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/cylinder] |
mdconfig |
-d -u unit
[-o
[no]force] |
mdconfig |
-l [-n]
[-v]
[-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 attach 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 allocated with
malloc(9). This limits the size to the malloc bucket
limit in the kernel. If the -o
reserve option 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 backing store for this memory
disk.
- swap
- Storage for this type of memory disk is allocated from
buffer memory. Pages get pushed out to the swap when the system is
under memory pressure, otherwise they stay in the operating memory.
Using swap backing is generally preferable over
malloc backing.
- -f
file
- Filename to use for the vnode type memory disk. Options
-a and -t vnode
are implied if not specified.
- -l
- List configured devices. If given with
-u, display details about that particular device. If
-v option specified, show all details.
- -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 denotes byte, kilobyte, megabyte, gigabyte and
terabyte respectively. Options -a and
-t swap are implied if not
specified.
- -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 useful for
constructing bootable images for later download to other 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 reduce memory
usage.
- [no]force
- Disable/Enable extra sanity checks to prevent 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.
The last form,
mdconfig file, is
provided for convenience as an abbreviation of
mdconfig
-a -t vnode
-f file.
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 backing storage:
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 a 128MByte swap backed disk, initialize an
ffs(7)
file system on it, and mount it 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 (
-a and
-t
vnode are implied):
dd if=/dev/zero of=somebackingfile bs=1k count=5k
mdconfig -f somebackingfile -u 0
bsdlabel -w md0 auto
newfs md0c
mount /dev/md0c /mnt
To create an
md(4) device out of an ISO 9660 CD image file
(
-a and
-t vnode are
implied), using the first available
md(4) device, and then
mount the new memory disk:
mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt
SEE ALSO¶
md(4),
ffs(7),
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⟩.