Currently there is no way to easily share files between multiple local users. I am talking about full read-write access to particular folder, eg. music folder.
Example: Alice and Bob uses the same computer. Alice has read access to Bob's home folder. Bob has read access to Alice's home folder. They want to fully share (read/write) their music. So they should ideally create /home/music folder, put all the music there and use it. Everything Bob puts into there, Alice should be able to read and remove, and vice versa. This is currently impossible in Ubuntu. Bob has to manually fix permissions every time Alice wants to delete something Bob's (Bob creates /home/music/Britney, but Alice can't delete /home/music/Britney/song1.mp3).
I have discussed this issue with several linux gurus and there is currently no easy nor difficult way to achieve this in Linux on the same (ext3) partition. With every proposed solution I can give you counterexample (group permissions, ACLs, local Samba, local NFS, etc - there is always problem when moving files). There would have to be created utility to set shared folders and some daemon would have to monitor changes and modify permissions.
Currently the easiest solution known for me is to share files on separate (ironically) NTFS partition, because when mounting NTFS you can force user/group/permissions on file access. What a shame, we use Microsoft technologies just to share files between Ubuntu users.
This problem is quite serious, give it a thought or two. Everyone who is not using Ubuntu computer alone and wants to share music/films/etc between multiple users knows what I am talking about.
//New info:
Atany has proposed in the comment that BindFS project can be used to achieve this functinality:
http://code.google.com/p/bindfs/
I have tried it and it works very well. Developers which would like to implement this idea should have a look on BindFS, it's very promising tool, it could provide all necessary background for this.
Developer comments
The proposed inotify/chmod hack in
https://wiki.ubuntu.com/LocalFileShare would probably work to some degree, but I think it is subject to race conditions, and also not very flexible.
A slightly better solution would IMHO be to provide the shared directory through FUSE; then we can impose dynamic size limitations (at most use 2/3 of the available space in /home, etc.), fine-grained dynamic permissions, and avoid a lot of inotifying and permission race conditions.
Once this is solved and provided by default, we should reconsider "
#6106: Make so other people cant access your home directory", which we didn't do yet in order for people to be able to share files r/o.
