Hi there,

I'm trying to merge some users shared folders with read only permission, to allow each user to only see/copy/download shared files of other users.
If I understand well aufs "whiteout", I don't want it. I just want users to not be able to delete anything through aufs, without "hiding" files they tried to delete.

So I tried this :

Each user has 2 folders in his /home/user/sub/ : "SharedFolder" and "OtherUsers" (read only access to the merged SharedFolder of other users).
*Note : each user's home is mounted on a different LV (LVM)

At first it seems to work nicely. But sometimes when a user deletes one of his file in /home/user/SharedFolder the file seems to be deleted from his LV and disappears from all aufs mounts, but the LV space of the user who deleted the file is not free up... It seems to be random, maybe older files are more problematic than recent ones but idk.
When I dismount all aufs mount the LV disk space is freed instantly.

What am I doing wrong ? Is there any other way than aufs to do this ?
Many thanks in advance!

So the folders are at the same PC as I can see. Why are you using autofs at all? You can simply add all users to a group 'users'. Then recursively change the group of users home folders and its contents to 'users' and recursively set the content permissions to read-only for the group. Finally make symlinks in each user's home directory to other user's home folders.

I thought an union file system would be better in my case cause I need my users to be able to access a merged shared folders via ftp, sftp and a web file manager app. Plus, when users and apps add files to their shared folder the ownerships/permissions are set by default.
And I also thought 1 symlink was not able to point multiple folders exactly like they were merged (that's what I read). But idk I'm a newbie... I tried to use them at the beginning, but rapidly abandon them for bind mounts.

Bind mounts work perfectly and are very easy for that : no need to manage permissions/ownership or anything else in my case. Users can directly read only other users files via ftp/sftp/web apps, any modification on one side is immediately reflected on the other side. But each user needs 1 mount point for each other user.
So I would need something that acts exactly like a bind mount but with the capability to display the contents of several directories (like they were merged) from only 1 mount point. That's why I thought an union file system would be the easiest way to achieve this.

Edit :
I forgot that my own user (lets say user1) had a bind mount to another user's home sub-folder :
I'm wondering if a bind mount pointing the parent folder of an aufs mount could cause the problem ?
I'll dismount the mount bind, then remount all aufs ones to see if the problem still occurs in the next days/weeks.

It's feasible using symlinks, though if you absolutely want to create a merged folder it will require more work. A possible approach can be found there
Just think about is it really necessary to have a merged folder? Wouldn't it be more usefull to have different subfolders for each user inside a folder?

Thanks redfox, I'll first see if the problem persists (see my edit). I may also try mergerFS I heard of, but if it fails too, then I'll look to the approach with symlinks.

And yes it's necessary for me, cause users can already list all the shared files in a web app library, but are unable to know the ownership (or real locations) of each file. So without merged folders, they would have to manually try every user's shared folder to find a specific file through the web file-manager/ftp.