Uh oh, so you're working on some super l33t code or other stuff that is super important and Linux Mint's MATE or Cinnamon window manager freezes. This means maybe you can move your mouse but you can't click anything, you can't Alt + Tab to another program but everything appears to be working other than that.
The first thing you would do is Ctrl + Alt + F1 (or whatever virtual terminal you want) and get into the Linux bash prompt (the black screen where things really happen :))........
I never found a solution to do it live (nothing worked that I found) so it looks like a relogin is required.
Check your maximum file limit
This is different than your actual's user limit which you'll see below
Try and set it higher but it won't work
ulimit -n 65000........
xmessage "Your message here" -display :0
This will popup a window with the message, it would be cool if it allowed two way communication though.
I found the info in this post: http://en.andregondim.eti.br/?p=72........