2.1.5 Assignment of the SUPER and HYPER Keys

Most keyboards do not, by default, have SUPER or HYPER modifier keys. Under X, you can simulate the SUPER or HYPER key if you want to bind keys to sequences using super and hyper. You can use the xmodmap program to do this.

For example, to turn your CAPS-LOCK key into a SUPER key, do the following:

Create a file called ~/.xmodmap. In this file, place the lines

        remove Lock = Caps_Lock
        keysym Caps_Lock = Super_L
        add Mod2 = Super_L

The first line says that the key that is currently called Caps_Lock should no longer behave as a “lock” key. The second line says that this should now be called Super_L instead. The third line says that the key called Super_L should be a modifier key, which produces the Mod2 modifier.

To create a META or HYPER key instead of a SUPER key, replace the word Super above with Meta or Hyper.

Just after you start up X, execute the command xmodmap /.xmodmap. You can add this command to the appropriate initialization file to have the command executed automatically.

If you have problems, see the documentation for the xmodmap program. The X keyboard model is quite complicated, and explaining it is beyond the scope of this manual. However, we reprint the following description from the X Protocol document for your convenience:

A list of keysyms is associated with each keycode. If that list (ignoring trailing NoSymbol entries) is a single keysym ‘K’, then the list is treated as if it were the list ``K NoSymbol K NoSymbol''. If the list (ignoring trailing NoSymbol entries) is a pair of keysyms ‘K1 K2’, then the list is treated as if it were the list ``K1 K2 K1 K2''. If the list (ignoring trailing NoSymbol entries) is a triple of keysyms ‘K1 K2 K3’, then the list is treated as if it were the list ``K1 K2 K3 NoSymbol''.

The first four elements of the list are split into two groups of keysyms. Group 1 contains the first and second keysyms; Group 2 contains third and fourth keysyms. Within each group, if the second element of the group is NoSymbol, then the group should be treated as if the second element were the same as the first element, except when the first element is an alphabetic keysym ‘K’ for which both lowercase and uppercase forms are defined. In that case, the group should be treated as if the first element were the lowercase form of ‘K’ and the second element were the uppercase form of ‘K’.

The standard rules for obtaining a keysym from a KeyPress event make use of only the Group 1 and Group 2 keysyms; no interpretation of other keysyms in the list is given here. (That is, the last four keysyms are unused.)

Which group to use is determined by modifier state. Switching between groups is controlled by the keysym named Mode_switch. Attach that keysym to some keycode and attach that keycode to any one of the modifiers Mod1 through Mod5. This modifier is called the group modifier. For any keycode, Group 1 is used when the group modifier is off, and Group 2 is used when the group modifier is on.

Within a group, which keysym to use is also determined by modifier state. The first keysym is used when the Shift and Lock modifiers are off. The second keysym is used when the Shift modifier is on, or when the Lock modifier is on and the second keysym is uppercase alphabetic, or when the Lock modifier is on and is interpreted as ShiftLock. Otherwise, when the Lock modifier is on and is interpreted as CapsLock, the state of the Shift modifier is applied first to select a keysym, but if that keysym is lower-case alphabetic, then the corresponding upper-case keysym is used instead.

In addition to the above information on keysyms, we also provide the following description of modifier mapping from the InterClient Communications Conventions Manual:

X11 supports 8 modifier bits, of which 3 are pre-assigned to Shift, Lock, and Control. Each modifier bit is controlled by the state of a set of keys, and these sets are specified in a table accessed by GetModifierMapping() and SetModifierMapping().

A client needing to use one of the pre-assigned modifiers should assume that the modifier table has been set up correctly to control these modifiers. The Lock modifier should be interpreted as Caps Lock or Shift Lock according to whether the keycodes in its controlling set include XK_Caps_Lock or XK_Shift_Lock.

Clients should determine the meaning of a modifier bit from the keysyms being used to control it.

A client needing to use an extra modifier, for example Meta, should:

1. Scan the existing modifier mappings.
   1. If it finds a modifier that contains a keycode whose set of keysyms includes XK_Meta_L or XK_Meta_R, it should use that modifier bit.
   2. If there is no existing modifier controlled by XK_Meta_L or XK_Meta_R, it should select an unused modifier bit (one with an empty controlling set) and:
2. If there is a keycode with XL_Meta_L in its set of keysyms, add that keycode to the set for the chosen modifier, and then:
   1. If there is a keycode with XL_Meta_R in its set of keysyms, add that keycode to the set for the chosen modifier, and then:
   2. If the controlling set is still empty, interact with the user to select one or more keys to be Meta.
3. If there are no unused modifier bits, ask the user to take corrective action.

This means that the Mod1 modifier does not necessarily mean Meta, although some applications (such as twm and emacs 18) assume that. Any of the five unassigned modifier bits could mean Meta; what matters is that a modifier bit is generated by a keycode which is bound to the keysym Meta_L or Meta_R.

Therefore, if you want to make a META key, the right way is to make the keycode in question generate both a Meta keysym and some previously-unassigned modifier bit.