journalctl: a log analyser from systemd
You can use
journalctl to analyse logs from systemd services by using a wide variety of filters. In order to access all logs, you need to be a root user or have superuser privileges.
These are some of the most useful parameters you can use with
-n: shows the ten most recent logs. You can add a number after the parameter to specify a different amount.
-u <unit>: filter by a systemd unit.
journalctl -u cronie
-p <priority>: filters by priority. Shows logs with that priority or higher (which corresponds to a lower number): “emerg” (0), “alert” (1), “crit” (2), “err” (3), “warning” (4), “notice” (5), “info” (6), “debug” (7).
journalctl -p err
-S <date>: shows logs since
<date>. Date format:
2021-01-01 12:00:00(use double quotes, time part can be ommitted).
journalctl -S "2021-10-01 12:00:00"
-U <date>: shows logs until
-f: shows most recent logs and updates the list in real time.
More parameters on the man page (