Issue with DB9 RS232-USB adapter

June 4th 2016

When i bought my Cisco Router and Switch I had to get an RS232 to USB adapter, because my PC doesn't have any serial port, to connect to Cisco CLI. On the Internet you can find pretty cheap Serial to USB adapter. So I bought one on Ebay and found out that the adapter didn't work on Ubuntu 14.04. I used dmesg that leds me discovering that the chinese adapter uses chip ch341 (instead of the ftdi_sio drivers supplied by the seller).

I started searching and found out, on this page, that the driver for the chip ch341 is bugged on Ubuntu 12.04 and 14.04 (I confirm the bug also in Ubuntu 16.04).

The linked guide didn't work on my Ubuntu (I have Ubuntu 14.04 with Xenial kernel version). A friend of mine, Valerio De Benedetto, helped me to solve that problem and he compiled the patched driver. So you can either follow the linked guide or download the patched driver.

If you decide to download the patched driver, you must compile it for your Kernel Version. So click here and download the sources of your Kernel Version. Afer that, extract the archive and go to drivers/usb/serial and copy all the contents (except for ch341.c) into the folder where the downloaded patched driver sits. Finallly, type this commands:

Move into directory where the downloaded driver sits
make -C /lib/modules/$(uname -r)/build M=$(pwd) modules
sudo cp ch341.ko /lib/modules/$(uname -r)/kernel/drivers/usb/serial/ch341.ko
sudo rmmod ch341
sudo modprobe ch341

That's all.