Setting up your Linux workstation to display a graphical login screen is easy—all you have to do is make the appropriate selection during the installation. Even if you have not initially elected to have a graphical login screen, you can easily set it up once you know the details. The following sections explain how your Red Hat Linux system displays the graphical login screen.
A process named init starts the initial set of processes on your Red Hat Linux system. What
init starts depends on the current run level, the contents of the
/etc/inittab file, and the shell scripts located in the
/etc/rc.d directory and its subdirectories. For now, you don’t need to understand the details; you must know, however, that the graphical login screen starts at run level 5.
| Cross Ref |
Chapter 20 describes in detail the init process, the /etc/inittab file, and the Red Hat Linux boot process. |
The last line of the
/etc/inittab file is responsible for starting the graphical login process with the following entry (the number 5 denotes run level 5):
x:5:respawn:/etc/X11/prefdm -nodaemon
This command runs
/etc/X11/prefdm , a shell script that contains the following lines:
#!/bin/sh PATH=/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin # Shut down any graphical boot that might exist. if [ -x /usr/bin/rhgb-client ]; then /usr/bin/rhgb-client -quit fi # We need to source this so that the login screens are translated. [ -f /etc/profile.d/lang.sh ] && . /etc/profile.d/lang.sh # Run preferred X display manager # Try autologin first, if wanted... if [ -f /etc/sysconfig/autologin -a -x /usr/sbin/autologin ]; then if /usr/sbin/autologin; then exit 0 fi # If autologin fails (bad permissions, etc.), we get here - # time to start a real display manager. fi preferred= if [ -f /etc/sysconfig/desktop ]; then . /etc/sysconfig/desktop if [ "$DISPLAYMANAGER" = GNOME ]; then preferred=gdm elif [ "$DISPLAYMANAGER" = KDE ]; then preferred=kdm elif [ "$DISPLAYMANAGER" = XDM ]; then preferred=xdm fi fi if [ -z "$preferred" ]; then if which gdm >/dev/null 2>&1; then preferred=gdm elif which kdm >/dev/null 2>&1; then preferred=kdm elif which xdm >/dev/null 2>&1; then preferred=xdm fi fi if [ -n "$preferred" ] && which $preferred >/dev/null 2>&1; then exec `which $preferred` $* >/dev/null 2>&1 fi if which gdm >/dev/null 2>&1; then exec `which gdm` $* >/dev/null 2>&1 elif which kdm >/dev/null 2>&1; then exec `which kdm` $* >/dev/null 2>&1 elif which xdm >/dev/null 2>&1; then exec `which xdm` $* >/dev/null 2>&1 fi # Catch all exit error exit 1
This script starts a specific display manager—gdm, kdm, or xdm—depending on the setting of the
DISPLAYMANAGER variable in the
/etc/sysconfig/desktop file. The display manager is a program responsible for displaying the graphical login window, authenticating users who log in, running initialization scripts at the start of a session, and cleaning up after the session. The display manager process manages the display, making it available to the users and cleaning up after the user finishes a session. Note that of the three display managers—gdm, kdm, or xdm—xdm is the most generic.
If the
DISPLAYMANAGER variable is not defined, the
/etc/X11/prefdm script checks for
gdm ,
kdm , and
xdm —in that order—and runs whichever display manager it finds first. The end result is that you get
gdm if you installed GNOME and
kdm if you installed KDE as your sole desktop. If you install both GNOME and KDE, you get
gdm by default because the
prefdm script looks for
gdm first. If you do have both GNOME and KDE installed on your system and you want the
kdm as the display manager, define the
DISPLAYMANAGER variable in
/etc/sysconfig/desktop like this:
DISPLAYMANAGER="KDE"
Then, the next time you reboot the system, the kdm display manager will run.
To summarize, regardless of your choice of GUI, at run level 5 init starts a display manager. The display manager, in turn, displays the graphical login dialog box, which enables you to log in to the system.
If you have not enabled the graphical login screen during Red Hat installation, you can do so by editing the
/etc/inittab file. Locate the line containing
initdefault , and make sure that it reads as follows:
id:5:initdefault:
| Caution |
Before you edit the /etc/inittab file, you should know that any errors in this file may prevent Linux from starting up to a point at which you can log in. If you cannot log in, you cannot use your system. |
After editing the default run level in
/etc/inittab , you can either reboot the system or type the following command to switch to run level 5:
telinit 5
The gdm program is a display manager similar to xdm, the X display manager. Like xdm, gdm starts an X server for each local display, displays a login dialog box, and enables the user to log in to the system. Figure 9-1 shows a typical graphical login screen displayed by gdm.
Figure 9-1: Graphical Login Screen Managed by gdm.
