LightDM is a cross-desktop display manager. A display manager is a daemon that:
- Runs display servers (e.g. X) where necessary.
- Runs greeters to allow users to pick which user account and session type to use.
- Allows greeters to perform authentication using PAM.
- Runs session processes once authentication is complete.
- Provides remote graphical login options.
Key features of LightDM are:
- Cross-desktop - supports different desktop technologies.
- Supports different display technologies (X, Mir, Wayland ...).
- Lightweight - low memory usage and fast performance.
- Guest sessions.
- Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable).
- Comprehensive test suite.
The core LightDM project does not provide any greeter with it and you should install a greeter appropriate to your system. Popular greeter projects are:
- LightDM GTK+ Greeter - a greeter that has moderate requirements (GTK+).
- LightDM KDE - greeter used in KDE (Qt)
- LXqt Greeter - greeter used in LXqt (Qt)
- Pantheon Greeter - greeter used in elementary OS (GTK+/Clutter).
- Unity Greeter - greeter used in Unity.
- WebKit2 Greeter - greeter that can be themed using HTML/CSS/Javascript
- Run with no greeter (automatic login only)
- Write your own...
LightDM configuration is provided by the following files:
/usr/share/lightdm/lightdm.conf.d/*.conf
/etc/lightdm/lightdm.conf.d/*.conf
/etc/lightdm/lightdm.conf
System provided configuration should be stored in /usr/share/lightdm/lightdm.conf.d/. System administrators can override this configuration by adding files to /etc/lightdm/lightdm.conf.d/ and /etc/lightdm/lightdm.conf. Files are read in the above order and combined together to make the LightDM configuration.
For example, if a sysadmin wanted to override the system configured default session (provided in /usr/share/lightdm/lightdm.conf.d) they should make a file /etc/lightdm/lightdm.conf.d/50-myconfig.conf with the following:
[Seat:*]
user-session=mysession
Configuration is in keyfile format. For most installations you will want to change the keys in the [Seat:*] section as this applies to all seats on the system (normally just one). A configuration file showing all the possible keys is provided in data/lightdm.conf.
Discussion about LightDM should be done on the forum. All questions are welcome.
Stack Overflow and Ask Ubuntu are good sites for frequently asked questions.