rwho —
who is logged in on local machines
The rwho command produces output similar to
  who(1), but for all machines on the
  local network. If no report has been received from a machine for 11 minutes
  then rwho assumes the machine is down, and does not
  report the users last known to be logged into that machine.
If a user hasn't typed to the system for a minute or more, then
    rwho reports this idle time.
  - -a
- Include all users. By default, if a user hasn't typed to the system for an
      hour or more, then the user will be omitted from the output.
- -H
- Write column headings above the regular output.
- -q
- “Quick mode”: List only the names and the number of users
      currently logged on. When this option is used, all other options are
      ignored.
  - /var/rwho/whod.*
- information about other machines
Therwho command appeared in
  4.3BSD.
This is unwieldy when the number of machines on the local net is large.