[svlug] KVM problems

Dan Martinez dfm at area.com
Tue Aug 20 14:54:47 PDT 2002

Josh wrote:

> When I switch to linux using the kvm switch, if linux is running X,
> it screws up the mouse, causing wild movements and uncalled-for
> spontaneous clicking. Here's a sample scene:
> <1> I'm in windows. Everything is working normally. I decide to go
> configure sendmail, because I love doing it so goddamn much.
> <2> I switch to linux on my KVM. I see KDE 3.01 in all it's glory.
> <3> I move the mouse. Two context menus appear and the panel slides
> out of view.
> <4> I become confused and move the mouse again. The cursor moves
> wildly, the panel slides back in and the K menu pops up. An
> application asks me if I want to save before closing.
> <5> I remember that my kvm switch sucks, kill X via ctrl-alt-bkspc,
> put a different mouse on the linux box and restart X.
> So, I have a functional install now, in that I can make things work,
> but I have a profusion of mice - I count three on my desk at this
> writing - a problem that the kvm switch was supposed to fix. What do
> I have to do to use just one mouse? Anyone else ever have this
> problem - actually, I know at least one other person that does, so
> it's not just me.

I've had this problem, too. The root cause is that the Explorer
supports multiple versions of the PS/2 mouse protocol: one in which it
behaves like an older member of the MS mouse family, for backward
compatibility, and one in which the fourth and fifth button are

When talking to Windows, it goes into the latter mode; when you switch
to Linux, X tries to talk to the mouse using the older protocol, but
the mouse has already decided that it's using the newer one. Much
confusion ensues.

What Protocol is X configured to use with your mouse? You might try
specifying "ExplorerPS/2" instead, and seeing if that helps.

The solution I resorted to, back when I grappled with this problem,
was to take the plunge and switch to USB input devices, in conjunction
with a USB KVM switch. (I think that X didn't support the Explorer
protocol back then, so something that effectively dis- and reconnected
the mouse every time one switched between computers was actually the
most expedient solution.)

You may also find the following links helpful as you tweak your
mouse-related configuration. (Note that some of the material is
tailored to FreeBSD, but the X-related parts are at least partly


Good luck,

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