From LQWiki

The command uptime typed at the command line in a terminal, will show:

• The current time,
• The time this machine has been up and running (in hours, days, etc),
• How many shell instances are running (the number of users),
• And finally the load average.

Example:

$ uptime
  3:09pm  up 3 days 17:31,  6 users,  load average: 0.22, 0.15, 0.05

In this example, the computer has not been powered off since 3 days and 17 hours. There are 6 users logged in.

See also

• uptime man page