Problems with sharing a directory amongst multiple users (permissions are preserved)

[Brucevdk]

The problem
The most problematic issue I've encountered in trying to make a locally shared directory is that copying files/directories into the shared directory will preserve the existing permissions, both using standard UGO permissions and POSIX ACLs. Manually or even using a cronjob to correct the permissions is obviously not a solution. Also note that I cannot tell the end-user to copy without preserving permissions, I don't have that much control over them.

If somebody were able to present a solution for this issue I'd be satisfied.

I'll summarize several methods which one can use to create a shared directory.

Common methods for sharing directories

Using standard UGO permissions

• Set a default umask of 002 in /etc/login.defs (i.e. umask u=rwx,g=rwx,o=rx
• Add users to a shared group
• Create a directory
• Change the group of the directory to the shared group
• chmod g+s the directory (the setgid bit, the group will be inherited for any created directory/file inside the directory)

However this method is a little bit too inflexible for certain scenarios.

Using POSIX ACLs
For a more extensive discussion, see the following posts: HOWTO: Local shared folder and Re: Permissions on a shared directory.

• Create a directory
• Change the ACLs and default ACLs to allow a shared group (in this case foo) read/write access
  
  • setfacl -m g:foo:rwx && setfacl -dm g:foo:rwx

The default ACL will take care of the permissions.

References

General references
Here are some links that should give you some more insight into the topic.

• Eiciel 0.8 - Users guide (describes POSIX ACLs versus UGO permissions)
• Debian mailing list, Re: Umask 002 policy
• Wikipedia umask
• Launchpad Bug #173267 :Kernel ACL support for NFS/CIFS in 8.04?

Ubuntu Forum discussions
There are several other threads where the topic of creating a shared directory is discussed. However, the reason I have for creating this thread is to for once and for all solve the issue of files/directories preserving their permissions when being copied into a shared directory (thereby not allowing other users access to these files).

• HOWTO: Local shared folder
• Permissions on a shared directory
  
  • Specific post in this thread talking about this issue by user alex.vice.grab
• [IDEA] Easy Shared documents between multiple users
• Shared folder permissions (not samba/nfs)
• acl & permissions for sharing folder on same computer
• Shared folder on single machine
• how to share folders

[TuxCrafter]

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