SDDM

Simple Desktop Display Manager (SDDM) is Article description::a modern [[display manager that supports both the X11 server and the Wayland protocol.]]

Emerge
Install :

If there are performance issues, it might help to add the sddm user to the video group:

Files
SDDM has two configuration files: the package installed and  which is used to override specific options. The second is not created by the package. KDE Plasma writes user changed options to. Both files have the same format. See comments in the file and for details on available options.

Prior to 0.18.0
Prior to 0.18.0 the configuration was only in. Some of the files may have had to be generated manually. If installing 0.18.0, skip ahead to Service

Keymap
To select the correct keymap on the login screen, add following lines to the file:

This file is not created automatically when the package is installed so you'll need to create it if you haven't done so already.

Next create the directory

and the file.

the first country code is the default. Finally set execute permissions on the file.

OpenRC
Set SDDM as the default display manager:

To start SDDM on boot, add xdm to the default runlevel:

To start SDDM now:

After logging in to the X session via sddm, it is a good idea to verify that ConsoleKit is working as intended. By typing all active sessions can be listed. The list should include your session, typically running on. This session should also read. Active being FALSE indicates an issue.

systemd
To start SDDM on boot:

To start SDDM now:

Plasma
Graphical configuration is integrated in Plasma 5 system settings by installing :

Permission denied errors in Xorg.log
The X server will not start and permission denied errors (such as the following) are present in the log file:

It is likely the sddm user has not been added to the video group. Running the following command should fix the problem:

Missing users
If the login screen is missing some user(s) to choose from, this might be caused by sddm.conf - standard MinimumUid is 1000 and some existing users may have lower Uids.