages. These are:



      set spool_inn_root        "/var/spool/news/slrnpull"
      set spool_root                "/var/spool/news/slrnpull/news"
      set spool_nov_root        "/var/spool/news/slrnpull"
      set use_slrnpull 1
      hostname "your.host.name"
      username "your_user_name"

The remainder of the .slrnrc file is the same as in previous Slrn versions, so if you already have one customized to your liking the Slrnpull-specific sections can be lifted from the sample and pasted in.

I initially had some trouble convincing slrnpull to talk to my news-server. I asked John Davis for help and he sent me a patch for one source file which caused slrnpull to generate a debugging log; from the logfile he determined that the problem was with the proprietary Dnews server software which my provider uses. The currently available version has this patch included.

If you want to find out what software your news-server uses, just telnet into the news machine:


    telnet [IP address] :nntp

The server will identify itself when you log in.

Conclusion

Slrnpull is probably most useful with low-volume newsgroups, such as comp.os.linux.announce. You would most likely want to see all of the messages anyway in such a group and Slrnpull will fetch them all. High-volume groups, such as comp.os.linux.advocacy, typically have a high chaff-to-wheat ratio, and in these a quick scan of the headers for the few of interest (while online) might be more efficient. Slrnpull is also effective for obtaining a quick idea of the the flavor and tone of a group: just tell it to suck down the most recent twenty messages in the group, and see what you think.

If you have never used Slrn, I highly recommend this program, especially if you read news over a PPP or SLIP connection. It's fast and efficient, and its behaviour can be easily molded to your needs. Users of the Emacs news interface Gnus will find the transition painless, as most of the keystroke commands are identical. Gnus has many more features but it's slower to use over a network and is much more demanding of system resources.


*Larry Ayers<layers@vax2.rainis.net>

Last modified: Thu Feb 27 18:39:52 CST 1997


Copyright © 1997, Larry Ayers
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Sigrot: BBS Taglines for the Net

By Paul Anderson, <paul@geeky1.ebtech.net>


Have you ever called BBSes and downloaded QWK packets? If you have, then you most likely will have either seen or used a tagline. For those of you who haven't, a tagline is one line of text for a witty saying. It's usually at the bottom of a persons signature. QWK packets, by the way, are like UUCP for DOS in that you downloaded this zipped file with all your mail in it, then you open it in a QWK mail reader, and upload your replies. The QWK mail reader often supports the ability to change taglines with each message.

These short witticisms are nice to have at the end of a message, and sometimes they prove to be the best part! This brings me to the program featured in this article. Sigrot is currently in version 1.0 and is maintained by Christopher Morrone, <cmorrone@udel.edu>. It can be obtained from gilb5.gilb.udel.edu:/pub/linux/sigrot_v1.0.tar.gz

Got the tar-file? Good. Untar it with:

tar -xzvf sigrot_v1.0.tar.gz

Look in the current directory and you'll find a directory named sigrot_v1.0/ Change into that directory, read the README and INSTALL.help files, then run make

geeky1,1:~/tar-stuff/sigrot_v1.0% make
done
geeky1,1:~/tar-stuff/sigrot_v1.0%

You'll have a program named sigrot in the current directory, sigrot.1 is the manpage. Then you can test it:

geeky1,1:~/tar-stuff/sigrot_v1.0% sigrot -w testfile
testfile copied over signature archive.
Type "sigrot -r" to restore the previous archive.
geeky1,1:~/tar-stuff/sigrot_v1.0% sigrot
geeky1,1:~/tar-stuff/sigrot_v1.0%

Well, what have we just done? We've put the signatures in testfile into sigrot's signature archive, and we've just nuked your ~/.signature file. Check it out and you'll see that it contains:

This is the first signature entry.

Okay, so if we check testfile we see that the first line contains the first signature. Let's run it again. Okay, what's in ~/.signature now? Check it out and you'll see:

This is
       the
          second signature
                          entry.
                        

