It may be necessary to know what to expect in the logs to figure out if the machine suddenly rebooted or if someone manually reboot with eg. "init 6", "reboot", or "shutdown" commands.
Red Hat Enterprise Linux 5
When the machine is booting up the logs will display information about syslog restarting and kernel bootup message...
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase of over 48,000 articles and solutions.