When gdm runs, it reads various configuration parameters from the configuration file
/etc/X11/gdm/gdm.conf , which has a structure similar to a Windows
INI file. For example, here is a typical
gdm.conf file:
[daemon] AlwaysRestartServer=false AutomaticLogin= AutomaticLoginEnable=false Chooser=/usr/bin/gdmchooser Configurator=/usr/sbin/gdmsetup --disable-sound --disable-crash-dialog DefaultPath=/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin DisplayInitDir=/etc/X11/gdm/Init FailsafeXServer= FirstVT=7 FlexibleXServers=5 GnomeDefaultSession=/usr/share/gnome/default.session Greeter=/usr/bin/gdmgreeter Group=gdm HaltCommand=/usr/bin/poweroff;/sbin/poweroff;/sbin/shutdown -h now;/usr/sbin/shutdown -h now KillInitClients=true LocalNoPasswordUsers= LogDir=/var/log/gdm PidFile=/var/run/gdm.pid PostSessionScriptDir=/etc/X11/gdm/PostSession/ PreSessionScriptDir=/etc/X11/gdm/PreSession/ RebootCommand=/sbin/shutdown -r now;/usr/sbin/shutdown -r now RemoteGreeter=/usr/bin/gdmlogin RootPath=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin ServAuthDir=/var/gdm SessionDir=/etc/X11/gdm/Sessions/ StandardXServer=/usr/X11R6/bin/X SuspendCommand= TimedLogin= TimedLoginDelay=30 TimedLoginEnable=false User=gdm UserAuthDir= UserAuthFBDir=/tmp UserAuthFile=.Xauthority VTAllocation=true XKeepsCrashing=/etc/X11/gdm/XKeepsCrashing Xnest=/usr/X11R6/bin/Xnest -name Xnest [security] AllowRemoteAutoLogin=false AllowRemoteRoot=true AllowRoot=true RelaxPermissions=0 RetryDelay=1 SessionMaxFile=524388 UserMaxFile=65536 [xdmcp] DisplaysPerHost=1 Enable=false HonorIndirect=true MaxPending=4 MaxPendingIndirect=4 MaxSessions=16 MaxWait=15 MaxWaitIndirect=15 Port=177 Willing=/etc/X11/gdm/Xwilling [gui] GtkRC=/usr/share/themes/Bluecurve/gtk-2.0/gtkrc MaxIconHeight=128 MaxIconWidth=128 [greeter] BackgroundColor=#27408b BackgroundImage= BackgroundProgram= BackgroundRemoteOnlyColor=true BackgroundScaleToFit=true BackgroundType=0 Browser=false ConfigAvailable=false DefaultFace=/usr/share/pixmaps/nobody.png Exclude= bin,daemon,adm,lp,sync,shutdown,halt,mail,news,uucp,operator,nobody,gdm,postgres,pvm,rpm GlobalFaceDir=/usr/share/faces/ GraphicalTheme=Bluecurve GraphicalThemeDir=/usr/share/gdm/themes/ Icon=/usr/share/pixmaps/gdm.png LocaleFile=/etc/X11/gdm/locale.alias LockPosition=true Logo= MinimalUID=500 PositionX=0 PositionY=0 Quiver=true RunBackgroundProgramAlways=false SetPosition=false ShowGnomeChooserSession=false ShowGnomeFailsafeSession=false ShowXtermFailsafeSession=false SystemMenu=true TitleBar=false Use24Clock=false UseCirclesInEntry=false Welcome=Welcome to %n XineramaScreen=0 [chooser] Broadcast=true DefaultHostImg=/usr/share/pixmaps/nohost.png HostImageDir=/usr/share/hosts/ Hosts= ScanTime=3 [debug] Enable=false [servers] 0=Standard [server-Standard] command=/usr/X11R6/bin/X flexible=true name=Standard server
The
[servers] section of the file specifies the displays on which gdm displays the login dialog box. Each line of this section starts with a display number and shows the command needed to start the X server.
You see the term
greeter used often in the display manager configuration file. Greeter refers to the login screen—the user interface through which the display manager prompts the user to log in to the system.
The different sections in the configuration file control different aspects of the graphical login screen as well as the tasks the user can perform from that screen. Table 9-1 describes the gdm configuration options, organized by sections.
