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<refentry id="gdm-1m">

<refmeta><refentrytitle>gdm</refentrytitle><manvolnum>1m</manvolnum>

<refmiscinfo class="date">2 Sep 2004</refmiscinfo>

<refmiscinfo class="sectdesc">&man1;</refmiscinfo>

<refmiscinfo class="software">&release;</refmiscinfo>

<refmiscinfo class="arch">generic</refmiscinfo>

<refmiscinfo class="copyright">&suncopy;</refmiscinfo>

</refmeta>

<indexterm><primary>gdm</primary></indexterm><indexterm><primary>GNOME Display

Manager</primary></indexterm>

<refnamediv id="gdm-1m-name"><refname>gdm</refname><refname>gdm-binary</refname>

<refname>gdmchooser</refname><refname>gdmgreeter</refname><refname>gdmlogin

</refname><refpurpose>GNOME Display Manager</refpurpose></refnamediv>

<refsynopsisdiv id="gdm-1m-synp"><title>&synp-tt;</title>

<cmdsynopsis><command>&cmd; | gdm-binary</command><arg choice="opt"><option>-config=<replaceable>file</replaceable></option></arg><arg choice="opt"><option>-monte-carlo-sqrt2</option></arg><arg choice="opt"><option>-no-console</option></arg><arg choice="opt"><option>nodaemon</option></arg><arg choice="opt"><option>-preserve-ld-vars</option></arg><arg choice="opt"><option>-version</option></arg><arg choice="opt"><option>-wait-for-go</option></arg>

</cmdsynopsis>

<cmdsynopsis><command>gdmlogin | gdmgreeter</command><arg choice="opt"><option role="nodash"><replaceable>gnome-std-options</replaceable></option></arg>

</cmdsynopsis>

<cmdsynopsis><command>gdmchooser</command><arg choice="opt"><option>clientaddress=<replaceable>address</replaceable></option></arg><arg choice="opt"><option>connectionType=<replaceable>type</replaceable></option></arg><arg choice="opt"><option>xdmaddress=<replaceable>socket</replaceable></option></arg><arg choice="opt"><option role="nodash"><replaceable> gnome-std-options</replaceable></option></arg>

</cmdsynopsis></refsynopsisdiv>

<refsect1 id="gdm-1m-desc"><title>&desc-tt;</title>

<para>GDM is the GNOME Display Manager, a program used for login session management.

When no user is logged in on the console, GDM displays a graphical user interface

that enables the user to enter their username and password. GDM supports

XDMCP and supports flexible or on-demand servers via the

<citerefentry><refentrytitle>gdmflexiserver</refentrytitle><manvolnum>1</manvolnum></citerefentry>

command.</para>

<para><command>&cmd;</command> is a wrapper script that launches

<command>gdm-binary</command> and passes along any options. Before launching

<command>gdm-binary</command> the <command>&cmd;</command> wrapper script sources the

<citerefentry><refentrytitle>profile</refentrytitle><manvolnum>4</manvolnum></citerefentry>

file to set the standard system environment variables. To support internationalization,

<command>&cmd;</command> also sets the LC_MESSAGES environment variable to LANG if

neither LC_MESSAGES nor LC_ALL is set.</para>

<para>On startup, the GDM daemon parses its config file

<filename>/usr/share/gdm/defaults.conf</filename> where system defaults are

stored. It also reads <filename>/etc/X11/gdm/custom.conf</filename> and

any user settings defined there override the default settings. Per-display

configuration settings can be set in

<filename>/etc/X11/gdm/custom.conf<replaceable>display</replaceable></filename>

where <replaceable>display</replaceable> is the display number, such as ":0".

Only the "security/PamStack" setting and the settings in the [gui] and

[greeter] sections of the configuration file may be specified in the

per-display configuration file, any others are ignored. When GDM displays

a GUI on the display, these per-display values override the values in the other

configuration files.</para>

<para>

For each local display, <command>gdm-binary</command> forks an Xserver and a slave

process. The main <command>gdm-binary</command> process then listens to XDMCP

requests from remote displays, if so configured, and monitors the local display

sessions. The main daemon process also allows new local Xservers to start on demand

using the

<citerefentry><refentrytitle>gdmflexiserver</refentrytitle><manvolnum>1</manvolnum></citerefentry>

command.</para>

<para>The GDM slave process opens the display and starts either the Themed

Greeter or the Plain Greeter. This choice is set by the "daemon/Greeter" parameter

in the configuration file for console login and the "daemon/RemoteGreeter"

parameter for XDMCP logins. The parameter should be set to "gdmgreeter" to

use the Themed Greeter or "gdmlogin" to use the Plain Greeter. The

Plain Greeter is lower-bandwidth, which tends to be more appropriate for

remote logins. The GDM daemon communicates asynchronously with the slave process

through a pipe.</para>

<para>From either the Themed Greeter or the Plain Greeter, it is possible

to launch the Chooser program <command>gdmchooser</command> to start remote

XDMCP login sessions.</para>

<para>Although disabled by default, it is also possible to launch the Setup

program

<citerefentry><refentrytitle>gdmsetup</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

to edit the configuration choices in the

<filename>/etc/X11/gdm/custom.conf</filename> file. The root password must be

entered to launch the Setup program. The ability to launch the Setup program

is disabled by default as

<citerefentry><refentrytitle>gdmsetup</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

runs with root permissions and changing GDM configuration can affect security.</para>

