wall Command
  
  
  Purpose
  
  Writes a message to all users that are logged in.
  
   Syntax
  
  wall [ Message ]
  
  Description
  
  If the Message parameter is not specified, the wall command reads
  a Message from standard input until it reaches an end-of-file
  character.  The message is then sent to all logged in users. The
  message is preceded by the following heading:
  
  Broadcast Message from user
  
  To override any protections other users have set up, you must
  operate  with root user authority.  Typically, the root user uses
  the wall command to warn all other users of an impending system
  shutdown.
  
  Notes:
  
  1.	The wall command only sends messages to the local node.
  
  2.	Messages can contain multibyte characters.
  
  Implementation Specifics
  
  This command is part of Base Operating System (BOS) Runtime.
  
  Files
  
  /dev/tty	Specifies device.
  
  Related Information
  
  The  mesg command,  su command,  write command.