We have already discussed about last command on previous post, the following content remote the ssh logged, reboot, shutdown information from logs.
 

​# last


root     pts/0        192.168.1.100     Thu Feb 19 21:43   still logged in

root     pts/0        192.168.1.100     Thu Feb 19 16:56 - 20:31  (03:35)

root     pts/0        192.168.1.113     Thu Feb 19 03:14 - 03:15  (00:01)

root     pts/0        192.168.1.100     Sat Jan 24 02:19 - 03:33  (01:14)

reboot   system boot  2.6.32-71.29.1.e Sat Jan 24 02:18 - 21:55 (26+19:36)

wtmp begins Sat Jan 24 02:18:28 2015

logged information stored into /var/log/wtmp, /var/log/btmp binary files, but you could erase these files.
 
#  > /var/log/wtmp
# > /var/log/btmp