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

1. Changed XServers File located at /etc/X11/xdm/Xservers by adding these lines to get 4 xdm sessions running so that 4 different people can log in. It seems like all the neat stuff only happened on the last session. It is probably easy to fix this. Perhaps I will mention it in the next article.

   :0 A local /usr/X11R6/bin/X :0
   :1 B local /usr/X11R6/bin/X :1
   :2 C local /usr/X11R6/bin/X :2
   :3 D local /usr/X11R6/bin/X :3
   

1. Resources
2. What is XDM? -- the graphical login interface
3. My configurations
4. Conclusion

Resources

1. Chris Carlson's article in the Linux Gazette.
2. man xdm
3. My old xdm cheat sheet back in 12/1996 when I was just a hacker (in the good sense). I guess this was around right when the Gazette got started? How time flies. I should have posted this there at that time.

What is XDM?

In theory, most of configurations here should work for any Linux distribution. This is configured for RedHat 6.0 though. RedHat 6.0 uses gdm instead of xdm when it starts its graphical login screen. However, I haven't got gdm to work in the exact way I want it, even though it seems much better than xdm. Once I figure out a few things, I will write a brief article on gdm also.

Here are some things to note ,

1. If you want xdm (or gdm) to start when you computer starts, you need to make sure this line
   id:3:initdefault:
   Looks like this
   id:5:initdefault:
   in the file "/etc/inittab". Please, whatever you do, get Xwindows working before you set xdm to start at bootup. If Xwindows doesn't work, xdm won't work, and that can cause problems.
2. RedHat 6.0 switched to gdm instead of using xdm which is apparent at the bottom of the /etc/inittab with the line
   x:5:respawn:/etc/X11/prefdm -nodaemon
   thus, change that line to this,
   x:5:respawn:/usr/bin/X11/xdm -nodaemon
3. All the files I am changing are in "/etc/X11/xdm".

My config files

Here is the goal, I want to change xdm to make it so it has xeyes, santa, a clock, a graphics image, and my choice of background color on the desktop before someone logs in. After they log in, I want santa to die. Cruel huh?

Okay, let us do this in order:

1. Copy my graphics perl script to "/etc/rc.d/rc.change_graphic". This changes the image which appears on the screen. Images are stored in /etc/X11/xdm/graphics as gif files.
2. Copy my kill santa perl script to "/etc/X11/xdm/KillXsnow". This kills santa. Santa slows down the desktop.
3. Copy my Xsetup script to "/etc/X11/xdm/Xsetup_0". Programs to run with the graphical login screen.
4. Copy my Xresources script to "/etc/X11/xdm/Xresources". How the setup of xdm should look like.
5. Copy my GiveConsole script to "/etc/X11/xdm/GiveConsole". Stuff to get executed before Xwindows is handed over to the user. Also, changes the background image for xdm.
6. Add this command to "/etc/rc.d/rc.local". Make sure we get a graphics image to look at when we boot up.
7. Copy my gif files to "/etc/X11/xdm/graphics/" and issue this command on the file
   tar -C / -zxvf xdm.tgz
   These are just my silly images I use.

Here are the rest of my config files:

Change graphics perl script

#!/usr/bin/perl

@Files = </etc/X11/xdm/graphics/*.gif>;

#print @Files;

$Length = @Files;
$Seconds = `date +%S`;
chomp $Second;
$Frac = $Seconds/60;
if (!($Frac > 0)) {$Frac=1}

$Random = $Frac*$Length;
($Random,$Junk) = split(/\./, $Random,2);

if (($Random < 1) || ($Random > $Length -1))  {$Random = 1} 
$File = $Files[$Random]; 

$Rand2 = rand $Length;
($Rand2,$Junk) = split(/\./, $Rand2,2);

$Random = $Random + $Rand2;
if ($Random > $Length - 1) {$Random = $Random - $Length + 1;}

#print "$Length $Random $File\n";

if (-e "/etc/X11/xdm/xdm_front.gif") {system "rm /etc/X11/xdm/xdm_front.gif"}

if (@Files < 1)
  {
  ## Some sort of error messege should be here.  
  } 
else
  {system "ln -s $File /etc/X11/xdm/xdm_front.gif";}

