Comment 4 for bug 700316

The network-manager + network-manager-gnome hypothesis may not be true. I encountered this problem with Kubuntu 10.10, which doesn't have the network-manager-gnome package installed. LiveCD test is enough.

How I did the test:

    strace cat /dev/ttyUSB0

When it doesn't work, it gets stuck at:

    open("/dev/ttyUSB0", O_RDONLY|O_LARGEFILE)

When it works, it will go all the way to a "read" operation.

Unloading usbserial and the corresponding modules that depend on it, and then loading them back, fixes the issue until reboot.

Tested with Kubuntu 10.10 LiveCD and desktop install on HDD. Tested with Ubuntu 10.10 LiveCD. Tested with Ubuntu 11.04 alpha1 LiveCD. All of them gave the same experience as described above. I tested on 4 machines: two desktops, two laptops, very different hardware between them. I tested with three different USB serial adapters, each using a distinct kernel driver (pl2303, cp210x, ch341), all with the same result.

I didn't try getting rid of the network-manager package completely though. I'll give that a try, and if it fixes the issue, someone needs a beating, since I was about to start debugging the kernel :)