Xmodmap clear modifier not working

keyboard shortcutsxkb

Trying to understand XKB and how to customize keyboard mappings, specially for modifiers.

A little experiment on disabling modifiers, leads to an unexpected result:

(1) Modifier maps before

$ xmodmap -pm
xmodmap:  up to 4 keys per modifier, (keycodes in parentheses):

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

(2) Clear lock modifier

$ xmodmap -e 'clear Lock'

(3) Cleared ok

$  xmodmap -pm
xmodmap:  up to 4 keys per modifier, (keycodes in parentheses):

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

I expected to disable CapsLock from setting the lock state, but it does't.
It works as usual, and using xev to see the key press events, I see that the lock flag still changes (state 0x0 when CapsLock is off, state 0x2 when on).

What is actually the clear command doing?

How can I detach keys(keycodes) to disable their function as modifiers?

Best Answer

Actually, CapsLock functionality is bound to keysym value of pressed key. To see mapping of keycodes to keysyms execute xmodmap -pke. The mapping of CapsLock (keycode 66) should be (| grep 'keycode 66'):

keycode  66 = Caps_Lock NoSymbol Caps_Lock

You may play around a bit with xev. Read more at ArchWiki: Xmodmap#Introduction.

How can I detach keys(keycodes) to disable their function as modifiers?

You need to change mapping of CapsLock.

To disable CapsLock, you need to unmap it:

xmodmap -e 'keycode  66 = NoSymbol NoSymbol NoSymbol'

To enable CapsLock, you need to map it again to default values:
```
xmodmap -e 'keycode  66 = Caps_Lock NoSymbol Caps_Lock'
```

What is actually the clear command doing?

It clears mapping of a modifier, not mapping of keycodes. More at ArchWiki: Xmodmap#Modifier_keys

Related Solutions

How to get keycodes for xmodmap

There are a lot of players between your keyboard and the process that finally handles the keyboard event. Among the major pieces of the landscape are the fact that the X system has its own keyboard-handling layer, and X associates different "keycodes" with keys than your Linux base system does. The showkey command is showing you the keycodes in Linux-base-system lingo. For xmodmap you need the X keycodes, which are what xev is displaying. So long as you're planning to work in X and do your key rebinding with xmodmap, then, ignore showkeys and just listen to what xev says.

What you want to look for in your xev output are blocks like this:

KeyPress event, serial 27, synthetic NO, window 0x1200001,
    root 0x101, subw 0x0, time 6417361, (340,373), root:(342,393),
    state 0x0, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 27, synthetic NO, window 0x1200001,
    root 0x101, subw 0x0, time 6417474, (340,373), root:(342,393),
    state 0x8, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

xev tends to generate a lot of output, especially when you move your mouse. You may have to scroll back a while to find the output you're looking for. In the previous output, we see that the keysym Alt_L is associated with the X keycode 64.

Best Answer

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How to get keycodes for xmodmap

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