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 journalctl:

  • -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 <date>.
  • -f: shows most recent logs and updates the list in real time.

More parameters on the man page (man journalctl).