wall is a command-line utility that displays a message on the terminals of all logged-in users. The messages can be either typed on the terminal or the contents of a file. wall stands for write all, to send a message only to a specific user use the write command.

Broadcasting a Message

The syntax for the wall command is as follows:

wall [OPTIONS] [<FILE>|<MESSAGE>]

If no file is specified wall reads the message from the standard input.

The most straightforward way to broadcast a message is to invoke the wall command with the message as the argument:

wall "The system will be restarted in 10 minutes."

Broadcast message from root@nexonhost.host (pts/0) (Sun Oct  4 19:22:07 2020):

The system will be restarted in 10 minutes.

The message will be broadcasted to all users that are currently logged in.

To see all the logged-in users, run the w or who command.

To suppress the banner and show only the text you types to the logged-in users, invoke the command with the -n (--nobanner) option:
wall -n "The system will be restarted in 10 minutes."

The system will be restarted in 10 minutes.

If you want to write multi-line messages, invoke the command without an argument:

wall

The wall command will wait for you to enter text. When you’re done typing the message, press Ctrl+D to end the program and broadcast the message.

You can also use the here-string redirection or pipe the output of another command to wall. Here is an example showing how to use the echo command to broadcast multi-line messages:

echo "The system will be restarted in 10 minutes. \nPlease save your work."  | wall

Broadcasting a Message From a File

If you are regularly sending the same messages, you can write each one of them to a file, so that you don’t need to re-type the same text. wall reads from the file only when invoked as root.

To broadcast the contents of a file, invoke the wall command followed by the file name:

The system will be restarted in 10 minutes.

wall message1_file.txt

Broadcast message from root@nexonhost.host (pts/0) (Sun Oct  4 19:25:06 2020):

The system will be restarted in 10 minutes.

Broadcasting a Message to a Group

To send a message only to members of a given group, run the command with the -g (--group) option, followed by the group name. For example, to write only on the terminals of the members of the “devs” group, you would run:

wall -g devs "The system will be restarted in 10 minutes."

The group can also be specified by its GID (group ID).

Conclusion

The wall command writes a message on the terminals of all currently logged-in users.