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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 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 backingstore
		      for this memory disk.

	     swap     swapspace is used to back this memory disk.

     -f file
	     Filename to use for the vnode type memory disk.

     -l      List information about configured md(4) devices.  If the -u
	     option is used in conjuction with this, the output is limited to
	     information on the specified 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 k, m, or g which denotes kilobyte,
	     megabyte and gigabyte 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 useful for con-
		     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 sys-
		     tem.

	     [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 backing:

	   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

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