rwall reads a message from standard input until EOF. 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.

-n netgroup

Send the broadcast message to the specified network groups.

-h hostname

Specify the hostname, the name of the host machine.

See attributes(5) for descriptions of the following attributes:

inetd(1M), listen(1M), pmadm(1M), sacadm(1M), wall(1M), attributes(5)

The timeout is fairly short to allow transmission 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.