Problem: The USB ports on a modern linux PC do not always show up with the same port numbers if you unplug/replug the device. (It is a dynamic allocation by design.) This is an issue for things like logging software which is configured to look for my K1EL USB Winkeyer on a certain port. Sometimes it works, sometimes it doesn't until I change the port number. (I am running Ubuntu 12.04, 12.10, and 13.04 as I type this.)

Resolution: I added a UDEV rule to create a symbolic link between the usb product tied to the exact serial number of the USB device and a simple name like "KX3" or "WINKEYER"

Now I can point my software at the simple name without needing to know about the port info. This is typically just a problem when I am adding/removing USB devices but it happens often enough to be a PiA. In the past I had just dealt with it an update the configuration… now it is seamless to me.

It was about a 5 minute fix once I read through a couple of articles to explain the how & why.

http://www.linuxforu.com/2012/06/some-nifty-udev-rules-and-examples/

http://manpages.ubuntu.com/manpages/quantal/en/man7/udev.7.html

http://hintshop.ludvig.co.nz/show/persistent-names-usb-serial-devices/

You can use the following two commands to get more info about the USB port:
udevadm info -a -n /dev/ttyUSB0 | grep '{serial}' | head -n1
udevadm info -n /dev/ttyUSB0 -a

I then created called /etc/udev/rules.d/99-usb-serial.rules with my product info

Screen Shot 2013-10-26 at 5.19.45 PM.png

You are looking for the idVendor, idProduct, and serial key values and then you can put what ever name you want into the symlink field. If you unplug & replug the the USB device and then ls -la /dev you should see the device listed twice; once with the ttyUSB0 id, and the second time with the symbolic link name.

It is a quick & simple hack that restores some level of simplicity back to the software stack that wants to look at a stack location.