Karabiner PID Failure Fix
Run the following commands on Terminal: chflags -R nouchg ~/.local/share/karabiner/pid sudo chmod -R 777 ~/.local/share/karabiner/pid
Just to provide context, the bundle of symptoms this issue comes with is following: Karabiner not modifying keys, cannot open the app without sudo command, sudo Karabiner still doesn’t modify keys.
update Nov 10, 2017: complete overhaul of the post for readability.