mdconfig(8)

NAME

mdconfig - configure and enable memory disks

SYNOPSIS

mdconfig -a -t type [-n] [-o [no]option] ... [-f  file]  [-s
size]
         [-S  sectorsize]  [-u  unit] [-x sectors/track] [-y
heads/cyl]
mdconfig -d -u unit
mdconfig -l [-n] [-u unit]

DESCRIPTION

The mdconfig utility configures and enables md(4) devices.

Options indicate an action to be performed:

-a Attach a memory disk. This will configure and at

tach a memory

disk with the parameters specified and attach it to

the system.

-d Detach a memory disk from the system and release all

resources.

-t type

Select the type of the memory disk.

malloc Storage for this type of memory disk is al

located with

malloc(9). This limits the size to the

malloc bucket
limit in the kernel. If the -o reserve op

tion is not
set, creating and filling a large malloc

backed memory
disk is a very easy way to panic a system.

vnode A file specified with -f file becomes the

backingstore

for this memory disk.

swap Swap space is used to back this memory

disk.

-f file

Filename to use for the vnode type memory disk.

-l List configured devices. If given with -u, display

details about

that particular device.

-n When printing md device names, print only the unit

number without

the md prefix.

-s size

Size of the memory disk. Size is the number of 512

byte sectors
unless suffixed with a b, k, m, g, or t which de

notes byte, kilobyte, megabyte, gigabyte and terabyte respectively.

-S sectorsize

Sectorsize to use for malloc backed device.

-x sectors/track

See the description of the -y option below.

-y heads/cylinder

For malloc or vnode backed devices, the -x and -y

options can be
used to specify a synthetic geometry. This is use

ful for constructing bootable images for later download to oth

er devices.

-o [no]option

Set or reset options.

[no]async

For vnode backed devices: avoid IO_SYNC for

increased
performance but at the risk of deadlocking

the entire
kernel.

[no]reserve

Allocate and reserve all needed storage from

the start,
rather than as needed.

[no]cluster

Enable clustering on this disk.

[no]compress

Enable/Disable compression features to re

duce memory
usage.

[no]force

Disable/Enable extra sanity checks to pre

vent the user
from doing something that might adversely

affect the system.

[no]readonly

Enable/Disable readonly mode.

-u unit

Request a specific unit number for the md(4) device

instead of
automatic allocation.

EXAMPLES

To create a 4 megabyte malloc(9) backed memory disk. The

name of the
allocated unit will be output on stdout like ``md3'':

mdconfig -a -t malloc -s 4m

To create a disk named /dev/md4 with /tmp/boot.flp as back

ing:

mdconfig -a -t vnode -f /tmp/boot.flp -u 4

To detach and free all resources used by /dev/md4:

mdconfig -d -u 4

To create and mount a 128MByte swap backed file system on

/tmp:

mdconfig -a -t swap -s 128M -u 10
newfs -U /dev/md10
mount /dev/md10 /tmp
chmod 1777 /tmp

To create a 5MB file-backed disk:

dd if=/dev/zero of=somebackingfile bs=1k count=5k
mdconfig -a -t vnode -f somebackingfile -u 0
bsdlabel -w md0 auto
newfs md0c
mount /dev/md0c /mnt

SEE ALSO

md(4), bsdlabel(8), fdisk(8), mdmfs(8), malloc(9)

HISTORY

The mdconfig utility first appeared in FreeBSD 5.0 as a

cleaner replacement for the vn(4) and vnconfig(8) combo.

AUTHORS

The mdconfig utility was written by Poul-Henning Kamp

<phk@FreeBSD.org>.

BSD November 6, 2004

BSD