Checking who is access your PC

In linux, simple to know who is access your computer.
open terminal, and type :

~$ w

ubuntu@ubuntu:~$ w
 00:47:53 up 17:36,  2 users,  load average: 0.35, 0.39, 0.42
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
retnet   tty7     :0               Thu07   17:35m 45:13   0.83s gnome-session
retnet   pts/0    :0.0             00:47    0.00s  0.24s  0.01s w
ubuntu@ubuntu:~$ 

tty7 = your GDM Desktop
pts0 = your terminal right now