| Insider Insight |
Edit the Welcome= line to change the welcome message on the graphical login screen. The default message says welcome to the hostname, which can be somewhat cryptic. You can edit that line and change the message to something more meaningful with the syntax |
|
Configuration Option |
Description |
|---|---|
|
[daemon] section | |
|
AlwaysRestartServer=true or false |
If set to true, gdm always kills the existing X server and starts a new one. |
|
AutomaticLoginEnable=true or false |
If set to true, automatically log in the user specified in the AutomaticLogin option without asking for any password. |
|
AutomaticLogin=username |
If a user name is specified and AutomaticLogin Enable is true, that user is logged without asking for a password. |
|
Chooser=chooserprogram |
Full path and name of the gdmchooser executable file (typically, this should be /usr/bin/gdmchooser ) |
|
Configurator=chooserprogram |
Full path and name of the gdmconfig executable file (typically, this should be /usr/bin/gdmconfig ) |
|
DefaultPath=pathname |
Path (names of directories separated by colons) to be used for the user’s session |
|
DisplayInitDir=pathname |
Directory containing the initialization scripts (the default is /etc/X11/gdm/Init ) |
|
FailsafeXServer = safex-script |
Full path name of script that gdm should run to provide a failsafe GUI login screen |
|
FirstVT =number |
The virtual terminal (VT) number where X should be run (default is 7) |
|
FlexibleXServers =count |
Maximum number of X servers to run |
|
GnomeDefaultSession= sessionfile |
Full path name of file that gdm should read if there are no user GNOME session files (the default is /usr/share/gnome/default.session ) |
|
Greeter=greeterprogram |
Full path and name of the greeter executable file, followed by arguments (typically, this should be /usr/ bin/gdmlogin ) |
|
Group=groupname |
Group name under which gdmlogin and gdmchooser are run (the default is gdm ) |
|
HaltCommand=haltprogram |
Full path and arguments to the commands to be executed when the user selects Halt from the System menu (typically, this should be /sbin/shutdown -h now ) |
|
KillInitClients=true or false |
When set to true, gdm kills the X clients started by the Init scripts after the user logs in (the default is true). |
|
LocalNoPasswordUsers = userlist |
Comma-separated list of users that are allowed to log in without password |
|
LogDir=pathname |
Directory containing the log files for the displays (the default is /var/log/gdm ) |
|
PidFile=pidfile |
Name of the file where the process ID (pid) of the gdm process is stored (the default is /var/run/gdm.pid ) |
|
PostSessionScriptDir=pathname |
Directory that contains the PostSession scripts—scripts run after the user logs out (the default is /etc/X11/gdm/ PostSession/ ) |
|
PreSessionScriptDir=pathname |
Directory that contains the PreSession scripts—scripts run right after the user logs in (the default is /etc/X11/ gdm/PreSession/ ) |
|
RebootCommand=rebootprogram |
Full path and arguments to the command to be executed when the user selects Reboot from the System menu (typically, this should be /sbin/shutdown -r now ) |
|
RemoteGreeter =pathname |
Full path name of the greeter executable file for remote displays |
|
RootPath=pathname |
Path (names of directories separated by colons) to be used for the root user’s session |
|
ServAuthDir=pathname |
Directory (the default is /var/gdm ) containing the X authentication files for the displays (this directory should be owned by user gdm , group gdm , with permission 750) |
|
SessionDir=pathname |
Directory containing scripts for all session types available on the system (the default is /etc/X11/gdm/Sessions ) |
|
StandardXServer =pathname |
Path name of standard X server (the default is /usr/X11R6/bin/X ) |
|
TimedLogin=username |
If a user name is specified and TimedLoginEnable is true, then that user is logged without asking for any password after the login screen is inactive for the number of seconds specified in the TimedLoginDelay option |
|
TimedLoginDelay=N |
The number of seconds delay before the user specified in TimedLogin is automatically logged in |
|
TimedLoginEnable=true or false |
If set to true, automatically logs in the user specified in the TimedLogin option without asking for any password |
|
User=username |
User name under which gdmchooser and gdmlogin are run (the default is gdm ) |
|
UserAuthDir=pathname |
Directory where the user’s .Xauthority file should be saved (if this field is empty, the user’s home directory is used, which is the default) |
|
UserAuthFBDir=pathname |
Directory where a fallback cookie (which simply refers to the small amount of authentication information) is created if gdm fails to update the user’s .Xauthority file (the default is /tmp ) |
|
UserAuthFile=filename |
Name of the file for storing the user’s authentication cookies (the default is .Xauthority ) |
|
VTAllocation =true or false |
If true, automatically allocate virtual terminal (VT) for use by X server (default is true ) |
|
XKeepsCrashing=sessionfile |
Full path name of a script that gdm should run if X keeps crashing (the default script is /etc/X11/gdm/ XKeepsCrashing ) |
|
Xnest = pathname |
Full path name of the nested X server ( Xnest ) that runs as an X client, but also manages graphics on behalf of the X server (default is /usr/X11R6/bin/Xnest -name Xnest ) |
|
[security] section | |
|
AllowRemoteAutoLogin =true or false |
When set to true, allows remote timed login (the default is false ) |
|
AllowRemoteRoot=true or false |
When set to true, the root user can log in remotely (the default is true ) |
|
AllowRoot=true or false |
When set to true, the root user can log in at the console (the default is true ) |
|
RelaxPermissions=0, 1, or 2 |
