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e461c7bc7d
It's never had any effect. The kernel ignores it. Remove it from the documentation. But continue to parse it on the command line, for backwards-compatibility. Reviewed by: imp Pull Request: https://github.com/freebsd/freebsd-src/pull/1271
385 lines
10 KiB
Groff
385 lines
10 KiB
Groff
.\" Copyright (c) 1993 University of Utah.
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.\" Copyright (c) 1980, 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" Copyright (c) 2000
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.\" Poul-Henning Kamp All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the Systems Programming Group of the University of Utah Computer
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.\" Science Department.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29
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.\"
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.Dd June 1, 2024
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.Dt MDCONFIG 8
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.Os
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.Sh NAME
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.Nm mdconfig
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.Nd create and control memory disks
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.Sh SYNOPSIS
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.Nm
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.Fl a
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.Fl t Ar type
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.Op Fl n
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.Oo Fl o Oo Cm no Oc Ns Ar option Oc ...
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.Op Fl f Ar file
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.Op Fl s Ar size
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.Op Fl S Ar sectorsize
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.Op Fl u Ar unit
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.Op Fl x Ar sectors/track
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.Op Fl y Ar heads/cylinder
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.Op Fl L Ar label
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.Nm
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.Fl d
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.Fl u Ar unit
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.Op Fl o Oo Cm no Oc Ns Ar force
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.Nm
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.Fl r
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.Fl u Ar unit
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.Fl s Ar size
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.Op Fl o Oo Cm no Oc Ns Ar force
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.Nm
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.Fl l
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.Op Fl n
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.Op Fl v
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.Op Fl f Ar file
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.Op Fl u Ar unit
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.Nm
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.Ar file
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.Sh DESCRIPTION
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The
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.Nm
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utility creates and controls
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.Xr md 4
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devices.
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.Pp
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Options indicate an action to be performed:
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.Bl -tag -width indent
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.It Fl a
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Attach a memory disk.
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This will configure and attach a memory disk with the
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parameters specified and attach it to the system.
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If the
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.Fl u Ar unit
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option is not provided, the newly created device name will be printed on stdout.
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.It Fl d
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Detach a memory disk from the system and release all resources.
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.It Fl r
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Resize a memory disk.
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.It Fl t Ar type
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Select the type of the memory disk.
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.Bl -tag -width "malloc"
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.It Cm malloc
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Storage for this type of memory disk is allocated with
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.Xr malloc 9 .
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This limits the size to the malloc bucket limit in the kernel.
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If the
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.Fl o Cm reserve
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option is not set, creating and filling a large
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malloc-backed memory disk is a very easy way to
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panic the system.
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.It Cm vnode
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A file specified with
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.Fl f Ar file
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becomes the backing store for this memory disk.
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.It Cm swap
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Storage for this type of memory disk is allocated from buffer
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memory.
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Pages get pushed out to swap when the system is under memory
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pressure, otherwise they stay in the operating memory.
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Using
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.Cm swap
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backing is generally preferred instead of using
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.Cm malloc
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backing.
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.It Cm null
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Bitsink; all writes do nothing, all reads return zeroes.
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.El
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.It Fl f Ar file
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Filename to use for the vnode type memory disk.
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The
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.Fl a
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and
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.Fl t Cm vnode
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options are implied if not specified.
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.It Fl l
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List configured devices.
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If given with
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.Fl u ,
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display details about that particular device.
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If given with
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.Fl f Ar file ,
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display
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.Xr md 4
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device names of which
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.Ar file
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is used as the backing store.
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If both of
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.Fl u
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and
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.Fl f
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options are specified,
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display devices which match the two conditions.
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If the
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.Fl v
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option is specified, show all details.
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.It Fl n
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When printing
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.Xr md 4
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device names, print only the unit number without the
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.Xr md 4
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prefix.
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.It Fl s Ar size
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Size of the memory disk.
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.Ar Size
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is the number of 512 byte sectors unless suffixed with a
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.Cm b , k , m , g , t ,
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or
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.Cm p
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which
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denotes byte, kilobyte, megabyte, gigabyte, terabyte and petabyte respectively.
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When used without the
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.Fl r
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option, the
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.Fl a
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and
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.Fl t Cm swap
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options are implied if not specified.
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.It Fl S Ar sectorsize
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Sectorsize to use for the memory disk, in bytes.
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.It Fl x Ar sectors/track
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See the description of the
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.Fl y
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option below.
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.It Fl y Ar heads/cylinder
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For
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.Cm malloc
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or
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.Cm vnode
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backed devices, the
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.Fl x
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and
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.Fl y
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options can be used to specify a synthetic geometry.
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This is useful for constructing bootable images for later download to
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other devices.
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.It Fl L Ar label
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Associate a label (arbitrary string) with the new memory disk.
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The label can then be inspected with
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.Bd -literal -offset indent
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.Nm Fl l v
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.Ed
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.It Fl o Oo Cm no Oc Ns Ar option
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Set or reset options.
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.Bl -tag -width indent
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.It Oo Cm no Oc Ns Cm async
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For
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.Cm vnode
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backed devices: avoid
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.Dv IO_SYNC
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for increased performance but
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at the risk of deadlocking the entire kernel.
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.It Oo Cm no Oc Ns Cm cache
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For
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.Cm vnode
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backed devices: enable/disable caching of data in system caches.
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The default is to not cache.
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.Pp
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Accesses via the device are converted to accesses via the vnode.
