GDM

From GDM - GNOME Display Manager: "The GNOME Display Manager (GDM) is a program that manages graphical display servers and handles graphical user logins."

Related articles

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

Installation

GDM can be installed with the gdm package, and is installed as part of the gnome group.

Starting

To start GDM at boot time, enable gdm.service.

Autostarting applications

To automatically start applications after logging in, follow the instructions in Autostarting#On desktop environment startup that pertain to your desktop environment.

Configuration
Note: Most of the configuration options listed below can be easily set using the gdm-settingsAUR GUI application.

Login screen background image
Note:
  • Since GNOME 3.16, GNOME Shell themes are now stored as binary files (gresource).
  • This change will be overwritten on subsequent updates of gnome-shell.

Firstly, you need to extract the existing GNOME Shell theme to a directory in your home directory. You can do this using the following script:

extractgst.sh
#!/bin/sh
gst=/usr/share/gnome-shell/gnome-shell-theme.gresource
workdir=${HOME}/shell-theme

for r in `gresource list $gst`; do
	r=${r#\/org\/gnome\/shell/}
	if [ ! -d $workdir/${r%/*} ]; then
	  mkdir -p $workdir/${r%/*}
	fi
done

for r in `gresource list $gst`; do
        gresource extract $gst $r >$workdir/${r#\/org\/gnome\/shell/}
done

Navigate to the created directory. You should find that the theme files have been extracted to it. Now copy your preferred background image to this directory.

Next, you need to create a file in the directory with the following content:

gnome-shell-theme.gresource.xml
<?xml version="1.0" encoding="UTF-8"?>
<gresources>
  <gresource prefix="/org/gnome/shell/theme">
    <file>calendar-today.svg</file>
    <file>calendar-today-light.svg</file>
    <file>checkbox.svg</file>
    <file>checkbox-focused.svg</file>
    <file>checkbox-off-focused-light.svg</file>
    <file>checkbox-off-focused.svg</file>
    <file>checkbox-off-light.svg</file>
    <file>checkbox-off.svg</file>
    <file>gnome-shell.css</file>
    <file>gnome-shell-high-contrast.css</file>
    <file>gnome-shell-start.svg</file>
    <file>pad-osd.css</file>
    <file>process-working.svg</file>
    <file>toggle-off.svg</file>
    <file>toggle-off-hc.svg</file>
    <file>toggle-off-light.svg</file>
    <file>toggle-on.svg</file>
    <file>toggle-on-hc.svg</file>
    <file>toggle-on-light.svg</file>
    <file>workspace-placeholder.svg</file>
    <file>'''filename'''</file>
  </gresource>
</gresources>

Replace filename with the filename of your background image or remove the line to use a hex color value instead.

Now, open the file in the directory and change the definition as follows:

#lockDialogGroup {
  background: url(filename);
  background-size: widthpx heightpx;
  background-repeat: no-repeat;
}

Set to the resolution that GDM uses; this might not necessarily be the resolution of the image. For a list of display resolutions, see Display resolution. Again, set filename to be the name of the background image.

If you only want to change the background color, adjust the definition as follows:

#lockDialogGroup {
  background-color: #color;
}

where color is the new hex-encoded background color.

Next, compile the theme using the following command:

$ glib-compile-resources gnome-shell-theme.gresource.xml

Then, copy the resulting file to the /usr/share/gnome-shell directory.

Finally, restart gdm.service (note that simply logging out is not enough) and you should find that it is using your preferred background image.

For more information, please see the following forum thread. A shell script to automate the above steps is available on DimaZirix's github repository.

dconf configuration

Some GDM settings are stored in a dconf database. They can be configured either by adding keyfiles to the directory and then recompiling the GDM database by running as root or by logging into the GDM user on the system and changing the setting directly using the gsettings command line tool. Note that for the former approach, a GDM profile file is required—this must be created manually as it is no longer shipped upstream, see below:

For the latter approach, you can log into the GDM user with the command below:

# machinectl shell gdm@ /bin/bash

Create the following keyfile:

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and change the logo:

$ sudo -u gdm dbus-launch gsettings set org.gnome.login-screen logo '/path/to/logo.png'

Changing the cursor theme

GDM disregards GNOME cursor theme settings and it also ignores the cursor theme set according to the XDG specification. To change the cursor theme used in GDM, create the following keyfile: 

/etc/dconf/db/gdm.d/10-cursor-settings
[org/gnome/desktop/interface]
cursor-theme='<nowiki/>''theme-name''<nowiki/>'

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and change the cursor theme:

$ sudo -u gdm dbus-launch gsettings set org.gnome.desktop.interface cursor-theme 'theme-name'

Changing the icon theme

The same methods can be used to change the icon theme. Create the following keyfile:

Then, recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and change the icon theme:

$ sudo -u gdm dbus-launch gsettings set org.gnome.desktop.interface icon-theme 'theme-name'

Larger font for log-in screen

Click on the accessibility icon at the top right of the screen (a white circle with the silhouette of a person in the centre) and check the Large Text option.

