At the meeting the other day a member asked about an interesting problem. He has 2 monitors on a linux box and one monitor is in a different room. He wants to be able to see what is on the other-room monitor on the first monitor (monitor the monitor??).
Got the ol' hamster spinning. My hunch that VNC could do it is correct. Here's the solution I just hacked out:
1. install x11vnc package (dnf install x11vnc in Fedora/RH/CentOS; something similar in other distros). install tigervnc package (or any other compatible vnc client).
2. as root: x11vnc -storepasswd -- enter in a pw
3. as root (*might* work as normal user if the stars are aligned?): x11vnc -many -usepw -clip xinerama1 -viewonly -scale 1/4 \ -auth /var/run/lightdm/root/:0 -display :0
4. as normal user: vnc localhost
This will put a little 1/4 scaled copy of the 2nd monitor on your current one.
IMPORTANT: the above -auth voodoo works only for lightdm display manager setups like I use on XFCE. Any other DM will need slightly different voodoo, which you can probably divine by poking around /var/run for dm-sounding entries. There's probably plenty of google hits to help you too.
Notes: - Change xinerama1 to 0 depending on which xinerama screen is which. Any modern non-tweaked linux will use xinerama under the hood for any multi-monitor setup. If for some reason you don't have xinerama then -clip lets you specify actual X,Y WxH coords instead! Neat
- -viewonly is probably what you want, and without it I lost keyboard repeat and if I ventured into the vnc window with the cursor it was very hard to get out again as I entered some sort of recursive dimension effect where many have perished.
- -scale adjust to make it as big/little as you want.
Now, for the ambitious reader: figure out a way to do this with just X (no VNC). I'm thinking something that works like the old xmag but in reverse and with a stationary target? If xmag can do its magic, surely something like this is possible.
For bonus points, figure out how you can do this in wayland. BZZZZZZZ. Trick question, it's almost certainly impossible (though I could be proven wrong). If you're using wayland (i.e. new install of F25) then read the docs on how to switch back to X and then curse wayland three times while spinning in circles on the spot. Good for the soul.
(P.S. You might want to block external port 5900 (but not loopback!) with iptables on your box if it's world-accessible... default vnc security stinks.)