wall — Send a message to everybody’s terminal.Summary : Wall sends a message to everybody logged. The length of the message is limited to 20 lines. You MAY need root permission, on some system, to run this command. This command is used to pass the some critical information to all. Examples :
# wall "Welcome" -- Send the string "Welcome" to all. # wall < mesg.txt -- Send the file content to all. # wall -- Enter the message in stdin and terminate with Ctrl+D.
Read : man wall