To set a specific scaling factor, create the following keyfile:

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and change the font:

$ sudo -u gdm dbus-launch 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.

Create the following keyfile:

Then recompile the GDM database. Alternatively execute the following to log in to the GDM user temporarily and turn off the sound:

$ sudo -u gdm dbus-launch gsettings set org.gnome.desktop.sound event-sounds 'false'

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

Create the following keyfile:

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and configure the behavior:

$ sudo -u gdm dbus-launch gsettings set org.gnome.settings-daemon.plugins.power power-button-action 'action'

where action can be one of , or .

Enabling tap-to-click

Tap-to-click is disabled in GDM (and GNOME) by default, but you can easily enable it with a dconf setting.

To enable tap-to-click, create the following keyfile:

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and enable the action:

$ sudo -u gdm dbus-launch gsettings set org.gnome.desktop.peripherals.touchpad tap-to-click 'true'

Disable/Enable Accessibility Menu

To disable or enable the Accessibility Menu, create the following keyfile:

Then recompile the GDM database. Alternatively, execute the following to log in to the GDM user temporarily and change the status:

$ sudo -u gdm dbus-launch gsettings set org.gnome.desktop.interface toolkit-accessibility 'boolean'

The menu is disabled when the key is , enabled when it is .

Enable Night Light on GDM

To enable Night Light on GDM, run

Keyboard layout

The system keyboard layout will be applied to GDM. See Keyboard configuration in Xorg#Using X configuration files.

To list the all available keymaps with localectl:

$ localectl list-keymaps

When using Wayland, you may need to specify the X keyboard layout manually with localectl:

# localectl set-x11-keymap fr

If a system has multiple users, it is possible to specify a keyboard layout for GDM to use which is different from the system keyboard layout. Firstly, ensure the package gnome-control-center is installed. Then start gnome-control-center and navigate to Region & Language > Input Sources. In the header bar, hit the Login Screen toggle button and then choose a keyboard layout from the list. Note that the Login Screen button will not be visible in the header bar unless multiple users are present on the system .

Users of GDM 2.x (legacy GDM) may need to edit as shown below:

Change the language

The system language will be applied to GDM. If a system has multiple users, it is possible to set a language for GDM different to the system language. In this case, firstly ensure that gnome-control-center is installed. Then, start gnome-control-center and choose Region & Language. In the header bar, check the Login Screen toggle button. Finally, click on Language and choose your language from the list. You will be prompted for your root password. Note that the Login Screen button will not be visible in the header bar unless multiple users are present on the system .

Automatic login

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

or for an automatic login with a delay:

You can set the session used for automatic login (replace with desired session):

/var/lib/AccountsService/users/''username''
XSession=gnome-xorg

Passwordless login

If you want to bypass the password prompt in GDM then simply add the following line on the first line of :

auth sufficient pam_succeed_if.so user ingroup nopasswdlogin

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

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

Passwordless shutdown for multiple sessions

GDM uses polkit and logind to gain permissions for shutdown. You can shutdown the system when multiple users are logged in 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/software/polkit/policyconfig-1.dtd">

<!-- 
Policy definitions for logind
 -->

<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) in .

Enable root login in GDM

It is not advised to login as root, but if necessary you can edit and add the following line before the line :

The file should look something like this:

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

Hide user from login list

The users for the gdm user list are gathered by AccountsService. It will automatically hide system users (UID < 1000). To hide ordinary users from the login list create or edit a file named after the user to hide in to contain at least:

Setup default monitor settings

Some desktop environments store display settings in ~/.config/monitors.xml. xrandr commands are then generated on the base of the file content. GDM has a similar file stored in .

If you have your monitors setup as you like (resolution, refresh rate, orientation, scaling, primary and so on) in ~/.config/monitors.xml and want GDM to honor those settings:

# cp ~/.config/monitors.xml /var/lib/gdm/.config/

To automatically re-configure the monitor setup on each boot, use a drop-in file for gdm.service:

The relevant parts of for screen rotation and scaling are:

<monitors version="2">
  <configuration>
    <logicalmonitor>
      ...
      <scale>2</scale>
      ...
      <transform>
        <rotation>right</rotation>
        <flipped>no</flipped>
      </transform>
      ...
    </logicalmonitor>
  </configuration>
</monitors>

Changes will take effect on logout. This is necessary because GDM does not respect .

Configure X server access permission

You can use the xhost command to configure X server access permissions.

For instance, to grant GDM the right to access the X server, use the following command:

Troubleshooting

Wayland and the proprietary NVIDIA driver

To use Wayland in GDM with the NVIDIA driver, you must first enable NVIDIA#DRM kernel mode setting.

