Feature description

The new logging framework doesn't seem to integrate with system logging at all. It only logs to stdout, which means it prefixes its own timestamps (even though the system already does that to all received log messages), and it doesn't have a way to fill in message priority (meaning that all messages – from debug to fatal error – become just 'info').

Would it be acceptable to add support to output log messages through Unix syslog() (e.g. --log-target=syslog, which currently I didn't find in syncthing serve --help)?

Problem or use case

Support for standard logging API would make it easier to read logs by 1) avoiding duplicate fields, and 2) allowing e.g. journalctl to highlight important messages in more obvious ways than just the 'WRN' field.

The latter would also allow existing "alert server owner on warning/error log messages" to function with Syncthing, without having to special-case syncthing's own log format.

Alternatives or workarounds

None.