Determining hotkey strings

The process of determining the appropriate string to put in a hotkey line in your config can be a bit non-obvious -- on X11, xev and xmodmap can help.

First, pick which physical keys on your keyboard you want to act as your hotkey combination (one non-modifier key and zero or more modifier keys). Start xev and press each of these keys individually, noting what keysym each one comes out as (things like, say, Super_L or h or F3). Your non-modifier key will appear in the hotkey string exactly as it does in xev's output. For the modifier keys, you'll need to trace them through your xmodmap to determine what "logical" modifier they map to. To do this, run xmodmap, and for each modifier keysym you found through xev, find the logical modifier (things like control or shift or mod2) in the first column of the line containing the desired keysym. Then just concatenate all the resulting strings together with + as a separator to produce the string to put in your hotkey config line.

Full example: I run xev and see that for my hotkey combination I want the keysym Left with the modifier keysyms Control_L and Alt_L. I then run xmodmap, which shows the following:

[me@host: ~]% xmodmap 
xmodmap:  up to 3 keys per modifier, (keycodes in parentheses):

shift       Shift_L (0x32),  Shift_R (0x3e)
lock      
control     Control_L (0x25),  Control_L (0x42),  Control_R (0x69)
mod1        Alt_L (0x85),  Alt_R (0x86),  Alt_L (0xce)
mod2        Num_Lock (0x4d)
mod3      
mod4        Super_L (0x40),  Super_R (0x6c),  Super_L (0xcc)
mod5        ISO_Level3_Shift (0x5c),  Mode_switch (0xcb)

From that, we see that Control_L maps to control and Alt_L maps to mod1. The resulting config line might then look like hotkey["control+mod1+Left"] = switch left.

Note that while the modifier names are matched case-insensitively (mod1 and Mod1 are equivalent), Xlib matches the keysym name for the non-modifier key case-sensitively, so be sure to use e.g. Left and not left.

If you don't have xev or xmodmap installed, the name of the relevant package may vary depending on your system. For the three I have on hand at the moment, these are:

     | RHEL6                    | Debian Jessie     | FreeBSD 10

--------:|:------------------------:|:-----------------:|:-----------: xev | xorg-x11-utils | x11-utils | xev xmodmap| xorg-x11-server-utils | x11-server-utils | xmodmap