Why does US International Keyboard break Alt_R

Question

All adding the U.S. English International (with dead keys) keyboard layout breaks my Alt_R key. Any ideas why?

I'm working on RHEL 5.5 using GNOME. The problem disappears if I remove the additional layout and reappears if I add it back.

Specific problems include Alt-F2 not working to start the run application app if using Alt_R and CTRL-Alt-L not working for screen looking again if using Alt_R.

I tried using xev to troubleshoot. Here's what I get with just the U.S. English layout:

KeyPress event, serial 29, synthetic NO, window 0x1e00001,
    root 0x3a2, subw 0x0, time 1766794207, (169,-13), root:(2099,35),
    state 0x0, keycode 113 (keysym 0xffea, Alt_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 29, synthetic NO, window 0x1e00001,
    root 0x3a2, subw 0x0, time 1766794447, (169,-13), root:(2099,35),
    state 0x8, keycode 113 (keysym 0xffea, Alt_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False  

Here's what I get with the U.S. English International (with dead keys) layout:

KeyPress event, serial 26, synthetic NO, window 0x1e00001,
    root 0x3a2, subw 0x0, time 1766853750, (169,-13), root:(2099,35),
    state 0x0, keycode 113 (keysym 0xffea, Alt_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 29, synthetic NO, window 0x1e00001,
    root 0x3a2, subw 0x0, time 1766853872, (169,-13), root:(2099,35),
    state 0x80, keycode 113 (keysym 0xffea, Alt_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

It makes no difference whether that layout is actually being used at the moment. Just having it in the selected list breaks things. If this is a bug, does anyone know where it should be filed (GNOME, Xorg, Redhat)?

EDIT: I realized now that I can see my modifier mapping using xmodmap. Initially, mod5 was mapped to mod5 Mode_switch (0x5d) and ISO_Level3_Shift (0x7c). Adding the international layout, maps Alt_R (0x71) to mod5 as well, which why I'm having this problem. Based on Caleb's recommendation, I switched Alt_R to be an ISO_Level3_Shift such that mod5 is now mapped to "mod5 Mode_switch (0x5d), ISO_Level3_Shift (0x71), ISO_Level3_Shift (0x7c)". This still breaks Alt_R as an Alt_L alternative though.

Answer 1

On most international layouts, Alt_R becomes an AltGr (alternate group?) key, otherwise known as a 3rd level chooser that gives you access to alternate letters, symbols, accents etc. Even though the keycode you are seeing is not properly remapped to this, I suspect the layout is EXPECTING it to be is hiccuping on the keycode.

I suggest you look through the other tabs of gnome keyboard options and manually setup an AltGr key, maybe as that one, so the international layout will work to full effect.

Answer 2

Most keyboard layouts outside the U.S. attribute the right Alt key to a different purpose, called AltGr (Alt Graph), which sort of makes the U.S. the exception to the rule. The AltGr key is sort of another kind of Shift key, intended to select extra characters available on the other keys. See the Wikipedia article on AltGr.

So, if you want to issue a key combination with the Alt modifier, like Alt-F2 or Ctrl-Alt-L, be sure to press the left Alt key, since the right one has another purpose. It is just in the U.S. English layout that has no other use for that key that reassigns it (or better, keeps the original old assignment) as an additional Alt key. Even the British English layout uses AltGr to issue characters like “€” and “£”.