wall command in Linux with Examples

wall command in Linux system is used to write a message to all users. This command displays a message, or the contents of a file, or otherwise its standard input, on the terminals of all currently logged in users. The lines which will be longer than 79 characters, wrapped by this command. Short lines are whitespace padded to have 79 characters.

A carriage return and newline at the end of each line is put by wall command always. Only the superuser can write on the terminals of users who have chosen to deny messages or are using a program which automatically denies messages. Reading from a file is refused when the invoker is not superuser and the program is suid(set-user-ID) or sgid(set-group-ID).

Syntax:

wall [-n] [-t timeout] [message | file]

where,

• message: The string of text you want to broadcast to all users. You can directly type the message or redirect it from a file.
• file: A file containing the message to broadcast.
• OPTION: Various options that modify the behavior of the wall command.

Key Options used with the wall command

1. wall -n:

Suppress the default banner, so the message is displayed without the standard header.

wall -n

2. wall -t:

This option will abandon the write attempt to the terminals after timeout seconds. This timeout needs to be a positive integer. The by default value is 300 seconds, which is a legacy from the time when peoples ran terminals over modem lines.

Example:

wall -t 30

3. wall -V:

This option display version information and exit.

wall -V

4. wall -h:

Show help information about the wall command and its options, then exit.

wall -h

Conclusion

The wall command is an essential tool for system administrators who need to communicate system-wide messages to all logged-in users. Whether it's a scheduled maintenance notification, emergency shutdown alert, or a general announcement, wall ensures that the message reaches every user in real-time. With its syntax, flexible options like timeouts and banners, and the ability to broadcast from files, wall is a must-know command for any Linux administrator.