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+.\" Copyright (c) 2020 Gordon Bergling
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd April 27, 2020
+.Dt UNIONFS 4
+.Os
+.Sh NAME
+.Nm unionfs
+.Nd "UNION FS"
+.Sh SYNOPSIS
+To compile this driver into the kernel,
+place the following lines in your
+kernel configuration file:
+.Bd -ragged -offset indent
+.Cd "option UNIONFS"
+.Ed
+.Pp
+Alternatively, to load the driver as a
+module at boot time, place the following line in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+unionfs_load="YES"
+.Ed
+.Sh DESCRIPTION
+The UNIONFS driver is an implementation of a stackable unification filesystem.
+.Sh SEE ALSO
+.Xr mount_unionfs 8
+.Sh STANDARDS
+.Rs
+.%T Union mounts in 4.4BSD-Lite
+.%A J. S. Pendry
+.%A M. K. McKusick
+.%R Proceedings of the USENIX Technical Conference on UNIX and Advanced Computing Systems
+.%D December 1995
+.Re
+.Pp
+.Rs
+.%T Jails: Confining the omnipotent root
+.%A P. H. Kamp
+.%A R. N. M. Watson
+.%R Proceedings of the Second International System Administration and Networking Conference (SANE2000)
+.%D May 2000
+.Re
+.Sh HISTORY
+The
+.Nm
+device driver first appeared in
+.Fx 5.0 .
+.Sh AUTHORS
+.An -nosplit
+The
+.Nm
+device driver was written by Jan-Simon Pendry for
+.Bx 4.4
+and
+.An Masanori OZAWA Aq Mt ozawa@ongs.co.jp
+reimplemented the handling of the locking for
+.Fx 7.0 .
+The manual page was written by
+.An Gordon Bergling Aq Mt gbe@FreeBSD.org .
+.Sh BUGS
+Please see the
+.Xr mount_unionfs 8
+manual page for a list of bugs regarding the
+.Nm
+filesystem.