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

     mdconfig - configure and enable memory disks

     mdconfig -a -t type [-o [no]option] [-s size] [-f file] [-u unit]
     mdconfig -d -u unit
     mdconfig -l [-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.

             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.

     -s size
             Size of the memory disk.  Size is the number of 512 bytes sectors
             unless suffixed with a k, m, or g which denotes kilobyte,
             megabyte and gigabyte respectively.

     -o [no]option
             Set or reset options.

                     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

                     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:

           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

     md(4), disklabel(8), fdisk(8), malloc(9)

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

     The mdconfig utility was written by Poul-Henning Kamp <>.

FreeBSD 11.0-PRERELEASE        December 31, 2000       FreeBSD 11.0-PRERELEASE


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