Everything this process writes to stdout reaches the journal as PRIORITY=6,
whatever the Python level was, because journald has nothing else to go on.
Measured on a live rig over 24 hours:
lines containing " - ERROR - " 55
lines containing " - WARNING - " 13
journald PRIORITY recorded 6, for every one of them
So `journalctl -p err -u ledmatrix` returns nothing while errors are being
logged, and `-p warning` likewise. Triage falls back to grepping message text,
which is slower and unreliable: during this audit a search for "oom" matched
the radar logging "zoom=9" twenty-four times and briefly looked like the OOM
killer had been firing.
systemd reads a leading "<N>" on each stdout line and takes it as the priority
(sd-daemon(3)), so a formatter that prefixes one costs no dependency. Every
line of a multi-line record is tagged, not just the first -- the journal splits
them, and an untagged continuation reverts to the default, which would leave
the body of a traceback filed as informational while its first line was an
error.
Applied only when JOURNAL_STREAM is set, which systemd sets for services whose
output it captures. Run from a terminal, in the emulator or under pytest the
prefixes would be literal noise, and the file handler keeps the plain
formatter for the same reason.
Mutation-checked three ways: prefixing unconditionally fails the
outside-systemd test, prefixing only the first line fails the multi-line test,
and mapping ERROR to 6 fails the level mapping. 39 tests pass across the
logging suites.
ChuckBuilds
780fca6365