Ubuntu 20.04 with Panda PAU09 N600 Wireless USB dongle

Greetings fellow Linux hackers!

I ran into a rather hard-to-diagnose issue the other day, so I am sharing the details here to help anyone else who runs into the same or a similar problem.

I have a GNU/Linux workstation in my lab that's running Ubuntu 20.04, configured to download and install updates from Canonical as soon as they're available.  The workstation uses a Panda PAU09 N600 wireless USB dongle for Internet access.  The dongle has been working flawlessly for quite some time.

One recent update included kernel/BIOS level updates, so a reboot was needed.  After rebooting, BOOM! my internet connection stopped working.  I narrowed the problem down to something to do with the USB dongle.  

Panda PAU09 Wireless Adaptor

Reviewing dmesg output, I determined there was a driver conflict.  Two separate drivers were competing for the same hardware.  It appears a second driver was provided by Canonical as part of the update, or they changed some configuration files.  Not sure.

Symptom was, dmesg showed an authentication attempt to the wireless router, which was successful, then a bit later, it showed a SECOND authentication attempt, which failed.

Looking carefully, I saw that the first authentication was done by driver rt2800usb, whereas the second attempt was done by rt2x00usb. Two different drivers controlling the same hardware doesn't seem right.

I decided to disable one of them, to see if that would resolve things.  (it did!)

Specifically, I added the following lines to the end of /etc/modprobe.d/blacklist.conf

blacklist rt2x00usb 

blacklist rt2x00lib

One reboot later, my workstation was back on the Internet.

I didn't do a deep dive on why this occurred, or even on if the above is the ideal resolution.

What I do know is, it worked.  Hope this helps.

Happy hacking!

-Paul