Index: head/sbin/mount_unionfs/mount_unionfs.8
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--- head/sbin/mount_unionfs/mount_unionfs.8	(revision 306612)
+++ head/sbin/mount_unionfs/mount_unionfs.8	(revision 306613)
@@ -1,395 +1,399 @@
 .\" Copyright (c) 1994
 .\" The Regents of the University of California.  All rights reserved.
 .\"
 .\" This code is derived from software donated to Berkeley by
 .\" Jan-Simon Pendry.
 .\"
 .\" 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.
 .\" 4. Neither the name of the University nor the names of its contributors
 .\"    may be used to endorse or promote products derived from this software
 .\"    without specific prior written permission.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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)
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 .\"
 .\"	@(#)mount_union.8	8.6 (Berkeley) 3/27/94
 .\" $FreeBSD$
 .\"
-.Dd November 30, 2006
+.Dd October 3, 2016
 .Dt MOUNT_UNIONFS 8
 .Os
 .Sh NAME
 .Nm mount_unionfs
 .Nd mount union file systems
 .Sh SYNOPSIS
 .Nm
 .Op Fl b
 .Op Fl o Ar options
 .Ar directory
 .Ar uniondir
 .Sh DESCRIPTION
 The
 .Nm
 utility attaches
 .Ar directory
 above
 .Ar uniondir
 in such a way that the contents of both directory trees remain visible.
 By default,
 .Ar directory
 becomes the
 .Em upper
 layer and
 .Ar uniondir
 becomes the
 .Em lower
 layer.
 .Pp
 The options are as follows:
 .Bl -tag -width indent
 .It Fl b
 Deprecated.
 Use
 .Fl o Cm below
 instead.
 .It Fl o
 Options are specified with the
 .Fl o
 flag followed by an option.
 The following options are available:
 .Bl -tag -width indent
 .It Cm below
 Inverts the default position, so that
 .Ar directory
 becomes the lower layer and
 .Ar uniondir
 becomes the upper layer.
 However,
 .Ar uniondir
 remains the mount point.
 .It Cm copymode No = Cm traditional | transparent | masquerade
 Specifies the way to create a file or a directory in the upper layer
 automatically when needed.
 The
 .Cm traditional
 mode
 uses the same way as the old unionfs for backward compatibility, and
 .Cm transparent
 duplicates the file and directory mode bits and the ownership in the
 lower layer to the created file in the upper layer.
 For behavior of the
 .Cm masquerade
 mode, see
 .Sx MASQUERADE MODE
 below.
 .It Cm whiteout No = Cm always | whenneeded
 Specifies whether whiteouts should always be made in the upper layer
 when removing a file or directory or only when it already exists in the
 lower layer.
 .It Cm udir Ns = Ns Ar mode
 Specifies directory mode bits in octal for
 .Cm masquerade
 mode.
 .It Cm ufile Ns = Ns Ar mode
 Specifies file mode bits in octal for
 .Cm masquerade
 mode.
 .It Cm gid Ns = Ns Ar gid
 Specifies group for
 .Cm masquerade
 mode.
 .It Cm uid Ns = Ns Ar uid
 Specifies user for
 .Cm masquerade
 mode.
 .El
 .El
 .Pp
 To enforce file system security, the user mounting a file system
 must be superuser or else have write permission on the mounted-on
 directory.
 In addition, the
 .Va vfs.usermount
 .Xr sysctl 8
 variable must be set to 1 to permit file system mounting by ordinary users.
 However, note that
 .Cm transparent
 and
 .Cm masquerade
 modes require
 .Va vfs.usermount
 to be set to 0 because this functionality can only be used by superusers.
 .Pp
 Filenames are looked up in the upper layer and then in the
 lower layer.
 If a directory is found in the lower layer, and there is no entry
 in the upper layer, then a
 .Em shadow
 directory will be created in the upper layer.
 The ownership and the mode bits are set depending on the
 .Cm copymode
 option.
 In
 .Cm traditional
 mode, it will be owned by the user who originally did the
 union mount, with mode 0777
 .Pq Dq Li rwxrwxrwx
 modified by the umask in effect at that time.
 .Pp
 If a file exists in the upper layer then there is no way to access
 a file with the same name in the lower layer.
 If necessary, a combination of loopback and union mounts can be made
 which will still allow the lower files to be accessed by a different
 pathname.
 .Pp
 Except in the case of a directory,
 access to an object is granted via the normal file system access checks.
 For directories, the current user must have access to both the upper
 and lower directories (should they both exist).
 .Pp
 Requests to create or modify objects in
 .Ar uniondir
 are passed to the upper layer with the exception of a few special cases.
 An attempt to open for writing a file which exists in the lower layer
 causes a copy of the
 .Em entire
 file to be made to the upper layer, and then for the upper layer copy
 to be opened.
 Similarly, an attempt to truncate a lower layer file to zero length
 causes an empty file to be created in the upper layer.
 Any other operation which would ultimately require modification to
 the lower layer fails with
 .Er EROFS .
 .Pp
 The union file system manipulates the namespace, rather than
 individual file systems.
 The union operation applies recursively down the directory tree
 now rooted at
 .Ar uniondir .
 Thus any file systems which are mounted under
 .Ar uniondir
 will take part in the union operation.
 This differs from the
 .Cm union
 option to
 .Xr mount 8
 which only applies the union operation to the mount point itself,
 and then only for lookups.
 .Sh MASQUERADE MODE
 When a file
 (or a directory)
 is created in the upper layer, the
 .Cm masquerade
 mode sets it the fixed access mode bits given in
 .Cm ufile
 (for files)
 or
 .Cm udir
 (for directories)
 option and the owner given in
 .Cm udir
 and
 .Cm gid
 options, instead of ones in the lower layer.
