Two step process:
- Go to your web-browser and search for "postgresql permissions data
directory" - look down the list for the page from the official manuals
(it's the top one for me).
- Read the page from the official manuals and follow the
Presumably it's complaining that it "could not change permissions"
because you aren't running this as user "_postgres". Note - it's normally
user "postgres". I don't know if the name-change is something you've done
or something common on Mac installations.
Oh - and I can't see why this is tagged "linux"