Bug#978589: systemd based startup not working

[Jamie Zawinski]

The fact that $DISPLAY is not set at the time xscreensaver is launched is not a 
good sign. The cookie error suggests that ~/.Xauthority does not exist or is 
not readable. However you do appear to be running as yourself, not as "nobody". 
Perhaps $HOME is set to something weird? Maybe try setting your command to 
"printenv ; pwd ; xdpyinfo ; xscreensaver" and see if that provides some clues.