$ last -f /var/log/wtmp.1 reboot
reboot   system boot  4.2.0-30-generic Tue Mar  1 03:04   still running
reboot   system boot  4.2.0-30-generic Mon Feb 29 23:38   still running
reboot   system boot  4.2.0-30-generic Mon Feb 29 23:18   still running
reboot   system boot  4.2.0-30-generic Mon Feb 29 18:43   still running
reboot   system boot  4.2.0-30-generic Mon Feb 29 03:23   still running
reboot   system boot  4.2.0-30-generic Mon Feb 29 02:33 - 03:23  (00:50)
reboot   system boot  4.2.0-30-generic Mon Feb 29 02:11 - 03:23  (01:12)
reboot   system boot  4.2.0-30-generic Mon Feb 29 01:56 - 03:23  (01:27)
reboot   system boot  4.2.0-30-generic Mon Feb 29 01:28 - 01:53  (00:25)
reboot   system boot  4.2.0-30-generic Sun Feb 28 20:49 - 01:00  (04:11)
reboot   system boot  4.2.0-16-generic Sun Feb 28 19:32 - 01:00  (05:28)
reboot   system boot  4.2.0-16-generic Sun Feb 28 16:41 - 19:32  (02:51)
reboot   system boot  4.2.0-16-generic Sun Feb 28 15:48 - 19:32  (03:44)
reboot   system boot  4.2.0-16-generic Sun Feb 28 04:01 - 19:32  (15:30)
reboot   system boot  4.2.0-16-generic Sun Feb 28 03:07 - 04:01  (00:54)
reboot   system boot  4.2.0-16-generic Sun Feb 28 01:11 - 03:06  (01:55)
reboot   system boot  4.2.0-16-generic Sun Feb 28 00:40 - 00:47  (00:07)
reboot   system boot  4.2.0-16-generic Sun Feb 28 00:31 - 00:40  (00:09)
reboot   system boot  4.2.0-16-generic Sat Feb 27 23:14 - 23:57  (00:43)
reboot   system boot  4.2.0-16-generic Sat Feb 27 22:38 - 23:14  (00:35)
reboot   system boot  4.2.0-16-generic Sat Feb 27 21:22 - 23:14  (01:52)
reboot   system boot  4.2.0-16-generic Sat Feb 27 21:03 - 23:14  (02:10)
reboot   system boot  4.2.0-16-generic Sat Feb 27 20:40 - 20:51  (00:11)
reboot   system boot  4.2.0-16-generic Sat Feb 27 20:01 - 20:39  (00:38)
reboot   system boot  4.2.0-16-generic Sat Feb 27 18:25 - 20:39  (02:13)
reboot   system boot  4.2.0-16-generic Sat Feb 27 18:02 - 18:25  (00:22)
reboot   system boot  4.2.0-16-generic Sat Feb 27 05:07 - 18:25  (13:17)
reboot   system boot  4.2.0-16-generic Sat Feb 27 04:49 - 18:25  (13:35)
reboot   system boot  4.2.0-16-generic Sat Feb 27 04:03 - 18:25  (14:21)
reboot   system boot  4.2.0-16-generic Sat Feb 27 03:58 - 04:03  (00:04)
reboot   system boot  4.2.0-16-generic Sat Feb 27 03:41 - 03:58  (00:17)
reboot   system boot  4.2.0-16-generic Sat Feb 27 03:36 - 03:58  (00:22)

wtmp.1 begins Sat Feb 27 03:36:13 2016