What is in the "machine-id" file? Is it readable?
I may even have one on the desktop (Ubuntu), but I can't be bothered turning it on at this time of night just to look for that.
Yes you have this file. It is part of Linux and, very possibly, all other OSs.
If you run
$ man machine-id
you will get a man page for it. Didn't give me a clue as to what it is actually good for.
If you run
$ cat /etc/machine-id
you will get output of a 32 alpha/numeric character string. This is the unique, supposedly anyway, machine-id for your system.
If you look it up online you will find a lot of content on it but nothing that seemed to me to explain what the damned thing is actually for or why they tell you that you shouldn't disclose this in public which is the reason I am not posting my output of that file.
All I know is that I have checked via the cat command 3 of my installs and they do indeed have different output that seems to be persistent.
Some function(s) must call on this for some reason.
Running on the popular OwnBox brand computer; AMD 6 core 3.5GHz, 8G ram, 3 500G HDD and 1 320G HDD, antique SB Audigy1 card, cheap old Radeon HD 6450