Write a message to all users' terminals
The wall command is used to send a message to all users currently logged into the system. It displays the message on every terminal that is set to receive public messages. If no message is provided as an argument, the wall command reads from standard input until an EOF character is received.
wall [message]
message: The broadcast message to be sent.
[root@localhost ~]# wall this is a test line
Broadcast message from root (pts/1) (Fri Dec 20 11:36:51 2013):
this is a test line