GDM

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• Display Manager
• GNOME

From GDM - GNOME Display Manager:

GDM is the GNOME Display Manager, it is the little program that runs in the background, runs your X sessions, presents you with a login box and then tells you to bug off because you forgot your password. It does pretty much everything that you would want to use xdm for, but does not involve as much crack. It does not use any code from xdm. It supports XDMCP, and in fact extends XDMCP a little bit in places where I thought xdm was lacking (but is still compatible with xdm's XDMCP).

Display managers provide X Window System users with a graphical login prompt.

Installation

GDM (which is also part of gnome) can be installed with the gdm package, available in the Official repositories.

To make GDM the default display manager for the system, use the packaged systemd service file, gdm.service. Simply run the following command once to bring up GDM on boot:

# systemctl enable gdm.service

The arguments passed to the X server by ~/.xinitrc (such as those of xmodmap and xsetroot) can also be added through xprofile:

~/.xprofile

#!/bin/sh

#
# ~/.xprofile
#
# Executed by gdm at login
#

xmodmap -e "pointer =1 2 3 6 7 4 5" # set mouse buttons up correctly
xsetroot -solid black              # sets the background to black

Configuration

There are two tools that can be used to configure recent version of GDM - the official gsettings tool (plus the dconf frontend) and the gdm3setup tool.

gesttings and dconf

Login background image

Once session variables have been exported, you may issue commands to retrieve or set items used by GDM.

The easiest way to changes all the settings is by launching the Configuration Editor gui with the command

$ dconf-editor

The location of each setting is the same as in the command line style of configuration shown below:

The following is the command-line approach to retrieve or set the file name used for GDM's wallpaper.

 $  GSETTINGS_BACKEND=dconf gsettings get org.gnome.desktop.background picture-uri
 $  GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.background picture-uri 'file:///usr/share/backgrounds/gnome/SundownDunes.jpg'
 
 $  GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.background picture-options 'zoom'
 ## Possible values: centered, none, scaled, spanned, stretched, wallpaper, zoom

Note: You must specify a file which user "gdm" has permission to read. GDM cannot read files in your home directory.

Larger font for login

This tweak enlarges the login font with a scaling factor. It is the same method employed by Accessibility Manager on the desktop.

$ GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.interface text-scaling-factor '1.25'

Turning off the sound

This tweak disables the audible feedback heard when the system volume is adjusted (via keyboard) on the login screen.

$ GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.sound event-sounds 'false'

If the above tweak does not work for you or you are unable to export the GDM session variables, try muting the volume in the GDM login screen using your multimedia keys.

Make the power button interactive

The default installation sets the power button to suspend the system. Power off or Show dialog is a better choice.

 $ GSETTINGS_BACKEND=dconf gsettings set org.gnome.settings-daemon.plugins.power button-power 'interactive'
 $ GSETTINGS_BACKEND=dconf gsettings set org.gnome.settings-daemon.plugins.power button-hibernate 'interactive'
 $ gsettings list-recursively org.gnome.settings-daemon.plugins.power

Warning: Please note that the acpid daemon also handles the "power button" an "hibernate button" event. Running both systems at the same time may lead to unexpected behaviour.

GDM keyboard layout

To change keyboard settings used by GDM, set your layout using Xorg configuration. Refer to this section of the Beginner's Guide.

gdm3setup

You can install the gdm3setup^AUR tool from the AUR to configure GDM. It will allow you to change few settings such as the theme, the automatic connexion or the date format.

Change the language

To change the GDM language, edit the file /var/lib/AccountsService/users/gdm and change the language line. You should see something similar to the text below:

/var/lib/AccountsService/users/gdm

[User]
Language=fr_FR.UTF-8
XSession=
SystemAccount=true

Now just reboot your computer.

Once you've rebooted, if you look at the /var/lib/AccountsService/users/gdm file again, you'll see that the language line is cleared - don't worry, the language is still changed for the next reboots.

Old configuration

You can no longer use the gdmsetup command to configure GDM as of version 2.28. The command has been removed and GDM has been standardized and integrated with the rest of GNOME.

You can use the following instructions.

Configure X server access permission:

# xhost +SI:localuser:gdm

Change the theme:

$ sudo -u gdm dbus-launch gnome-control-center

For more configuration options, do:

$ sudo -u gdm dbus-launch gconf-editor

and modify the following hierarchies:

/apps/gdm/simple-greeter
/desktop/gnome/interface
/desktop/gnome/background

If these commands fail with an error (e.g. "Cannot open display") you can bring the two windows up when GDM starts by adding them to GDM's autostart. To do this first create the entry:

# cp -t /usr/share/gdm/autostart/LoginWindow/ /usr/share/applications/gnome-appearance-properties.desktop /usr/share/applications/gconf-editor.desktop

Then go back to GDM, do your changes and log back in. When you're done and want the window to stop opening with GDM run this:

# rm /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow/gconf-editor.desktop

Note: By using the logout/configure method you can view the changes while you're making them.