As of GDM 42 and NVIDIA driver 510, GDM defaults to Wayland. For older NVIDIA drivers (in between version 470 and 510), GDM has chipset-dependent udev rules to use Xorg rather than Wayland. To force-enable Wayland, override these rules by creating the following symlink:

# ln -s /dev/null /etc/udev/rules.d/61-gdm.rules

If, instead of GDM, a black screen appears, try disabling integrated graphics in your computer's BIOS settings.

Failure 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

Rootless Xorg

See Xorg#Rootless Xorg.

Use Xorg backend

The Wayland backend is used by default, and the Xorg backend is used only if the Wayland backend cannot be started. You may wish to use the Xorg backend instead if, for example:

To use the Xorg backend by default, uncomment the following line in /etc/gdm/custom.conf:

#WaylandEnable=false

GDM does not start until input is provided

If, after booting, the screen stays black and GDM does not start until the mouse is moved or something is typed on the keyboard, it may be due to a lack of entropy required for random number generation. To confirm, check that the following line appears inside systemd-random-seed’s log (which can be read by running with root privileges):

Kernel entropy pool is not initialized yet, waiting until it is.

To fix this, you can pass the random.trust_cpu=on kernel parameter if your CPU supports the RDRAND instruction, or you can use haveged which also provides entropy, albeit it is of allegedly low quality. See Debian’s article on the topic for other solutions.

Incomplete removal of gdm

After removing gdm, systemd may report the following:

user 'gdm': directory '/var/lib/gdm' does not exist

To remove this warning, login as root and delete the primary user and then delete the group :

Verify that is successfully removed via and with root privileges. To round it off, you may want to double-check no unowned files for gdm remain.

GDM auto-suspend (GNOME 3.28)

GDM uses a separate dconf database to control power management. To apply your user's power settings, copy them to GDM's dconf database:

$ IFS=
\n'; for x in $(sudo -u username gsettings list-recursively org.gnome.settings-daemon.plugins.power); do eval "sudo -u gdm dbus-launch gsettings set $x"; done; unset IFS

where is your username.

To only disable auto-suspend on AC, run:

$ sudo -u gdm dbus-launch gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'nothing'

(To also disable auto-suspend on battery, run the command with instead of .)

Restart GDM to activate your changes.

gollark: That wouldn't help. It would still be, very obviously, there.
gollark: Yes, I agree, it must be destroyed as soon as possible.
gollark: Oh, I thought you meant we would only have the moon removed by 2093.
gollark: 2093 is too far away.
gollark: Those who deny it are wilfully ignorant.

GDM ignores Wayland and uses X.Org by default

Wayland requires Kernel Mode Setting (KMS) running in order to work, and on some machines the GDM process start earlier than KMS, resulting in GDM unable to see Wayland and working only with X.Org. This might result in messages like the following showing up in your log:

gnome-shell[569]: Failed to open gpu '/dev/dri/card0': GDBus.Error:org.freedesktop.DBus.Error.AccessDenied: Operation not permitted
gnome-shell[569]: Failed to create backend: No GPUs found
systemd[505]: org.gnome.Shell@wayland.service: Failed with result 'protocol'.
systemd[505]: Failed to start GNOME Shell on Wayland.

Alternatively, the same issue may lead to GDM not appearing or monitor only displaying the TTY output.

You can solve this problem by starting KMS earlier. You may also wish to just verify that Wayland is enabled in the GDM config (see above).

Also, if you use a NVIDIA driver, the Wayland session might be blocked by a udev rule (see the notes under GNOME#Wayland sessions). This might result in messages like the following:

systemd[1022]: Condition check resulted in GNOME Shell on Wayland being skipped.
systemd[1022]: org.gnome.Shell@wayland.service: Skipped due to 'exec-condition'.
systemd[1022]: org.gnome.Shell@wayland.service: Control process exited, code=exited, status=2/INVALIDARGUMENT

See #Wayland and the proprietary NVIDIA driver for a workaround.

Black screen on AMD or Intel GPUs when an NVidia (e)GPU is present

At first, without an NVidia device, GDM starts and works normally on Wayland, but stops working once an NVidia eGPU is plugged in (or the module is loaded for other reasons). A typical symptom of the problem is a black screen with a blinking cursor upon logouts and GDM restarts and the following message in GDM's logs (accessed by running journalctl -u gdm -b as root):

Gdm: Child process -<some PID> was already dead.

The solution is the same as above: Prevent from running upon module loading.

Notice that GDM on Wayland will no longer work once has run. This is because has been written into , which overrides /etc/gdm/custom.conf. To fix the situation without a reboot, remove and then restart GDM.

GDM cannot be enabled

See systemd/FAQ#Failure to enable unit due to preexisting symlink.

See also
This article is issued from Archlinux. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.