I have set up my parents with an Ubuntu 14.04 LTS box. In order to assist them, because they are parents, I set up VNC / Desktop Sharing (using the Desktop Sharing GUI) with "Allow others to view..." and "You must confirm access..." and forwarded the relevant ports through their access point, and I have a VNC client on my computer.
The server computer has three users. I've made the Desktop Sharing settings in each user's profile.
The problem is that when I try to connect the VNC, it always directs the VNC request to a certain user, say fred. If a different user is logged in, nothing happens - the message requesting access pops up on fred's desktop, which is inactive, not on the desktop of the active user (so if we switch to fred's login, the access window is there). So it works fine for fred, but not for anyone else. I'm not sure if it matters whether fred is logged in, or if there is some other reason it prefers fred. They tend to switch users, usually leaving the other users logged in in the background.
Any idea how I can direct my VNC actions to certain users, or to whichever one is active? My goal is to use it to assist the person who is currently at the terminal.
EDIT: It depends on which users are logged in. If only one user is logged in, it goes to that person. If there are multiple, it appears to go to whichever was logged in first. So there's a workaround; make sure only one user is logged in. But that's pretty lame. Still investigating...