How:

Since we are going to do some privileged system administration tasks, you need to login as root:

As the name suggested, every login and logout are logged, i.e. leaving some fingerprints in the system. To check the log, you can use a command - last.

last

yuni     :0                            Sun Jul 15 02:18 - 02:19  (01:00)    
yuni     :0                            Sun Jul 15 00:15 - 01:28  (01:13)    
root     :0                            Wed Jul  4 11:34 - 11:44 (3+00:09)   

wtmp begins Wed Jul  4 11:34:35 2001