MOUNT_VND(8) OpenBSD System Manager's Manual MOUNT_VND(8)NAME
mount_vnd, vnconfig - configure vnode disks
SYNOPSISmount_vnd [-k] [-K rounds] [-o options] [-S saltfile] [-t disktype] image
vnd_dev
vnconfig [-ckluv] [-K rounds] [-S saltfile] [-t disktype] vnd_dev image
DESCRIPTION
The vnconfig command configures vnode pseudo disk devices. It will
associate (or disassociate) the special file vnd_dev with the regular
file 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.
Both traditional devices, vnd(4), and the cache-coherent devices, svnd,
are configured through vnconfig. svnd should be mounted with the
mount(8) option ``sync'' if image is being read from, to ensure
consistency in the buffer cache. For normal operation this is not
necessary.
mount_vnd works similarly to vnconfig, but it provides an interface that
can be used by the fstab(5) infrastructure, so that an image file can be
configured to a device node while booting. mount_vnd defaults to the
svnd0 device.
For fstab(5) lines with type ``ffs'', the ``noauto'' option must be set
to prevent a mount(8) of the FFS partitions before the necessary vnd
devices are configured. Also, the ``fs_passno'' field has to be set to 0
to prevent fsck(8) from checking the file system for the same reasons.
mount_vnd is invoked by mount(8) when using the following syntax:
mount [options] -t vnd image node
The options are as follows:
-c vnconfig only. Configures the device. If successful, references
to vnd_dev will access the contents of image. This is the
default operation.
-K 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 -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. rounds is a number between 1000
and INT_MAX. DO NOT LOSE THE SALT FILE. Encryption only works
with svnd.
-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 svnd.
-l vnconfig only. List the (s)vnd devices and indicate which ones
are in use. If a specific vnd_dev is given, then only that one
will be described.
-o options
mount_vnd only. Options are specified with a -o flag followed by
a comma separated string of options. See the mount(8) man page
for possible options and their meanings.
At the moment, -o is only here for compatibility reasons, but no
use is made of supplied options.
-S saltfile
When -K is used, specify the saltfile.
-t disktype
Specify a disktype entry from the disktab(5) database. The
vnd_dev will have the sector size, sectors per track, and tracks
per cylinder values of the specified disktype. The defaults are
512-byte sectors, 100 sectors per track and 1 track per cylinder.
-u vnconfig only. Unconfigures a vnd_dev.
-v vnconfig only. Print messages to stdout describing actions
taken.
FILES
/dev/{,r}{,s}vnd*
EXAMPLES
Configure a CD-ROM or DVD image file as vnode disk svnd0 and mount the
ISO 9660 file system contained in it:
# vnconfig svnd0 /tmp/diskimage
# mount -t cd9660 /dev/svnd0c /mnt
Configure an encrypted image file as vnode disk svnd0 and mount the FFS
file system contained in the `a' partition of the disklabel. The
encryption key does not echo and must be entered every time the vnode
disk is configured.
# vnconfig -k svnd0 /tmp/cryptimg
Encryption key:
# mount /dev/svnd0a /mnt
An equivalent fstab(5) entry is:
/tmp/cryptimg /dev/svnd0c vnd rw,noauto,-k 0 0
/dev/svnd0a /mnt ffs rw,noauto 0 0
Same as above, but now configure the vnode using PKCS #5 PBKDF2 and a
salt file with 20000 rounds:
# vnconfig -K 20000 svnd0 /tmp/cryptimg
Encryption key:
Salt file: /tmp/cryptsalt
# mount /dev/svnd0a /mnt
An equivalent fstab(5) entry is:
/tmp/cryptimg /dev/svnd0c vnd rw,noauto,-K=20000 0 0
/dev/svnd0a /mnt ffs rw,noauto 0 0
Unmount the file system and unconfigure the vnode device:
# umount /mnt
# vnconfig -u svnd0
A sample of commands to put in rc.local(8) in order to have vnd images
configured at boot time is listed here:
# Example for automatically configuring a vnd device on startup
echo "configuring vnd devices:"
mount /dev/svnd0c
fsck -p /dev/rsvnd0a
mount /mnt
Mounting images during the first pass of fsck(8) and 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.
SEE ALSOvnd(4), disktab(5), fstab(5), mount(8), swapon(8), umount(8)HISTORY
The mount_vnd command first appeared in OpenBSD 4.2.
CAVEATS
The `c' partition of a vnd image should not be used. When a superblock
becomes damaged, 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 `c' partition, so checking the file
system image will fail.
OpenBSD 4.9 December 18, 2010 OpenBSD 4.9