So what good is this to me, you say? Plenty. Create a new file called 'mysigs' with couple of your favourite one-liners. Now we run our dear friend sigrot again:

geeky1,1:~/tar-stuff/sigrot_v1.0% sigrot -w mysigs

Okay, run sigrot with no command-line options and check ~/.signature. Is one of the signatures from mysigs in ~/.signature? If so, put the following in your crontab:

00 * * * *      sigrot

That'll run sigrot once every hour. Now, you're ready to send e-mail with your new cool .sig!

Of prefixes and space reduction.

Sometimes, when you've got .sig like mine, the majority of my .sig never changes. If you get a significant number of one-liners in your signature archive, it can became quite large. What a waste of space. But, wait! There's a way to reduce the amount of space it takes! To show you what I mean, Here's my .signature:

                            ---
                        Paul Anderson
    Author of Star Spek(a tongue in cheek pun on Star trek)
e-mail: starspek-request@lowdown.com with subscribe as the subject
I hear it's hilarious.               Maintainer of the Tips-HOWTO.
          http://www.netcom.com/~tonyh3/speck.html
    Manuals out, after all possible keystrokes have failed.

Only the last line ever changes. Why waste disk space when you can use a more efficient method? Here's what I've done, you see sigrot creates a directory called ~/.sigrot, and it lets you specify a prefix. A prefix is what's put before the .sigs from your .sig archive, it's used for stuff that doesn't change. So, I created a file named ~/.sigrot/prefix, and put the following in it:

                            ---
                        Paul Anderson
    Author of Star Spek(a tongue in cheek pun on Star trek)
e-mail: starspek-request@lowdown.com with subscribe as the subject
I hear it's hilarious.               Maintainer of the Tips-HOWTO.
          http://www.netcom.com/~tonyh3/speck.html

See? Sigrot picks a .sig from your .sig-archive, then it appends it to the file ~/.sigrot/prefix.


Now you know how to spiff up your e-mail with a wonderful program called sigrot. I have a file of 1,000 signatures for use with sigrot, send me some e-mail at paul@geeky1.ebtech.net if you want a copy, or some help on setting up sigrot.


Copyright © 1997, Paul Anderson
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


Thoughts on Multi-threading

By Andrew L. Sandoval, sandoval@perigee.net


As I read the article "What Is Multi-Threading?" in the February issue of LJ my mind went back a couple of months ago to the time I decided it would be fun to write a multi-threaded FTP daemon to replace the wu-ftpd we were using on a very heavily hit FTP server. As the author explains in his article, threads make a lot of sense for server applications. Just the memory savings on 250 copies of the FTP daemon makes it all worth investigating. BUT, just as you were about to go out and make all of you favorite server applications multi-threaded, I thought a couple of notes from my project might come in handy.

First, if you plan on allowing a high number of concurrent connections to your server, a single multi-threaded process will not do. Most OS's, Linux included limit the number of file descriptors a process is allowed to have open at any one time. You can usually use getrlimit() and setrlimit() to give your process the maximum number of file descriptors allowed, rather than the default (usually 64), but, even still most operating system (NOFILE) hard limits are set to 1024. In the case of an FTP server you must keep in mind that you will need at least three file descriptors for every client connection. (1 for commands, 1 for file transfers, and 1 to open the file or directory listing to transfer.) This quickly adds up. Supporting 500 concurrent connections would require an absolute minimum of 1500 descriptors, and that is not even counting the ones you need just to get up and running (like the socket used to listen for incoming connections.) The best way I have found to solve this problem is to fork() a predetermined number of child processes that all accept file descriptors that are passed from the parent and then create a thread to handle the incoming descriptor/connection. On Linux you would use the proc filesystem to pass the descriptor. On other OS's such as Solaris (that support Streams) you would use ioctl() with the I_SENDFD and I_RECVFD functions.

