Pokud je tam validní jméno, ale neexistujícího uživatele, tak se unita vůbec nespustí a přímo to vyplivne chybu na řádek (a unita je prostě failed):
# systemctl start t
Job for t.service failed because the control process exited with error code.
See "systemctl status t.service" and "journalctl -xe" for details.
# systemctl status t
t.service
Loaded: loaded (/etc/systemd/system/t.service; static; vendor preset: enabled)
Active: failed (Result: exit-code) since Mon 2017-07-03 10:02:47 CEST; 4s ago
Process: 19175 ExecStart=/usr/bin/id (code=exited, status=217/USER)
Main PID: 19175 (code=exited, status=217/USER)
Kdežto s nulou na počátku prostě proběhne:
# systemctl status t
t.service
Loaded: loaded (/etc/systemd/system/t.service; static; vendor preset: enabled)
Active: inactive (dead)
A spustí se (ExecStart) to jako root:
Jul 03 10:03:43 raid systemd[1]: /etc/systemd/system/t.service:3: Invalid user/group name or numeric ID, ignoring: 0tomasxxx
Jul 03 10:03:43 raid systemd[1]: Starting t.service...
Jul 03 10:03:43 raid id[19569]: uid=0(root) gid=0(root) groups=0(root)
Jul 03 10:03:43 raid systemd[1]: Started t.service.