journalctl

Query the systemd journal. More information: https://manned.org/journalctl.

• Show all messages with priority level 3 (errors) from this [b]oot:

journalctl -b --priority=3

• Delete journal logs which are older than 2 days:

journalctl --vacuum-time=2d

• Show only the last N li[n]es and [f]ollow new messages (like tail -f for traditional syslog):

journalctl --lines {{N}} --follow

• Show all messages by a specific [u]nit:

journalctl --unit {{unit}}

• Show logs for a given unit since the last time it started:

journalctl _SYSTEMD_INVOCATION_ID=$(systemctl show --value --property=InvocationID {{unit}})

• Filter messages within a time range (either timestamp or placeholders like "yesterday"):

journalctl --since {{now|today|yesterday|tomorrow}} --until "{{YYYY-MM-DD HH:MM:SS}}"

• Show all messages by a specific process:

journalctl _PID={{pid}}

• Show all messages by a specific executable:

journalctl {{path/to/executable}}