This has another advantage as well. In addition to accepting file descriptors from the parent process which is listening for connections on port n, you can now receive connections from any process that chooses to pass clients on to your multi-threaded server through a named pipe. A good example might be a small appliction that is started by inetd and then decides (by say IP address) whether to pass your connection to the multi-threaded server or to the standard ftpd. (This was useful in my case, since our ftpd was for anonymous FTP only. The daemon did not support any functions unneccesary for typical anonymous FTP such as chmod or delete. On the otherhand, we wanted employees of the company to be able to do just that while still logging in as anonymous. So, if you came from an IP address that we knew was ours, the inetd application exec()'d ftpd after clearing the close-on-exec flag. If you came from the outside world you went directly to the multi-threaded FTP daemon which also limited your access beyond what the file system already provided.)

Just when you finally think you have out smarted the file descriptor problem, here comes another one: fopen(). The standard i/o fuctions like fopen(), fprintf(), fgets(), etc., are extremely useful when working with a command driven application like FTP. Unfortunately the fileno element of the FILE struct is usually defined as an unsigned char. Simply put, once you have more than 255 open file descriptors in a single process you can no longer reliably use fopen(), fprintf(), etc. The solution here: don't use these functions. Instead use open(), read(), write(), etc. A possible second solution is to make sure you have enough child processes accepting file descriptors to keep each process from exceeding the 255 limit.

If you choose to write such a multi-threaded server, you will also have to deal with the possibility of concurrent threads in multiple processes accessing a delicate resource. (i.e. even something as simple as a global count of the number of concurrent connections.) In this case you will still want to use a Mutex to protect data, but, the mutex will need to mmap()'d by all child processes, so that a lock in thread A in process 1 will also block thread C in process 2. In the case of a resource such as a "current user count" you will want that variable to be included in the mmap()'ing anyway.

Aside from all of this, threads really are fun. Threaded applications are a great deal more painful to debug, and given the OS and stdio limits I have mentioned there may even be more programming overhead, but, the trade off in system performance and resource utilization for major client/server applications is worth it. Besides, this is the stuff that makes programming fun!

I hope this is helpful.

Andrew L. Sandoval


Copyright © 1997, Andrew L. Sandoval
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"


USENIX Notes

By Arnold D. Robbins, arnold@gnu.ai.mit.edu


Sun, 19 Jan 97
I am writing this on my Linux portable after USENIX. I hadn't been to USENIX in four years, and had been looking forward to it for a while. Some things were really great, and others were disappointing. Overall, I enjoyed it and it was worthwhile.

I took two tutorials. The first was on Win32 programming, and it was most of the justification for getting my company to pay for the conference, since I'll be doing a lot of Windows NT programming starting soon after I return. The tutorial was good, but the notes were not in sync with the slides, which was very frustrating.

The second tutorial, well, the less said about it the better; it was below the usual standard for USENIX tutorials, which are usually quite good.

Of course, the best part of the conference is the conference. There are several components: the refereed papers, the invited talks, the vendor show, and then the general "networking" (not the computer and wires kind, the other kind) that goes on.

The refereed papers didn't seem that exciting. They all either dealt with enhancements to proprietary versions of Unix, or had WWW in their title. Of course, maybe when I get to read some of the papers, I'll revise my opinion.

The invited talks were better, particularly from the guys at Bell Labs; Matt Blaze on why encryption isn't used more often, Rob Pike on Inferno (they gave out an Inferno CD to all registrants) and Bill Cheswick's "Stupid Net Tricks" talk.

The vendor show was ok. O'Reilly, and especially the San Diego Technical Bookstore did a bang-up business. All the Linux CD-ROM vendors were there and did OK too. The biggest hit was SSC's t-shirt (see photos elsewhere), which sold like hot cakes. Fortunately, I got mine early.

This was the first joint USELINUX conference. I must say, Linux is certainly invigorating the USENIX community. The Linux talks I went too were all well attended. Dave Miller and Miguel de Icaza (sp?) gave a neat talk on Linux/SPARC. It doesn't yet support the Minix filesystem, due to endian issues. Most people in the room didn't seem to mind... Otherwise, it's Linux, and it's cool. You can get a real distribution from Red Hat.

