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# LightDM Display Manager
[](https://github.com/canonical/lightdm/actions/workflows/test.yaml)
[](https://discourse.ubuntu.com/c/light-dm/107)
[](https://askubuntu.com/questions/tagged/lightdm)
LightDM is a lightweight, 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 (X, Wayland, Mir, etc)
- Lightweight - low memory usage and fast performance
- Supports remote login (incoming: XDMCP and VNC; outgoing: XDMCP and pluggable)
- Supports guest sessions
- Has a comprehensive test suite
The core LightDM project does not provide any greeter with it; you should install a greeter appropriate to your system. Popular greeter projects are:
* [LightDM GTK+ Greeter](https://github.com/Xubuntu/lightdm-gtk-greeter) - a greeter that has moderate requirements (GTK+).
* [LightDM KDE](http://projects.kde.org/lightdm) - greeter used in [KDE](http://kde.org) (Qt)
* [LXQt Greeter](https://github.com/lxde/lxqt-lightdm-greeter) - greeter used in [LXQt](http://lxqt.org/) (Qt)
* [Pantheon Greeter](https://github.com/elementary/greeter) - greeter used in [elementary OS](https://elementary.io/) (GTK+/Clutter).
* [Unity Greeter](https://launchpad.net/unity-greeter) - greeter used in [Unity](https://launchpad.net/unity).
* [WebKit2 Greeter](https://github.com/antergos/lightdm-webkit2-greeter) - greeter that can be themed using HTML/CSS/Javascript
* Run with no greeter (automatic login only)
* [Write your own...](https://www.freedesktop.org/wiki/Software/LightDM/Development/)
## Configuration
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`](https://github.com/canonical/lightdm/blob/main/data/lightdm.conf).
### Display Setup Script
LightDM can be configured to run an external shell script to setup displays.
If an display setup script is used, it must be:
- Located under `/usr/share`
- Owned by the user `lightdm` and group `lightdm`
- It cannot print or log to any destination not accessible to LightDM
To test a configuration:
- Install `xserver-xephyr`: `sudo apt install xserver-xephyr`
- Run the test as user lightdm: `sudo -u lightdm lightdm --test-mode --debug`
Put the shell script reference in the LightDM configuration:
```
[Seat:*]
display-setup-script=/usr/share/example_display_setup_script.sh
```
## Questions
Discussion about LightDM should be done on the [forum](https://discourse.ubuntu.com/c/light-dm/107). All questions are welcome.
[Stack Overflow](http://stackoverflow.com/search?q=lightdm) and [Ask Ubuntu](http://askubuntu.com/search?q=lightdm) are good sites for frequently asked questions.
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