uptime - Tell how long the system has been running.

uptime was written by Larry Greenfield and Michael K. Johnson

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.

       This is the same information contained in the header line displayed by w(1).

       System load averages is the average number of processes that are either in a runnable or  uninterruptable
       state.   A  process  in a runnable state is either using the CPU or waiting to use the CPU.  A process in
       uninterruptable 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 normalized 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.

/var/run/utmp
              information about who is currently logged on

       /proc  process information

       uptime - Tell how long the system has been running.

-p, --pretty
              show uptime in pretty format

       -h, --help
              display this help text

       -s, --since
              system up since, in yyyy-mm-dd HH:MM:SS format

       -V, --version
              display version information and exit

       Please send bug reports to procps@freelists.org

procps-ng                                         December 2012                                        UPTIME(1)

ps(1), top(1), utmp(5), w(1)

uptime [options]