Goal

I would like to get the Thumb Button on my Logitech MX Master mouse to work under Ubuntu 17.10. Specifically, I want it to serve as a "Meta" key, by which I mean pressing it will show me all the open programs at that moment (this is called exposé in Mac computers).

I'm pretty stuck at this point. I'm not an advanced user, and need some help. Thank you in advance!

What I have tried so far:

• I have attempted to follow this guide. I installed xbindkeys, xautomation, and x11-utils. Unfortunately, because the thumb button does not emit a specific button press in xev, I am unable to move forward.


• I have also tried using this guide, found in the Arch Linux forums. The author correctly identifies that the button is not received as a button, but rather seems to be some synthetic key press. I tried copying & pasting, but it didn't work.

Xev Results

These are the results that I receive when I use xev to map the input generated by the thumb button press.

FocusOut event, serial 38, synthetic NO, window 0x5000001,

    mode NotifyUngrab, detail NotifyPointer



LeaveNotify event, serial 38, synthetic NO, window 0x5000001,

    root 0x2a1, subw 0x0, time 18824278, (162,35), root:(1276,64),

    mode NotifyGrab, detail NotifyNonlinear, same_screen YES,

    focus NO, state 20



EnterNotify event, serial 38, synthetic NO, window 0x5000001,

    root 0x2a1, subw 0x0, time 18824342, (162,35), root:(1276,64),

    mode NotifyNormal, detail NotifyNonlinear, same_screen YES,

    focus NO, state 16



KeymapNotify event, serial 38, synthetic NO, window 0x0,

    keys:  1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   

           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   



FocusIn event, serial 38, synthetic NO, window 0x5000001,

    mode NotifyGrab, detail NotifyPointer



KeymapNotify event, serial 38, synthetic NO, window 0x0,

    keys:  4294967201 0   4294967168 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   

By default, a Ctrl+Alt+Tab event is sent after releasing the thumb button.

Since this shortcut is not really useful for me I managed to add a new action for it thanks to xautomation (sudo apt-get install xautomation) :

• Go to Settings > Keyboard > Shortcut and add a new personal shortcut.


• Give it the name you want and the following command : xte 'usleep 100000' 'keydown Super_L' 'key S' 'keyup Super_L'
  


• Click on your new shortcut to assign a new trigger and press the thumb button (or press Ctrl+Alt+Tab)

That's it !

With a Logitech Master MX 2s, I am using @Jdlm 's approach above but with a simpler command binding:

xte 'key Super_L'

This is working fine in ubuntu 18.04, and is a bit more snappy than the original answer

The command xbindkeys -k helps you to determine what you need to set in its config file under ~/.xbindkeysrc.

An example entry:

# Logitech special thumb button

"/usr/bin/xdotool key Super_L+c"

    m:0x1c + c:23

    Control+Alt+Mod2 + Tab

It helps you to make use of this special thumb button.

The example turns the special button into a Win+C, which shows all open windows on my desktop.

xbindkeys

xbindkeys is a program that allows you to launch shell commands with
your keyboard or your mouse under the X Window System.
It links commands to keys or mouse buttons, using a configuration file.
It's independent of the window manager and can capture all keyboard keys
(ex: Power, Wake...).

It optionally supports a guile-based configuration file layout, which enables
you to access all xbindkeys internals, so you can have key combinations,
double clicks or timed double clicks take actions. Also all functions that work
in guile will work for xbindkeys.

To install xbindkeys type:

 sudo apt install xbindkeys

I managed to fix it, as you guys mentioned the thumb button on this model triggers the Control + Right Alt (aka AltGr) + Tab combination in linux.
So go to Settings > Keyboard > select Navigation Switch system controls
Change its shortcut to some other key binding and replace the default. (I changed to Shift + Control + Tab)
Once you replaced this binding (Control + Right-Alt (aka AltGr) + Tab) with a new one, this combination (and the thumb button) is available to be set on another shortcut option.
Move to System Show the overview and set a new shortcut, do this clicking on the MX's thumb button.
No dependencies on any configuration edit is needed, it works like a charm on Ubuntu 18.04 LTS.

Seems like thumb button on MX Master sends Ctrl+Alt+Tab shortcut as you release it in Linux.

So you may install

sudo apt-get install compizconfig-settings-manager

Launch it and then go to > Window Management > Scale > Bindings > Initiate Window Scale

You should change keyboard shortcut since Thumb button is basically keyboard emulation and map it to Ctrl+Alt+Tab.

Note: it will replace your current Ctrl+Alt+Tab behaviour which is set to Switch to next window by default.

I used the same answer as @Jdlm, but whenever I went to reassign the CTRL+ALT+TAB shortcut, it kept triggering it.

I had to switch the Switch System Controls shortcut under navigation so it wouldn't be triggered. After that, I could reassign it to whichever xte shortcut I wanted.