<para>GDM relies on

<citerefentry><refentrytitle>PAM</refentrytitle><manvolnum>3PAM</manvolnum></citerefentry>

(Pluggable Authentication Modules) for password authentication,

but supports regular crypt() and shadow passwords on legacy systems. On Solaris,

GDM uses

<citerefentry><refentrytitle>logindevperm</refentrytitle><manvolnum>4</manvolnum></citerefentry>

to set proper device permissions for the user on login.</para>

<para>All operations on user files are done with the effective user id of

the user. If the sanity check fails on the user's <filename>.Xauthority</filename>

file, a fallback cookie is created in <filename>/tmp</filename>.</para>

</refsect1>

<refsect1 id="gdm-1m-opts"><title>&opts-tt;</title>

<para>The following options are supported by <command>&cmd;</command> and

<command>gdm-binary</command>:</para>

<variablelist termlength="medium">

<varlistentry><term><option>-config=<replaceable>file</replaceable></option></term>

<listitem><para>Specify alternate default configuration file.</para>

</listitem></varlistentry>

<varlistentry><term><option>-monte-carlo-sqrt2</option></term><listitem></listitem>

</varlistentry>

<varlistentry><term><option>-no-console</option></term><listitem><para>Tell

the daemon that it should not run anything on the console. This means that

none of the local servers from the [servers] section of the GDM configuration

are run, and the console is not used to communicate errors to the user.

An empty [servers] section automatically implies this option.</para>

</listitem></varlistentry>

<varlistentry><term><option>nodaemon</option></term><listitem><para>If this

option is specified, GDM does not fork into the background when run. You can

use a single dash with this option to preserve compatibility with XDM.</para>

</listitem></varlistentry>

<varlistentry><term><option>-preserve-ld-vars</option></term><listitem><para>

When clearing the environment internally, preserve all variables starting

with LD_. This is mostly for debugging purposes.</para>

</listitem></varlistentry>

<varlistentry><term><option>-version</option></term><listitem><para>Print

the version of the GDM daemon.</para>

</listitem></varlistentry>

<varlistentry><term><option>-wait-for-go</option></term><listitem>

<para>

If started with this option, GDM initiates, but only starts the first local display

and then waits for a GO message in the fifo protocol. No greeter is shown

until the GO message is sent. Also, flexiserver requests are denied and XDMCP

is not started until GO is given. This is useful for initialization scripts

that wish to start X early, but where you do not yet want the user to start

logging in: the script sends the GO to the fifo when ready and GDM then continues.

</para>

</listitem></varlistentry>

</variablelist>

<para>The following options are supported by <command>gdmlogin</command> and

<command>gdmgreeter</command>:</para>

<variablelist termlength="medium">

<varlistentry><term><option role="nodash"><replaceable>gnome-std-options</replaceable></option></term>

<listitem><para>Standard options available for use with most GNOME applications.

See <citerefentry><refentrytitle>gnome-std-options</refentrytitle><manvolnum>

5</manvolnum></citerefentry> for more information.</para>

</listitem></varlistentry>

</variablelist><para>The following options are supported by <command>gdmchooser</command>:</para>

<variablelist termlength="medium">

<varlistentry><term><option>clientaddress=<replaceable>address</replaceable></option></term>

<listitem><para>Client address to return in response to xdm. This option is

for running <command>gdmchooser</command> with xdm, and is not used within

GDM.</para>

</listitem></varlistentry>

<varlistentry><term><option>connectionType=<replaceable>type</replaceable></option></term>

<listitem><para>Connection type to return in response to xdm. This option

is for running <command>gdmchooser</command> with xdm, and is not used within

GDM.</para>

</listitem></varlistentry>

<varlistentry><term><option>xdmaddress=<replaceable>socket</replaceable></option></term>

<listitem><para>Socket for XDM communication.</para>

</listitem></varlistentry>

<varlistentry><term><option role="nodash"><replaceable>gnome-std-options</replaceable></option></term>

<listitem><para>Standard options available for use with most GNOME applications.

See <citerefentry><refentrytitle>gnome-std-options</refentrytitle><manvolnum>

5</manvolnum></citerefentry> for more information.</para>

</listitem></varlistentry>

</variablelist></refsect1>

<refsect1 id="gdm-1m-exde"><title>&exde-tt;</title>

<refsect2 id="gdm-1m-exde-standard">

<title>Plain Greeter</title>

<para>The Plain Greeter is the default graphical user interface that is

presented to the user. The greeter contains a menu at the top, an optional

face browser, an optional logo, and a text entry field. The Plain Greeter

corresponds to the executable <command>gdmlogin</command>.</para>

<para>The text entry field is used to enter logins, passwords, passphrases,

and so on. The field is controlled by the underlying daemon and is basically

stateless. The daemon controls the greeter through a simple protocol where

the daemon can ask the greeter for a text string with echo turned on or off.