It was particularly interesting that Linus's talk on the future of Linux overflowed the smaller conference room into the very large main speaking hall. The majority of the conference attendees were there. As always, I found Linus amusing, intelligent, and very insightful about the computer / desktop industry. Linus's goal: World Domination. But to achieve this, we need real end-user applications (spreadsheets, word processors, etc). Linus made the insightful observation that the Unix vendors have made a mistake concentrating on the market for the server in the back room; no-one sees it, and no-one cares if it's replaced with something else.

And last, but not least, the "networking" part. Figuring that I probably wouldn't get to another USENIX for a long time, I took advantage of the opportunity to chat with Dennis Ritchie for a few minutes, and thank him for the courtesy with which he always replies to my email. I enjoyed it; he's a really neat person.

I got to meet Jeffrey Friedl (author of O'Reilly's new book on regular expressions); he had found a number of strange cases in gawk's behavior (that have since been fixed). I also finally met Larry Wall, author of Perl. Larry is one of the few people who generally doesn't wear a name badge at USENIX; otherwise he wouldn't be able to move around much.

I was there when Greg Wettstein (sp?) of the Roger Maris Cancer Center came over, introduced himself to Larry, and told him that many cancer patients were having an easier life thanks to Perl. It was a humbling experience, since I certainly haven't made that kind of an impact on anything, and Larry too seemed a bit awed. Larry's a neat guy; I hope to get to know him better in the future.

Conclusions: 1. It's worthwhile for Linux people to be involved in USENIX; we're all on the same Open Systems / Free Software team, even if we don't realize it. 2. Linux is invigorating USENIX, it's brought the fun back into the Unix world.

Arnold Robbins -- The Basement Computer
Internet: arnold@gnu.ai.mit.edu
UUCP: dragon!skeeve!arnold


Copyright © 1997, Arnold D. Robbins
Published in Issue 15 of the Linux Gazette, March 1997


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"Linux Gazette...making Linux just a little more fun!"

What You Can Do with tcpd

By Kelly Spoon, mars@loeffel.txdirect.net

If you have read my article on security, then you know that tcpd can be used to keep people from getting on your machine, and, thusly, it makes a nice first line defense against Bad Guys. You also know that there is an extra option you can put in the /etc/hosts.allow and /etc/hosts.deny files that the man pages refer to as the "shell_command".

So....are you wondering what all you can do with the "shell_command" option?

Me too. According to the hosts_access man(5) page, you can use it to finger the person who is trying to get to your services. However, the feature that I think is pretty neat is that this gives you the ability to set up personalized banners for whenever someone tries to connect to your machine.

Here's the catch, though. In order to enable this option, you're going to need to recompile and turn this sucker on yourself. The binaries that your favorite Linux distribution installed on your machine probably weren't set up to take advantage of this neat little feature. (At least, they weren't on mine)

Getting and installing tcpd


The first thing you need to do is get a hold of is the source for tcpd. * Here is where it's been hidden.

Those of you with keen eyes will note that the name of the file we have downloaded is tcp_wrappers*.tar.gz and not tcpd*.tar.gz. Don't sweat it, this really is the package you want.

tar -zxvf tcp_wrappers*.tar.gz will unpack everything for you into the tcp_wrappers_7.4 directory. It doesn't really matter where you do this, since after we have compiled and installed the binaries, we can get rid of this directory.

Go in there as root. Normally, all we have to do is type make, and Linux will automagically compile the program for us. However, we have to pass some extra options to the make with this program.

Unfortunately, the Makefile for tcpd doesn't have an install option, so you have to put things in place yourself. Here's a quick list of where things should go after you've compiled:

Bin File			Location on Your Machine
--------			-----------------------
safe_finger			/usr/sbin/real-daemon-dir/safe_finger
tcpd				/usr/sbin/tcpd
tcpdchk				/usr/sbin/real-daemon-dir/tcpd-chk
tcpdmatch			/usr/sbin/real-daemon-dir/tcpdmatch
try-from			/usr/sbin/real-daemon-dir/try-from
*.3				/usr/man/man3/*.3
*.5				/usr/man/man5/*.5
*.8				/usr/man/man8/*.8

As always, make sure you back up your *old* files before installing the new ones.


