Broadcast Message from . . .
If filename is given, then the message is read in from that file. Normally, pseudo-terminals that do not correspond to rlogin sessions are ignored. Thus, when using a window system, the message appears only on the console window. However, -a will send the message even to such pseudo-terminals.
The wall command is used to warn all users, typically prior to shutting down the system.
The sender can use the
file_dac_write privilege to override terminal permissions that users may have set using the mesg command. See the mesg(1) man page. The
file_mac_write privilege can be used to write to terminals whose label is dominated by the sending process.
wall runs setgid() to the group ID tty, in order to have write permissions on other user's terminals. See the setuid(2) man page.
wall will detect non-printable characters before sending them to the user's terminal. Control characters will appear as a " ‸ " followed by the appropriate ASCII character. Characters with the high-order bit set will appear in “meta” notation. For example, `\003' is displayed as `‸C' and `\372' as `M-z'.
The following options are supported:
broadcast message to the console and pseudo-terminals.
broadcast to a specified group only.
If the LC_* variables ( LC_CTYPE, LC_TIME, LC_COLLATE, LC_NUMERIC, and LC_MONETARY ) are not set in the environment, the operational behavior of wall for each corresponding locale category is determined by the value of the LANG environment variable. See environ(5). If LC_ALL is set, its contents are used to override both the LANG and the other LC_* variables. If none of the above variables are set in the environment, the "C" (U.S. style) locale determines how wall behaves.
See attributes(5) for descriptions of the following attributes:
file_dac_write privilege can be used to override terminal permissions that users may have set. Similarly, the
file_mac_write privilege can be used to write to terminals whose label is dominated by the sending
wall displays ``Cannot send to . . .'' when the open on a user's tty file fails.