Unionfs: A Stackable Unification File System

This project builds a stackable unification file system, which can appear to merge the contents of several directories (branches), while keeping their physical content separate. Unionfs is useful for unified source tree management, merged contents of split CD-ROM, merged separate software package directories, data grids, and more. Unionfs allows any mix of read-only and read-write branches, as well as insertion and deletion of branches anywhere in the fan-out. To maintain unix semantics, Unionfs handles elimination of duplicates, partial-error conditions, and more. Unionfs is part of the larger FiST project which includes the Wrapfs wrapper stackable file system.

Software Download:

Unionfs releases of kernel code and user-level utilities, as well as snapshots, are available via FTP or HTTP. Full kernel versions patched with Unionfs can be accessed via Git from our git server.

Download Unionfs 2.x with experimental On Disk Format (ODF) support. Read the ODF Design Document.

Unionfs 2.x is maintained in a Git repository. Here are instructions how to check out the latest code with Git.

See list of mirror sites.

Kernel Version Compatibility:

• Latest Stable Code (unionfs-2.6) by kernel version (supported kernels include 2.6.9, and every kernel since 2.6.18).
• All Stable versions of Unionfs, by kernel version.
• All Stable versions of Unionfs, by kernel version.
• Experimental Unionfs ODF 2.x (last was 2.1.1) of Unionfs, by kernel version.
• Old Unionfs 1.x (last was 1.4) of Unionfs, by kernel version. No longer supported.
• Legacy: Old CVS Snapshots: no longer used. Unionfs software is distributed via Git and diff patches.

Mailing Lists:

List Name	Purpose	Who Can Subscribe	Who Can Post	Comments
unionfs	For users' and developers' questions, announcements, bug reports, and general.	Anyone	Subscribers only
unionfs-cvs	For CVS commit logs	Anyone	No one: automated CVS logs only

Miscellaneous:

If you find a problem, please describe it in detail and submit a bug report via Bugzilla.

Some Unionfs users congregate in #unionfs on the FreeNode IRC network.

Users of Real Time (RT) Linux can find additional RT patches for Unionfs.

Various articles and tutorials involving Unionfs:

• Hopeless, a system for building disk-less clusters (Christian Pellegrin, November 2005)
• Unionfs in examples (Tomas Matejicek, July 20, 2005)
• Flavio's TechnoTalk: Filesystem snapshots with Unionfs (Flavio Villanustre, Flavio's TechnoTalk, June 28, 2005)
• Open source opens opportunities (Mark Gibbs, LinuxWorld, April 22, 2005).
• Insight: Open source opens opportunities (Mark Gibbs, TechWorld, April 21, 2005).
• Gearhead: Open source opens opportunities (Mark Gibbs, Network World, April 18, 2005).
• Belarussian translation (Paul Bukhovko, May 8, 2016).
• German translation (Anastasiya Romanova, August 22, 2012).

Projects Using Unionfs:

Journal Articles:

Past Students:

Sponsors: