From: zbyszek@in.waw.pl
much like -u equates to _SYSTEMD_UNIT.
Just to clear up potential confusion: -u is *not* equivalent to
_SYSTEMD_UNIT.
You can show the match by looking at the (stricly unofficial) debug
output:
$ SYSTEMD_LOG_LEVEL=debug journalctl -u XXXXX |& grep 'Journal filter'
Journal filter: ((OBJECT_SYSTEMD_UNIT=XXXXX.service AND _UID=0) OR (UNIT=XXXXX.service AND _PID=1) OR (COREDUMP_UNIT=XXXXX.service AND _UID=0 AND MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1) OR _SYSTEMD_UNIT=XXXXX.service)
The output is still authoritative, but you get more than just messages originating from the unit.
I just *knew* I was going to be corrected on that. Thanks for the explanation though.
-- John Florian