Setting default permissions for newly created files and sub-directories under a directory in Linux?

Question

I have a bunch of long-running scripts and applications that are storing output results in a directory shared amongst a few users. I would like a way to make sure that every file and directory created under this shared directory automatically had u=rwxg=rwxo=r permissions.

I know that I could use umask 006 at the head off my various scripts, but I don't like that approach as many users write their own scripts and may forget to set the umask themselves.

I really just want the filesystem to set newly created files and directories with a certain permission if it is in a certain folder. Is this at all possible?

Update: I think it can be done with POSIX ACLs, using the Default ACL functionality, but it's all a bit over my head at the moment. If anybody can explain how to use Default ACLs it would probably answer this question nicely.

Answer 1

To get the right ownership, you can set the group setuid bit on the directory with

chmod g+rwxs dirname

This will ensure that files created in the directory are owned by the group. You should then make sure everyone runs with umask 002 or 007 or something of that nature---this is why Debian and many other linux systems are configured with per-user groups by default.

I don't know of a way to force the permissions you want if the user's umask is too strong.