Bdtyktl

Notice: As of 2013, Ubuntu and derivatives no longer use xmodmap, but instead use xkb. For more information see this answer. The answer below is no longer relevant for current releases.

For remapping certain keys you need two tools. First xev (command-line tool) and second xmodmap (also command-line tool). Both should be available in Ubuntu without extra installing them.

1. Start terminal window and run xev. Now it's active and waits for you to press a key. Then press the key whose behaviour you want to change. i.e. PgUp.



2. 
   

   xev will output some information about the pressed key. The third line is important. It should look similar to:

   
   
   

   state 0x10, keycode 110 (keysym 0xff55, Prior), same_screen YES,
   
   

   
   
   

   in this example Prior is the name of the behaviour the key is assigned to at the moment, the number keycode is the internal id to recognize the key.
   Now do this with another key i.e. PgDown give this output

   
   
   

   state 0x10, keycode 115 (keysym 0xff56, Next), same_screen YES,
   
   

   
   
   

   Here again the interesting part for us is keycode 115 and Next - the name of the behaviour.

   
   


3. 
   

   now when you want to swap the two keys use xmodmap.

   
   
   

    xmodmap -e "keycode 110 = Next"
   
   

   
   
   

   This changes the key with keycode 110 on your keyboard to the action Next. It's pretty simple.

   
   
   

   Note that if the key you are mapping should have a different meaning when used with the Shift key (for example for British keyboard layouts, Shift+2 gives quotation marks) then you can simply list the secondary command after the first. For example if you want the key with code 53 to map to backslash normally, but to the bar symbol when used with shift, you might do:

   
   
   

    xmodmap -e "keycode 53 = backslash bar"
   
   

   
   

Additional information: The sequence of these mappings is Key, Shift+Key, mode_switch+Key, mode_switch+Shift+Key, AltGr+Key, AltGr+Shift+Key. To skip a column use NoSymbol. Moreover, here is a comprehensive list of all keysyms.

Note: These change are for the active X session only and will be lost after reboot.
When you want to save the changes permanently you have to run the following commands after the ones above:

xmodmap -pke >~/.Xmodmap

(it creates a file named .Xmodmap in your home directory (~))

Then you have to create a file named .xinitrc in your home directory where you put command xmodmap .Xmodmap in.

You can now modify .Xmodmap and run xmodmap .Xmodmap from console to see the changes immediately. The changes in .Xmodmap will persist.

source: Ubuntu Foruns

Bonus stuff:

If the key you are remapping has different behavior depending on a state (
like how the keys in the numeric keyboard depend on NumLock) you simply have to do xmodmap -pm to get a list of modifiers and then do:

xmodmap -e "KEYCODE MODIFIER = behaviour behaviour_with_modifier"

Suppose, for example, that you want to get a period instead of a comma on the numeric keyboard (useful for most programmers), but you want to keep the "delete" behavior when NumLock is off.

xmodmap -e "keycode 91 mod2 = KP_Delete period"

mod2, because xmodmap -pm tells us that mod2 is Num_Lock, the other names are obtained by pressing the keys in xev.

If you're trying to move a Shift key, there are a few extra steps:

 xmodmap -e "keycode 62 = Up" # Shift => Up

 xmodmap -e "keycode 111 = Shift_R" # Up => Shift

 xmodmap -e "add shift = Shift_R" # Make the new Shift key actually do shifting

 xmodmap -e "remove shift = Up" # Prevent the old Shift key from shifting

 xset r 62 # Make the new Up key autorepeat

 xset -r 111 # Prevent the new Shift key from autorepeating

I've just had an afterthought.. I think you may mean something entirely different by "remap".. but I'll leave my answer as it is... (I don't know how to re-assign one key to behave as another)

UPDATE: my 'afterthought' has been confirmed; ( I've answered the wrong question :)... please see NES's Community Wiki answer (accepted above).

There are two general ways to remap rebind a key.

• locally to a particular program
  
  (a key can be used for different things in different apps/windows)


• globally for a specific user
  
  (a key has the same function in all windows)

For 'local to a program' methods, there is sometimes a way to change keybindings offered by the app itself... eg.

Firefox has an addon called keyconfig ... for some info see this MozillZine post

Most Ubuntu programs are Gnome based and there is a specific utility to modify the keybinding for any menu item of these Gnome apps... It is called Editable Menu Accelerator ... It is a very 'touchy' tool, but quite powerful.. You can enable it by running gconf-editor (via Terminal or Alt+F2)... navigate to desktop--gnome--interface and select can_change_accels .... You can then change menu items to virtual anything you like (per program/window)... I suggest you disable it as soon as you've done what you need..

Otherwise you can set up Global hotkeys. I use a program called xbindkeys , and there is also an option available via the Main Menu -- Preferences, called Keyboard Shortcuts

If you use xbindkeys, you will need to add it to your "Startup Applications" (Main Menu -- Preferences) ... Also (as suggested by Stefano Palazzo) I have previously written a more detailed description of xbindkeys in an answer on this askubuntu page

Here is how I tried to switch the mapping of the ENTER key to the SHIFT key
(and vice versa):

$ uname -a

REPORTS:

Linux box 2.6.32-37-generic #81-Ubuntu SMP Fri Dec 2 20:35:14 UTC 2011 i686 GNU/Linux



$ which xmodmap

REPORTS:

/usr/bin/xmodmap



$ which xev

REPORTS:

/usr/bin/xev



$ xev

(ignore the next fifty lines or so)

PRESS THE ENTER KEY (notice the third line):

KeyPress event, serial 33, synthetic NO, window 0x5600001,

    root 0x110, subw 0x0, time 263441120, (738,242), root:(771,314),

    state 0x0, keycode 36 (keysym 0xff0d, Return), same_screen YES,

    XLookupString gives 1 bytes: (0d)

    XmbLookupString gives 1 bytes: (0d)

    XFilterEvent returns: False



KeyRelease event, serial 33, synthetic NO, window 0x5600001,

    root 0x110, subw 0x0, time 263441271, (738,242), root:(771,314),

    state 0x0, keycode 36 (keysym 0xff0d, Return), same_screen YES,

    XLookupString gives 1 bytes: (0d)

    XFilterEvent returns: False



PRESS THE SHIFT KEY (notice the third line):

KeyPress event, serial 30, synthetic NO, window 0x5600001,

    root 0x110, subw 0x0, time 263592202, (464,368), root:(497,440),

    state 0x0, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,

    XLookupString gives 0 bytes:

    XmbLookupString gives 0 bytes:

    XFilterEvent returns: False



KeyRelease event, serial 33, synthetic NO, window 0x5600001,

    root 0x110, subw 0x0, time 263592298, (464,368), root:(497,440),

    state 0x1, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,

    XLookupString gives 0 bytes:

    XFilterEvent returns: False

What's important is the third line of each keypress:

FOR:

state 0x0, keycode 36 (keysym 0xff0d, Return), same_screen YES,

The name "Return" is the name of the behavior of the key pressed.

The number of the key pressed is "36".



state 0x0, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,

The name "Shift_R" is the name of the behavior of the key pressed.

The number of the key pressed is "62".

REVERSE THE MAPPING:

$ xmodmap -e "keycode 62 = Return"

$ xmodmap -e "keycode 36 = Shift_R"

SAVE THE RESULTS:

$ xmodmap -pke > ~/.Xmodmap

$ vi ~/.xinitrc

ADD

 xmodmap ~/.Xmodmap



$ sudo reboot

The main problem was that the reversal did NOT work.
The ENTER key was mapped to the SHIFT_R key; but the SHIFT_R key was not mapped to the ENTER key. Go figure.