SDDM tips (1)

SDDM is the abbreviation of Simple Desktop Display Manager, which is a default display manager for LXQt and KDE Plasma.
It officially supports Linux and FreeBSD, but should also work well with other Unix-like system.

User HOME

SDDM works under a special user in an UNIX-like system: sddm. Its HOME directory is set to /var/lib/sddm.

If we want to install it ourselves, an sddm user needs to be created, with its home set to /var/lib/sddm by default.

In this directory, a state.conf will be created. The content of it on my PC is:

[Last]
# Name of the last logged-in user.
# This user will be preselected when the login screen appears
User=inoki


# Name of the session for the last logged-in user.
# This session will be preselected when the login screen appears.
Session=/usr/share/xsessions/plasma.desktop

which notes the latest login user and the correspond session. This will accelerate the next login.

The file is declared in src/common/configuration.h and will be loaded later.

Configurations

Like the other programs, SDDM also reads configuration from /etc. The file is /etc/sddm.conf, which contains several sections:

• General
• Theme
• Users
• Wayland
• X11

Icons

User icons are stored in $(DATADIR)/faces/ or ~/.face.icon (for each user).

Themes

Themes are stored in $(DATADIR)/themes/. SDDM loads Main.qml file in it to create an user interface.

Scripts

Scripts to launch a specific session under an environment are stored in $(DATADIR)/scripts/. These scripts will start the desktop environment.

For example, for X11, the configuration items are:

[X11]
DisplayCommand=/usr/share/sddm/scripts/Xsetup
DisplayStopCommand=/usr/share/sddm/scripts/Xstop
EnableHiDPI=false
MinimumVT=1
ServerArguments=-nolisten tcp
ServerPath=/usr/bin/X
SessionCommand=/usr/share/sddm/scripts/Xsession
SessionDir=/usr/share/xsessions
SessionLogFile=.local/share/sddm/xorg-session.log
UserAuthFile=.Xauthority
XauthPath=/usr/bin/xauth
XephyrPath=/usr/bin/Xephyr

The script is Xsetup, Xsession, Xstop, etc. The desktop entries for desktop environments are placed in /usr/share/xsessions.

In my case, the plasma.desktop indicates the executable:

[Desktop Entry]
Type=XSession
Exec=/usr/bin/startplasma-x11
TryExec=/usr/bin/startplasma-x11
DesktopNames=KDE
Name=Plasma
...

Conclusion

Unfinished. TBC…