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I have multiple users on my system. I'd like to have shared directories like music, video. pictures etc. The problems is that I want users to be able to write any new files to any directory, but not be able to delete or modify any files they don't own. With standard unix perms if you can add a file to a directory you can also delete others. I'd also like to make sure all the files in these directories are always readable by the user group.

Can I do this with POSIX ACL's? or do I need something more advanced like SELinux (or other security framework).

example of what I don't want to work.

su - root
mkdir /home/music
chmod 775 /home/music
chgrp users /home/music
su - user1 /home/music
touch /home/music/testfile
ll /home/music/testfile
su - user2
rm /home/music/testfile
ll /home/music
share|improve this question
You are right, I deleted the wrong answer. – fschmitt Oct 10 '10 at 19:28
@fschmitt yeah you can't write to the other persons file (modify it) but that unfortunately doesn't prevent you from deleting the last reference to it. – xenoterracide Oct 10 '10 at 19:38
up vote 8 down vote accepted

If I understand you correctly you want for your music/video etc. directories the same semantic as for /tmp.

For this, you could put the sticky bit on the directories. To quote from the chmod man-page:

RESTRICTED DELETION FLAG OR STICKY BIT The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type. For directories, it prevents unprivileged users from removing or renaming a file in the directory unless they own the file or the directory; this is called the restricted deletion flag for the directory, and is commonly found on world-writable directories like /tmp.

share|improve this answer
hmm... I didn't realize that's part of what the sticky bit does... I will have to test it. – xenoterracide Oct 10 '10 at 19:42
I guess I forgot that's what it's for... I think this is an adequate solution. /me -- for overthinking the issue – xenoterracide Oct 10 '10 at 19:57

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