This post is older than a year. Consider some information might not be accurate anymore.
uptime gives a one line display of the following information. The current 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.
System load averages is the average number of processes that are either in a runnable or uninterruptible state. A process in a runnable state is either using the CPU or waiting to use the CPU.
A process in uninterruptible state is waiting for some I/O access, eg waiting for disk. The averages are taken over the three time intervals. Load averages are not normalised for the number of CPUs in a system, so a load average of 1 means a single CPU system is loaded all the time while on a 4 CPU system it means it was idle 75% of the time.
-p, --pretty = show uptime in pretty format
-h, --help = display this help text
-s, --since = system up since, in yyyy-mm-dd MM:HH:SS format
-V, --version = display version information and exit
uptime was written by Larry Greenfield ⟨greenfie@gauss.rutgers.edu⟩ and Michael K. Johnson ⟨johnsonm@sunsite.unc.edu⟩
Examples
root@cinhtau:~# uptime
19:41:41 up 1 min, 1 user, load average: 0.31, 0.15, 0.05
root@cinhtau:~# uptime -p
up 6 minutes
root@cinhtau:~# uptime -s
2015-09-12 19:39:53
root@cinhtau:~# uptime -V
uptime from procps-ng 3.3.9
