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.
- Bug#978589: systemd based startup not working Eduard Bloch
- Bug#978589: systemd based startup not working Jamie Zawinski
- Bug#978589: systemd based startup not working Eduard Bloch
- Bug#978589: systemd based startup not working Jamie Zawinski
- Bug#978589: systemd based startup not work... Eduard Bloch
- Bug#978589: systemd based startup not... Jamie Zawinski
- Bug#978589: systemd based startup... Eduard Bloch
- Bug#978589: systemd based sta... Jamie Zawinski
- Bug#978589: systemd based sta... Eduard Bloch
- Bug#978589: systemd based sta... Eduard Bloch