Systemd has its own logging system called the journal, and the log files are stored in /var/log/journal.

Check current disk usage of journal files

sudo journalctl --disk-usage

Rotate journal files

• Active journal files will be marked as archived, so that they are never written to in future.

sudo journalctl --rotate

Delete journal logs older than 5 days:

sudo journalctl --vacuum-time=5days

Delete log files until the disk space taken falls below 200M:

sudo journalctl --vacuum-size=200M

Delete old logs and limit file number to 10:

sudo journalctl --vacuum-files=10

The configuration file is located at /etc/systemd/journald.conf. After editing to your preference, reload systemd daemon using sudo systemctl daemon-reload