which wall
/usr/bin/wall

In ancient times (xdm, X11, fvmw*) I used to send myself messages out of scripts using /usr/bin/wall .
So I knew that e.g. a job is finished or some action to be taken.
This message showed up on all consoles and xterms or similar.

Recently I tested with wall to learn about progress of a script, but lightdm traps the message .
Does not show up on an open mate terminal.
Actually lightdm traps the message.
It shows then up on logout from Xorg and keeps the xserver to restart.
Manually I must do

service lightdm restart 

to get a fresh login window until I logout again. Same game.

wall used to inform users  from impending administration actions like shutdown or restart.
This function has been destroyed from the new habit of lightdm.

Apart from being a bug.
Now I have to find where this messages hang and they should be deleted on a restart of xserver.

It seems that the new generation of maintainers has no idea about multiuser systems.