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The caching policy for the vnode is used initially.
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This is normally to cache.
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This caching policy is retained if the
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.Cm cache
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option is used.
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Otherwise, caching is limited
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by releasing data from caches soon after each access.
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The release has the same semantics as the
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.Dv POSIX_FADV_DONTNEED
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feature of
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.Xr posix_fadvise 2 .
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The result is that with normal (non-zfs) caching,
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buffers are released from the buffer cache soon after they are constructed,
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but their data is kept in the page cache at lower priority.
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.Pp
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The
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.Cm cache
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option tends to waste memory by giving unwanted double caching,
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but it saves time if there is memory to spare.
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.It Oo Cm no Oc Ns Cm reserve
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Allocate and reserve all needed storage from the start, rather than as needed.
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.It Oo Cm no Oc Ns Cm compress
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Enable/disable compression features to reduce memory usage.
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.It Oo Cm no Oc Ns Cm force
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Disable/enable extra sanity checks to prevent the user from doing something
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that might adversely affect the system.
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This can be used with the
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.Fl d
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flag to forcibly destroy an
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.Xr md 4
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disk that is still in use.
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.It Oo Cm no Oc Ns Cm mustdealloc
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For
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.Cm vnode
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backed devices: detect whether hole-punching is supported by the underlying file
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system.
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If the file system supports hole-punching, then to handle a
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.Dv BIO_DELETE
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request, some or all of the request's operation range may be turned into a hole
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in the file used for backing store.
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Any parts which are not turned into holes are zero-filled in
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the file.
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If the file system does not support
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hole-punching,
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.Dv BIO_DELETE
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requests to the device are not handled and will fail with
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.Er EOPNOTSUPP .
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.Pp
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When
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.Cm mustdealloc
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is not specified or
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.Oo Cm no Oc Ns Cm mustdealloc
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is specified, for a
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.Dv BIO_DELETE
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request, if the file system supports hole-punching, some or all of the request's
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operation range may be turned into a hole in the file used for backing store.
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Any parts which are not turned into holes are zero-filled in the file.
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If the file system of the vnode type memory disk does not support hole-punching,
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the request's operation range is zero-filled in the file.
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.It Oo Cm no Oc Ns Cm readonly
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Enable/disable readonly mode.
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.It Oo Cm no Oc Ns Cm verify
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For
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.Cm vnode
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backed devices: enable/disable requesting verification of the
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file used for backing store.
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The type of verification depends on which security features are available.
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One example of verification is testing file integrity with
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checksums or cryptographic signatures.
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.El
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.It Fl u Ar unit
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Request a specific unit number or device name for the
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.Xr md 4
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device instead of automatic allocation.
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If a device name is specified, it must start with
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.Dq md
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followed by the unit number.
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.El
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.Pp
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The last form,
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.Nm
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.Ar file ,
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is provided for convenience as an abbreviation of
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.Nm
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.Fl a
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.Fl t Cm vnode
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.Fl f Ar file .
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.Sh EXAMPLES
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Create a disk with
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.Pa /tmp/boot.flp
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as backing storage.
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The name of the allocated unit will be printed on stdout, such as
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.Dq Li md0 :
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.Bd -literal -offset indent
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mdconfig /tmp/boot.flp
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.Ed
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.Pp
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Create a 1 gigabyte swap backed memory disk named
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.Dq Li md3 :
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.Bd -literal -offset indent
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mdconfig -s 1g -u md3
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.Ed
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.Pp
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Detach and free all resources used by
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.Pa /dev/md3 :
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.Bd -literal -offset indent
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mdconfig -du md3
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.Ed
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.Pp
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Show detailed information on current memory disks:
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.Bd -literal -offset indent
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mdconfig -lv
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.Ed
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.Pp
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Resize the
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.Dq Li md3
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memory disk to 2 gigabytes:
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.Bd -literal -offset indent
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mdconfig -rs 2g -u md3
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.Ed
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.Pp
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Create a 1 gigabyte swap backed disk, initialize an
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.Xr ffs 4
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file system on it, and mount it on
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.Pa /tmp :
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.Bd -literal -offset indent
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mdconfig -s 1g -u md10
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newfs -U /dev/md10
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mount /dev/md10 /tmp
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chmod 1777 /tmp
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.Ed
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.Pp
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Create a memory disk out of an ISO 9660 CD image file,
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using the first available
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.Xr md 4
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device, and then mount it:
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.Bd -literal -offset indent
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mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt
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.Ed
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.Pp
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Create a file-backed device from a hard disk image that begins
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with 512K of raw header information.
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.Xr gnop 8
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is used to skip over the header information, positioning
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.Pa md1.nop
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to the start of the filesystem in the image.
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.Bd -literal -offset indent
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mdconfig -u md1 -f diskimage.img
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gnop create -o 512K md1
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mount /dev/md1.nop /mnt
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.Ed
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.Sh SEE ALSO
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.Xr fpathconf 2 ,
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.Xr fspacectl 2 ,
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.Xr open 2 ,
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.Xr ffs 4 ,
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.Xr md 4 ,
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.Xr gpart 8 ,
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.Xr mdmfs 8 ,
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.Xr malloc 9 ,
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.Xr vn_deallocate 9
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.Sh HISTORY
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The
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.Nm
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utility first appeared in
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.Fx 5.0
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as a cleaner replacement for the vn kernel module
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and the vnconfig utility combo.
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.Sh AUTHORS
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The
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.Nm
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utility was written by
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.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
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