msconfig —
Show or change the middle button emulation mode
  
    | msconfig | [ -fmouse-device]
      [on|off] | 
msconfig is used to modify or examine the state of the
  middle-button emulation mode of the NetBSD/Atari mouse
  driver. When msconfig is used without the
  on|off parameter, it prints the current state of the
  emulation mode. The default mouse device is
  /dev/mouse. This can be overridden by means of the
  -f option.
When the emulation is turned on, a middle-button event can be
    generated by simultaneously pressing the left and right buttons. When turned
    off, a middle-button event is generated by pushing the fire-button of
    joystick1. Note that you'll need a special type of mouse to use this.
The msconfig command appeared in NetBSD
  1.3