Ftdi - device or resource busy

Using Fedora 12, my various FTDI devices are inaccessible to any user other than root. Of course I have added my user to the dialout and uucp groups to no avail.

The error message presented by trying to use minicom is:

$ minicom
minicom: cannot open /dev/ttyUSB0: Device or resource busy
$ 

This has been driving me crazy for weeks. I have been using su to access the serial ports, but I have finally found a reason!

In /lib/udev/rules.d/95-devkit-power-wup.rules (or /lib/udev/rules.d/95-upower-wup.rules on Ubuntu 10.04) you may well find the following line:

SUBSYSTEM=="tty", SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A80?????", ENV{...{bla bla}

This line is very over aggressive with its match. The serial number (A80?????) will match far too many devices, and as the Vendor ID and Product ID are that of an FTDI chip... well... It seems that the "Watts Up? Pro" uses an FTDI chip.

My fix is to comment this line out and restart - it worked a treat :D

It might also be worth uninstalling ModemManager if you have it installed...