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VNCONFIG(8) FreeBSD System Manager's Manual VNCONFIG(8)
NAME
vnconfig -- configure and enable vnode disks
SYNOPSIS
vnconfig [-cdeguvTZ] [-s option[,option...]] [-r option[,option...]]
[-S value] special_file [regular_file] [feature]
vnconfig -a [-cdeguv] [-s option] [-r option] [-f config_file]
DESCRIPTION
The vnconfig command configures and enables vnode pseudo disk devices.
The first form of the command will associate the special file
special_file with the regular file regular_file allowing the latter to be
accessed as though it were a disk. Hence a regular file within the
filesystem can be used for swapping or can contain a filesystem that is
mounted in the name space. If you want to use swap backing store for
your device instead of a file, you can leave regular_file out and specify
the size of the block device with the -S option.
Options indicate an action to be performed:
-a Read a command file and performs the specified actions for each
device/file pair.
-c Configure the device. If successful, references to special_file
will access the contents of regular_file.
-d Disable (if possible) the specified feature.
-e Configure the device and enables any feature that was specified.
If no feature was specified, -e is the same as -c.
-f config_file
Use config_file as an alternate config file.
-g Fiddle global options.
-r flag
Reset flag. The list of allowed flags and their meanings are:
labels use disk/slice labels.
reserve
Pre-reserve the blocks underlying the file or swap back-
ing store. Currently only works for swap backing store.
This option also disables on-the-fly freeing of the
underlying backing store (for example, when you remove a
large file). Use this option if you wish to avoid long-
term fragmentation of the backing store. Also note that
when this option is used, the initial contents of the
backing store may contain garbage rather then zeros. It
may even be possible to recover the prior contents of a
swap-backed VN across a reboot if the VN device is con-
figured before any swap is allocated by the system.
follow debug flow in the vn(4) driver.
debug debug data in the vn(4) driver.
io debug I/O in the vn(4) driver.
all turn on all flags.
none turn off all flags.
-s flag
Set flag. The list of allowed flags and their meanings are the
same as for the -r option.
-S value{k,m,g,t}
If no regular file is specified, VN will use swap for backing
store. This option specifies the size of the device. For exam-
ple, '23m' for 23 megabytes. The VN device will round the size
up to a machine page boundary. Filesystems up to 7.9 terabytes
are supported. When specified along with a regular file, this
option overrides the regular file's size insofar as VN is con-
cerned.
-T When a regular file is specified, VN will ftruncate() the file to
0 first. Normally you should also specify the -S option to set
the size of the file. This option also creates the file if it
did not previously exist. This option is only meaningful if the
-S option has been specified.
-Z When a regular file is specified, VN will zero the contents of
the file to ensure that all blocks have been allocated by the
filesystem. This option is only meaningful if the -S option has
been specified.
-u Disable and ``unconfigure'' the device.
-v Print messages to stdout describing actions taken.
If no action option is given, -c is assumed.
The feature argument specifies a feature that can be enabled via the -e
option:
swap Swapping is enabled on the special file. See swapon(2).
mountro=mount_point
The special file is mounted read-only on mount_point. See
mount(2).
mountrw=mount_point
The special file is mounted read-write on mount_point. See
mount(2).
mount=mount_point
Same as ``mountrw=''.
A configuration file contains one line per device/file pair in the form:
special_file regular_file [ feature ]
where fields are separated by white space. The previously described
action options serve to configure, enable, disable or unconfigure all
devices in the configuration file.
FILES
/etc/vntab default configuration file for -a option
EXAMPLES
vnconfig vn0c /tmp/diskimage
Configures the vnode disk vn0c.
vnconfig -e vn0c /var/swapfile swap
Configures vn0c and enables swapping on it.
vnconfig -c -v /dev/vn0 cdimage.iso
mount -t cd9660 -o ro /dev/vn0 /mnt
Mount an ISO9660 CD image file.
umount /mnt
vnconfig -u vn0c
Unmount the CD image file.
vnconfig -d vn0c myfilesystem mount=/mnt
Unmounts (disables) vn0c.
vnconfig -ae
Configures and enables all devices specified in /etc/vntab.
vnconfig -s labels -c vn0 somebackingfile
disklabel -r -w vn0 auto
disklabel -e vn0
Is an example of how to configure a file-backed VN disk with a disk label
and to initialize and then edit the label. Once you create the label,
you can partition your VN disk and, for example, create a filesystem on
one of the partitions. If you are using a file as backing store, it may
be possible to recover your VN disk after a crash by vnconfig'ing the
same file again and using the VN configuration already stored in the file
rather then relabeling and recreating the filesystem. It is even possi-
ble to fsck the VN partitions that previously contained filesystems.
vnconfig -e -s labels,reserve -S 400m vn1
disklabel -r -w vn1 auto
newfs /dev/vn1c
mount /dev/vn1c /usr/obj
Is an example of a swap-backed VN disk configuration. This example
assumes that you have at least 400 megabytes of swap free (and hopefully
much more). The swap space is pre-reserved in order to maintain maximum
performance. We then label the disk, newfs it, and mount it as /usr/obj.
Swap-backed VN devices are recoverable after a crash if you (A) use the
reserve flag, and if (B) the same swap is reserved as was the last time,
meaning that such vnconfig's would have to be run in your rc.local. In
general, though, you only use swap-backed VN devices to hold information
you don't mind losing on every reboot.
SEE ALSO
mount(2), swapon(2), unmount(2), vn(4)
FreeBSD 4.9 July 8, 1993 FreeBSD 4.9
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