How to use set-user-ID bit on directories?

Question

I want all files in directory /home/alex/foo to be owned by alex, no matter who creates them. I'm trying this technique, but it doesn't work (on CentOS 5, under root):

$ cd /home/alex
$ mkdir foo
$ chmod u+s foo
$ chown alex foo
$ ls -al . | grep "foo"
drwsr-xr-x  2 alex root      4096 Nov 14 14:18 foo
$ echo "test" > foo/test.txt
$ ls -al foo
total 12
drwsr-xr-x  2 alex root   4096 Nov 14 14:19 .
drwxr-x--- 13 alex root   4096 Nov 14 14:18 ..
-rw-r--r--  1 root root      6 Nov 14 14:19 test.txt

As you see, the file is owned by root, but should be owned by alex. What am I doing wrong?

You know you can do `ls -ld foo` instead of using `grep`? – Dennis Williamson Nov 14 '10 at 15:52 — Dennis Williamson, Nov 14 '10 at 15:52

score 3 · Accepted Answer · answered Nov 14 '10 at 14:25

3

setuid on directories does not work like setgid on directories in *nix.

answered Nov 14 '10 at 14:25

Ignacio Vazquez-Abrams

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to expound, an average user (not root) doesn't have the permission to set a file as another's userid. Technically this is CAP_FOWNER (and maybe CAP_FCHOWN) and as far as I'm aware, root is the only user with a CAP_FOWNER capability in Linux. – Nov 14 '10 at 14:43
1

You mean that my use case is not going to work, by design? – yegor256 Nov 14 '10 at 15:14
That is correct. – Ignacio Vazquez-Abrams Nov 14 '10 at 15:17

How to use set-user-ID bit on directories?

1 Answers1