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.\" Copyright (c) 1993 University of Utah. .\" Copyright (c) 1980, 1989, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" Copyright (c) 2000 .\" Poul-Henning Kamp All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" the Systems Programming Group of the University of Utah Computer .\" Science Department. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)vnconfig.8 8.1 (Berkeley) 6/5/93 .\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29 .\" .\" $FreeBSD$ .\" .Dd November 6, 2020 .Dt MDCONFIG 8 .Os .Sh NAME .Nm mdconfig .Nd create and control memory disks .Sh SYNOPSIS .Nm .Fl a .Fl t Ar type .Op Fl n .Oo Fl o Oo Cm no Oc Ns Ar option Oc ... .Op Fl f Ar file .Op Fl s Ar size .Op Fl S Ar sectorsize .Op Fl u Ar unit .Op Fl x Ar sectors/track .Op Fl y Ar heads/cylinder .Op Fl L Ar label .Nm .Fl d .Fl u Ar unit .Op Fl o Oo Cm no Oc Ns Ar force .Nm .Fl r .Fl u Ar unit .Fl s Ar size .Op Fl o Oo Cm no Oc Ns Ar force .Nm .Fl l .Op Fl n .Op Fl v .Op Fl f Ar file .Op Fl u Ar unit .Nm .Ar file .Sh DESCRIPTION The .Nm utility creates and controls .Xr md 4 devices. .Pp Options indicate an action to be performed: .Bl -tag -width indent .It Fl a Attach a memory disk. This will configure and attach a memory disk with the parameters specified and attach it to the system. If the .Fl u Ar unit option is not provided, the newly created device name will be printed on stdout. .It Fl d Detach a memory disk from the system and release all resources. .It Fl r Resize a memory disk. .It Fl t Ar type Select the type of the memory disk. .Bl -tag -width "malloc" .It Cm malloc Storage for this type of memory disk is allocated with .Xr malloc 9 . This limits the size to the malloc bucket limit in the kernel. If the .Fl o Cm reserve option is not set, creating and filling a large malloc-backed memory disk is a very easy way to panic the system. .It Cm vnode A file specified with .Fl f Ar file becomes the backing store for this memory disk. .It Cm swap Storage for this type of memory disk is allocated from buffer memory. Pages get pushed out to swap when the system is under memory pressure, otherwise they stay in the operating memory. Using .Cm swap backing is generally preferred instead of using .Cm malloc backing. .It Cm null Bitsink; all writes do nothing, all reads return zeroes. .El .It Fl f Ar file Filename to use for the vnode type memory disk. The .Fl a and .Fl t Cm vnode options are implied if not specified. .It Fl l List configured devices. If given with .Fl u , display details about that particular device. If given with .Fl f Ar file , display .Xr md 4 device names of which .Ar file is used as the backing store. If both of .Fl u and .Fl f options are specified, display devices which match the two conditions. If the .Fl v option is specified, show all details. .It Fl n When printing .Xr md 4 device names, print only the unit number without the .Xr md 4 prefix. .It Fl s Ar size Size of the memory disk. .Ar Size is the number of 512 byte sectors unless suffixed with a .Cm b , k , m , g , t , or .Cm p which denotes byte, kilobyte, megabyte, gigabyte, terabyte and petabyte respectively. When used without the .Fl r option, the .Fl a and .Fl t Cm swap options are implied if not specified. .It Fl S Ar sectorsize Sectorsize to use for the memory disk, in bytes. .It Fl x Ar sectors/track See the description of the .Fl y option below. .It Fl y Ar heads/cylinder For .Cm malloc or .Cm vnode backed devices, the .Fl x and .Fl y options can be used to specify a synthetic geometry. This is useful for constructing bootable images for later download to other devices. .It Fl L Ar label Associate a label (arbitrary string) with the new memory disk. The label can then be inspected with .Bd -literal -offset indent .Nm Fl l v .Ed .It Fl o Oo Cm no Oc Ns Ar option Set or reset options. .Bl -tag -width indent .It Oo Cm no Oc Ns Cm async For .Cm vnode backed