This question already has an answer here:
- Mapping key combination with xmodmap 2 answers
I recently moved to Linux from OSx and in there I had mapped Caps lock to Ctrl+b. This was mostly done because of tmux.
How can I do this in Ubuntu 14?
There is a very comprehensive answer here how to remap keys: https://askubuntu.com/questions/296155/how-can-i-remap-keyboard-keys
But this doesn't cover a key combination like Ctrl+b. It only covers remaping a single key to another key.