systemd-journald.service
▻https://www.freedesktop.org/software/systemd/man/systemd-journald.service.html
By default, the journal stores log data in /run/log/journal/. Since /run/ is volatile, log data is lost at reboot. To make the data persistent, it is sufficient to create /var/log/journal/ where #systemd-journald will then store the data:
mkdir -p /var/log/journal
systemd-tmpfiles —create —prefix /var/log/journal
See journald.conf(5) for information about the configuration of this service.