tldr/pages/linux/journalctl.md

journalctl

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

• Show all messages with priority level 3 (errors) from this boot:

journalctl {{[-b|--boot]}} {{[-p|--priority]}} 3

• Delete journal logs which are older than 2 days:

journalctl --vacuum-time 2d

• Show only the last n lines and follow new messages (like tail -f for traditional syslog):

journalctl {{[-n|--lines]}} {{n}} {{[-f|--follow]}}

• Show all messages by a specific unit:

journalctl {{[-u|--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 {{[-S|--since]}} {{now|today|yesterday|tomorrow}} {{[-U|--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}}