Similarly, the daemon can change the label above the text entry field to correspond

to the value that the authentication system wants the user to enter.</para>

<para>The menu bar in the top of the greeter enables the user to select the

requested session type or desktop environment, change the GTK+ theme (if enabled),

select an appropriate locale or language, and optionally shutdown, reboot,

or suspend the machine, configure GDM (if the user knows the root password),

or start an XDMCP chooser.</para>

<para>Optionally, the greeter can provide a face browser that contains icons

for all of the users on a system. The icons can be installed globally by the

system administrator, or in the user home directories. If installed globally,

the icons should be in the <filename><replaceable>share</replaceable>/faces

</filename> directory (though this can be configured with the GlobalFaceDir

configuration option) and the filename should be the name of the user, optionally

with &ldquo;.png&rdquo; appended.</para>

<para>Users can place their icons in a file called <filename>~/.face</filename>,

and can use

<citerefentry><refentrytitle>gdmphotosetup</refentrytitle><manvolnum>1</manvolnum></citerefentry>

to graphically configure this.

Face icons placed in the global face directory must be readable to the GDM

user. However, the daemon proxies user pictures to the greeter. Therefore,

those do not have to be readable by the GDM user, but must be readable by

the root user.</para>

<para>Note that loading and scaling face icons located in user home directories

can be a very time-consuming task, especially on large systems or systems

running NIS. The browser feature is only intended for systems with relatively

few users. Also, if home directories are on an on-demand mounted file system

such as AFS, GDM might mount all of the home directories just to check for

pictures if the face browser is on. However, GDM will try to give up after

5 seconds of activity, and only display the users whose pictures have been

received so far.</para>

<para>To filter out unwanted user names in the browser, the "greeter/Exclude" parameter

in the GDM configuration can be set with a list of usernames separated

by commas. The greeter automatically ignores the usernames listed, and excludes

users whose UIDs are lower than the "greeter/MinimalUID" parameter, which is 100 by

default.</para>

<para>When the browser is turned on, valid usernames on the machine are exposed

to a potential intruder. This might be a bad idea if you do not know who has

access to a login screen. This is especially true if you run XDMCP. Note that

you should never run XDMCP on an open network. </para>

<para>The greeter can optionally display a logo in the login window. The image

must be in a format readable to the <filename>gdk-pixbuf</filename> library

(GIF, JPG, PNG, TIFF, XPM), and must be readable by the GDM user.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-graphical">

<title>Themed Greeter</title>

<para>The Themed Greeter is a greeter interface that is displayed on the

whole screen and is themable. The Themed Greeter corresponds to the executable

<command>gdmgreeter</command>

.</para>

<para>Themes can be selected and new themes can be installed by running

<citerefentry><refentrytitle>gdmsetup</refentrytitle><manvolnum>1m</manvolnum></citerefentry>,

or by setting the "greeter/GraphicalTheme" parameter in the GDM configuration.

The location of themes is specified by the "greeter/GraphicalThemeDir" parameter.</para>

<para>The look and feel of this greeter is controlled by the theme, so the

user interface elements that are present might differ. The only item that

must always be present is the text entry field, as described in the Plain

Greeter section above. You can display a menu of available actions by pressing

the F10 key. This can be useful if the theme does not provide certain buttons

when you wish to perform a particular action. </para>

</refsect2>

<refsect2 id="gdm-1m-exde-chooser">

<title>Chooser</title>

<para>The Chooser displays a list of local machines that accept XDMCP connections.

The user can also specify a machine by entering its name directly. Once a

machine is selected, a remote XDMCP session can be started. The Chooser can

be launched on the console directly from the Plain or Themed Greeter.

The chooser corresponds to the executable <command>gdmchooser</command>.

</para>

</refsect2>

<refsect2 id="gdm-1m-exde-xdmcp">

<title>XDMCP</title>

<para>GDM can be configured to enable XDMCP so that users can log in remotely

and launch a graphical chooser that allows a remote login session to be started.

See the [xdmcp] section of the default GDM configuration file.</para>

<para>GDM grants access to the hosts specified in the GDM service section

of your TCP Wrappers configuration file. GDM does not support remote display

access control on systems without TCP Wrappers.</para>

<para>GDM includes several measures that make GDM more resistant to denial-of-service

attacks on the XDMCP service. Several protocol parameters, handshaking timeouts,

and so on can be fine-tuned. The default values should work for most systems,

however. Do not change these values unless you know what you are doing.</para>

<para>By default, GDM listens to UDP port 177, although this can be configured.

GDM responds to QUERY and BROADCAST_QUERY requests by sending a WILLING packet

to the originator.</para>

<para>GDM can also be configured to honor INDIRECT queries and present a host

chooser to the remote display. GDM remembers the user's choice and forwards

subsequent requests to the chosen manager. GDM also supports an extension

to the protocol which makes GDM forget the redirection once the user's connection

succeeds. This extension is only supported if both daemons are GDM. This extension

is transparent and is ignored by XDM or other daemons that implement XDMCP.

