Simple Desktop Display Manager (SDDM)

https://en.wikipedia.org/wiki/Simple_Desktop_Display_Manager

http://linux.overshoot.tv/etc/sddm.conf
http://linux.overshoot.tv/usr/share/sddm
http://linux.overshoot.tv/x11-misc/sddm
https://github.com/sddm/sddm

Theming

https://github.com/sddm/sddm/wiki/Theming

sddm-greeter --test --theme /usr/share/sddm/themes/breeze/

Configuration

/etc/conf.d/xdm:

The variables in your theme's theme.conf.user override those in theme.conf.

Video background

Make sure to add sddm user to the video group.
$ sudo gpasswd -a sddm video

User icons

For user avatars:
- Rename images as username.face.icon and place them in the folder
/usr/share/sddm/faces/

or:
- Edit /etc/sddm.conf and change the FaceDir setting.

or:
put a .face.icon file in your home directory
~/.face.icon

Logs

Log handling is one of the major shortcomings of sddm.
1) As can be seen by browsing sddm's official bug tracker, a "black screen" is a common symptom that may be caused by a viarity of mis-configurations. The problem is that users are left, almost litterally, in the dark because there is no explicit log entry that may point the user in the right direction.
2) A "black screen" is itself a major useability issue. sddm should detect the failure to start the session and provide some visible feedback.
3) In some situations, errors that are supposed to be logged are not. See: Error did not get logged, issue #770: https://github.com/sddm/sddm/issues/770
4) Logs such as ~/.local/share/sddm/xorg-session.log do not include any timestamps, so it is harder to connect the occurence of a bug to specific log entries.

Relevant logs:

• /var/log/sddm.log
• ~/.local/share/sddm/xorg-session.log
• /var/log/messages : search for sddm-helper.

System settings

Simple things can be configured in KDE system settings > Workspace > Startup and shutdown > Login screen (SDDM).

You can change the background. Note that when selecting a new picture as background, the picture will be copied to the theme folder within /usr/share/sddm/themes/. Changing the picture again might leave the old copy of the previous picture in the theme's directory. Pay attention when using videos as background, as it may lead to disk space issues!