Many times you find out that your server has been rebooted, but that information comes to late for you. For those cases, and not only, you can set a cron job that would sent a notification to your email address, each time when your server is rebooted. For this run first
crontab -e
(this opens up vi as your crontab editor) and at the end of the file add this command:
@reboot echo “`date +%r` `date +%b-%d-%Y` the server has been restarted.” | mail -s “`hostname` restart” dragos@fedorovici.com
This way each time when your server is restarted a notification is sent to your email address. The notification includes the hostname of the machine (in title) and the date when the server has been restarted (on body).