The Fun Part -- Banners and Other Stuff


Now that we have our new tcpd in place, it's time to get the frame work in place for our banners. You can do this in any directory on your machine, but, in keeping with my own warped view of where things belong, I suggest creating a dir called /etc/banners and using that for our homebase. And since I get to be the author, that's the dir I'm going to refer to.

Once we've got /etc/banners created, we're going to need to do this from the tcp_wrappers_7.4 dir:

cp Banners.Makefile /etc/banners/Makefile

And now that the hall is rented and the orchestra engaged, it is time to dance. (ObNiftyStarTrekQuoteThatI'veBeenDyingToUse)

Creating your banners

In order to make a banner, all you have to do is go into /etc/banners, and create a file called prototype. Put anything you want in here. It's your banner. Since this would be a good place for an example, here's what I put for my banner whenever someone is denied access to my machine:

^[[44m*****************************************************************
                    This is a ^[[m^[[44;01mprivate^[[m^[[44m machine
*******************************************************************^[[m

          If you wish to access this machine, please send email to 
            ^[[01root@loeffel.txdirect.net^[[m

This prints out a nice looking little banner with the first 3 lines in blue, and the word "private" and root's email address set in bold. Looks pretty official.

Once you have created your prototype, then all you need to do is run a make in the /etc/banners directory. This will then produce 4 files (or more, depending on whether you've hacked the Makefile).

They are in.telnetd, in.ftpd, in.rlogind, and nul. What you need to do next is create another dir, and move these files into it. Since the above example is for the connections that get refused, I put these in /etc/banners/general-reject. The last thing to do is to move the in.* and nul into the new directory. It's also a good idea to stick your prototype in there in case you want to change the banner later on.

Making tcpd use the banners

This is the last step. I promise.

You need to edit your /etc/hosts.allow or /etc/hosts.deny files so that tcpd knows it should throw up a banner whenever someone tries to connect. Basically, my /etc/hosts.deny looks like this:

# /etc/hosts.deny for linux.home.net

ALL:	ALL except .home.net:	banners /etc/banners/general-reject

And that's it. You can now put up customized banners that will be shown based upon the hostname of the person who tries to connect to your machine. Finally, you can take advantage of the "shell_command" option listed in man 5 hosts_access. To see what else you can do with this, check out man 5 hosts_options.

And, if you're scratching your head wondering what's going on, keep reading.


Behind the Scenes


How tcpd Works

As you know, tcpd hangs around on your system and waits for something to wake it up. When that happens, it looks at /etc/hosts.deny and /etc/hosts.allow to see if the person who is trying to connect matches any of the patterns you have listed in these files. If it finds a match, then it either lets the connection go through, or it closes the socket. If it finds a match with a "shell_command" in it, then it will execute that command.

The banners option tells tcpd that it needs to send back a text message to the client that's trying to connect. When it sees banners in the allow or deny file, it goes into the directory that you listed (/etc/banners/general-reject in my example), and tries to find a file with the same name as the service that the client requested. If it finds a file, the contents of the file get pumped back down to the client, and then tcpd either closes the connection or lets it go through. It it doesn't find a file, then tcpd doesn't send anything back.

In plain English, if someone tries to telnet in (which would invoke in.telnetd) and you have a banners options listed for their entry in one of the hosts.* files, then tcpd looks for a file called /etc/banners/general-reject/in.telnetd. If it finds it, it displays the file, if not, ah well.

This is important to remember when setting up a banner for your ftp service. The Banners.Makefile will create a banner file called in.ftpd. Since most Linux distributions use the Washington University FTP server, the service name is actually wu.ftpd. Therefore, if you intend for your banner to also be shown to people trying to ftp to your machine, you either need to change the /etc/banners/general-reject/in.ftpd to wu.ftpd, or you need to change the name of the service.

