path: root/sbin/mount_vnd/mount_vnd.8

.\"	$OpenBSD: mount_vnd.8,v 1.17 2010/04/15 23:19:14 tedu Exp $
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.\"     @(#)vnconfig.8	8.1 (Berkeley) 6/5/93
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.\" Copyright (c) 2007 Alexander von Gernler <grunk@openbsd.org>
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.Dd $Mdocdate: April 15 2010 $
.Dt MOUNT_VND 8
.Os
.Sh NAME
.Nm mount_vnd ,
.Nm vnconfig
.Nd configure vnode disks
.Sh SYNOPSIS
.Nm mount_vnd
.Bk -words
.Op Fl k
.Op Fl K Ar rounds
.Op Fl o Ar options
.Op Fl S Ar saltfile
.Op Fl t Ar disktype
.Ar image
.Ar vnd_dev
.Ek
.Nm vnconfig
.Bk -words
.Op Fl ckluv
.Op Fl K Ar rounds
.Op Fl S Ar saltfile
.Op Fl t Ar disktype
.Ar vnd_dev
.Ar image
.Ek
.Sh DESCRIPTION
The
.Nm vnconfig
command configures vnode pseudo disk devices.
It will associate (or disassociate) the special file
.Ar vnd_dev
with the regular file
.Ar image ,
allowing the latter to be accessed as though it were a disk.
Hence a regular file within the file system can be used for swapping
or can contain a file system that is mounted in the name space.
.Pp
Both traditional devices,
.Xr vnd 4 ,
and the cache-coherent devices,
.Pa svnd ,
are configured through
.Nm vnconfig .
.Pa svnd
should be mounted with the
.Xr mount 8
option
.Dq sync
if
.Ar image
is being read from,
to ensure consistency in the buffer cache.
For normal operation this is not necessary.
.Pp
.Nm mount_vnd
works similarly to
.Nm vnconfig ,
but it provides an interface that can be used by the
.Xr fstab 5
infrastructure, so that an
.Ar image
file can be configured to a device
.Ar node
while booting.
.Nm mount_vnd
defaults to the
.Pa svnd0
device.
.Pp
For
.Xr fstab 5
lines with type
.Dq ffs ,
the
.Dq noauto
option must be set to prevent a
.Xr mount 8
of the FFS partitions
before the necessary vnd devices are configured.
Also, the
.Dq fs_passno
field has to be set to 0 to prevent
.Xr fsck 8
from checking the file system for the same reasons.
.Pp
.Nm mount_vnd
is invoked by
.Xr mount 8
when using the following syntax:
.Bd -ragged -offset 4n
.Nm mount Op options
-t vnd
.Ar image Ar node
.Ed
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl c
.Nm vnconfig
only.
Configures the device.
If successful, references to
.Ar vnd_dev
will access the contents of
.Ar image .
This is the default operation.
.It Fl K Ar rounds
Associate an encryption key with the device.
All data will be encrypted using the Blowfish cipher before it is
written to the disk.
The user is asked for both a passphrase and the name of a salt file.
The salt file can also be specified on the command line using the
.Fl S
option.
The passphrase and salt are combined according to PKCS #5 PBKDF2 for the
specified number of
rounds to generate the actual key used.
.Ar rounds
is a number between 1000 and
.Dv INT_MAX .
DO NOT LOSE THE SALT FILE.
Encryption only works with
.Pa svnd .
.It Fl k
Associate an encryption key with the device.
All data will be encrypted using the Blowfish cipher before it is
written to the disk.
Encryption only works with
.Pa svnd .
.It Fl l
.Nm vnconfig
only.
List the (s)vnd devices and indicate which ones are in use.
If a specific
.Ar vnd_dev
is given, then only that one will be described.
.It Fl o Ar options
.Nm mount_vnd
only.
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.
.Pp
At the moment,
.Fl o
is only here for compatibility reasons, but no use is made of supplied
options.
.It Fl S Ar saltfile
When
.Fl K
is used, specify the
.Pa saltfile .
.It Fl t Ar disktype
Specify a
.Ar disktype
entry from the
.Xr disktab 5
database.
The
.Ar vnd_dev
will have the sector size, sectors per track, and tracks per cylinder values
of the specified
.Ar disktype .
The defaults are 512-byte sectors, 100 sectors per track and 1 track per
cylinder.
.It Fl u
.Nm vnconfig
only.
Unconfigures a
.Ar vnd_dev .
.It Fl v
.Nm vnconfig
only.
Print messages to stdout describing actions taken.
.El
.Sh FILES
.Bl -tag -width /etc/rvnd?? -compact
.It Pa /dev/{,r}{,s}vnd*
.El
.Sh EXAMPLES
Configure a CD-ROM or DVD image file as vnode disk svnd0
and mount the ISO 9660 file system contained in it:
.Bd -literal -offset indent
# vnconfig svnd0 /tmp/diskimage
# mount -t cd9660 /dev/svnd0c /mnt
.Ed
.Pp
Configure an encrypted image file as vnode disk svnd0 and mount the FFS
file system contained in the
.Sq a
partition of the disklabel.
The encryption key does not echo and must be entered every time
the vnode disk is configured.
.Bd -literal -offset indent
# vnconfig -k svnd0 /tmp/cryptimg
Encryption key:
# mount /dev/svnd0a /mnt
.Ed
.Pp
An equivalent
.Xr fstab 5
entry is:
.Bd -literal -offset indent
/tmp/cryptimg /dev/svnd0c vnd rw,noauto,-k       0 0
/dev/svnd0a   /mnt        ffs rw,noauto          0 0
.Ed
.Pp
Same as above, but now configure the vnode using PKCS #5 PBKDF2 and
a salt file with 20000 rounds:
.Bd -literal -offset indent
# vnconfig -K 20000 svnd0 /tmp/cryptimg
Encryption key:
Salt file: /tmp/cryptsalt
# mount /dev/svnd0a /mnt
.Ed
.Pp
An equivalent
.Xr fstab 5
entry is:
.Bd -literal -offset indent
/tmp/cryptimg /dev/svnd0c vnd rw,noauto,-K=20000 0 0
/dev/svnd0a   /mnt        ffs rw,noauto          0 0
.Ed
.Pp
Unmount the file system and unconfigure the vnode device:
.Bd -literal -offset indent
# umount /mnt
# vnconfig -u svnd0
.Ed
.Pp
A sample of commands to put in
.Xr rc.local 8
in order to have vnd images configured at boot time is listed here:
.Bd -literal -offset indent
# Example for automatically configuring a vnd device on startup
echo "configuring vnd devices:"
mount /dev/svnd0c
fsck -p /dev/rsvnd0a
mount /mnt
.Ed
.Pp
Mounting images during the first pass of
.Xr fsck 8
and
.Xr mount 8
is not possible, because the image to be configured to a vnd itself
resides on a file system that first has to be checked and mounted.
.Sh SEE ALSO
.Xr vnd 4 ,
.Xr disktab 5 ,
.Xr fstab 5 ,
.Xr mount 8 ,
.Xr swapon 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm
command first appeared in
.Ox 4.2 .
.Sh AUTHORS
.An David Krause .
.Sh CAVEATS
The
.Sq c
partition of a vnd image should not be used.
When a superblock becomes damaged,
.Xr fsck_ffs 8
needs information contained in the disklabel
to determine the location of alternate superblocks.
This information is not available when directly using the
.Sq c
partition,
so checking the file system image will fail.