How to unlock 5th generation iPod Nano
Solution 1:
The first trick was to remember where I put the cable, which is apparently called the "Apple 30-pin cable".
Having the original Mac or iTunes was not necessary. I plugged the iPod in to a Linux device (although this should also work from any Mac with a Terminal window). I located where the device was mounted (let's say it was /Volumes/iPod) and then ran the following command in a terminal:
rm /Volumes/iPod/iPod_Control/Device/_locked
I then ejected the device and it was unlocked!