wall

Broadcast messages to all logged-in users

TLDR

Send a message to all logged-in users

$ wall [message]

Send a message to a specific group

$ wall -g [group_name] [message]

Send a message from a file

$ wall [file]

Send a message with timeout

$ wall -t [seconds] [file]

SYNOPSIS

wall [options] [message | file]

wall (write all) displays a message or the contents of a file on the terminals of all currently logged-in users. This is typically used by system administrators for system-wide announcements like pending shutdowns.
Messages are preceded by a banner showing the sender and time.

PARAMETERS

-g, --group _group_

Send only to members of the specified group

-n, --nobanner

Suppress the banner

-t, --timeout _seconds_

Timeout for writing to terminals (default 300)

CAVEATS

Users can use mesg n to prevent receiving wall messages. Only root can override this. Messages may interrupt terminal sessions.