</para>

<para>GDM only supports the MIT-MAGIC-COOKIE-1 authentication system. Because

of this, the cookies are transmitted as clear text. Therefore, you should

be careful about the network where you use this. That is, be careful about

where your XDMCP connection is going. Note that if snooping is possible, an

attacker could snoop your password as you log in, so a better XDMCP authentication

would not help you much anyway. If snooping is possible and undesirable, you

should use <filename>ssh</filename> for tunneling an X connection, rather

then using GDM's XDMCP. Think of XDMCP as a sort of graphical telnet, with

the same security issues.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-control">

<title>Controlling GDM</title>

<para>You can control GDM behavior during runtime in several different ways.

You can run certain commands, or you can talk to GDM using either a UNIX socket

protocol, or a FIFO protocol.</para>

<para>You can control GDM behavior as follows:</para>

<itemizedlist>

<listitem><para>To stop GDM, you can either send the TERM signal to the main

daemon, or run the

<citerefentry><refentrytitle>gdm-stop</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

command.</para></listitem>

<listitem><para>To restart GDM, you can either send the HUP signal to the

main daemon, or run the

<citerefentry><refentrytitle>gdm-restart</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

command.</para></listitem>

<listitem><para>To restart GDM but only after all users have logged out, you

can either send the USR1 signal to the main daemon, or run the

<citerefentry><refentrytitle>gdm-safe-restart</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

command.</para></listitem>

</itemizedlist>

<para>The

<citerefentry><refentrytitle>gdm-stop</refentrytitle><manvolnum>1m</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdm-restart</refentrytitle><manvolnum>1m</manvolnum></citerefentry>, and

<citerefentry><refentrytitle>gdm-safe-restart</refentrytitle><manvolnum>1m</manvolnum></citerefentry>

commands are in the <filename>/sbin</filename> directory.</para>

<para>The

<citerefentry><refentrytitle>gdmflexiserver</refentrytitle><manvolnum>1</manvolnum></citerefentry>

command can be used to communicate with the GDM daemon and to start new flexible

(on demand) servers.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-config">

<title>Configuration</title>

<para>The GDM configuration files contain comments that explain each

configuration parameter.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-security">

<title>Security</title>

<para>GDM is best used with a dedicated user id and group id that GDM uses

for graphical interfaces such as <command>gdmgreeter</command>, <command>

gdmlogin</command>, and <command>gdmchooser</command>. You can specify the

name of this user and group in the [daemon] section of the GDM configuration

file.</para>

<para>The GDM user and group, which are normally just "gdm", should not be a

user or group of any particular privilege. The reason for using the GDM user

and group is to have the user interface run as a user without privileges,

so that in the unlikely case that someone finds a weakness in the GUI, they

cannot access root on the machine.</para>

<para>Note that the GDM user and group have some privileges that make them

somewhat dangerous. This user and group has access to the server authorization directory

(specified by the "daemon/ServAuthDir" parameter in the GDM configuration

file) which contains all of the X server authorization files and other private information.

This means that someone who gains the GDM user/group privileges can then connect

to any session. Do not, under any circumstances, make the GDM user/group a

user/group that might be easy to get access to, such as the user <literal>

"nobody"</literal>.</para>

<para>The server authorization directory (daemon/ServAuthDir) is used for a host

of random internal data, in addition to the X server authorization files,

and the naming is really a relic of history. The GDM daemon forces this directory

to be owned by root:gdm with permissions of 1770. This means that only the

root user and the GDM group have write access to this directory, but the GDM

group cannot remove the root-owned files from this directory, such as the

X server authorization files.</para>

<para>By default, GDM does not trust the server authorization directory and

treats it in the same way as a temporary directory with respect to creating

files. This means that someone breaking the GDM user cannot mount attacks

by creating links in this directory. Similarly, the X server log directory

is treated safely, but that directory should really be owned and writable

only by the root user.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-accessibility">

<title>Accessibility</title>

<para>GDM supports "Accessible Login" to allow users to log in to their desktop

session even if they cannot easily use the screen, mouse, or keyboard in the

usual way. This feature enables the user to launch assistive technologies

at login time by means of special "gestures" from the standard keyboard and

from a keyboard, pointing device, or switch device attached to the USB or

PS/2 mouse port. This also enables the user to change the visual appearance

of the login UI before logging in, for example to use a higher-contrast color

scheme for better visibility. GDM only supports accessibility with the Plain

Greeter, so the "daemon/Greeter" parameter in the GDM configuration must

be set to the Plain Greeter "gdmlogin".</para>

<para>To enable Accessible Login, the system administrator must modify the

default login configuration by manually modifying the standard GDM configuration

files, and the <filename>AccessKeyMouseEvents</filename>, and

<filename>AccessDwellMouseEvents</filename> module configuration files.

