Use uptime command which tells you how long the system has been running:
O/p:
23:25:40
up 60 days, 23:13, 1 user, load average: 0.55, 0.14, 0.05
uptime gives a one line display of the following information (as above). The current time (23:25:40), how long the system has been running (60 day

, how many users are currently logged on (1 user), and the system load averages for the past 1, 5, and 15 minutes.