rwall reads a message from standard input until
end-of-file. It then sends this message, preceded by the
line ``Broadcast Message ...'', to all users logged in on
the specified host machines. With the -n option,
it sends to the specified network groups, which are defined
in
netgroup(NF).
A machine can only receive such a message if it is running
rwalld(NADM).
The timeout is fairly short in order to send to a large
group of machines (some of which may be down) in a
reasonable amount of time. Thus, the message may not get
through to a heavily loaded machine.