Aufs

Another Union File System (Aufs) is an advanced multi-layered unification filesystem. Aufs was originally a re-design and re-implementation of the popular UnionFS, however after adding many new original ideas it became entirely separate from UnionFS. Aufs is considered a UnionFS alternative as it supports many of the same features. Currently Aufs is in version 3.

Features
 * The ability to unite several directories into a single virtual filesystem. Calling the member directory as a branch.
 * Specification of the permission flags on each branch (readonly, readwrite, and whiteout-able.)
 * Via upper writable branch, internal copyup and whiteout is possible (files and directories on the readonly branch are logically modifiable).
 * Dynamic branch manipulation (add, delete, etc.).

Installation
Currently, the Aufs3 package is the only version of Aufs in the Portage tree.

Alternatively, it is possible to emerge the in order to build a kernel with the Genpatchset and aufs3 support already applied:

See the aufs-sources entry in the kernel overview for more information.

There are several USE flag options for Aufs:

External Resources
Aufs at SourceForge