 Note that in the
 .Cm masquerade
 mode and when owner of the file or directory matches
 one specified in
 .Cm uid
 option, only mode bits for the owner will be modified.
 More specifically, the file mode bits in the upper layer will
 be
 (mode in the lower layer)
 OR
 (mode given in
 .Cm ufile
 AND 0700), and the ownership will be the same as one in the lower layer.
 .Pp
 The default values for
 .Cm ufile , udir , uid ,
 and
 .Cm gid
 are as follow:
 .Pp
 .Bl -bullet -compact
 .It
 If none of
 .Cm ufile
 and
 .Cm udir
 were specified, access mode bits in the mount point will be used.
 .It
 If none of
 .Cm uid
 and
 .Cm gid
 were specified, ownership in the mount point will be used.
 .It
 If one of
 .Cm udir
 or
 .Cm ufile
 is not specified, the value of the other option will be used.
 .It
 If one of
 .Cm uid
 or
 .Cm gid
 is not specified, the value of the other option will be used.
 .El
 .Sh EXAMPLES
 The commands
 .Bd -literal -offset indent
 mount -t cd9660 -o ro /dev/cd0 /usr/src
 mount -t unionfs -o noatime /var/obj /usr/src
 .Ed
 .Pp
 mount the CD-ROM drive
 .Pa /dev/cd0
 on
 .Pa /usr/src
 and then attaches
 .Pa /var/obj
 on top.
 For most purposes the effect of this is to make the
 source tree appear writable
 even though it is stored on a CD-ROM.
 The
 .Fl o Cm noatime
 option is useful to avoid unnecessary copying from the lower to the
 upper layer.
 .Pp
 The commands
 .Bd -literal -offset indent
 mount -t cd9660 -o ro /dev/cd0 /usr/src
 chown 2020 /usr/src
 mount -t unionfs -o noatime -o copymode=masquerade -o uid=builder \\
     -o udir=755 -o ufile=644 /var/obj /usr/src
 .Ed
 .Pp
 also mount the CD-ROM drive
 .Pa /dev/cd0
 on
 .Pa /usr/src
 and then attaches
 .Pa /var/obj
 on top.
 Furthermore, the owner of all files and directories in
 .Pa /usr/src
 is a regular user with UID 2020
 when seen from the upper layer.
 Note that for the access mode bits,
 ones in the lower layer
 (on the CD-ROM, in this example)
 are still used without change.
 Thus, write privilege to the upper layer can be controlled
 independently from access mode bits and ownership in the lower layer.
 If a user does not have read privilege from the lower layer,
 one cannot still read even when the upper layer is mounted by using
 .Cm masquerade
 mode.
 .Pp
 The command
 .Bd -literal -offset indent
 mount -t unionfs -o noatime -o below /sys $HOME/sys
 .Ed
 .Pp
 attaches the system source tree below the
 .Pa sys
 directory in the user's home directory.
 This allows individual users to make private changes
 to the source, and build new kernels, without those
 changes becoming visible to other users.
 Note that the files in the lower layer remain
 accessible via
 .Pa /sys .
 .Sh SEE ALSO
 .Xr intro 2 ,
 .Xr mount 2 ,
 .Xr unmount 2 ,
 .Xr fstab 5 ,
 .Xr mount 8 ,
 .Xr mount_nullfs 8
 .Sh HISTORY
 The
-.Nm
+.Nm mount_null
 utility first appeared in
 .Bx 4.4 .
+It was renamed to
+.Nm
+in
+.Fx 5.0 .
 .Pp
 The
 .Fl r
 option for hiding the lower layer completely was removed in
 .Fx 7.0
 because this is identical to using
 .Xr mount_nullfs 8 .
 .Sh AUTHORS
 .An -nosplit
 In
 .Fx 7.0 ,
 .An Masanori OZAWA Aq Mt ozawa@ongs.co.jp
 reimplemented handling of locking, whiteout, and file mode bits, and
 .An Hiroki Sato Aq Mt hrs@FreeBSD.org
 wrote about the changes in this manual page.
 .Sh BUGS
 THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
 AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM.
 USE AT YOUR
 OWN RISK.
 BEWARE OF DOG.
 SLIPPERY WHEN WET.
 BATTERIES NOT INCLUDED.
 .Pp
 This code also needs an owner in order to be less dangerous - serious
 hackers can apply by sending mail to
 .Aq Mt freebsd-fs@FreeBSD.org
 and announcing
 their intent to take it over.
 .Pp
 Without whiteout support from the file system backing the upper layer,
 there is no way that delete and rename operations on lower layer
 objects can be done.
 .Er EOPNOTSUPP
 is returned for this kind of operations as generated by VOP_WHITEOUT()
 along with any others which would make modifications to the lower
 layer, such as
 .Xr chmod 1 .
 .Pp
 Running
 .Xr find 1
 over a union tree has the side-effect of creating
 a tree of shadow directories in the upper layer.
 .Pp
 The current implementation does not support copying extended attributes
 for
 .Xr acl 9 ,
 .Xr mac 9 ,
 or so on to the upper layer.
 Note that this may be a security issue.
 .Pp
 A shadow directory, which is one automatically created in the upper
 layer when it exists in the lower layer and does not exist in the
 upper layer, is always created with the superuser privilege.
 However, a file copied from the lower layer in the same way
 is created by the user who accessed it.
 Because of this,
 if the user is not the superuser, even in
 .Cm transparent
 mode the access mode bits in the copied file in the upper layer
 will not always be the same as ones in the lower layer.
 This behavior should be fixed.