Re: how to share a directory tree with files in it with multiple users (Re: [gentoo-user] local shared directory)

[Michael Orlitzky <mjo@gentoo.org>]

On 04/23/2016 10:42 AM, hw wrote:
> 
> Has it become entirely impossible to share a directory tree and the 
> files in it with multiple users when Linux is involved?  This should be 
> a very simple thing to accomplish.
> 

It was never possible. It's ridiculous, but there it is. The UNIX
permissions model is too simple. ACLs were bolted on top, but most tools
retain legacy behavior with respect to group masks that breaks default
ACLs. You're seeing that same problem with your Samba share.

Filesystem permissions are one thing that Windows got right. There's
ongoing work to bring that model to Linux,

  https://en.wikipedia.org/wiki/Richacls

but they're going to make the same mistake again[0] and allow the group
bits to act as a mask. That means mkdir, tar, cp, 7z -- anything that
tries to mess with group bits -- isn't going to work. They'll be DOA
just like POSIX ACLs were.

I think you can manage this with incron and POSIX ACLs. Instead of
running "chmod g+w", use sys-apps/apply-default-acl to reset the
permissions to the defaults that you set.

I wrote apply-default-acl to solve exactly this problem. You just need
to figure out a way to run it whenever things get screwed up. Which
means, whenever a file or directory is created.


[0] http://www.bestbits.at/richacl/man/richacl.7.txt

 Changing the file mode permission bits:

  When changing the file mode permission bits with chmod(1), the
  owner, group, and other file permission bits are set to the
  permission bits in the new mode... In addition, the masked and
  write_through ACL flags are set. This has the effect of limiting the
  permissions granted by the ACL to the file mode  permission bits...