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vn(4) [freebsd man page]

MD(4)							   BSD Kernel Interfaces Manual 						     MD(4)

md -- memory disk SYNOPSIS
The md driver provides support for four kinds of memory backed virtual disks: malloc Backing store is allocated using malloc(9). Only one malloc-bucket is used, which means that all md devices with malloc backing must share the malloc-per-bucket-quota. The exact size of this quota varies, in particular with the amount of RAM in the system. The exact value can be determined with vmstat(8). preload A file loaded by loader(8) with type 'md_image' is used for backing store. For backwards compatibility the type 'mfs_root' is also recognized. If the kernel is created with option MD_ROOT the first preloaded image found will become the root file system. vnode A regular file is used as backing store. This allows for mounting ISO images without the tedious detour over actual physical media. swap Backing store 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. For more information, please see mdconfig(8). EXAMPLES
To create a kernel with a ramdisk or MD file system, your kernel config needs the following options: options MD_ROOT # MD is a potential root device options MD_ROOT_SIZE=8192 # 8MB ram disk makeoptions MFS_IMAGE=/h/foo/ARM-MD options ROOTDEVNAME="ufs:md0" The image in /h/foo/ARM-MD will be loaded as the initial image each boot. To create the image to use, please follow the steps to create a file-backed disk found in the mdconfig(8) man page. Other tools will also create these images, such as NanoBSD. SEE ALSO
disklabel(8), fdisk(8), loader(8), mdconfig(8), mdmfs(8), newfs(8), vmstat(8) HISTORY
The md driver first appeared in FreeBSD 4.0 as a cleaner replacement for the MFS functionality previously used in PicoBSD and in the FreeBSD installation process. The md driver did a hostile takeover of the vn(4) driver in FreeBSD 5.0. AUTHORS
The md driver was written by Poul-Henning Kamp <>. BSD
October 30, 2007 BSD

Check Out this Related Man Page

TMPFS(5)						      BSD File Formats Manual							  TMPFS(5)

tmpfs -- efficient memory file system SYNOPSIS
To compile this driver into the kernel, place the following line in your kernel configuration file: options TMPFS Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): tmpfs_load="YES" DESCRIPTION
The tmpfs driver will permit the FreeBSD kernel to access tmpfs file systems. OPTIONS
The following options are available when mounting tmpfs file systems: gid Specifies the group ID of the root inode of the file system. Defaults to the mount point's GID. uid Specifies the user ID of the root inode of the file system. Defaults to the mount point's UID. mode Specifies the mode (in octal notation) of the root inode of the file system. Defaults to the mount point's mode. inodes Specifies the maximum number of nodes available to the file system. If not specified, the file system chooses a reasonable maximum based on the file system size, which can be limited with the size option. size Specifies the total file system size in bytes. If zero (the default) or a value larger than SIZE_MAX - PAGE_SIZE is given, the available amount of memory (including main memory and swap space) will be used. maxfilesize Specifies the maximum file size in bytes. Defaults to the maximum possible value. EXAMPLES
To mount a tmpfs memory file system: mount -t tmpfs tmpfs /tmp SEE ALSO
nmount(2), unmount(2), fstab(5), mdmfs(8), mount(8) HISTORY
The tmpfs driver first appeared in FreeBSD 7.0. AUTHORS
The tmpfs kernel implementation was written by Julio M. Merino Vidal <> as a Google SoC project. Rohit Jalan and others ported it from NetBSD to FreeBSD. This manual page was written by Xin LI <>. BUGS
Some file system mount time options may not be well-supported. BSD
April 23, 2012 BSD

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