Greeting,

This is my first post to this list, I'm hoping for some insight into a 
vexing problem.

My situation is 4 computers running various operating systems: Ubuntu, 
Scientific Linux 6.2, Debian Squeeze, MacOS X lion, and Windows 7. All 
except the Mac and one Ubuntu are multiple boot and used for cross 
platform development and testing.

I have a manual switch box with computers on ports 1-4 and a powered USB 
hub with mouse, keyboard, scanner, microphone and a USB headset adapter.

There is also an HDMI and DVI switch box but they are not part of of the 
problem. Together they give me a more flexible KVM switch. I can watch a 
long running job on Monitor #2 connected to one system while working on 
another using Monitor #1.

When I boot up everything works fine. I can also switch between systems 
freely. However if I leave one of the Linux systems disconnected for a 
long while it doesn't respond when I switch back to it. I have not seen 
this behavior with Windows or Mac. The Mac is sometimes disconnected for 
days but Windows usually gets booted back into Linux when I'm done with it.

SL6 usually dies but I can usually ssh into Ubuntu and reboot cleanly.  
SL6 doesn't respond to pings or ssh.  As long as I keep the switch box 
on SL6 it has run for weeks.

Now I have tried 2 different USB switch boxes and when it doesn't 
respond it doesn't respond even if I plug the hub, or the mouse and 
keyboard directly into the usb ports on the system. I don't believe it 
has anything to do with the KVM the OP mentioned or my switch boxes.

Searching the web I found a comment that said a powered hub per system 
worked with his USB KVM switch. I suspect we're seeing some sort of USB 
timeout. I suppose I can get a powered hub per system but I built these 
machines with 6 or 10 USB 2 and 2 or 4 USB 3 ports so I really don't 
need them. The powered hub may however convince Linux that there is 
something plugged into that port and keep it alive.

Does anyone know of a reason for this or even better a fix for it?

Thanks
Joe