who
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.. code-block:: text

  usage: who [-c] [-n] [-z] [-a] [-m] [-s]                             :  print statistics about active users (idle<5min)
    -c                                                   -  break down by client host
    -n                                                   -  print id's instead of names
    -z                                                   -  print auth protocols
    -a                                                   -  print all
    -s                                                   -  print summary for clients
    -m                                                   -  print in monitoring format <key>=<value>