If it makes slacktee fail with an error code, yes, it would prevent startup. The fix is a - sign: ExecStartPre=-/usr/bin/foo Would still mark the service

If it makes slacktee fail with an error code, yes, it would prevent startup. The fix is a - sign: ExecStartPre=-/usr/bin/foo Would still mark the service as "failed" but wouldn't prevent it from starting.