journalctl flags & options

-u, --unit

Show logs for a specific systemd unit.

journalctl -u nginx

journalctl -u ssh -u docker

-f, --follow

Stream new log entries in real time like tail -f.

journalctl -f

journalctl -fu nginx

-n

Show only the last N log entries.

journalctl -n 50

journalctl -u mysql -n 100

--since, --until

Filter logs by time range.

journalctl --since "2024-01-15 09:00:00"

journalctl --since "1 hour ago"

journalctl --since "2024-01-15" --until "2024-01-16"

-p, --priority

Filter by log priority level (emerg, alert, crit, err, warning, notice, info, debug).

journalctl -p err

journalctl -p warning -u nginx

-b

Show logs from a specific boot, where 0 is current boot and -1 is previous.

journalctl -b

journalctl -b -1

--no-pager

Print output directly without a pager, useful for scripting.

journalctl -u nginx --no-pager

-o, --output

Control the output format (short, json, json-pretty, verbose, cat).

journalctl -u nginx -o json-pretty

journalctl -o cat -n 20