Command = w
Utility = Show who is logged on and what they are doing.

Command line :
delorimier:/# w

Sample output :
 14:05:19 up  9:11,  2 users,  load average: 0.10, 0.22, 0.20
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU  WHAT
eth1     :0       -                05:01   ?xdm?   0.00s   ?     -
eth1     pts/0    :0.0             05:02    0.00s  0.16s  0.03s  w 

Usage :
usage: w -hlsufV [user]
    -h    skip header
    -l    long listing (default)
    -s    short listing
    -u    ignore uid of processes
    -f    toggle FROM field (default on)
    -V    display version

Note :