0 = gdm only accepts files and directories owned by the user; 1 = gdm allows group writeable files and directories; 2 = gdm allows world writeable files and directories (the default is 1 ) |
|
RetryDelay=N |
Number of seconds to wait before gdm displays the login window again after a failed login (the default is 3 seconds) |
|
UserMaxFile=N |
Maximum size (in bytes) of files that gdm will read or write (the default is 64KB, or 65,536 bytes) |
|
[xdmcp] section | |
|
DisplaysPerHost =number |
Number of displays per host (the default is 1 ) |
|
Enable=true or false |
When set to true, gdm listens on port 177 and supports the X Display Manager Control Protocol (XDMCP) that enables users to log in to other hosts on the network (the default is false ) |
|
HonorIndirect=true or false |
When set to true, gdm allows remote execution of the gdmchooser client on X terminals (the default is true ) |
|
MaxPending=N |
Maximum number of pending connections (the default is 4 ) that gdm should allow (this helps avoid any denial of service attacks) |
|
MaxPendingIndirect=N |
Maximum number of gdmchooser clients that gdm will run simultaneously on remote displays (the default is 4 ) |
|
MaxSessions=N |
Maximum number of remote display connections that gdm will accept (the default is 16 ) |
|
MaxWait=N |
Maximum number of seconds that gdm waits for a response from a display before assuming that the display is not active anymore (the default is 15 seconds) |
|
MaxWaitIndirect=N |
Maximum number of seconds that gdm waits for a remote display to complete protocol negotiations after the display requests a chooser (the default is 15 seconds) |
|
Port=177 |
The UDP port number where gdm listens for XDMCP requests (the default is 177 ) |
|
Willing =pathname |
Full path name of script to run to generate replies to XDMCP BroadcastQuery requests (the default is /etc/X11/gdm/Xwilling ) |
|
[gui] section | |
|
GtkRC=pathname |
Path name of file that contains the theme to be used by the gdmlogin and gdmchooser programs (the default is the BlueCurve theme, defined in the file /usr/ share/themes/Bluecurve/gtk-2.0/gtkrc ) |
|
MaxIconWidth=N |
Maximum width (the default is 128 pixels) of icons that the face browser will display (gdmlogin can display a face browser containing icons for all the users on a system; these icons can be installed globally by the system administrator or in the users’ home directories) |
|
MaxIconHeight=N |
Maximum height (the default is 128 pixels) of icons that the face browser will display |
|
[greeter] section | |
|
BackgroundColor =#colornum |
Background color |
|
BackgroundImage =pathname |
Pathname of image to use as background (when BackgroundType =1) |
|
BackgroundProgram =pathname |
Pathname of program to run to draw the background |
|
BackgroundRemoteOnlyColor = true or false |
When set to true , displays a solid color background for remote displays (the default is true ) |
|
BackgroundScaleToFit = true or false |
When set to true , scales image to fit screen (the default is true ) |
|
BackgroundType =0, 1, or 2 |
Type of background for the greeter, 0 = None, 1 = Image, 2 = Color (the default is 0) |
|
Browser=true or false |
When set to true , displays a browser, called the face browser, where the faces of all system users are displayed (the default is false ) |
|
ConfigAvailable =true or false |
When set to true , configuration option is available from the System menu (default is false ) |
|
DefaultFace=imagefile |
A file, readable by the gdm user, containing an image that is to be displayed if a user does not have a personal picture in the ~/gnome/photo directory (which refers to the gnome/photo subdirectory of the user’s home directory). The default is the /usr/share/pixmaps/ nobody.png file. |
|
Exclude=usernames |
Comma-separated list of user names to be excluded from the face browser; the excluded users will still be able to log in |
|
GlobalFaceDir=pathname |
Directory where face files (each containing an icon showing a user’s face) are located (the default is /usr/share/faces/ ) |
|
GraphicalTheme =themename |
Name of graphical theme to use (default is BlueCurve ) |
|
GraphicalThemeDir =pathname |
Directory where graphical theme files are located (the default is /usr/share/gdm/themes/ ) |
|
Icon=imagefile |
A file, readable by the gdm user, containing the image to be displayed when the login window is in iconified state (the default is /usr/share/pixmaps/gdm.xpm ) |
|
LocaleFile=localefile |
Full pathname for the file in GNU locale format, with entries for all languages supported on the system (the default is /etc/X11/gdm/locale.alias ) |
|
LockPosition =true or false |
When set to true , the user cannot move the greeter window (the default is true ) |
|
Logo=imagefile |
A file, readable by the gdm user, with the image to be displayed in the logo area (the default is /usr/share/ pixmaps/gnome-logo-large.png ). |
|
MinimalUID =number |
Users with this user ID or higher can log in (the default is 500) |
|
PositionX =xpos |
Horizontal and vertical position of greeter window PositionY=ypos |
|
Quiver=true or false |
When set to true , the gdmlogin program shakes the display (not physically, but by moving the graphics output) when a user enters an incorrect password (the default is false) |
|
RunBackgroundProgramAlways = true or false |
When set to true , runs the background program specified by BackgroundProgram (the default is false ) |
|
SetPosition =true or false |
When set to true , the gdmlogin program shakes the display (not physically, but by moving the graphics output) when a user enters an incorrect password (the default is false ) |
|
ShowGnomeChooserSession = true or false |
When set to true , shows previous GNOME sessions in the chooser (the default is false ) |
|
ShowGnomeFailsafeSession = true or false |
