*nix file systems

> Is a *nix file system guranteed to be acyclic?
>
> That is no:
>
> File-a links to file-b and file-b links to file-a
>
> And more important
>
> No directory-a contains link-b where link-b points to directory-a.
>
> Also
>
> Directory-a contains no link-b to directory-c where directory-c contains
> link-d to directory-a.

I think it all depends on which FS you are using. Linux has ext2, ext3 (ext2 +
journalling), XFS, ReiserFS, etc...