</para>

<para>To allow users to change the color and contrast scheme of the login

dialog, set the "gui/AllowGtkThemeChange" parameter in the GDM configuration

to "true".</para>

<para>To restrict user changes of the visual appearance to a subset of available

themes, the "gui/GtkThemesToAllow" parameter in the GDM configuration

can be set to a list of acceptable themes separated by commas. For example: <screen><userinput>

GtkThemesToAllow=blueprint,HighContrast,HighContrastInverse</userinput></screen></para>

<para>To enable the use of assistive technologies such as the On-screen Keyboard,

Screen Reader, or Magnifier, the "daemon/AddGtkModules" parameter in the

GDM configuration must be uncommented and set to "true". Also, the "daemon/GtkModulesList"

parameter must be uncommented and set to "gail:atk-bridge:/usr/lib/gtk-2.0/modules/libdwellmouselistener:/usr/lib/gtk-2.0/modules/libkeymouselistener".

</para>

<para>System administrators might wish to load only the minimum subset of

these modules that is required to support their user base. Depending on the

end-user needs, it might not be necessary to load all of the GtkModules:</para>

<itemizedlist>

<listitem><para>If a user needs the integrated Screen Reader and Magnifier,

you must include "gail" and "atk-bridge".</para></listitem>

<listitem><para>If a user needs a pointing device without buttons or switches,

include "dwellmouselistener".</para></listitem>

<listitem><para>If a user needs a pointing device with switches, alternative

physical keyboard, or switch/button device, include "keymouselistener".</para>

</listitem>

</itemizedlist>

<para>Including all four modules is suitable for most system configurations.

The Onscreen Keyboard can operate without gail and atk-bridge, but with a

reduced feature set. For optimum accessibility, we recommend including gail

and atk-bridge.</para>

<para>When "keymouselistener" or "dwellmouselistener" have been added to the

GtkModules loaded by GDM, you can assign user actions to the launching of

specific assistive technologies. These gesture associations are contained

in the files AccessKeyMouseEvents and AccessDwellMouseEvents, respectively.

The gesture format is described in the two files.</para>

<para>The AccessKeyMouseEvents file controls the keymouselistener Gesture

Listener and is used to define key-press, mouse button, or XInput device sequences

that can be used to launch programs needed for accessibility. To reduce the

likelihood of unintentional launch, these 'gestures' may be associated with

multiple switch presses and/or minimum durations.</para>

<para>The DwellKeyMouseEvents file controls the dwellmouselistener and supports

gestures that involve only motion of a pointing device such as the system

mouse. Motion of an alternative pointing device such as a head pointer or

trackball can also be defined. All gestures are specified by the same syntax,

there is no distinction between a 'core mouse' gesture and motion from an

alternate input device.</para>

<para>Motion gestures are defined as "crossing events" into and out of the

login dialog window. If the 'dwellmouselistener' GtkModule is loaded, alternative

pointing devices are temporarily "latched" to the core pointer, such that

motion from alternative devices results in movement of the onscreen pointer.

</para>

<para>To use text-to-speech services at login time (for instance, when using

the Screen Reader in speech mode) on some operating systems, the gdm user

must be a member of the "audio" group.</para>

</refsect2>

<refsect2 id="gdm-1m-exde-logging">

<title>Logging</title>

<para>GDM uses syslog to log errors or status. GDM can also log debugging

information, if enabled in the GDM configuration.</para>

<para>Output from the various X servers is stored in the GDM log directory,

which is configurable but is usually <filename><replaceable>var</replaceable>/log/gdm

</filename>. The output from the session can be found in a file called <filename><replaceable>

display</replaceable>.log</filename>. Four older versions of this file are

also stored, by appending 1 through 4 to the filename. These files are rotated,

as new sessions on that display are started. You can use these logs to view

what the X server said when it started up.</para>

<para>The output from the user session is redirected to <filename>~/.xsession-errors

</filename> before even the PreSession script is started, so it is not necessary

to redirect this again in the session setup script. If the user session lasted

less then 10 seconds, GDM assumes that the session crashed and allows the

user to view this file in a dialog before returning to the login screen. This

enables the user to view the session errors from the last session and correct

the problem.</para>

<para>You can suppress the 10&ndash;second warning by returning code 66 from

the Xsessionscript or from your session binary (the default Xsession script

propagates those codes back). This is useful if you have special logins for

which it is not an error to return less than 10 seconds later, or if you already

set up the session to display an error message and the GDM message would be

confusing and redundant.</para>

<para>The session output is piped through the GDM daemon, so the <filename>

~/.xsession-errors</filename> file is capped by GDM at about 200 kilobytes,

to prevent a possible denial-of-service attack on the session. An application

could, on reading some wrong data, print out warnings or errors on stderr

or stdout. This could fill up the user's home directory, the user would then

have to log out and log back in to clear this. This could be especially nasty

if quotas are set. GDM also correctly traps the XFSZ signal and stops writing

the file, which would lead to killed sessions if the file was redirected in

the old-fashioned way from the script.</para>

<para>Note that some distributors seem to override the <filename>~/.xsession-errors

</filename> redirection and redirect in their own Xsession script (set by

the BaseXsession configuration key), which means that GDM cannot trap the

output and cap this file. You also lose output from the PreSession script

which can make debugging more difficult, as perhaps useful output of what

is wrong is not printed out. See the description of the BaseXsession configuration

key for more information, especially on how to handle multiple display managers

using the same script.</para>

<para>Note that if the session is a failsafe session, or if GDM cannot open

this file for some reason, a fallback file is created named <filename>/tmp/xses-<replaceable>

user</replaceable>.XXXXXX</filename>, where XXXXXX are random characters.