When set to true , shows the GNOME failsafe session in the chooser (the default is false ) |
|
ShowXtermFailsafeSession = true or false |
When set to true , show the failsafe session that runs an xterm window (the default is false ) |
|
SystemMenu =true or false |
When set to true , show the System menu on the greeter (the default is true ) |
|
TitleBar =true or false |
When set to true, show a title bar on the greeter window (the default is false ) |
|
Use24Clock =true or false |
When set to true , use a 24-hour clock no matter what the locale (the default is false ) |
|
UseCirclesInEntry =true or false |
When set to true , echo the typed password as circles (the default is false ) |
|
Welcome=message |
The English welcome message that the gdmlogin program displays next to the logo on the login screen (the default message is Welcome to %n , where %n means the node name—the hostname without the domain) |
|
XineramaScreen =number |
The Xinerama screen where greeter is displayed (default is 0 ) |
|
[chooser] section | |
|
Broadcast =true or false |
When set to true , an XDMCP query is broadcast to get the names of all the hosts that accept login (the default is true ) |
|
DefaultHostImg=filename |
File containing an image to be displayed for those hosts that do not have a unique icon file (the default is /usr/ share/pixmaps/nohost.png ) |
|
HostImageDir=pathname |
Directory (the default is /usr/share/hosts/ ) that contains host icon files; each filename matches the host system’s fully qualified domain name (such as yourhost.yourdomain.com ). |
|
Hosts=hostnames |
Comma-separated names of hosts to list |
|
ScanTime=N |
Number of seconds the chooser should wait for replies to its XDMCP broadcast query (the default is 3 seconds) |
|
[debug] section | |
|
Enable=true or false |
When set to true, gdm saves information that can help isolate any bugs in gdm (the default is false ) |
|
[servers] section | |
|
N=ServerName |
Name of the X server to start on local display number N (if your system has a single monitor, N is 0). Default is Standard |
|
[server-Standard] section | |
|
command=ServerPathName |
Full pathname of the Standard X server (the default is /usr/X11R6/bin/X ) |
|
flexible=true or false |
When set to true , the Standard server is considered a flexible server (the default is true ) |
|
name=servername |
A descriptive name of the Standard server (default is Standard server) |
For the default configuration (after you install Red Hat Linux and X from the companion CD-ROMs), gdm manages the login session as follows:
The gdm program starts the X server and looks for a script named after the local display’s name (for the first display, the filename is
:0 ) in the
/etc/X11/gdm/ Init directory. If it does not find that file, gdm executes the file named
Default from that directory. The
/etc/X11/gdm/Init/Default script in Red Hat Linux contains the following commands:
#!/bin/sh # Xsetup for Red Hat Linux # Copyright (c) 1999, 2000, 2001 Red Hat, Inc. sysresources=/etc/X11/Xresources # merge in defaults if [ -f "$sysresources" ]; then xrdb -merge "$sysresources" fi /usr/X11R6/bin/xsetroot -solid "#5477A0" if [ -z "$RUNNING_UNDER_GDM" ] ; then /sbin/pidof -s kdm &> /dev/null && [ $? -eq 0 -a -x /usr/bin/kdmdesktop ] && /usr/bin/kdmdesktop && sleep 1s # Only set the background if the xsri program is installed. if [ -x /usr/bin/xsri -a -f /etc/X11/xsrirc ]; then /usr/bin/xsri --redhat-login --set fi fi
In this case, the script sets the background to a solid color and displays the Red Hat logo. The gdm program runs this script as
root and waits until the commands finish.
The gdm program runs the
/usr/bin/gdmlogin program, which displays a dialog box that contains fields in which the user can enter a name and a password.
After a user enters a name and password and presses Enter, gdm verifies the password and tries to execute the startup script
/etc/X11/gdm/PreSession/ DisplayName , where
DisplayName is
:0 for the first display. If that file is not found,
gdm executes the
/etc/X11/gdm/PreSession/Default script, if it exists.
The gdm program runs the session script from the
/etc/X11/gdm/Sessions directory. The exact script that gdm runs depends on the session the user selects in the Sessions menu in the login dialog box
gdmlogin is displayed. If the user has not explicitly selected a specific type of session (GNOME or KDE), gdm runs the
/etc/X11/gdm/Default script, which, in turn, executes the
/etc/ X11/xdm/Xsession script. This script looks for another script file, named
.xsession , in the user’s home directory and executes that script, if it exists. Next, it looks for the
.Xclients script file in the user’s home directory and executes that file, if it exists. Otherwise,
Xsession executes the
/etc/X11/ xinit/Xclients script. When you follow through these scripts, you find that the
Xclients script executes the
/usr/bin/gnome-session program if the
/etc/sysconfig/desktop file contains the line
DESKTOP="GNOME" . The gnome-session program then starts the GNOME session (which includes a set of applications and a window manager). Initially, gnome-session uses the session file
/usr/share/gnome/default.session (a text file) to start the applications and the window manager. Later, the GNOME session is restored to the values saved in a file in the
~/.metacity/sessions directory (this refers to a subdirectory in the user’s home directory). The default session file runs a script named
/usr/bin/gnome-wm , which, in turn, starts an appropriate window manager. The default window manager is
metacity , but you can specify a different window manager by defining the
WINDOW_MANAGER environment value to the name of a window manager you want.
From this point on, the user can interact with the system through the X display and through the window manager (started by the gnome-session program).
