On Mac using terminal and "chown" command I can set owner for a folder like this:

sudo chown -R _www somefolder

However this replaces me with _www. I.e. I'm not in the list of owners anymore.

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I then have to open folder properties in Finder, add myself as a second owner and set permissions using the GUI.

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And this is what the ACL looks like:

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Is there a way to add TWO owners using terminal? In other words how to add a second owner to a folder using terminal? Not necessarily chown.

PS: Just in case.. on the screenshots users "_www" and "Oleg (Я)" have permissions "Read and write".

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    How do the permissions of the file with two owners look like in terminal. I doubt the Mac does this via POSIX file attributes, but via some ACL stuff. – Philippos Feb 9 '18 at 14:01
  • You can't add a second owner. You may check for ACLs, if ordinary group-based security permission is not enough. You may also consider to own the file by a third user (root, nobody, or any neutral third account), and giving the access to both of users by group-based rules or by acls. – peterh - Reinstate Monica Feb 9 '18 at 14:25

Found the answer (type this in Terminal):

sudo chmod +a 'Oleg allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity' somefolder

Where 'Oleg' is a user name and 'somefolder' is a folder name in question.

The permissions inside single quotes after the 'allow' keyword are just copied from the output of ls -le

Now both users '_www' and 'Oleg' can read, write files and subdirectories, etc.

That was the intention.

Strictly speaking yes, you can not add a second "owner" in POSIX attributes sense, e.g. via Chown.

However in Mac you can give owner-like permissions to numerous users via ACL like Philippos commented (thanks for hinting).

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This is not possible because a Unix file have one owner, try to use a group instead.

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  • Side note: surprising, but in Unix, the Owner and the Group are both a single integer, and nothing forbids for multiple users to have the same user-id. Thus, in the view of the kernel permission checking, there is no essential difference between uid and gid. – peterh - Reinstate Monica Feb 9 '18 at 14:23
  • @peterh "two users" with the same uid are not "two users" but one user with two names. The uid is what defines a user, not the name. Also, "there is no essential difference between uid and gid" is just nonsense - were you drunk when you wrote that? – cas Feb 10 '18 at 1:59

this is a xy-problem

X:problem, how can two user access same file, with same right ?

solution I use multiple chown => Y:problem

Solution for X problem

according to http://aplawrence.com/MacOSX/acl.html

you can use

 chmod +a "allow Oleg list,search,add_file,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,writesecurity,chown"
 chmod +a "allow _www list,search,add_file,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,writesecurity,chown"

I can't test it right now, I don't have mac OS 10.5 available.

You might replace the long string above with the result of ls -e

Y:solution: I try to use multiple chown.

This is not possible: Unix/Linux/OS X's file have only one owner at a time.

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