The easiest way to see how long a LINUX computer has been running is to issue the uptime command.
A typical output of the uptime command is:
15:43:37 up 41 days, 16:10, 1 user, load average: 0.11, 0.08, 0.08
The fields are:
Further information can be found by using the 'man uptime' command.
The current uptime of this machine is: