coreutils: uptime invocation

 
 21.7 ‘uptime’: Print system uptime and load
 ===========================================
 
 ‘uptime’ prints the current time, the system’s uptime, the number of
 logged-in users and the current load average.
 
    If an argument is specified, it is used as the file to be read to
 discover how many users are logged in.  If no argument is specified, a
 system default is used (‘uptime --help’ indicates the default setting).
 
    The only options are ‘--help’ and ‘--version’.  ⇒Common
 options.
 
    For example, here’s what it prints right now on one system I use:
 
      $ uptime
       14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04
 
    The precise method of calculation of load average varies somewhat
 between systems.  Some systems calculate it as the average number of
 runnable processes over the last 1, 5 and 15 minutes, but some systems
 also include processes in the uninterruptible sleep state (that is,
 those processes which are waiting for disk I/O). The Linux kernel
 includes uninterruptible processes.
 
    ‘uptime’ is installed only on platforms with infrastructure for
 obtaining the boot time, and other packages also supply an ‘uptime’
 command, so portable scripts should not rely on its existence or on the
 exact behavior documented above.
 
    An exit status of zero indicates success, and a nonzero value
 indicates failure.