The default X server configuration varies from distribution to
distribution and release to release of GNU/Linux. If your system fails
to recognize the keypad keys as distinct keys, change the NumLock state,
turning it on or off, as the case may be, then try again. If this
doesn't solve your problem, you may have to modify the X keysym mappings
with xmodmap.
On one distribution on an Intel PC, the following .xmodmaprc set things up nicely.
! File: .xmodmaprc
!
! Set up PC keypad under GNU/Linux for the Emacs EDT Emulation
!
clear mod2
keycode 77 = F12
keycode 96 = Num_Lock Pointer_EnableKeys
add mod2 = Num_Lock
In this example, after feeding the file to the xmodmap command,
the PC <NumLock> keypad key will be configurable for the emulation
of the <PF1> key. The PC keypad can now emulate an LK-201 keypad
(less the comma key), the standard keyboard supplied with DEC terminals
VT-200 and above. This .xmodmaprc file switches the role of the
<F12> and <NumLock> keys. It has been tested on RedHat
GNU/Linux 5.2. Other versions of GNU/Linux may require different
keycodes. (Unix for further help on how to do this.)
Please note: Remember, it may be necessary to have <NumLock> in one position (ON) or the other (OFF) for the PC keypad to emulate the LK-201 keypad properly.