The GNU manpage (what you'll find on a Linux system) – but pretty much any Unix manpage – of
chown (the command for changing the owning user and owning group in Unix) appeal to an “owner” and, as you see, the very name of this command hints at “change owner”, too.
When people first learn this, they get the wrong idea, that for the command
chmod (which sets the file/directory permissions), the abbreviation
o (as in
chmod o+w file) stands for “owner / owning user”.
In reality it stands for “other users”. So
chmod o+w file really adds the writing permission (
+w) for other users (who are not the owner or a member of the owning group). It doesn't help that what really refers to the “owner”, namely
u (= owning user), makes it possible for one confusion to give rise to another:
u is then confused for “‘normal’ users”: anybody not the owner or in the owning group.
Sure, it helps to make people directly aware of this, but even if they can remind themselves that there's some trap here, the idea
o = “owner”,
u = “normal users” is so seductive, that they retain some insecurity until enough (sometimes a lot is necessary) rote memorization makes it finally sink in.
What would be a mnemonic or other way to explain it which makes the correct notion stick right from the start, so rote memorization isn't necessary?
PS: I'm not formally teaching anyone, it's just what I want to tell coworkers/friends. When I took a university course on Linux I first came across this confusion. There's a lot more about the Unix permission system which is very counter-intuitive, but those are issues arising necessarily from technical aspects. Not an (surprisingly very) annoying and trivial issue caused by bad historical choices for abbreviations.