Linux · System Logging (syslog & journald)

Beyond -b and -f, how do you make journalctl show only kernel messages, only a logger tag, only one syslog facility, or split system vs user logs?

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More in System Logging (syslog & journald)

syslog groups messages by facility. Which facilities are reserved for admins to use freely, and why is authpriv treated more carefully than auth?

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An rsyslogd rule looks like mail.err written before /var/log/mail.err. What are the two structural halves of every such rule, and what does each one decide?

Kernel messages land in a fixed 16 KiB RAM ring buffer. What happens to old kernel messages over time, and how does that structure make persistent kernel logs a separate concern?

Left alone, log files grow without bound. What sequence of actions does logrotate perform on a log, and how often is it triggered?

logwatch is meant to save you from reading raw logs, but on a freshly configured box its daily report never arrives. What does logwatch do, and what dependency silently blocks it?

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