mdconfig man page on FreeBSD

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MDCONFIG(8)		  BSD System Manager's Manual		   MDCONFIG(8)

     mdconfig — configure and enable memory disks

     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 [-o [no]force]
     mdconfig -l [-n] [-v] [-u unit]

     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 gener‐
		      ally 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

     -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, kilo‐
	     byte, 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 con‐
	     structing bootable images for later download to other devices.

     -o [no]option
	     Set or reset options.

		     For vnode backed devices: avoid IO_SYNC for increased
		     performance but at the risk of deadlocking the entire

		     Allocate and reserve all needed storage from the start,
		     rather than as needed.

		     Enable clustering on this disk.

		     Enable/Disable compression features to reduce memory

		     Disable/Enable extra sanity checks to prevent the user
		     from doing something that might adversely affect the sys‐

		     Enable/Disable readonly mode.

     -u unit
	     Request a specific unit number for the md(4) device instead of
	     automatic allocation.

     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

     md(4), ffs(7), bsdlabel(8), fdisk(8), mdmfs(8), malloc(9)

     The mdconfig utility first appeared in FreeBSD 5.0 as a cleaner replace‐
     ment for the vn(4) and vnconfig(8) combo.

     The mdconfig utility was written by Poul-Henning Kamp ⟨⟩.

BSD				 June 21, 2008				   BSD

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