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GDM is the GNOME Display Manager, a graphical login program that uses the X Window System.
Contents
In addition to being a GUI alternative to the console login prompt, GDM has the following advantages:
it pre-loads the X Window System (though this can be a disadvantage for servers)
users can select various desktop environments and windows managers on a per-login basis
- assistance for users with disabilities
- per-login regional settings and keyboard layout
- consistent look and feel of other GTK/GNOME-themed applications
- all other functionalities of XDM, including XDMCP support for managing remote displays
By default, the greeter is run as an unprivileged user and logging in as root is forbidden.
Controlling the GDM daemon
To temporarily stop the gdm service, you can run the following command as root:
#invoke-rc.d gdm3 stop
Other available options include: start, restart, reload and force-reload. For more information about general daemon management, see Daemon.
systemd
To use systemd commands for controlling gdm.
Temporarily stop gdm.
# systemctl stop gdm
See status of gdm
# systemctl status gdm
Start gdm
# systemctl start gdm
To disable gdm3 the usual systemd command 'systemctl disable gdm' doesn't work as the 'gdm.service' is loaded as static. By editing:
/etc/X11/default-display-manager
and changing
/usr/sbin/gdm3
to
#/usr/sbin/gdm3
Will prevent gdm3 from loading on startup.
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:
Edit /etc/gdm3/greeter.gconf-defaults as root
- Uncomment and/or modify the desired settings
- Save and close the editor
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.