When the user ends the GNOME session (by selecting Log out from the Main Menu button), gdm attempts to run the script
/etc/X11/gdm/PostSession/ DisplayName , where
DisplayName is
:0 for the first display. If that file does not exist, gdm executes the
/etc/X11/gdm/PostSession/Default script, if it exists.
Although this brief description of gdm does not show you all the details, gdm provides a user-friendly interface for user login and for starting a GNOME session. Moreover, like many other X programs, gdm is highly configurable. For example, the names of the script files in the preceding list are the typical ones, but you can specify other names through the file named
gdm.conf , which, by default, also resides in the
GNOME and KDE are both capable GUI environments. Red Hat Linux comes with both of these GUIs, but you get GNOME as the default GUI. However, Red Hat also includes the utility script
/usr/bin/switchdesk , which enables you easily to switch from one GUI to another, and vice versa. To switch from GNOME to KDE, follow these steps:
From your GNOME desktop, select Main Menu>System Settings>More System Settings>Desktop Switching Tool, or type switchdesk in a terminal window. The Desktop Switcher dialog box appears.
In the Desktop Switcher dialog box, click the KDE radio button to select it (see Figure 9-2), then click the OK button.
Figure 9-2: Switching to KDE by Using the Desktop Switching Tool.
A message informs you that the desktop configuration has been changed, but you must restart X for the change to take effect. Click the OK button to dismiss the dialog box.
Although the message in Step 3 states that you must restart X, all you need to do is log out of the session and log back in. To log out, select Main Menu>Log Out. When you log in again, you should get the KDE GUI.
The
switchdesk utility changes the GUI by creating the appropriate scripts in your home directory. It leaves the display manager unchanged. This means that you use the GNOME display manager, gdm, for login, even when you switch to the KDE GUI. After you log in, gdm executes a session script that eventually executes the
.Xclients script in your home directory, if that script exists.
When you run the switchdesk utility, you execute a shell script in the
/usr/bin/ switchdesk file that contains the following lines:
#!/bin/sh echo "Red Hat Linux `basename $0` 3.9" echo "Copyright (C) 1999-2001 Red Hat, Inc" echo "Redistributable under the terms of the GNU General Public License" kicker=`/sbin/pidof "kdeinit: kicker"` [ -z "$kicker" ] && kicker=`/sbin/pidof kicker` [ -z "$kicker" ] && kicker=`/sbin/pidof kpanel` [ -z "$kicker" ] && kicker=`/sbin/pidof kpanel1` good=1 if [ "$DISPLAY" != " -a "$1" = " ]; then if [ -n "$kicker" -a -x /usr/bin/switchdesk-kde ]; then exec switchdesk-kde elif [ -x /usr/bin/switchdesk-gnome ]; then exec switchdesk-gnome elif [ -x /usr/bin/switchdesk-kde ]; then exec switchdesk-kde else echo "Desktop Switcher GUI unavailable." echo "Please install the switchdesk-kde or switchdesk-gnome packages or use" echo "switchdesk desktopname." good=0; fi else good=0; fi if [ "$good" = "0" ]; then exec switchdesk-helper $1 fi
If you are using GNOME, the
switchdesk script runs the switchdesk-gnome application that displays the GUI from which you change the desktop. In KDE, this script runs the switchdesk-kde GUI tool. The switchdesk-gnome GUI tool creates two scripts—
.Xclients and
.Xclients-default —in the home directory of the user. The
.Xclients script contains the following lines:
#!/bin/bash # Created by Red Hat Desktop Switcher if [ -e "$HOME/.Xclients-$HOSTNAME$DISPLAY" ]; then exec $HOME/.Xclients-$HOSTNAME$DISPLAY else exec $HOME/.Xclients-default fi
The
.Xclients-default script is simpler; it contains the following commands:
# Created by Red Hat Desktop Switcher exec startkde
The result of these changes is that when you log in the next time, gdm executes the
.Xclients script in your home directory, which, in turn, executes the startkde program (
/usr/bin/startkde ) to start a KDE session.
Because the switchdesk utility changes the GUI by creating the
.Xclients and
.Xclients-default scripts in a user’s home directory, these changes only affect that particular user.
To switch from KDE to GNOME, log in as
root , open a terminal window, and type switchdesk at the shell prompt, then select GNOME as the desktop. After you log out of KDE and log back in, you should get GNOME as your desktop.
Note that if you want to use GNOME for one session only (as opposed to making it your default GUI), simply click Session at the bottom of the login screen, and then select Gnome from the login window menu in the initial login screen, as shown in Figure 9-3.
Figure 9-3: Switching to GNOME for the Current Session Only.
You should get the GNOME desktop for this session. The next time you log in, the system reverts to KDE.
If you install only the KDE desktop or set the
DISPLAYMANAGER variable in the
/etc/ sysconfig/desktop file to
KDE , the kdm program starts the X server for the local display and displays the graphical login window through which you log in to the system. Figure 9-4 shows the graphical login screen that you see when you run the kdm display manager.