The 2 Ways to Use tcpd

You generally have 2 choices on how tcpd protects your services: Let inetd handle it, or do a substitution. In my humble opinion, it's best to let inetd handle it.

As you may know, inetd is the "super server". It basically monitors a bunch of ports, and whenever it detects someone trying to use one of them, it starts up the service you have listed in inetd.conf. This is handy because you don't run what you don't need, and thusly, unused daemons aren't sucking up all your system resources.

inetd can be configured to launch tcpd before it starts up the service. In fact, if you take a look in /etc/inetd.conf, you'll see that it already does for many of your services. I'll pull one out so you don't have to flip over to a virutal console:

Service	Socket  Proto   Flags   User     Server name     Arguments
-------	------	-----	-----	----	-----------	---------
telnet  stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/in.telnetd

The "Service" entry is just the name of the connection from the file /etc/services. This tells inetd what port to listen on.

The other entries that we're concerned about is the "Server Name" and "Arguments". "Server Name", as you can see, points to our good friend tcpd. Whenever inetd gets a request for the "Service", it starts up tcpd with the path to the actual service passed as an "Argument". This lets tcpd know what program to run if it exits and the client has permission to use the service.

See. It's pretty easy.

Your other option is to substitute tcpd for the service directly, and not even bother with inetd. To do this, you just move the daemon you want to protect to /usr/sbin/real-daemon-dir, and then either copy tcpd over to where the service used to be, or put in a symbolic link.

For example, let's say I want to use tcpd on /usr/sbin/in.telnetd. I would simply give the following commands:

mv /usr/sbin/in.telnetd /usr/sbin/real-daemon-dir/in.telnetd
ln -s /usr/sbin/tcp /usr/sbin/in.telnetd

This method is even eaiser than inetd, but I prefer not to have 30 million sym links laying around my system.

One Last Thing to Keep in Mind

Quoting directly from tcpd's man page:

       The  tcpd  program  can  be  set  up  to  monitor incoming
       requests for telnet, finger, ftp, exec, rsh, rlogin, tftp,
       talk,  comsat  and  other  services that have a one-to-one
       mapping onto executable files.

Check out that "...services that have a one-to-one mapping onto executable files" part.

What that means is that tcpd is designed to be used by services that spawn 1 daemon for 1 client. In other words, tcpd won't work for stuff like ircd or Samba. Luckily, these programs usually give you the option to deny access to certain hosts, which accomplishes the same thing as what tcpd does.


And In Closing...


For the answer to any questions you have that I didn't address, please check the README file that comes with tcp_wrapper. It does an excellent job of explaining what's going on, and how to take advantage of some other features (although some of it is ambiguous about exact locations of where config files should live due to the fact that the author created tcp_wrappers to work on a lot of different machines). Also peruse the Makefile sometime and see if there's anything else you want to turn on once you've got a good idea of how this all works.

And last but not least, the author of tcp_wrappers has given us a very useful tool free of charge. If you like it and use it, please take the time to send him a postcard (snail mail addy at the bottom of the README)....he's earned it.


Mail to:mars@loeffel.txdirect.net


Copyright © 1997, Kelly Spoon
Published in Issue 15 of the Linux Gazette, March 1997


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Linux Gazette Back Page

Copyright © 1997 Specialized Systems Consultants, Inc.
For information regarding copying and distribution of this material see the Copying License.


Contents:


About This Month's Authors


Paul Anderson

Paul Anderson currently maintains the Tips-HOWTO, and writes episodes for a parody on Star Trek called Star Spek whilst going through highschool. Also fascinated with steam engines and a few months away from purchasing his first lathe, metalworking being one of numerous hobbies of his(get's expensive ya know!). Model rocketry, model airplanes, amateur science, inventing, antique engine collecting and electronics with a dash of old computer collecting are among his hobbies.

Larry Ayers

Larry Ayers lives on a small farm in northern Missouri, where he is currently engaged in building a timber-frame house for his family. He operates a portable band-saw mill, does general woodworking, plays the fiddle and searches for rare prairie plants, as well as growing shiitake mushrooms. He is also struggling with configuring a Usenet news server for his local ISP.

