I am looking for a way to control my other computer (win/linux) remotely (ideally via VNC) via USB or serial - without using network or virtual network. It can be fully software based, hardware based or combined.
Do you know about such solution ?
Yes there are VNC based KVMs that rely on seperate programs to be run, client and server style on the 2 computers, They can fully control the other computer & they could pass file data over USB2 at ~25MB/s they neither conflict nor live on the normal network of the system.
They work similar to the old 9pin type Serial based method, which was terribly slow, then parallel method, using the printer type port which was a bit faster e-bay Link for referance ONLY then USB 1.1 boxes that had built in buffers that would do 1.2MB/s. To todays USB2.0 with buffer boxes, and built in flash ram that hold software. USB lap-link for referance ONLY Sometimes called "lap-link" or "Laplink", and dont forget "Easy Transfer" also exists.
Belkin, and IOgear http://www.iogear.com/solutions/kvm/?view=consoleUSB, and some china discount shops, were the last place that I have seen them. As mentioned some times the software was a separate part of the hardware. I have never seen or needed a Windows <--> linux version. USB-links are harder to find, because the method is not recommended everywhere, It is not wireless, and it doesnt say Gig on it :-) I am not recommending it :-) I just use it.
They can control the other computer, with VNC software, through the cables, on all the ones I used I could transfer files also using software file transfer utilities (propriatary stuff for the hardware). http://www.iogear.com/product/GCS661UW6/ Because they use common VNC software, it might be possible to take a winders one, and get it to work on linux, I have no idea how.
How secure they are anymore with all the interconnections in a system, and the fact that they now use modern well known VNC software , altered some for the usb path they take, i do not know.
I have used that method here through all the above versions and revisions of it. It can have terrible software, it can crash, and the in-between buffer/controller can overheat and breakdown. But I would not have it any other way :-) I have moved multiple terrabytes with them.
There is a low chance that a virus can figure out how to spawn itself through it, although the user can easily pass virus filled data around with it.
A KVM over IP solution would allow you to control the "VPN-PC" from a non-VPN-PC. There are some for sale at http://www.kvm-switches-online.com/kvm-switch-over-ip.html
If both machines have serial ports, you can use a crossover cable (aka Null Modem cable). This allows you to connect remotely with standard utilities, like telnet, ssh etc and some remote control programs. A quick goodle search brings up this how-to's: Setup instructions for a serial null modem connection You should be able to find others searching for "Null Modem Connection". PC utilities like CarbonCopy and PCAnywhere used this.