When kdm runs, it reads various configuration parameters from the configuration file
/usr/share/config/kdm/kdmrc , which has a structure similar to a Windows
INI file. For example, here is a typical
kdmrc file:
# KDM configuration example. [General] Xservers=/usr/share/config/kdm/Xservers PidFile=/var/run/kdm.pid [Xdmcp] Enable=false Xaccess=/usr/share/config/kdm/Xaccess Willing=/usr/share/config/kdm/Xwilling [Shutdown] HaltCmd=/sbin/poweroff [X-*-Core] # Core config for all displays Setup=/usr/share/config/kdm/Xsetup Startup=/usr/share/config/kdm/Xstartup Reset=/usr/share/config/kdm/Xreset Session=/usr/share/config/kdm/Xsession AutoReLogin=false AllowRootLogin=true AllowNullPasswd=true AllowShutdown=Root [X-*-Greeter] # Greeter config for all displays SessionTypes=default,kde,failsafe,gnome GUIStyle=Bluecurve LogoArea=Clock GreetFont=Sans,12,-1,5,75,0,0,0,0,0 StdFont=Sans,10,-1,5,50,0,0,0,0,0 FailFont=Sans,10,-1,5,75,0,0,0,0,0 AntiAliasing=true ShowUsers=None MinShowUID=500 SortUsers=true PreselectUser=None FocusPasswd=false EchoMode=OneStar [X-:*-Core] # Core configurations for local displays # place local display core configurations here [X-:*-Greeter] # Greeter configurations for local displays # place local display greeter configurations here
Figure 9-4: Graphical Login Screen Managed by kdm.
As you can see, the file is organized into sections, with each section identified by labels within square brackets. Each section specifies a related set of options that affects some aspect of the GUI login process.
You can configure the look and feel of the kdm greeter—the login dialog box—on each X display individually. The configuration of each display is specified by a section name that has the following format:
[X-host:number_class-subsection]
where
host refers to the hostname of the system to which the display is attached (can be empty for a local display),
number is the display number (
0 , if you have only one display),
class is a display class (it’s optional and ignored in most cases), and
subsection identifies the element of the display manager to which the options apply. For example, if the options apply to the desktop, subsection is
Desktop . If the options are for the greeter, the subsection is
Greeter . You can use an asterisk (
* ) for any of these elements—host, number, and class—as a wildcard.
Thus, to specify the options for the greeter for all displays, place the options in a section named
[X-*-Greeter] . To change some of these greeter options for the local displays, place the changed options in the
[X-:*-Greeter] section. On the other hand, if you want to customize some aspect of the greeter for the first local display (which is display number
0 ), place those options in the section labeled
[X-:0-Greeter] .
Table 9-2 summarizes some common
kdm configuration options, organized by sections. I show the X display options for all displays. To customize these for a specific display, you can add a section with a name that reflects the X display to which the options apply.
|
Configuration Option |
Description |
|---|---|
|
[General] section | |
|
LockPidFile=true or false |
If set to true, kdm locks the PidFile to prevent multiple instances of kdm from running simultaneously |
|
PidFile=/var/run/kdm.pid |
File where kdm should store its process ID (ID) |
|
Xservers= /usr/share/config/kdm/Xservers |
File containing list of X servers to start (one per display)
|
|
[Xdmcp] section | |
|
ChoiceTimeout=seconds |
Number of seconds to wait for display to respond after the user has selected a host from the chooser (default is 15 seconds) |
|
Enable=true or false |
If set to true , kdm listens on port 177 and supports the X Display Manager Control Protocol (XDMCP) that enables users to log in to other hosts on the network (the default is true ) |
|
Port=177 |
The UDP port number where kdm listens for XDMCP requests (default is 177 ) |
|
RemoveDomainname=true or false |
If set to true, strips domain name from remote display names if it is equal to the local domain (default is true ) |
|
SourceAddress=true or false |
Use the numeric IP address of the incoming connection instead of the hostname (useful on multihomed hosts, the default is false ) |
|
Willing= /usr/share/config/kdm/Xwilling |
Program to run to generate replies to XDMCP BroadcastQuery requests (the Xwilling program is a shell script that displays the number of users and current load average) |
|
[Shutdown] section | |
|
HaltCmd=/sbin/poweroff |
Full pathname of command to run to halt the system |
|
RebootCmd=/sbin/reboot |
Full pathname of command to run to reboot the system (default is / sbin/reboot ) |
|
[X-*-Core] section (core configuration for all displays) | |
|
AllowNullPasswd=true or false |
If set to true , kdm allows users with empty passwords to log in (default is true ) |
|
AllowRootLogin=true or false |
If set to true, kdm allows logins by root (default is true ) |
|
AllowSdForceNow=Root or All |
Specifies who can abort all currently running programs when shutting down system; choices are All for anyone or Root for root user (default is All ) |
|
AllowShutdown=Root or All |
Specifies who can shut down the system; possible values are All to enable anyone to shut down the system, None to prevent shutdown from the login screen, and Root to require root password for shutdown (default is All ) |
|
AutoReLogin=true or false |
