[root@localhost ~]# last
root pts/7 157.122.58.52 Thu Aug 11 16:55 still logged in
reboot system boot 2.6.32-431.el6.x Tue Aug 9 01:22 – 17:34 (2+16:12)
root tty1 Sun Aug 7 03:29 – down (00:00)
[root@localhost ~]# last reboot
reboot system boot 2.6.32-431.el6.x Tue Aug 9 01:22 – 17:40 (2+16:18)
reboot system boot 2.6.32-431.el6.x Sat Aug 6 19:48 – 03:30 (07:41)
reboot system boot 2.6.32-431.el6.x Fri Aug 5 11:41 – 03:30 (1+15:48)
or cat /var/log/boot.log
#cat /var/log/messages | grep shutdown ?
