Posted by Sven Crouse on Apr 14, 2011; 12:26am
URL: https://forum.world.st/mouse-buttons-in-Linux-deleting-certain-morphs-tp3447821p3448506.html

Mariano Martinez Peck:
"Settings -> System -> Keyboard -> Control and Alt keys..."

changes the modifier key, but I'm looking not to have to use a modifier
with a multiple button mouse.  

Markus Schlager:
"shift + middle button"

does bring up the halo allowing me do what I could not before.

So for any other beginners on Linux, middle button requires the use of
the shift modifier key and right button requires the use of the control
key or whatever modifier might be chosen from "Settings -> System ->
Keyboard -> Control and Alt keys".

Thanks for the replies,

Sven