How to debug keyboard shortcuts not working?

Question

I'm on XUbuntu 15.10. I noticed that some keyboard shortcuts don't reach my application (Sublime Text).

Ctrl+Alt+p is not visible by the application, while for example Ctrl+Alt+i is recognised correctly.

I tried to debug the problem with xev, here's what I'm seeing.

Ctrl+Alt+i gives me:

KeyPress event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473258, (88,-10), root:(4850,512),
    state 0x0, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473378, (88,-10), root:(4850,512),
    state 0x4, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473530, (88,-10), root:(4850,512),
    state 0xc, keycode 31 (keysym 0x69, i), same_screen YES,
    XLookupString gives 1 bytes: (09) " "
    XmbLookupString gives 1 bytes: (09) "       "
    XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473602, (88,-10), root:(4850,512),
    state 0xc, keycode 31 (keysym 0x69, i), same_screen YES,
    XLookupString gives 1 bytes: (09) " "
    XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473770, (88,-10), root:(4850,512),
    state 0xc, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 473778, (88,-10), root:(4850,512),
    state 0x4, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False

but Ctrl+Alt+P gives:

KeyPress event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 508401, (90,-17), root:(4852,505),
    state 0x0, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyPress event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 508497, (90,-17), root:(4852,505),
    state 0x4, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeymapNotify event, serial 28, synthetic NO, window 0x0,
    keys:  4294967289 0   0   0   32  0   0   0   1   0   0   0   0   0   0   0
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   

KeyRelease event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 508785, (90,-17), root:(4852,505),
    state 0xc, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 28, synthetic NO, window 0x3e00001,
    root 0xf9, subw 0x0, time 508793, (90,-17), root:(4852,505),
    state 0x4, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes:
    XFilterEvent returns: False

No KeyPress or KeyRelease for p, instead there's a cryptic KeymapNotify.

I've looked at xfce4-settings-editor but found no matching key binding there.

Where do I go from here? How can I find what steals this key combination?

Answer 1

I have had a similar issue before. Another application was already using the keyboard shortcut, but it was not showing in Keyboard > Application Shortcuts. Therefore, it could not re-assign.

In Terminal, use your favorite text editor to open the following:

gedit ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml

I assume you want to use ctrl+alt+p. Search for the line with <Primary><Alt>p and delete it. Now try to set your keyboard shortcut for Sublime Text.