Is it possible to write a shell script that enables any user (may not be root) to set a message(e.g. "Download on progress do not turn off" etc.) which will be conveyed like pop-up message (zenity or notify-send) to all other users. If any user is not there at the time of throwing the message they must get it on login or unlocking their screen.
Nice question. Will give just an half answer... just a seed to see if someone can prepare something starting on this. I have tested this in my system, two users (ubuntu and romano, the two administrators).
I go to a VC and log in as ubuntu --- then I run
sudo sudo -u romano DISPLAY=:0.0 zenity --warning
(the first sudo switch to superuser, the second sudo execute zenity as the user romano)
from a virtual console, the message will appear in "romano" graphical environment.
I suppose that with a bit of mangling the output of w to get the DISPLAY and the users and looping over them it would be possible to have a working solution. Non-graphical connected users can be informed using wall.
I see really difficult to do that without superuser privileges, tough.
