Clean /var/log/journal

cf: https://j7.lb168.tw/2019/07/vacuum-var-log-journal/

1. sudo vim /etc/systemd/journald.conf
2. Add the lines:

3. SystemMaxUse=10M
   SystemMaxFileSize=10M

4. sudo systemctl restart systemd-journald.service

cf: https://askubuntu.com/questions/1238214/big-var-log-journal 

1. sudo journalctl --vacuum-size=10M
2. sudojournalctl --vacuum-time=10d