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Manual Pages  — UNIONFS


unionfs – UNION FS



To compile this driver into the kernel, place the following lines in your kernel configuration file: option UNIONFS

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):



The UNIONFS driver is an implementation of a stackable unification filesystem.




J. S. Pendry, M. K. McKusick, Proceedings of the USENIX Technical Conference on UNIX and Advanced Computing Systems, Union mounts in 4.4BSD-Lite, December 1995.

P. H. Kamp, R. N. M. Watson, Proceedings of the Second International System Administration and Networking Conference (SANE2000), Jails: Confining the omnipotent root, May 2000.


The unionfs device driver first appeared in FreeBSD 5.0 .


The unionfs device driver was written by Jan-Simon Pendry for BSD 4.4 and Masanori OZAWA <Mt ozawa@ongs.co.jp> reimplemented the handling of the locking for FreeBSD 7.0 . The manual page was written by Gordon Bergling <Mt gbe@FreeBSD.org>.


Please see the mount_unionfs(8) manual page for a list of bugs regarding the unionfs filesystem.

UNIONFS (5) April 27, 2020

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