</para>

<para>If you run a system with quotas set, use the PostSession script to delete

the <filename>~/.xsession-errors</filename> file, so that this log file is

not stored unnecessarily.</para>

</refsect2>

</refsect1>

<refsect1 id="gdm-1m-exit"><title>&exit-tt;</title>

<para>The following exit values are returned:</para>

<variablelist termlength="xtranarrow">

<varlistentry><term><returnvalue>0</returnvalue></term><listitem><para>Application

exited successfully</para>

</listitem></varlistentry>

<varlistentry><term><returnvalue>>0</returnvalue></term><listitem><para>Application

exited with failure</para>

</listitem></varlistentry>

</variablelist></refsect1>

<refsect1 id="gdm-1m-file"><title>&file-tt;</title>

<para>The following files are used by this application:</para>

<variablelist termlength="medium">

<varlistentry><term><filename>/usr/sbin/&cmd;</filename></term><listitem><para>

Wrapper script that launches GNOME Display Manager</para>

</listitem></varlistentry>

<varlistentry><term><filename>/usr/sbin/gdm-binary</filename></term><listitem>

<para>Executable for GNOME Display Manager</para>

</listitem></varlistentry>

<varlistentry><term><filename>/usr/lib/gdmchooser</filename></term><listitem>

<para>Executable for GDM Chooser</para>

</listitem></varlistentry>

<varlistentry><term><filename>/usr/lib/gdmgreeter</filename></term><listitem>

<para>Executable for GDM Themed Greeter</para>

</listitem></varlistentry>

<varlistentry><term><filename>/usr/lib/gdmlogin</filename></term><listitem>

<para>Executable for GDM Plain Greeter</para>

</listitem></varlistentry>

</variablelist><para>The system administrator can specify, in the GDM

configuration file, the maximum file size that GDM should accept. If

the face browser is enabled, a tunable maximum icon size is also enforced.

On large systems, the face browser should be turned off for performance reasons.

Looking up icons in home directories, scaling, and rendering face icons can

take quite a long time.</para>

<para>In general, GDM is very reluctant to read or write user files. For instance,

GDM refuses to touch anything but regular files. Links, sockets, and devices

are ignored. The value of the "security/RelaxPermissions" parameter in the

GDM configuration determines whether GDM accepts files that are writable

by the user's group or others. These are ignored by default.</para>

<para>Note that normally it is assumed that the home directory is only readable

by the user. However, NFS traffic can be snooped. For setups with NFS directories,

set the "daemon/UserAuthDir" parameter in the GDM configuration

to a local directory such as <filename>/tmp</filename>. GDM tries to open

the normal authorization file for reading as root. If this fails, GDM concludes

that it is on an NFS mount and automatically uses "daemon/UserAuthFBDir" (usually <filename>

/tmp</filename>), as defined in the GDM configuration. This

can be changed by setting the "security/NeverPlaceCookiesOnNFS" parameter

to &ldquo;false&rdquo;.

</para>

<refsect2 id="gdm-1m-file-login">

<title>GDM Login Scripts and Session Files</title>

<para>The following GDM login scripts are discussed below:</para>

<itemizedlist>

<listitem><para><filename>/etc/X11/gdm/Init/<replaceable>hostname</replaceable></filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/Init/XDMCP</filename></para></listitem>

<listitem><para><filename>/etc/X11/gdm/Init/Default</filename></para></listitem>

<listitem><para><filename>/etc/X11/gdm/PostLogin/<replaceable>hostname</replaceable></filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PostLogin/XDMCP</filename></para></listitem>

<listitem><para><filename>/etc/X11/gdm/PostLogin/Default</filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PreSession/<replaceable>hostname</replaceable></filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PreSession/XDMCP</filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PreSession/Default</filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/Xsession</filename></para></listitem>

<listitem><para><filename>/etc/X11/gdm/PostSession/<replaceable>hostname</replaceable></filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PostSession/XDMCP</filename></para>

</listitem>

<listitem><para><filename>/etc/X11/gdm/PostSession/Default</filename></para>

</listitem>

</itemizedlist>

<para>The following session files are discussed below:</para>

<itemizedlist>

<listitem><para><filename>/usr/share/xsessions/*.desktop</filename></para>

</listitem>

<listitem><para><filename>~/.dmrc</filename> (default user session)</para>

</listitem>

</itemizedlist>

<para>When the X server has been successfully started, GDM tries to run the

Init/<replaceable>displayname</replaceable> script. For example, <filename>

Init/:0</filename> for the first local display. If this file is not found,

GDM attempts to run Init/<replaceable>hostname</replaceable>. For example, <filename>

