Using journalctl on embedded systems
Clear systemd journal
On any server, the logs can start to add up and take considerable amount of disk space. Systemd conveniently stores these in /var/log/journal and has a systemctl command to help clear them.
Take this example:
$ du -hs /var/log/journal/ 4.1G /var/log/journal/
4.1GB worth of journal files, with the oldest dating back over 2 months.
$ ls -lath /var/log/journal/*/ | tail -n 2 -rw-r-x---+ 1 root systemd-journal 8.0M Dec 24 05:15 user-xxx.journal
On this server, I really don't need that many logs, so let's clean them out. There are generally 2 ways to do this.
Clear systemd journals older than X days
The first one is time-based, clearing everything holder than say 10 days.
$ journalctl --vacuum-time=10d ... Vacuuming done, freed 2.3G of archived journals on disk.
Alternatively, you can limit its total size.
Clear systemd journals if they exceed X storage
This example will keep 2GB worth of logs, clearing everything that exceeds this.
$ journalctl --vacuum-size=2G ... Vacuuming done, freed 720.0M of archived journals on disk.
Afterwards, your /var/log/journal should be much smaller.
$ du -hs /var/log/journal 1.1G /var/log/journal
Saves you some GBs on