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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	10.1			 July 8, 1993			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | FILES | EXAMPLES | SEE ALSO

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