We have a remote linux server (ubuntu desktop). The system log indicates the system has been restarted on the timely fashion. Here is a part of the last output:

ut       pts/0        192.169.50.2-sta Sat Nov 24 22:17   still logged in
reboot   system boot  2.6.32-21-generi Sat Nov 24 22:04 - 22:17  (00:13)
ut       pts/0        server.local     Sat Nov 24 21:36 - crash  (00:27)
reboot   system boot  2.6.32-21-generi Sat Nov 24 15:55 - 22:17  (06:21)
reboot   system boot  2.6.32-21-generi Fri Nov 23 18:02 - 22:17 (1+04:14)
reboot   system boot  2.6.32-21-generi Fri Nov 23 10:39 - 22:17 (1+11:38)
reboot   system boot  2.6.32-21-generi Fri Nov 23 04:18 - 22:17 (1+17:59)
reboot   system boot  2.6.32-21-generi Fri Nov 23 03:57 - 22:17 (1+18:20)
reboot   system boot  2.6.32-21-generi Thu Nov 22 20:38 - 22:17 (2+01:38)
reboot   system boot  2.6.32-21-generi Thu Nov 22 11:13 - 22:17 (2+11:03)
reboot   system boot  2.6.32-21-generi Thu Nov 22 08:12 - 22:17 (2+14:05)
reboot   system boot  2.6.32-21-generi Wed Nov 21 11:16 - 22:17 (3+11:00)
reboot   system boot  2.6.32-21-generi Tue Nov 20 22:36 - 22:17 (3+23:41)
reboot   system boot  2.6.32-21-generi Tue Nov 20 14:12 - 22:17 (4+08:05)
reboot   system boot  2.6.32-21-generi Tue Nov 20 11:32 - 22:17 (4+10:44)
reboot   system boot  2.6.32-21-generi Tue Nov 20 01:52 - 22:17 (4+20:25)
reboot   system boot  2.6.32-21-generi Tue Nov 20 00:22 - 22:17 (4+21:55)
reboot   system boot  2.6.32-21-generi Mon Nov 19 17:27 - 22:17 (5+04:50)

It looks the system is set to be restarted at 22:17. Can anyone guide me why this happens?

Thanks in advance.