mjhjmtu

My mouse has an unfortunate feature. On the left side, right where my thumb sits ever so gently when I'm using it, there are two buttons that are so sensitive a mere brush will make them click.

I'm talking of course about the pesky forward/back buttons which, if pressed in a browser, can make watching that hour-long youtube video that much harder. Is there a way for me to disable them? Would this be handled by X?

Start the program xev in a terminal. Move the mouse inside the xev window; you'll see a lot of stuff scroll by. Press each button in turn. Then switch back to the terminal window and press Ctrl+C. xev shows a description of each input event, in particular ButtonPress and ButtonRelease for mouse clicks (you'll also see a number of MotionNotify for mouse movements and other events).

It's likely that your forward and back buttons are mapped to mouse buttons, maybe buttons 8 and 9:

ButtonPress event, serial 29, synthetic NO, window 0x2e00001,
 root 0x105, subw 0x0, time 2889100159, (166,67), root:(1769,98),
 state 0x0, button 8, same_screen YES

If that's the case, remap these buttons to a different action in your browser; or to disable the buttons altogether, put these lines in a file called ~/.Xmodmap:

! Disable buttons 8 and 9
pointer = 1 2 3 4 5 6 7 0 0

Test it with the command xmodmap ~/.Xmodmap. Most desktop environments and window managers run this command automatically when you log in; if yours doesn't, arrange for it to run when X starts.

It's also possible that your mouse sends a keyboard event when you press these buttons:

KeyPress event, serial 32, synthetic NO, window 0x2e00001,
 root 0x105, subw 0x0, time 2889100963, (957,357), root:(2560,388),
 state 0x0, keycode 166 (keysym 0x1008ff26, XF86Back), same_screen YES,
 XLookupString gives 0 bytes: 
 XmbLookupString gives 0 bytes: 
 XFilterEvent returns: False

In that case, put lines like these in ~/.Xmodmap:

keycode 166 = NoSymbol
keycode 167 = NoSymbol

You could use xev to find which key maps the button maps to and use the code below (in $HOME/.xsessionrc) to map it to something you are not using.

xmodmap -e 'keycode THE_CODE_HERE = XF86Launch1'

Alternatively, you should be able to do that from a GUI of you use Gnome/KDE or any other modern desktops.

Yet another option would be to hack the xorg.conf to remove the button definitions.

Can be done with xorg config file

Here is an example that disable horizontal scroll (Save the new file and reboot)

nano /etc/X11/xorg.conf.d/40-libinput-mouse-left-right.conf

Section "InputClass"
 Identifier "Logitech catchall"
 MatchIsPointer "on"
 Driver "libinput"
 Option "HorizontalScrolling" "false"
EndSection

Other useful commands

xinput list
xinput list-props 15

Now for this question xorg config file can be used to remap button here is an example

Section "InputClass"
 # ...
 Option "ButtonMapping" "1 9 3 4 5 6 7 8 2"
 # ...
EndSection