In linux/*nix, if your user have access to wall command, you can broadcast message to all users. Here is how to do it :
- in console, type : wall and hit enter
- directly type your message. for multiple line message, just hit enter and continue typing
- once you are done with your message, press Ctrl button together with D
- message will be sent to all users
If you don’t want to display your username in the message, in step 1 use wall -n instead
That is how easy to use wall command in linux to broadcast message.