To check the space occupied by the journals use command:

$ journalctl –disk-usage

or

$ du -sh /var/log/journal

or

$ journalctl --vacuum-size=500M

which deletes old log-files from /var/log/journal until total size of the directory becomes under specified threshold (500 megabytes in this example).

You can also clean based on time:

$ journalctl --vacuum-time=10d
Linux journal logs

Is it possible to delete journal files manually wihout harm? Yes!

Everything inside of /var/log/journal/* could bu deleted but do not delete the directory itself.

sudo rm -rf /var/log/journal/*

You can control the size of this directory using this parameter in your /etc/systemd/journald.conf:

SystemMaxUse=50M

You can force a log rotation:

$ sudo systemctl kill --kill-who=main --signal=SIGUSR2 systemd-journald.service

NOTE: You might need to restart the logging service to force a log rotation, if the above signaling method does not do it. You can restart the service like so:

$ sudo systemctl restart systemd-journald.service
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