Ubuntu connection woes, device not showing up in lsusb any more I have a really weird issue in connecting my Samsung GS2 to my Ubuntu 14.04 system. 

I found the ID via lsusb at first, and added a udev entry. Everything was perfect and I was happily ADBing away for a few minutes. Thereafter, I begun getting "Unable to mount samsung device" (or something similar) popups. 

Since then, my GS2 doesn't even show up in lsusb. When I plug it in, the phone behaves as if it has just been connected to a wall charger; MTP doesn't work any more, while it used to fine. I've tried removing the udev config file, restarting phone and pc, and enabling/disabling debugging mode, but still there's nothing in lsusb. Everything works perfectly on my other windows machine.

What on earth is going on here?
The most likely cause of the symptoms you describe is that a pin is bent or broken in the USB connection. With the data pin broken but the power pin connected, the connection is exactly as if As it works on a different machine, that would narrow the problem down to the cable (if you are using different cables on each) or the USB port on your PC. Try a different cable and a different USB port.

As your phone works fine with a Windows PC, that rules out it being a problem with Android itself, so if changing the physical connection doesn't help, we probably can't help you any further here.