KVM/Scroll Lock behavior

Todd Pytel tppytel at sophrosune.org
Thu Jan 19 05:41:14 PST 2012

On Thu, 2012-01-19 at 10:34 +0100, Samuel Thibault wrote:
> These are extremely surprising. I'd have thought that KVM uses the
> keyboard *keypresses*, not the LED changes, to achieve the switch...

Especially since it's not *just* the LED's that matter - otherwise it
would work after xmodmap. So, it's not just the LED's and not just the
keypresses. Very strange indeed.

It would be interesting to know whether this is standard KVM behavior.
They pretty much all use Scroll Lock, but I imagine that they could be
built on a variety of cheap, undocumented chips that exhibit different
quirks like these.

> I guess if you use setleds in the Linux console, the KVM switches too?

Yes, just checked it out. I forgot about setleds before.

> You could try to use strace to check the system call difference between
> lighting scroll lock through the key and through xset, but in principle
> there is none, thus the surprise with 3) vs 4) above.

I've straced binaries before, though the output tends to be over my
head. I could do that with xset, but what process would I strace to
follow the keypress? X? That seems likely to produce an insane amount of


More information about the xorg mailing list