How unique is /dev/serial/by-id

Question

So, the question is, is the content of /dev/serial/by-id unique?

Essentially the issue is I want to connect several (two or more) arduinos (potentially of different types, but they may all end up being leonardos) to the Raspberry Pi for the purposes of an automation system.

I'll be using the serial interfaces to communicate between the Raspberry Pi in Python and the Arduinos. I've run this on one of the leonardos (at present I only have one):

udevadm info -a -n /dev/ttyACM0| grep serial  
0000:00:1d.0

Is this a unique serial for my serial connection to the Pi? Can I rely on this to create a UDEV rule to assign a particular mount point, or does a unique and reliable mount point get already created in /dev/serial/by-id/, which I can use instead of hacked-udev rules?

Answer 1

In my experience using /dev/serial/by-id with USB devices has been unique. That is true as long as the manufacturer follows "the rules" about giving each device a unique serial number.

I just make symlinks to those long names in /dev/serial/by-id and use my symlinks as the handles for my serial devices in scripts. No muss, no fuss, NO UDEV.

Answer 2

It's NOT ALWAYS unique. In my experience, if you bought a cheap arduino clone from China, they mostly didn't bother to generate unique ID for every devices. The same applies for every devices. If the manufacturer didn't bother, then the devices will be identical. I ended up just using the by-path and symlink it.

Answer 3

The rules for the naming are in

/lib/udev/rules.d/60-persistent-serial.rules