Init/somehost</filename>. If this file is also not found, GDM tries <filename>

Init/XDMCP</filename> for all XDMCP logins or <filename>Init/Flexi</filename>

for all on-demand flexible servers. If none of the above are found, GDM runs <filename>

Init/Default</filename>. The script runs with root privileges and GDM blocks

until the script terminates. Use the <filename>Init/*</filename> script for

programs that are supposed to run alongside the GDM login window, for example <filename>

xconsole</filename>. Commands to set the background and so on should go in

this file too.</para>

<para>The system administrator decides whether clients started by the <filename>

Init</filename> script should be killed before starting the user session.

This is controlled by the "daemon/KillInitClients" parameter in the GDM

configuration.</para>

<para>When the user has been successfully authenticated, GDM tries the scripts

in the <filename>PostLogin</filename> directory in the same manner as for

the <filename>Init</filename> directory. This is done before any session setup

is done, so this is the script where you might set up the home directory if

you need to (though you should use the pam_mount module for this, if you can).

You have the USER and DISPLAY environment variables set for this script, and

again it is run with root privileges. The script should return 0 on success

as otherwise the user is not logged in. This is not true for failsafe session

however.</para>

<para>After the user session has been set up from the GDM perspective, GDM

runs the scripts in the <filename>PreSession</filename> directory, again in

the same manner as the <filename>Init</filename> directory. Use this script

for local session management or accounting. The USER environment variable

contains the login of the authenticated user and DISPLAY is set to the current

display. The script should return 0 on success. Any other value causes GDM

to terminate the current login process. This is not true for failsafe sessions

however. Also, the X_SERVERS environment variable is set and this points to

a fake generated X servers file for use with the

<citerefentry><refentrytitle>sessreg</refentrytitle><manvolnum>1</manvolnum></citerefentry>

accounting program.</para>

<para>After this, the user's session is started. The available session executables

are taken from the Exec= line in the <filename>.desktop</filename> files in

the path specified by SessionDesktopDir. The user chooses from these sessions

at login time and GDM reads the file <filename>~/.dmrc</filename> for the

user's default. The default GNOME session uses the Xsession script. The script

is run as the user, and this is the user session. This script should load

the user's profile and generally do all that is needed to launch a session.

As many systems reset the language selections done by GDM, GDM also sets the

GDM_LANG variable to the selected language. You can use this to reset the

language environment variables after you run the user's profile. If the user

elected to use the system language, then GDM_LANG is not set.</para>

<para>When the user terminates the session, the <filename>PostSession</filename>

scripts are run, similar to <filename>Init</filename>, <filename>PostLogin

</filename>, and <filename>PreSession</filename>. Again, the script is run

with root privileges, the slave daemon blocks, the USER environment variable

contains the name of the user who just logged out, and DISPLAY is set to the

display the user used. Note, however, that the X server for this display might

already be dead so you should not try to access it. Also, the X_SERVERS environment

variable is set and points to a fake generated X servers file for use with the

<citerefentry><refentrytitle>sessreg</refentrytitle><manvolnum>1</manvolnum></citerefentry>

accounting program.</para>

<para>Note that the <filename>PostSession</filename> script runs even when

the display fails to respond due to an I/O error or similar. Thus, there is

no guarantee that X applications will work during script execution.</para>

<para>Except for the <filename>Xsession</filename> script, all of these scripts

also have the environment variable RUNNING_UNDER_GDM set to yes, so that you

can use similar scripts for different display managers. The <filename>Xsession

</filename> always has GDMSESSION set to the basename of the session that

the user chose to run, without the <filename>.desktop</filename> extension.

In addition, DESKTOP_SESSION is also set to the same value.</para>

<para>None of the <filename>Init</filename>, <filename>PostLogin</filename>, <filename>

PreSession</filename>, or <filename>PostSession</filename> scripts are necessary

and they can be omitted. However, the <filename>Xsession</filename> script

is required, as is at least one session <filename>.desktop</filename> file.

</para>

</refsect2>

<refsect2 id="gdm-1m-file-config">

<title>Configuration Files</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/usr/share/gdm/defaults.conf</filename></term><listitem>

<para>Contains GDM default configuration and documentation.</para>

</listitem></varlistentry>

<varlistentry><term><filename>/etc/X11/gdm/custom.conf</filename></term><listitem>

<para>Contains user-specific GDM configuration and documentation.</para>

</listitem></varlistentry>

<varlistentry><term><filename>/etc/X11/gdm/custom.conf<replaceable>display</replaceable></filename></term><listitem>

<para>Contains per-display GDM configuration and documentation.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-themes">

<title>Themes</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/usr/share/gdm/themes</filename></term><listitem>

<para>Can be configured using the "greeter/GraphicalThemeDir" configuration parameter</filename>.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-face">

<title>Face Browser</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/usr/share/pixmaps/faces</filename></term><listitem><para>Global

directory for face images.</para>

</listitem></varlistentry>

<varlistentry><term><filename>~/.face</filename></term><listitem><para>User-defined

icon to be used by GDM face browser.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-gesture">

<title>Gesture Listener Configuration Files</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/etc/X11/gdm/modules/AccessDwellMouseEvents

</filename></term><listitem><para>Configuration for the dwellmouselistener.

