systemd-journald sometimes uses up a ridiculous amount of disk space under /var/log/journal. Here are the steps to limit systemd-journald to use 16MB of disk space under /var/log/journal.
1) Edit the configuration file /etc/systemd/journald.conf and set SystemMaxUse=16M uncommenting it if necessary.
2) Stop the service and its trigger sockets:
# systemctl stop systemd-journald-dev-log.socket systemd-journald.socket systemd-journald
# systemctl status systemd-journald-dev-log.socket systemd-journald.socket systemd-journald
3) If /var/log/journal does not exist, create it:
# ls -l /var/log/journal/*
If not found:
# mkdir -p /var/log/journal
# systemd-tmpfiles --create --prefix /var/log/journal
4) Clear out existing transient and persistent journals.
# rm -rvf /var/log/journal/*
# rm -rvf /run/log/journal/*
5) Start the service and its trigger sockets:
# systemctl start systemd-journald-dev-log.socket systemd-journald.socket systemd-journald
# systemctl status systemd-journald-dev-log.socket systemd-journald.socket systemd-journald
6) Flush any transient journal entries into persistent storage:
#killall -USR1 systemd-journald # forces in-memory journal to be written to /var/log/journal/*
7) Now you can check the disk space used by journals periodically using:
# du -h /var/log/journal
Note: A quick cleanup of journal storage can be done using the following command which clears up all old entries so that disk usage falls below the indicated parameter:
# journalctl --vacuum-size=2M --rotate