Linux and Unix wall command
wall writes a message to other users.
wall displays the contents of file or, by default, its standard input, on the terminals of all currently logged in users. The command will cut any lines that are over 79 characters to new lines. Short lines are white space padded to have 79 characters. The command will always put carriage return and new line at the end of each line.
Only the super-user 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 or sgid.
wall [-n] [-t TIMEOUT] [file]
|-n, --nobanner||Supress banner|
|-t, --timeout TIMEOUT||Write timeout to terminals in seconds. TIMEOUT must be positive integer. Default value is 300 seconds, which is a legacy from time when people ran terminals over modem lines.|
|-V, --version||Display version information and exit.|
|-h, --help||Display a help message and exit.|
sudo wall message.txt
Using the sudo command to run wall as the superuser, sends the contents of message.txt to all users.
mesg — Control if (non-root) users can send messages to your terminal.
talk — Talk with other logged in users.
write — Send a message to another user.
shutdown — Schedule a time for the system to be powered down.