Select menu Alt right mouse 279.b


i have blender 279b
linuxx mint
and a problem with select menu
becouse for to activate select menu is necessary the shortcut :
Alt right mouse

and when i writ alt Alt Right Mouse
open this menu

i try to see in user preferences the shortcut
but i dont see where is.
It should to stay in object or in wiew 3 d


+1 for Pixelfox’s answer. It makes more sense to change it for the system itself, and also easier as it’s not the only shortcut that clashes with the system.