</para>

</listitem></varlistentry>

<varlistentry><term><filename>/etc/X11/gdm/modules/AccessKeyMouseEvents</filename></term>

<listitem><para>Configuration for the keymouselistener.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-system-files">

<title>System files</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/etc/profile</filename></term><listitem><para>System environment</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-logging">

<title>Logging</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/var/log/gdm/<replaceable>display</replaceable>.log

</filename></term><listitem><para>Output from Xserver for each session. This

can be configured using the "daemon/LogDir" parameter in the GDM configuration.

</para>

</listitem></varlistentry>

<varlistentry><term><filename>~/.xsession-errors</filename></term><listitem>

<para>Output from user's session.</para>

</listitem></varlistentry>

<varlistentry><term><filename>/tmp/xsess-<replaceable>user</replaceable>.XXXXXX

</filename></term><listitem><para>Output from session in failsafe mode or

if <filename>~/.xsession-errors</filename> cannot be written.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-sockets">

<title>Sockets</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/tmp/.gdm_socket</filename></term><listitem>

<para>Temporary file used for GDM socket communications.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-pid">

<title>Process Id</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/var/run/gdm.pid</filename></term><listitem>

<para>Stores the ProcessID for the running GDM daemon. This can be configured

using the "daemon/PidFile" parameter in the GDM configuration.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="gdm-1m-file-xserver">

<title>Xserver Authentication Directory</title>

<variablelist termlength="wholeline">

<varlistentry><term><filename>/var/lib/gdm</filename></term><listitem><para>

Stores Xserver authentication files. This can be configured using the

"daemon/ServAuthDir" parameter in the GDM configuration.</para>

</listitem></varlistentry>

</variablelist></refsect2>

</refsect1>

<refsect1 id="gdm-1m-attr"><title>&attr-tt;</title>

<para>See <olink targetdocent="REFMAN5" localinfo="attributes-5"><citerefentry>

<refentrytitle>attributes</refentrytitle><manvolnum>5</manvolnum></citerefentry></olink>

for descriptions of the following attributes:</para>

<informaltable frame="all">

<tgroup cols="2" colsep="1" rowsep="1"><colspec colname="COLSPEC0" colwidth="1*">

<colspec colname="COLSPEC1" colwidth="1*">

<thead>

<row><entry align="center" valign="middle">ATTRIBUTE TYPE</entry><entry align="center"

valign="middle">ATTRIBUTE VALUE</entry></row>

</thead>

<tbody>

<row><entry><para>Availability</para></entry><entry><para>SUNWgnome-display-mgr

</para></entry></row>

<row><entry colname="COLSPEC0"><para>Interface stability</para></entry><entry

colname="COLSPEC1"><para>Volatile</para></entry></row>

<row><entry colname="COLSPEC0"><para>/usr/share/gdm/defaults.conf</para></entry><entry

colname="COLSPEC1"><para>Committed</para></entry></row>

<row><entry colname="COLSPEC0"><para>/etc/X11/gdm/custom.conf</para></entry><entry

colname="COLSPEC1"><para>Committed</para></entry></row>

</tbody>

</tgroup>

</informaltable>

</refsect1>

<refsect1 id="gdm-1m-also"><title>&also-tt;</title>

<para>Latest version of the <citetitle>GNOME Desktop User Guide</citetitle>

for your platform.</para>

<para>

<citerefentry><refentrytitle>gdmXnestchooser</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdmdynamic</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdmflexiserver</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdmphotosetup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdmthemetester</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>Xserver</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdm-restart</refentrytitle><manvolnum>1m</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gdmsetup</refentrytitle><manvolnum>1m</manvolnum></citerefentry>,

<citerefentry><refentrytitle>profile</refentrytitle><manvolnum>4</manvolnum></citerefentry>,

<citerefentry><refentrytitle>gnome-std-options</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pam</refentrytitle><manvolnum>3pam</manvolnum></citerefentry>,

<citerefentry><refentrytitle>logindevperm</refentrytitle><manvolnum>4</manvolnum></citerefentry>,

<citerefentry><refentrytitle>attributes</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

<refsect1 id="gdm-1-note"><title>&note-tt;</title>

<para>Original man page written by Martin K. Petersen &lt;mkp@mkp.net>, George

Lebl &lt;jirka@5z.com>. Copyright (c) 1998, 1999 by Martin K. Petersen. Copyright

(c) 2001, 2003, 2004 by George Lebl. Copyright (c) 2003 by Red Hat, Inc.</para>

<para>Updated by Brian Cameron, Sun Microsystems Inc., 2004, 2006.</para>

</refsect1>

</refentry>