I would like to give another member of my household (who has access to my computer and has an account on it) access to a particular folder & its contents. Simple enough: select the desired folder and command-I, and then "Sharing and Permissions" at the bottom of that window.
But I do NOT want to give the other user access to the parent directory (or directories), so how can the user actually navigate to the desired folder (the one to which they've been given permissions) ?
One thing that seems to work is to give the user permission on the desired folder, then give them permission on the parent folders (in this case, my home directory, as the folder in question is only one layer down in the hierarchy), have them select the desired folder and put it in their Finder sidebar, and then withdraw permissions from the parent folder. But is this a robust solution, might their access via their Finder sidebar vanish ? It seems to survive reboot, but what about other things such as an OS update ?
chmod o+xon the parent folders should be enough. But if they have a login on your Mac they may have other ways to access your data, or the can reboot into recovery (as you wrote yourself). So if you want to protect data you'll need an encrypted DMG or similar