if you want to know who is currently logged into the system and what they are doing, just type “w”:
/usr/bin/w [root@xxxxxx ~]# w 18:08:06 up 3:58, 5 users, load average: 0.14, 0.05, 0.02 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root tty1 - 17:18 50:04 0.04s 0.04s -bash root pts/0 10.0.2.2 18:05 0.00s 0.05s 0.00s w test1 pts/2 10.0.2.2 18:07 1.00s 0.03s 0.03s -bash test2 pts/3 10.0.2.2 18:07 4.00s 0.06s 0.01s ping localhost test3 pts/4 10.0.2.2 18:07 28.00s 0.09s 0.05s vim
… and to have some fun: if you want to send a message to e.g. the test1 user:
echo "i'll be watching you" >> /dev/pts/2
this will print the message on the test1 user’s screen:
[test1@xxxxxx ~]$ i'll be watching you
Daniel Westermann's Blog 