write a message to all users
wall [-n] [-t timeout] [-g group] [message|file]
wall displays a message, or the contents of a file, or otherwise its standard input, on the terminals of all currently logged in users. The command will wrap lines that are longer than 79 characters. Short lines are whitespace padded to have 79 characters. The command will always put a carriage return and new line at the end of each line.
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 set-user-ID or set-group-ID.
-n,--nobanner Suppress the banner.
-t,--timeouttimeout Abandon the write attempt to the terminals after timeout seconds. This timeout must be a positive integer. The default value is 300 seconds, which is a legacy from the time when people ran terminals over modem lines.
-g,--groupgroup Limit printing message to members of group defined as a group argument. The argument can be group name or GID.
-V,--version Display version information and exit.
-h,--help Display help text and exit.
Some sessions, such as wdm, that have in the beginning of utmp(5) ut_type data a ':' character will not get the message from wall. This is done to avoid write errors.
A wall command appeared in Version 7 AT&T UNIX.
The wall command is part of the util-linux package and is available from https:// www.kernel.org /pub /linux /utils /util-linux/ Linux Kernel Archive .