用意

ディレクトリ作成

$ mkdir -p ~/.xkb/keymap ~/.xkb/symbols

現状設定書き出し

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

~/.xkb/symbols/myswap作成

partial modifier_keys
xkb_symbols "myswapkeys" {
  replace key <LCTL> { [ Caps_Lock ] };
  replace key <CAPS> { [ Control_L] };
  key <LALT>  { [ Hiragana ] };
  key <RALT>  { [ Katakana ] };
};

~/.xkb/keymap/mykbdのxkb_symbolsのincludeにmyswap(myswapkeys)追加

xkb_keymap {
    xkb_keycodes  { include "evdev+aliases(qwerty)" };
    xkb_types     { include "complete" };
    xkb_compat    { include "complete" };
#    xkb_symbols   { include "pc+us+us:2+inet(evdev)+ctrl(swap_lwin_lctl)+myswap(myswapkeys)" };
    xkb_symbols   { include "pc+us+us:2+inet(evdev)+myswap(myswapkeys)" };
    xkb_geometry  { include "pc(pc105)" };
};

~~※+ctrl(swap_lwin_lctl)はalt単体で推したときに問題にならないようにするためのworkaround~~

システム反映

.bashrcに追記

xkbcomp -I$HOME/.xkb ~/.xkb/keymap/mykbd $DISPLAY 2> /dev/null

~/.xkb/symbols/myswapをコピー

sudo cp -i ~/.xkb/symbols/myswap /usr/share/X11/xkb/symbols/

/usr/share/X11/xkb/rules/evdev に追記

mysetting:myswapkeys = +myswap(myswapkeys)

gnomeのシステム設定に反映

$ export GIO_EXTRA_MODULES=/usr/lib/x86_64-linux-gnu/gio/modules/ # workaround for the issue* 
$ gsettings set org.gnome.desktop.input-sources xkb-options "['mysetting:myswapkeys']"

the issue*

$ gsettings set org.gnome.desktop.input-sources xkb-options "['mysetting:myswapkeys']"
GLib-GIO-Message: 02:13:03.500: Using the 'memory' GSettings backend.  Your settings will not be saved or shared with other applications.

再起動

設定保持確認