Information
Data from journald may be stored in volatile memory or persisted locally on the server. Logs in memory will be lost upon a system reboot. By persisting logs to local disk on the server they are protected from loss.
Rationale:
Writing log data to disk will provide the ability to forensically reconstruct events which may have impacted the operations or security of a system even after a system crash or reboot.
Solution
Edit the /etc/systemd/journald.conf file and add the following line:
Storage=persistent