What are c: and m: in xbindkeys configuration?

Question

In the default example configuration for xbindkeys, there is an example of specifying keycodes directly:

# set directly keycode (here control + f with my keyboard)
#"xterm"
#  c:41 + m:0x4

What do the c: and m: mean? The documentation for xbindkeys does not shed any light on this.

Also, I know you can use xbindkeys -k to find the codes for a key. If that does not work (for one of the nonstandard fn keys, the command does not respond to the keypress and it instead does its normal action), does that mean that xbindkeys cannot handle that key? Even if I know the keycode from showkey -k (217 in my case)?

Answer 1

c:41 + m:0x4 is whatever xbindkeys -k reports when you press the key that you want to bind.

If that does not work (for one of the nonstandard fn keys, the command does not respond to the keypress and it instead does its normal action), does that mean that xbindkeys cannot handle that key?

Probably, yes.

However, there's a chance that you can make it work, depending on what part of the system “steals” the key.

If it's an X11 application, stealing the key is called “grabbing”. Unfortunately, identifying who's grabbing a key is difficult. If you manage to disable the grab then xbindkeys will get its own chance to grab it.

If it's not an X11 application (or even if it is), check the system logs to see if anything is logged when you press the key. If there are any, this will give you a big clue as to who's handling the key press.

Even if I know the keycode from showkey -k (217 in my case)?

That's not the key code you want. showkey shows the Linux keycode, but Xorg has its own keycodes. The Xorg keycodes are normally shifted by 8, to the key code is probably 225. But xbindkeys -k is the way to show the key code, and if that doesn't work, it means xbindkeys can't detect your key.

Answer 2

This doesn’t seem to be documented, but the three modifiers b:, c:, and m: introduce numeric values, respectively for mouse buttons, key codes, and the modifier mask. So

c:41 + m:0x4

means “the key with code 41” (f on your keyboard) with modifier 4, i.e. Ctrl. The modifier values are defined in /usr/include/X11/X.h:

/* Key masks. Used as modifiers to GrabButton and GrabKey, results of QueryPointer,
   state in various key-, mouse-, and button-related events. */

#define ShiftMask               (1<<0)
#define LockMask                (1<<1)
#define ControlMask             (1<<2)
#define Mod1Mask                (1<<3)
#define Mod2Mask                (1<<4)
#define Mod3Mask                (1<<5)
#define Mod4Mask                (1<<6)
#define Mod5Mask                (1<<7)

I’m not certain of the answer to your second question, but you should try with c:217.