File: //etc/systemd/system/display-manager.service
[Unit]
Description=Light Display Manager
Documentation=man:lightdm(1)
Conflicts=getty@tty7.service plymouth-quit.service
After=systemd-user-sessions.service getty@tty7.service plymouth-quit.service
[Service]
# temporary safety check until all DMs are converted to correct
# display-manager.service symlink handling
ExecStartPre=/bin/sh -c '[ "$(basename $(cat /etc/X11/default-display-manager 2>/dev/null))" = "lightdm" ]'
ExecStart=/usr/sbin/lightdm
Restart=always
BusName=org.freedesktop.DisplayManager