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VNCONFIG(8) DragonFly System Manager's Manual VNCONFIG(8)
vnconfig - configure and enable vnode disks
vnconfig [-cdeguvTZ] [-s options] [-r options] [-S value]
special_file [regular_file] [feature]
vnconfig -a [-cdeguv] [-s options] [-r options] [-f config_file]
vnconfig -l [special_file ...]
The vnconfig command configures, enables and lists 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
-c Configure the device. If successful, references to special_file
will access the contents of regular_file.
A vn device is autocloned if special_file is given as vn, the
name of the resulting device is printed on stdout.
-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.
Specify configuration file. Default is /etc/vntab.
-g Fiddle global options.
-l special_file ...
List the vn devices and indicate which ones are in use. If a
special_file list is given, only those devices will be described.
Reset options, which is a comma separated string of options. The
list of allowed options and their meanings are:
reserve Pre-reserve the blocks underlying the file or swap
backing 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
than zeros. It may even be possible to recover the
prior contents of a swap-backed vn across a reboot if
the vn device is configured 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 options.
none Turn off all options.
Set options, which is a comma separated string of options. The
list of allowed options and their meanings are the same as for
the -r option.
If no regular file is specified, vn will use swap for backing
store. This option specifies the size of the device. For
example, `23m' for 23 megabytes. In the absence of a size
modifier, m is implied. 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 concerned.
-T When a regular file is specified, vnconfig will ftruncate() the
file to length 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, vnconfig 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
-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
swap Swapping is enabled on the special file. See swapon(2).
The special file is mounted read-only on mount_point. See
The special file is mounted read-write on mount_point. See
Same as mountrw=mount_point.
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. Lines starting with `#' are
ignored. The previously described action options serve to configure,
enable, disable or unconfigure all devices in the configuration file.
/etc/vntab default configuration file for -a option
vnconfig vn /tmp/diskimage
Configures an autocloned vnode disk, the name of the resulting device is
printed, e.g. vn4.
vnconfig vn0 /tmp/diskimage
Configures the vnode disk vn0.
vnconfig -e vn0 /var/swapfile swap
Configures vn0 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.
vnconfig -u vn0
Unmount the CD image file.
vnconfig -d vn0 myfilesystem mount=/mnt
Unmounts (disables) vn0.
Configures and enables all devices specified in /etc/vntab.
vnconfig -c vn0 somebackingfile
disklabel -r -w vn0s0 auto
disklabel -e vn0s0
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 than relabeling and recreating the filesystem. It is even
possible to fsck(8) the vn partitions that previously contained
vnconfig -e -s reserve -S 400m vn1
disklabel -r -w vn1s0 auto
mount /dev/vn1s0 /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 option, 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(8). In general, though, you only use swap-backed vn devices to
hold information you don't mind losing on every reboot.
mount(2), swapon(2), unmount(2), vn(4)
DragonFly 6.1-DEVELOPMENT January 19, 2022 DragonFly 6.1-DEVELOPMENT