I am on Linux Mint 17.2 (Cinnamon as DE) (with kernel 18.104.22.168 installed and loaded) and I'm getting this message when trying to add a PPA via the terminal: Cannot add ppa: 'no json object could be decoded'. What is the cause and what is the fix? Secondly, I think I installe GzDoom correctly) but I get: Something went wrong! If you haven't installed any Doom IWAD files yet or if GZDoom is unable to locate them, put the files or symlinks to them in '/home/dlf/.config/gzdoom' or start the game with the command 'DOOMWADDIR=/path/to/iwadfiledir gzdoom'. . . . So where do I put the files (IWAD? pk3?) I'd presume something like: /home/dlf/.config/gzdoom. And how could I get Wolfenstein 3d/SOD/Quake working with (G)zdoom. I'm on Linux Mint 17.2 with cinnamon (as the desktop environment) if it matters.