在root权限下用编辑器打开/etc/X11/xorg.conf文件，找到InputDevice字段，如下：
锟斤拷锟斤拷:Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
Option "Device" "/dev/input/mice"
Option "Protocol" "ImPS/2"
Option "Emulate3Buttons" "true"
Option "ZAxisMapping" "4 5"
EndSection
添加红色的那行，并保存。重启之后，鼠标中键有效。