path: root/sbin/mount_unionfs/mount_unionfs.8
diff options
authorCraig Rodrigues <rodrigc@FreeBSD.org>2006-12-02 19:35:56 +0000
committerCraig Rodrigues <rodrigc@FreeBSD.org>2006-12-02 19:35:56 +0000
commitd00947d83af65a3ff545b9494c5cf67b40398dd3 (patch)
tree9c239765475d2d432117d23b880498481836ab65 /sbin/mount_unionfs/mount_unionfs.8
parent2229d0cfa2dd5242d9e9a425b6f66d9346ed86a9 (diff)
Many, many thanks to Masanori OZAWA <ozawa@ongs.co.jp>
and Daichi GOTO <daichi@FreeBSD.org> for submitting this major rewrite of unionfs. This rewrite was done to try to solve many of the longstanding crashing and locking issues in the existing unionfs implementation. This implementation also adds a 'MASQUERADE mode', which allows the user to set different user, group, and file permission modes in the upper layer. Submitted by: daichi, Masanori OZAWA Reviewed by: rodrigc (modified for minor style issues)
Notes: svn path=/head/; revision=164829
Diffstat (limited to 'sbin/mount_unionfs/mount_unionfs.8')
1 files changed, 184 insertions, 23 deletions
diff --git a/sbin/mount_unionfs/mount_unionfs.8 b/sbin/mount_unionfs/mount_unionfs.8
index 20f1451aa884..9da461cf2153 100644
--- a/sbin/mount_unionfs/mount_unionfs.8
+++ b/sbin/mount_unionfs/mount_unionfs.8
@@ -31,7 +31,7 @@
.\" @(#)mount_union.8 8.6 (Berkeley) 3/27/94
.\" $FreeBSD$
-.Dd March 27, 1994
+.Dd November 30, 2006
@@ -64,6 +64,17 @@ layer.
The options are as follows:
.Bl -tag -width indent
.It Fl b
+Deprecated. Use
+.Fl o
+.Ar below
+.It Fl o
+Options are specified with a
+.Fl o
+flag followed by an option.
+The following options are available:
+.Bl -tag -width indent
+.It Cm below
Invert the default position, so that
.Ar directory
becomes the lower layer and
@@ -72,16 +83,36 @@ becomes the upper layer.
.Ar uniondir
remains the mount point.
-.It Fl o
-Options are specified with a
-.Fl o
-flag followed by a comma separated string of options.
-See the
-.Xr mount 8
-man page for possible options and their meanings.
-.It Fl r
-Hide the lower layer completely in the same way as mounting with
-.Xr mount_nullfs 8 .
+.It Cm copymode=traditional | transparent | masquerade
+Specifies the way to create a file or a directory in the upper layer
+automatically when needed.
+.Ar traditional
+uses the same way as the old unionfs for backward compatibility, and
+.Ar 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
+.Ar masquerade
+mode, see
+.It Cm udir=mode
+Specifies directory mode bits in octal for
+.Ar masquerade
+.It Cm ufile=mode
+Specifies file mode bits in octal for
+.Ar masquerade
+.It Cm gid=gid
+Specifies group for
+.Ar masquerade
+.It Cm uid=uid
+Specifies user for
+.Ar masquerade
To enforce file system security, the user mounting the file system
@@ -91,6 +122,13 @@ 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
+.Ar transparent
+.Ar masquerade
+mode require
+.Va vfs.usermount
+be set to 0 because this functionality can only be used by superusers.
Filenames are looked up in the upper layer and then in the
lower layer.
@@ -98,10 +136,14 @@ 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.
-It will be owned by the user who originally did the union mount,
-with mode
-.Dq rwxrwxrwx
-(0777) modified by the umask in effect at that time.
+The ownership and the mode bits are set depending on the
+.Ar copymode
+option. In
+.Ar traditional
+mode, it will be owned by the user who originally did the
+union mount, with mode 0777
+.Dq rwxrwxrwx
+modified by the umask in effect at that time.
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.
@@ -142,15 +184,74 @@ option to
.Xr mount 8
which only applies the union operation to the mount point itself,
and then only for lookups.
+When a file
+.Pq or a directory
+is created in the upper layer, the
+.Ar masquerade
+mode sets it the fixed access mode bits given in
+.Ar ufile Pq for files
+.Ar udir Pq for directories
+option and the owner given in
+.Ar udir
+.Ar gid
+options, instead of ones in the lower layer. Note that in the
+.Ar masquerade
+mode and when owner of the file or directory matches
+one specified in
+.Ar uid
+option, only mode bits for the owner will be modified.
+More specifically, the file mode bits in the upper layer will
+.Pq mode in the lower layer
+.Pq Po mode given in .Ar ufile
+AND 0700
+.Pc , and the ownership will be the same as one in the lower layer.
+The default values for
+.Ar ufile , udir , uid ,
+.Ar gid
+are as follow:
+.Bl -bullet -compact
+If both
+.Ar ufile
+.Ar udir
+are not specified, access mode bits in the mount point will be used.
+If both
+.Ar uid
+.Ar gid
+are not specified, ownership in the mount point will be used.
+If either
+.Ar udir
+.Ar ufile
+is not specified, the other will be the same as the specified one.
+If either
+.Ar uid
+.Ar gid
+is not specified, the other will be the same as the specified one.
The commands
.Bd -literal -offset indent
-mount -t cd9660 -o ro /dev/cd0a /usr/src
-mount -t unionfs /var/obj /usr/src
+mount -t cd9660 -o ro /dev/cd0 /usr/src
+mount -t unionfs -o noatime /var/obj /usr/src
mount the CD-ROM drive
-.Pa /dev/cd0a
+.Pa /dev/cd0
.Pa /usr/src
and then attaches
@@ -158,11 +259,42 @@ and then attaches
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.
+even though it is stored on a CD-ROM. The
+.Fl o Ar noatime
+option is useful to avoid unnecessary copying from the lower to the
+upper layer.
+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
+also mount the CD-ROM drive
+.Pa /dev/cd0
+.Pa /usr/src
+and then attaches
+.Pa /var/obj
+on top. Furthermore, the owner of all files and directories in /usr/src
+is a regular user with uid
+.Pq 2020
+when seen from the upper layer. Note that for the access mode bits,
+ones in the lower layer
+.Pq 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
+.Ar masquerade
The command
.Bd -literal -offset indent
-mount -t unionfs -o -b /sys $HOME/sys
+mount -t unionfs -o noatime -o below /sys $HOME/sys
attaches the system source tree below the
@@ -186,8 +318,20 @@ The
utility first appeared in
.Bx 4.4 .
-It first worked in
-.Fx Ns -(fill this in) .
+.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 .
+.Fx 7.0 ,
+.An Masanori OZAWA Aq ozawa@ongs.co.jp
+reimplemented handling of locking, whiteout, and file mode bits, and
+.An Hiroki Sato Aq hrs@FreeBSD.org
+wrote about the changes in this manual page.
@@ -198,7 +342,7 @@ SLIPPERY WHEN WET.
This code also needs an owner in order to be less dangerous - serious
hackers can apply by sending mail to
-.Aq hackers@FreeBSD.org
+.Aq freebsd-fs@FreeBSD.org
and announcing
their intent to take it over.
@@ -214,3 +358,20 @@ Running
.Xr find 1
over a union tree has the side-effect of creating
a tree of shadow directories in the upper layer.
+The current implementation does not support copying extended attributes
+.Xr acl 9 ,
+.Xr mac 9 ,
+or so on to the upper layer. Note that this may be a security issue.
+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
+.Ar 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.