Use setxkbmap to swap the Left Shift and Left Control

xmodmap is obsolete; so indeed it should be done with the xkb tools.

The swap you want seems not to be included by default with X11 files; so you have to write it yourself.

The page https://web.archive.org/web/20170825051821/http://madduck.net/docs/extending-xkb/ helped me to understand and find a way to do it.

Create a file ~/.xkb/keymap/mykbd where you put the output of setxkbmap, it will be your base keyboard definition; eg:

setxkbmap -print > ~/.xkb/keymap/mykbd

then, create a symbols file to define your key swapping, put it for example in ~/.xkb/symbols/myswap

there, put the following lines:

partial modifier_keys
xkb_symbols "swap_l_shift_ctrl" {
    replace key <LCTL>  { [ Shift_L ] };
    replace key <LFSH> { [ Control_L ] };
};

then, edit the ~/.xkb/keymap/mykbd file, and change the xkb_symbols line to add

+myswap(swap_l_shift_ctrl)

finally, you can load it with xkbcomp -I$HOME/.xkb ~/.xkb/keymap/mykbd $DISPLAY (you cannot use "~" for the -I parameter).

It will probably spit a lot of warnings about undefined symbols for some rare keys, but you can ignore them (eg, redirect error to dave: 2> /dev/null).

If you want to be able to easily swap between a normal and your inverted ctrl/shift one; just create under ~/.xkb/keymap/ another file, without the extra "myswap" option, and load it with xkbcomp. You can make two small scripts to load them.

I ran into some issues mapping LALT to Control_L using Pablo's solution, it appears you need to set the modifier_map options as well.

I copied a template from /usr/share/X11/xkb/symbols/altwin - look for xkb_symbols "ctrl_alt_win" - and modified it to set the following changes:

• LALT key to Control**
• LWIN key to Alt
• MENU key to Windows key

The final ~/.xkb/symbols/myswap file was:

partial modifier_keys
xkb_symbols "swap" {
   key <MENU> {     [   Super_L     ]   };
   key <LALT> { [ Control_L, Control_L  ] };
   key <RALT> { type[Group1] = "TWO_LEVEL",
                symbols[Group1] = [ Alt_R, Meta_R ] };
   key <LWIN> { [ Alt_L, Meta_L ] };
   key <LCTL> { [ Control_L ] };
   key <RCTL> { [ Control_R ] };
   modifier_map Control { <LALT>, <LCTL>, <RCTL> };
   modifier_map Mod1 { <LWIN>, <RALT> };
   modifier_map Mod4 { <MENU> };
};

I also added -w0 to the xkbcomp command to avoid any warning output when opening a new shell.

xkbcomp -w0 -I$HOME/.xkb $HOME/.xkb/keymap/mykbd $DISPLAY

**Switching between Mac and Linux a lot, I like to have two control keys on Linux to approximate the Mac keyboard for my muscle memory.