Boris Beletsky

Boris Beletsky is currently working as System Administrator at Institute Computer Science in Jerusalem, Israel. He is one of the Debian GNU/Linux developers.

John M. Fisk

John Fisk is most noteworthy as the former editor of the Linux Gazette. After three years as a General Surgery resident and Research Fellow at the Vanderbilt University Medical Center, John decided to ":hang up the stethoscope":, and pursue a career in Medical Information Management. He's currently a full time student at the Middle Tennessee State University and hopes to complete a graduate degree in Computer Science before entering a Medical Informatics Fellowship. In his dwindling free time he and his wife Faith enjoy hiking and camping in Tennessee's beautiful Great Smoky Mountains. He has been an avid Linux fan, since his first Slackware 2.0.0 installation a year and a half ago.

Michael J. Hammel

Michael J. Hammel, is a transient software engineer with a background in everything from data communications to GUI development to Interactive Cable systems--all based in Unix. His interests outside of computers include 5K/10K races, skiing, Thai food and gardening. He suggests if you have any serious interest in finding out more about him, you visit his home pages at http://www.csn.net/~mjhammel. You'll find out more there than you really wanted to know.

Mike List

Mike List is a father of four teenagers, musician, printer (not laserjet), and recently reformed technophobe, who has been into computers since April,1996, and Linux since July.

Dave Phillips

Dave Phillips is a blues guitarist & singer, a computer musician working especially with Linux sound & MIDI applications, an avid t'ai-chi player, and a pretty decent amateur Latinist. He lives and performs in Findlay OH USA.

Arnold Robbins

Arnold Robbins is a professional programmer and technical author. He has been working with Unix systems for longer than he cares to think about, and with AWK and gawk since 2988. He is the author of Effective Awk Programming, published by SSC.

Kelley Spoon

Kelley Spoon currently studies computer science at the University of Texas, San Antonio. Some of his hobbies include trying to learn how to play the guitar, playing Euchre, laughing at John C. Dvorak, converting pizza into source code, terrorizing villages along the Mexican border, and frightening small children. He has been a Linux user since August 1995, and still pronounces the name as "luh-eye-nucks".

Jay Sprenkle

Jay Sprenkle lives in the Kansas City area and currently works for DRT Systems Consulting. He has been a programming professional for about 20 years, since graduating from the University of Missouri with a degree in Computer Science and a minor in Electrical Engineering. He's written code in assembler up through C++ and various fourth generation languages.


Not Linux


Thanks to all our authors, not just the ones above, but also those who wrote giving us their tips and tricks and making suggestions. Thanks also to our new mirror sites. And, of course, thanks to Michael Montoure for all his help with graphics and HTML checking.

This month has been a very busy one for me. I've been discovering just how much more work there is to managing a print magazine, Linux Journal, as opposed to an electronic one. I'm afraid I've had much less time for LG than before. If you've written and didn't get a response, this is the reason. It also means that I'm too close to time to post LG and too little of it is together -- maybe half as I write this message.

However, I have hired an Administrative Assistant, Amy Kukuk, to help with LJ correspondence and article tracking. She's also going to help me with LG by reading the news groups and writing the News Bytes column. So with her good help, I expect the pace to slow considerably.

While Linux Gazette is free for all our readers, it is not free for its publisher, SSC -- they do pay me for the time I spend putting it together. In order to help pay for these costs, we've decided to make LG the PBS of online ezines by having sponsors from the Linux community. As I am sure most of you noticed, the Front Page now has a Sponsor section. We appreciate very much the financial contribution that InfoMagic, our first sponsor, has made to help us defray our costs.

Sorry to be late, I haven't been able to get to our web server since last Wednesday.

Have fun!


* Marjorie L. Richardson
Editor, Linux Gazette gazette@ssc.com


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Linux Gazette Issue 14, March 1997, http://www.ssc.com/lg/
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