KVM switch with FreeBSD-8.2

Polytropon freebsd at edvax.de
Mon Sep 12 19:21:01 UTC 2011

On Mon, 12 Sep 2011 10:45:59 -0700, David Brodbeck wrote:
> On Sun, Sep 11, 2011 at 4:43 PM, Polytropon <freebsd at edvax.de> wrote:
> > On Sun, 11 Sep 2011 15:10:48 -0600 (MDT), Warren Block wrote:
> >> On Sun, 11 Sep 2011, Daniel Feenberg wrote:
> >>
> >> > If you are asking, "Is there a FreeBSD command to cause the KVM switch to
> >> > move to the next system?" then the answer is "I don't know and it would amaze
> >> > me if there were."
> >>
> >> There's often a key sequence to advance to the next port or a specific
> >> port.
> >
> > That can _sometimes_ be a problem when the KVM switch
> > doesn't properly detect this sequence - or maybe the
> > user has already defined that sequence for some action
> > in X, so X "catches" the sequence and acts properly.
> X "catching" the sequence won't stop the switch from reacting to it --
> it's done in hardware in the switch.  But of course X may do something
> undesirable if the switch passes the key combination through.

Yes, I thought of something like that _might_ happen,
depending on the firmware of the KVM switch. You know,
keys that are useful to users may be a first-class
candidate for the manufacturer to say: "Oh look, nobody
uses *that* key, let's hardcode it as switching key!" :-)

> The two most common ones are Ctrl, Alt, Shift (rapidly in sequence)
> followed by a port number, or Ctrl twice.  The latter can be a little
> too easy to trigger accidentally.

Fully agree, that's not very well thought... but maybe
the product designers primarily orient at the "Windows"
main target group that hardly uses the keyboard. :-)

> The USB switches generally emulate a generic USB keyboard and mouse,
> so drivers aren't a problem.  Sometimes they work by simulating a USB
> disconnect from the machine they're switching to, though, so you need
> good keyboard and mouse hotplug support in the OS.

FreeBSD's devd should handle that fine. Also the absense
of a keyboard at system startup shouldn't matter.

> Generally these switches don't react well to having anything but a
> keyboard in the keyboard port and a mouse in the mouse port.  If you
> have a hub built into your keyboard the hub will be useless when
> you're using one of these switches.

Uh, that can be a problem when using professional desktop
equipment, e. g. a Sun keyboard where you can connect the
mouse directly to the keyboard (a feature known from the
Apple ADB configurations of the 80's, if I remember correct-
ly, but Sun also had this functionality in the pre-USB era;
it's also a feature returning in Apple's modern USB products
to attach the short-wired mouse to the keyboard's USB hub).
I furthermore assume using the keyboard's hub for attaching
other USB devices (memory sticks, MP3 players or cameras)
to the keyboard's hub is a no-go then.

Regarding the possible problem with monitors:

As an example, the Nvidia documentation (HTML version located 
at /usr/local/share/doc/NVIDIA_GLX-1.0/html/) contains this
interesting option:

	Option "ConnectedMonitor" "string"

	Allows you to override what the NVIDIA kernel module
	detects is connected to your graphics card. This may
	be useful, for example, if you use a KVM (keyboard,
	video, mouse) switch and you are switched away when
	X is started. In such a situation, the NVIDIA kernel
	module cannot detect which display devices are connected,
	and the NVIDIA X driver assumes you have a single CRT.

Something similar _may_ be useful in case of too much malfunctioning
autodetection magic. :-)

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

More information about the freebsd-questions mailing list