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### 4.4 General Notes on Using <NumLock> for the <PF1> Key on Unix Systems

Making the physical <NumLock> key available for use in the EDT Emulation requires some modification to the default X Window settings. Since the keycode assignments vary from system to system, some investigation is needed to see how to do this on a particular system.

You will need to look at the output generated by `xmodmap` invoked with the "-pm" switch. For example, on RedHat GNU/Linux 5.2 on a PC, we get the following output when running ‘`xmodmap -pm`’:

         xmodmap:  up to 2 keys per modifier, (keycodes in parentheses):

         shift       Shift_L (0x32),  Shift_R (0x3e)
         lock        Caps_Lock (0x42)
         control     Control_L (0x25),  Control_R (0x6d)
         mod1        Alt_L (0x40),  Alt_R (0x71)
         mod2        Num_Lock (0x4d)
         mod3
         mod4
         mod5        Scroll_Lock (0x4e)

Note that Num_Lock is assigned to the modifier ‘`mod2`’. This is what hides Num_Lock from being seen by Emacs.

Now, ‘`xmodmap -pke`’ yields:

            .
            .
            .
         keycode  77 = Num_Lock Pointer_EnableKeys
            .
            .
            .
         keycode  96 = F12
            .
            .
            .

So, in RedHat GNU/Linux 5.2 on a PC, Num_Lock generates keycode 77. The following steps are taken:

1. clear the assignment of Num_Lock to mod2;
2. swap the keycodes assigned to F12 and Num_Lock;
3. assign Num_Lock back to mod2.

The `.xmodmaprc` file looks like this:

         ! File:  .xmodmaprc
         !
         ! Set up PC keypad under GNU/Linux for the GNU Emacs EDT Emulation
         !
         clear  mod2
         keycode  77 = F12
         keycode  96 = Num_Lock Pointer_EnableKeys
         add mod2 = Num_Lock

So, after executing ‘`xmodmap .xmodmaprc`’, a press of the physical <F12> key looks like a Num_Lock keypress to X. Also, a press of the physical <NumLock> key looks like a press of the <F12> key to X.

Now, `edt-mapper.el` will see ‘`f12`’ when the physical <NumLock> key is pressed, allowing the <NumLock> key to be used as the EDT <PF1> (<GOLD>) key.