For more information and advanced settings read this.

Automatic login

To enable automatic login with GDM, add the following to /etc/gdm/custom.conf (replace username with your own):

/etc/gdm/custom.conf

# Enable automatic login for user
[daemon]
AutomaticLogin=username
AutomaticLoginEnable=True

or for an automatic login with a delay:

/etc/gdm/custom.conf

[daemon]
# for login with delay
TimedLoginEnable=true
TimedLogin=username
TimedLoginDelay=1

Passwordless login

If you want to bypass the password prompt in GDM then simply add the following line on the first line of /etc/pam.d/gdm-password:

auth sufficient pam_succeed_if.so user ingroup nopasswdlogin

Then, add the group nopasswdlogin to your system. See Groups for group descriptions and group management commands.

Now, add your user to the nopasswdlogin group and you will only have to click on your username to login.

Warning: Do not do this for a root account.

Warning: You won't be able to change your session type at login with GDM anymore. If you want to change your default session type, you will first need to remove your user from the nopasswdlogin group.

Passwordless shutdown

GDM is using polkit and logind to gain permissions for shutdown. You can allow it without entering a password first by setting:

/etc/polkit-1/localauthority.conf.d/org.freedesktop.logind.policy

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policyconfig PUBLIC
 "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">


<policyconfig>

  <action id="org.freedesktop.login1.power-off-multiple-sessions">
    <description>Shutdown the system when multiple users are logged in</description>
    <message>System policy prevents shutting down the system when other users are logged in</message>
    <defaults>
      <allow_inactive>yes</allow_inactive>
      <allow_active>yes</allow_active>
    </defaults>
  </action>

</policyconfig>

You can find all available logind options (e.g. reboot-multiple-sessions) here.

Changing default GDM session

If you want to change the default GDM session, you need to create (or edit) the file ~/.dmrc [1].

Note: This is on a per-user basis. If you want to change the default for more than one user, you will have to create this file for each user.

Here is an example to set the default session to Cinnamon:

~/.dmrc

[Desktop]
Session=cinnamon

GDM legacy

If you want to fall back to the old GDM, which also has a tool for configuring its settings, compile and install gdm-old^AUR from the AUR.

Troubleshooting

GDM fails on logout

If GDM starts up properly on boot, but fails after repeated attempts on logout, try adding this line to the daemon section of /etc/gdm/custom.conf:

GdmXserverTimeout=60

gconf-sanity-check-2 exited with status 256

If GDM pops up an error about gconf-sanity-check-2, you may check permissions in /home and /etc/gconf/gconf.xml.system (the latter should be 755). If GDM is still printing the message, try to empty the gdm home. Run as root:

rm -rf /var/lib/gdm/.*

If that doesn't help, try to set /tmp owner and permissions to:

# chown -R root:root /tmp
# chmod 777 /tmp

GDM root login

It is not advised to login as root, but if necessary you can edit /etc/pam.d/gdm-password and add the following line before the line auth required pam_deny.so: /etc/pam.d/gdm-password

auth            sufficient      pam_succeed_if.so uid eq 0 quiet

The file should look something like this: /etc/pam.d/gdm-password

...
auth            sufficient      pam_succeed_if.so uid eq 0 quiet
auth            sufficient      pam_succeed_if.so uid >= 1000 quiet
auth            required        pam_deny.so
...

You should be able to login as root after restarting GDM.

GDM always uses default US-keyboard

Problem: Keyboard layout always switches to us; layout is reset when a new keyboard is plugged in.

GDM 2.x

Solution: edit ~/.dmrc

~/.dmrc

[Desktop]
Language=de_DE.UTF-8   # change to your default lang
Layout=de   nodeadkeys # change to your keyboard layout

GDM 3.x

Solution: add the following line to /etc/X11/xorg.conf.d/10-evdev.conf, replacing fr with the appropriate keymap

/etc/X11/xorg.conf.d/10-evdev.conf

Section "InputClass"
        Identifier "evdev keyboard catchall"
        MatchIsKeyboard "on"
        MatchDevicePath "/dev/input/event*"
        Driver "evdev"
        Option "XkbLayout" "fr"
EndSection

Warning: Add the line to the keyboard InputClass section, not any of the other sections.

GDM will not load after attempting to set up automatic login

To solve this issue, edit /etc/gdm/custom.conf from a TTY and comment "AutomaticLoginEnable" and the "AutomaticLogin" lines.

# GDM configuration storage

[daemon]

#AutomaticLoginEnable=True
#AutomaticLogin=user

[security]

[xdmcp]

[greeter]

[chooser]

[debug]

GDM does not start after upgrading to 3.8 if using Intel graphics

To solve this problem, you may have to set your acceleration method to SNA. For more information, please refer to: Intel_Graphics#Choose_acceleration_method