|MDCONFIG(8)||FreeBSD System Manager's Manual||MDCONFIG(8)|
NAMEmdconfig — 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/cylinder]|
|mdconfig||-d -u unit [ -o [ no] force]|
|mdconfig||-r -u unit -s size [ -o [ no] force]|
|mdconfig||-l [ -n][ -v][ -f file][ -u unit]|
DESCRIPTIONThe mdconfig utility configures and enables md(4) devices.
Options indicate an action to be performed:
- Attach a memory disk. This will configure and attach a memory disk with the parameters specified and attach it to the system.
- Detach a memory disk from the system and release all resources.
- Resize a memory disk.
- -t type
Select the type of the memory disk.
- 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.
- A file specified with -f file becomes the backing store for this memory disk.
- Storage for this type of memory disk is allocated from buffer memory. Pages get pushed out to swap when the system is under memory pressure, otherwise they stay in the operating memory. Using swap backing is generally preferred instead of using malloc backing.
- -f file
- Filename to use for the vnode type memory disk. The -a and -t vnode options are implied if not specified.
- List configured devices. If given with -u, display details about that particular device. If given with -f file, display md(4) device names of which file is used as the backing store. If both of -u and -f options are specified, display devices which match the two conditions. If the -v option is specified, show all details.
- When printing md(4) device names, print only the unit number without the md(4) 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. The -a and -t swap options are implied if not specified.
- -S sectorsize
- Sectorsize to use for the memory disk, in bytes.
- -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.
EXAMPLESCreate a 4 megabyte malloc(9) backed memory disk. The name of the allocated unit will be printed on stdout, such as “
mdconfig -a -t malloc -s 4m
Create a disk named /dev/md4 with /tmp/boot.flp as backing storage:
mdconfig -a -t vnode -f /tmp/boot.flp -u 4
Detach and free all resources used by /dev/md4:
mdconfig -d -u 4
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
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
mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt
Create a file-backed device from a hard disk image that begins with 512K of raw header information. gnop(8) is used to skip over the header information, positioning md1.nop to the start of the filesystem in the image.
mdconfig -f diskimage.img -u 1 gnop create -o 512K md1 mount /dev/md1.nop /mnt
HISTORYThe mdconfig utility first appeared in FreeBSD 5.0 as a cleaner replacement for the vn(4) and vnconfig(8) combo.
AUTHORSThe mdconfig utility was written by <phk@FreeBSD.org>.
|June 20, 2013||FreeBSD|