Kill Santa perl script

#!/usr/bin/perl

     ### I had to add the -a option between RH 5.2 and 6.0
@Temp = `cd /proc; grep -a ^/usr/X11R6/bin/xsnow /proc/[0-9]*/cmdline`; 

if (@Temp > 0) 
  {
  $Xsnow = shift @Temp;
  ($Junk,$ProcJunk,$No,$RestOfJunk) = split(?/?,$Xsnow);

     ## I am really paranoid that I want to kill the right pid 
  if (($No > 0) && ($Xsnow =~ ?^/proc/$No/cmdline:/usr/X11R6/bin/xsnow?))   
    {
#    system "echo \"Killing pid $No for Xsnow.\n\" > /tmp/1.txt\n";
    system "kill $No";
    }
  }

Xsetup_0 script

#!/bin/sh
# $XConsortium: Xsetup_0,v 1.3 93/09/28 14:30:31 gildea Exp $
/usr/X11R6/bin/xconsole -geometry 480x130-0-0 -daemon -notify -verbose -fn fixed -exitOnFail
#/usr/X11R6/bin/xbanner

    ### Santa and snowflakes
    ### On some installs, I am missing xsnow for some reason. 
/usr/X11R6/bin/xsnow -snowflakes 50 -santa 2 -unsmooth &

    ### Load the random image 
/usr/bin/X11/xloadimage -onroot -at 1,210 /etc/X11/xdm/xdm_front.gif -border brown  &

    ### A clock would be nice to see
/usr/X11R6/bin/xclock -digital -update 1 -fn -adobe-times-medium-i-normal--34-240-100-100-p-168-iso8859-1 -geometry +410+1 &

    ### Let us turn on xeyes
/usr/X11R6/bin/xeyes -geometry +410+100 &

Xrsources file

! $XConsortium: Xresources /main/8 1996/11/11 09:24:46 swick $
xlogin*login.translations: #override\
        CtrlR: abort-display()\n\
        F1: set-session-argument(failsafe) finish-field()\n\
        CtrlReturn: set-session-argument(failsafe) finish-field()\n\
        Return: set-session-argument() finish-field()
xlogin*borderWidth: 3
xlogin*geometry: 400x200+1+1
xlogin*greeting: CLIENTHOST  
xlogin*namePrompt: login:\040
xlogin*fail: Login incorrect
#ifdef COLOR
xlogin*greetColor: CadetBlue
xlogin*failColor: red
*Foreground: black
*Background: #fffff0
#else
xlogin*Foreground: black
xlogin*Background: white
#endif
XConsole.text.geometry: 480x130
XConsole.verbose:       true
XConsole*iconic:        true
XConsole*font:          fixed

Chooser*geometry:               700x500+100+100
Chooser*allowShellResize:       false
Chooser*viewport.forceBars:     true
Chooser*label.font:             *-new century schoolbook-bold-i-normal-*-240-*
Chooser*label.label:            XDMCP Host Menu  from CLIENTHOST
Chooser*list.font:              -*-*-medium-r-normal-*-*-230-*-*-c-*-iso8859-1
Chooser*Command.font:           *-new century schoolbook-bold-r-normal-*-180-*

GiveConsole file

All you have to do is add "/etc/X11/xdm/KillXsnow & " as the first command in the file. Mine looks like this,

#!/bin/sh
# Assign ownership of the console to the invoking user
# $XConsortium: GiveConsole,v 1.2 93/09/28 14:29:20 gildea Exp $

# By convention, both xconsole and xterm -C check that the
# console is owned by the invoking user and is readable before attaching
# the console output.  This way a random user can invoke xterm -C without
# causing serious grief.

/etc/rc.d/rc.change_graphic &
/etc/X11/xdm/KillXsnow &

chown $USER /dev/console
/usr/X11R6/bin/sessreg  -a -w "/var/log/wtmp" -u "/var/run/utmp" \
-x "/etc/X11/xdm/Xservers" -l $DISPLAY -h "" $USER

/etc/rc.d/rc.local file

/etc/rc.d/rc.change_graphic

Conclusion

I will explain GDM next time. Gdm has the nice capability of letting you choose which desktop environment you want. In RedHat 6.0, you can choose KDE, GNOME, or other desktop environments when you login, which is pretty cool. Overall, I give gdm a B+, and if it becomes better documented, an A. Again, I hope to make an article about gdm for the August issue.