examples are taken here
Systemd stores its logs in
/var/log/journal.$ du -hs /var/log/journal/ 4.1G /var/log/journal/
Check the oldest logs date:
$ ls -lath /var/log/journal/*/ | tail -n 2 -rw-r-x---+ 1 root systemd-journal 8.0M Dec 24 05:15 user-xxx.journal
Clear by date: older than X days
Clearing everything older than 10 days:
$ journalctl --vacuum-time=10d ... Vacuuming done, freed 2.3G of archived journals on disk.
Clear by size: if they exceed X storage
Clearing everything that exceeds 2GB size:$ journalctl --vacuum-size=2G ... Vacuuming done, freed 720.0M of archived journals on disk.
