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GDM is the GNOME Display Manager, a graphical login program that uses Wayland or the X Window System.

In addition to being a GUI alternative to the console login prompt, GDM has the following advantages:

By default, the greeter is run as an unprivileged user and logging in as root is forbidden.


Controlling the GDM daemon

GDM is a service that can, like all other services in your system, be controlled with the systemctl command.

To temporarily stop GDM:

$ systemctl stop gdm

To see the status of GDM:

$ systemctl status gdm

To start GDM manually:

$ systemctl start gdm

To set your system to always boot to a console rather than GDM:

$ systemctl set-default multi-user.target

To revert the previous command and have your system always boot straight into GDM:

$ systemctl set-default graphical.target

To check the current boot target:

$ systemctl get-default


Configuration

Disabling Wayland

In Debian 10 and newer, GDM will use Wayland by default on supported hardware. This can be overridden in the /etc/gdm3/daemon.conf file by uncommenting the WaylandEnable=false line, forcing it to instead use X11.

Customizing the GDM appearance

GDM v3.0+ allows for some basic customization, such as changing the logo icon, display background, and GTK theme. To do so:

  1. Edit /etc/gdm3/greeter.dconf-defaults as root

  2. Uncomment and/or modify the desired settings
  3. Save and close the editor
  4. Finally, run as root: dpkg-reconfigure gdm3

The command 'dpkg-reconfigure gdm3' will cause gdm to reload its configuration upon the next logout or reboot.

Note: When changing the background image, the target file must be world-readable.

Removing autologin in gdm3 and getting more verbose output in GDM

This is with respect to GDM3 as it's known in GNOME 3 and above.

$ dpkg -S /etc/gdm3/daemon.conf
gdm3: /etc/gdm3/daemon.conf

This is just to have an idea of the ownership of the file.

Now the file would look something like this :-

    $ cat /etc/gdm3/daemon.conf
    # GDM configuration storage
    #
    # See /usr/share/gdm/gdm.schemas for a list of available options.

    [daemon]
    # Enabling automatic login
    AutomaticLoginEnable=true
    AutomaticLogin=$USERNAME

    # Enabling timed login
    #  TimedLoginEnable = true
    #  TimedLogin = user1
    #  TimedLoginDelay = 10

    # Reserving more VTs for test consoles (default is 7)
    #  FirstVT = 9

    [security]

    [xdmcp]

    [greeter]
    # Only include selected logins in the greeter
    # IncludeAll = false
    # Include = user1,user2

    [chooser]

    [debug]
    # More verbose logs
    # Additionally lets the X server dump core if it crashes
    Enable = false

Now at times if you remove the user you just cannot go into the DE esp. if only a user is automatically logged in. This is and should be a bug but that's another tale. Anyways the way to fix it is simple.

    $ cat /etc/gdm3/daemon.conf
    # GDM configuration storage
    #
    # See /usr/share/gdm/gdm.schemas for a list of available options.

    [daemon]
    # Enabling automatic login
    AutomaticLoginEnable=false

    # Enabling timed login
    #  TimedLoginEnable = true
    #  TimedLogin = user1
    #  TimedLoginDelay = 10

    # Reserving more VTs for test consoles (default is 7)
    #  FirstVT = 9

    [security]

    [xdmcp]

    [greeter]
    # Only include selected logins in the greeter
    # IncludeAll = false
    # Include = user1,user2

    [chooser]

    [debug]
    # More verbose logs
    # Additionally lets the X server dump core if it crashes
    Enable = true

I just added the bits which should help us in case anything does go wrong.


See also


CategoryBootProcess