Uptime : Tell how long the system has been running.

uptime gives a one line display of the following information.  The cur-
rent time, how long the system has been running,  how  many  users  are
currently  logged  on,  and the system load averages for the past 1, 5,
and 15 minutes

command : uptime

$uptime

10:00:51 up  2:20,  4 users,  load average: 0.57, 0.45, 0.24

first it gives the current time

second it gives the how long the system is running

third tells how many users  are logged in

fourth system load avg on  cpu