Pulling log messages for a particular log in systemd journal? I was wondering if it is possible to pull log messages for a particular log with systemd's journal logging. For example, when I open a log in C, `openlog('slog', LOG_CONS | LOG_PID, LOG_LOCAL1)`, to pull just messages logged under '`slog`' or `LOCAL1`? When I do something like `journalctl -u slog` or `journalctl -u LOG_LOCAL1`, it just tells me when the log begins and ends, not the actual log messages.

Yes, it is possible, but you passed the wrong switch to `journalctl`.

According to journalctl(1) man page:

* To read messages with a given syslog identifier (say, "foo"), issue `journalctl -t foo` or `journalctl SYSLOG_IDENTIFIER=foo`;

* To read messages with a given syslog facility, issue `journalctl SYSLOG_FACILITY=1` (note that facilities are stored and matched using their numeric values).




More generally, the syslog identifier and facility are stored in the journal as separate fields (`SYSLOG_IDENTIFIER` and `SYSLOG_FACILITY`). If you ever need to access the journal from, say, the C API, you will have to add matches on these fields directly.

The `journalctl -u` switch is used to add a match on the name of a systemd unit which owned the process which has generated the message. So this is the wrong switch to use.