I'm running Ubuntu 12.04 and have a multi-button Microsoft mouse. I would like to map the CTRL and ALT modifier keys to the left and right thumb buttons of my mouse, respectively, so I can ctrl-click and alt-click without touching the keyboard. My thumb buttons are buttons 8 and 9. I tried the solution in this question: How do I configure a mouse thumb button? which explained how to map a double click to a thumb button - this worked for the double-click but I couldn't figure out how to modify the solution for CTRL and ALT I also tried this: How to map Ctrl/Shift to thumb buttons of Mouse? which used xdotools and xbindkeys. I modified the script to this: ~/.xbindkeysrc: "xdotool keydown alt" b:9 "xdotool keyup alt" release + alt + b:9 "xdotool keydown ctrl" b:8 "xdotool keyup ctrl" release + control + b:8 Which ALMOST works. It simulates a CTRL-key press when I click the left thumb button, but I can't actually hold the button and click at the same time - holding the thumb button seems to prevent it from listening to other input until it is released. Does anyone know how I can make my mouse thumb button actually work as a modifier key, so I can use thumb_button+click instead of CTRL-click?