106.2 Setup a display manager

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Candidates should be able to describe the basic features and configuration of the LightDM display manager. This objective covers awareness of the display managers XDM (X Display Manger), GDM (Gnome Display Manager) and KDM (KDE Display Manager).

Key Knowledge Areas

Basic configuration of LightDM
Turn the display manager on or off
Change the display manager greeting
Awareness of XDM, KDM and GDM

Terms and Utilities

lightdm
/etc/lightdm/

Display Manager

A Display Manager is a graphical interface which lets you login into your system when you turn your computer on. There are many different display managers (say XDM, SDDM, KDM, GDM, ...) but their general functionality is same: show a login form and let the user the enter (or choose) its name, password and the Desktop she needs to use. Also many of the DMs let the user to choose Accessibility Tools (covered in 106.3), connect to the network, change the keyboard layout or change the system volume.

lightdm

Many of the distros use LightDM as their display/login manager. It shows the default user (last logged in user) and asks for password. If you have more than one desktop installed (say XFCE, KDE and Gnome) it also lets you choose the one you need.

lightdm can accept themes and calls them greeters.

/etc/lightdm

All of the lightdm configs are in /etc/lightdm.

$ ls -ltrh /etc/lightdm/
total 24K
-rw-r--r-- 1 root root   40 Sep 23 12:56 keys.conf
-rw-r--r-- 1 root root  801 Sep 27 13:03 lightdm-webkit2-greeter.conf
-rw-r--r-- 1 root root  452 Sep 27 13:08 users.conf
-rwxr-xr-x 1 root root 1.5K Sep 27 13:08 Xsession
-rw-r--r-- 1 root root 6.5K Sep 27 13:08 lightdm.conf

Some distributions like Ubuntu are using a lightdm.conf.d directory instead of a straight forward lightdm.conf and put their configs there.

[SeatDefaults]
...
user-session=gnome
#autologin-user=jadi
#allow-user-switching=true
allow-guest=true
greeter-session=lightdm-webkit2-greeter
...

The greeter-session tells which greeter (theme) should be used. You can install more greeters using your package manager. Another important config is user-session which tells the lightdm what desktop is the default one.

controlling DMs

The lightdm works as a service. You can start, stop & restart it or even use systemctl disable lightdm to disable it on next boots.

You already know how to reboot your computer in text mode from previous lessons (using grub, kernel parameters during the boot or using init command).

106.2. Setup a display manager