logger

Write to system logs using syslogd, rsyslogd, systemd-journald, etc.

Ad-hoc logging as any user:

logger -i "System rebooted by $USER"

[root@rhel9-a ~]# tail -n1 /var/log/messages
Jul 29 01:06:47 rhel9-a root[1373]: System rebooted by root

Potentially useful in cron jobs or admin scripts.