devices: avoid .Dv IO_SYNC for increased performance but at the risk of deadlocking the entire kernel. .It Oo Cm no Oc Ns Cm cache For .Cm vnode backed devices: enable/disable caching of data in system caches. The default is to not cache. .Pp Accesses via the device are converted to accesses via the vnode. The caching policy for the vnode is used initially. This is normally to cache. This caching policy is retained if the .Cm cache option is used. Otherwise, caching is limited by releasing data from caches soon after each access. The release has the same semantics as the .Dv POSIX_FADV_DONTNEED feature of .Xr posix_fadvise 2 . The result is that with normal (non-zfs) caching, buffers are released from the buffer cache soon after they are constructed, but their data is kept in the page cache at lower priority. .Pp The .Cm cache option tends to waste memory by giving unwanted double caching, but it saves time if there is memory to spare. .It Oo Cm no Oc Ns Cm reserve Allocate and reserve all needed storage from the start, rather than as needed. .It Oo Cm no Oc Ns Cm cluster Enable clustering on this disk. .It Oo Cm no Oc Ns Cm compress Enable/disable compression features to reduce memory usage. .It Oo Cm no Oc Ns Cm force Disable/enable extra sanity checks to prevent the user from doing something that might adversely affect the system. This can be used with the .Fl d flag to forcibly destroy an .Xr md 4 disk that is still in use. .It Oo Cm no Oc Ns Cm readonly Enable/disable readonly mode. .It Oo Cm no Oc Ns Cm verify For .Cm vnode backed devices: enable/disable requesting verification of the file used for backing store. The type of verification depends on which security features are available. One example of verification is testing file integrity with checksums or cryptographic signatures. .El .It Fl u Ar unit Request a specific unit number or device name for the .Xr md 4 device instead of automatic allocation. If a device name is specified, it must start with .Dq md followed by the unit number. .El .Pp The last form, .Nm .Ar file , is provided for convenience as an abbreviation of .Nm .Fl a .Fl t Cm vnode .Fl f Ar file . .Sh EXAMPLES Create a disk with .Pa /tmp/boot.flp as backing storage. The name of the allocated unit will be printed on stdout, such as .Dq Li md0 : .Bd -literal -offset indent mdconfig /tmp/boot.flp .Ed .Pp Create a 1 gigabyte swap backed memory disk named .Dq Li md3 : .Bd -literal -offset indent mdconfig -s 1g -u md3 .Ed .Pp Detach and free all resources used by .Pa /dev/md3 : .Bd -literal -offset indent mdconfig -du md3 .Ed .Pp Show detailed information on current memory disks: .Bd -literal -offset indent mdconfig -lv .Ed .Pp Resize the .Dq Li md3 memory disk to 2 gigabytes: .Bd -literal -offset indent mdconfig -rs 2g -u md3 .Ed .Pp Create a 1 gigabyte swap backed disk, initialize an .Xr ffs 7 file system on it, and mount it on .Pa /tmp : .Bd -literal -offset indent mdconfig -s 1g -u md10 newfs -U /dev/md10 mount /dev/md10 /tmp chmod 1777 /tmp .Ed .Pp Create a memory disk out of an ISO 9660 CD image file, using the first available .Xr md 4 device, and then mount it: .Bd -literal -offset indent mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt .Ed .Pp Create a file-backed device from a hard disk image that begins with 512K of raw header information. .Xr gnop 8 is used to skip over the header information, positioning .Pa md1.nop to the start of the filesystem in the image. .Bd -literal -offset indent mdconfig -u md1 -f diskimage.img gnop create -o 512K md1 mount /dev/md1.nop /mnt .Ed .Sh SEE ALSO .Xr open 2 , .Xr md 4 , .Xr ffs 7 , .Xr gpart 8 , .Xr mdmfs 8 , .Xr malloc 9 .Sh HISTORY The .Nm utility first appeared in .Fx 5.0 as a cleaner replacement for the vn kernel module and the vnconfig utility combo. .Sh AUTHORS The .Nm utility was written by .An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
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