File: //usr/lib/systemd/user/gnome-session-monitor.service
[Unit]
Description=Monitor Session leader for GNOME Session
CollectMode=inactive-or-failed
# All services started after gnome-session-pre.target need to be torn down
# before the session finish can be signalled back to the display manager.
PartOf=gnome-session-pre.target
Before=gnome-session-pre.target
# No After, as we want this to start up immediately
[Service]
Type=notify
ExecStart=/usr/libexec/gnome-session-ctl --monitor
TimeoutStopSec=5