If set to true, kdm will automatically restart a session after the X server crashes or if it is killed by pressing Ctrl-Alt-Backspace (default is false ) |
|
DefaultSdMode=ForceNow or ForceNow TryNow or Schedule |
The default mode for shutdown; choices are to shut down immediately, Schedule to shut down after the session exits, or TryNow to shutdown if no session is open and do nothing otherwise (default is Schedule ) |
|
OpenDelay=seconds |
Number of seconds to wait before retrying to open the display after any error (default is 15 seconds) |
|
OpenRepeat=seconds |
How many seconds to wait before trying to open display again (default is 5 seconds) |
|
OpenTimeout=seconds |
Number of seconds to wait before timing out on the attempt to open the display (default is 120 seconds) |
|
PingInterval=seconds |
How many minutes between successive pinging of remote displays (ping checks if network connection is up and running; default interval is 5 minutes) |
|
Reset= /usr/share/config/ |
Program to run after a user session ends kdm/Xreset |
|
ResetSignal=1 |
The signal to send to reset the local X server (default is 1 , which stands for SIGHUP) |
|
Session= /usr/share/config/kdm/Xsession |
Program that accepts the SessionTypes argument and starts an appropriate session |
|
SessSaveFile=.wmrc |
Filename (in user’s home directory) where the last session type is stored (default is .wmrc ) |
|
Setup= usr/share/config/ |
Program to run before showing the greeter window kdm/Xsetup |
|
StartAttempts=number |
The maximum number of times to try opening a display before the display is disabled (default is 4 ) |
|
StartInterval=seconds |
How many seconds to wait before resetting the StartAttempts counter (default is 30 seconds) |
|
Startup= usr/share/config/ |
Program to run before starting a user session kdm/Xstartup |
|
TerminateServer=true or false |
If set to true, restart the local X server instead of resetting after session ends (default is false) |
|
TermSignal=signum |
The signal to send to terminate the local X server (default is 15, which stands for SIGTERM) |
|
[X-*-Greeter] section (greeter configuration for all displays) | |
|
AntiAliasing=true or false |
If set to true, fonts shown in the greeter should be antialiased (default is false ) |
|
DefaultUser=username |
User preselected for login if PreselectUser = Default |
|
EchoMode=OneStar or ThreeStar or NoEcho |
What to show as user types the password; choices are NoEcho to show nothing at all, OneStar to show a * for each letter typed, or ThreeStars to show *** for each letter typed (default is OneStar ) |
|
FailFont= Sans,10,-1,5,75, |
Font used for the “Login Failed” message 0,0,0,0,0 |
|
FocusPasswd=true or false |
If set to true, the password input line is automatically selected to receive the keyboard input (default is false ) |
|
GreeterPosFixed=true or false |
If set to true , the position of the greeter window is fixed and specified by GreeterPosX and GreeterPosY (default is false ) |
|
GreeterPosX=pixels |
Horizontal position, in pixels, of greeter window |
|
GreeterPosY=pixels |
Vertical position, in pixels, of greeter window |
|
GreetFont=Sans,12,-1,5,75, |
The font to use for the welcome text 0,0,0,0,0 |
|
GreetString= welcometext |
Welcome text in greeter window (default is "Welcome to %s at %n" ); use following special characters strings: %d = current display %h = hostname, possibly with domain name %n = node name, most probably the hostname without domain name %s = operating system ( Linux ) %r = operating system’s version %m = machine (hardware) type %% = a single % |
|
GUIStyle=Bluecurve |
The look and feel of the greeter (other choices are Default , Windows , Motif , CDE , and any other styles installed on the system) |
|
HiddenUsers=user1,user2,... |
List of user names not to be listed in the greeter when ShowUsers is NotHidden |
|
Language=en_US |
Language to use in the greeter (default is en_US ) |
|
LogoArea=Clock |
What to show in the area to the right of the text input line (other options are Logo to display an image specified by LogoPixmap , Clock to display an analog clock, and None to display nothing) |
|
LogoPixmap= /usr/share/apps/ |
The image to show when LogoArea is set to Logo kdm/pics/kdelogo.png |
|
MinShowUID=500 |
Users with UID less than the specified number are not shown |
|
NumLock=Off |
What to do with the Num Lock key during the time when the greeter is running; choices are On to turn it on, Off to turn it off, and Keep to leave it at its previous state |
|
PreselectUser=None or Previous or Default |
User name to be preselected for login; choices are Previous to preselect the previous user, Default to select user listed in DefaultUser field, or None to not preselect at all (default is None ) |
|
SelectedUsers=user1,user2,... |
List of users to show when ShowUsers = Selected |
|
SessionTypes= default,kde, failsafe,gnome |
Names of session types that the user can select from the GUI login window |
|
ShowUsers=None |
Which user names, along with pictures, to show in the greeter; choices are NotHidden to show all users except those listed in HiddenUsers , Selected to show only those users listed in SelectedUsers , and None to show no users at all (default is NotHidden ) |
|
SortUsers=true or false |
If set to true , sort user names alphabetically (default is true ) |
|
StdFont= Sans,10,-1,5,50, |
Normal font used in the greeter 0,0,0,0,0 |