Linux › Section G · System configuration › Topic G.1
System logging: the journal and syslog
When a service fails at 3 a.m., the log is the only witness. Linux records messages from the kernel, services and login programs in two overlapping systems, the systemd journal and traditional syslog, and knowing how to query, route and trim both is a core administrator skill.
In this topic
- Two logging systems
- Reading the journal with journalctl
- Filtering: unit, priority, time and text
- Worked example: why did the service fail?
- Priorities from 0 to 7
- Keeping the journal across reboots
- Syslog and rsyslog selectors
- Worked example: reading two rsyslog rules
- Log rotation with logrotate
- Common mistakes to avoid
- Key takeaways
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