MDMFS(8) FreeBSD System Manager's Manual MDMFS(8)
NAME
mdmfs, mount_mfs - configure and mount an in-memory file system using the
md(4) driver or the tmpfs(5) filesystem
SYNOPSIS
mdmfs [-DLlMNnPStTUX] [-a maxcontig] [-b block-size]
[-c blocks-per-cylinder-group] [-d max-extent-size]
[-E path-mdconfig] [-e maxbpg] [-F file] [-f frag-size] [-i bytes]
[-k skel] [-m percent-free] [-O optimization] [-o mount-options]
[-p permissions] [-s size] [-T fstype] [-v version] [-w user:group]
md-device mount-point
DESCRIPTION
The mdmfs utility is designed to be a work-alike and look-alike of the
deprecated mount_mfs(8). The end result is essentially the same, but is
accomplished in a completely different way. Based on md-device, the
mdmfs utility either creates a tmpfs(5) filesystem, or it configures an
md(4) disk using mdconfig(8), puts a UFS file system on it (unless -P was
specified) using newfs(8), and mounts it using mount(8). It can handle
geom_uzip(4) compressed disk images, as long as the kernel supports this
GEOM class. All the command line options are passed to the appropriate
program at the appropriate stage in order to achieve the desired effect.
When md-device is `auto', mdmfs uses tmpfs(5) if it is present in the
kernel or can be loaded as a module, otherwise it falls back to using
md(4) auto-unit as if `md' had been specified.
When md-device is `tmpfs', mdmfs mounts a tmpfs(5) filesystem,
translating the -s size option, if present, into a `-o size=' mount
option. Any -o options on the command line are passed through to the
tmpfs(5) mount. Options specific to mdconfig(8) or newfs(8) are ignored.
When md-device does not result in tmpfs(5) being used, then an md(4)
device is configured instead. By default, mdmfs creates a swap-based
(MD_SWAP) disk with soft-updates enabled and mounts it on mount-point.
It uses the md(4) device specified by md-device. If md-device is `md'
(no unit number), it will use md(4)'s auto-unit feature to automatically
select an unused device. Unless otherwise specified with one of the
options below, it uses the default arguments to all the helper programs.
The following options are available. Where possible, the option letter
matches the one used by mount_mfs(8) for the same thing.
-a maxcontig
Specify the maximum number of contiguous blocks that will be laid
out before forcing a rotational delay (see the -d option).
-b block-size
The block size of the file system, in bytes.
-c blocks-per-cylinder-group
The number of blocks per cylinder group in the file system.
-D If not using auto-unit, do not run mdconfig(8) to try to detach
the unit before attaching it.
-d max-extent-size
The file system may choose to store large files using extents.
This parameter specifies the largest extent size that may be
used. It is presently limited to its default value which is 16
times the file system blocksize.
-E path-mdconfig
Use path-mdconfig as a location of the mdconfig(8) utility.
-e maxbpg
Indicate the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin
allocating blocks from another cylinder group.
-F file
Create a vnode-backed (MD_VNODE) memory disk backed by file.
-f frag-size
The fragment size of the file system in bytes.
-i bytes
Number of bytes per inode.
-k skel
Copy the content of directory skel into mount-point.
-l Enable multilabel MAC on the new file system.
-L Show the output of the helper programs. By default, it is sent
to /dev/null.
-M Create a malloc(9) backed disk (MD_MALLOC) instead of a swap-
backed disk.
-m percent-free
The percentage of space reserved for the superuser.
-N Do not actually run the helper programs. This is most useful in
conjunction with -X.
-n Do not create a .snap directory on the new file system.
-O optimization
Select the optimization preference; valid choices are space and
time, which will optimize for minimum space fragmentation and
minimum time spent allocating blocks, respectively.
-o mount-options
Specify the mount options with which to mount the file system.
See mount(8) for more information.
-P Preserve the existing file system; do not run newfs(8). This
only makes sense if -F is specified to create a vnode-backed
disk.
-p permissions
Set the file (directory) permissions of the mount point
mount-point to permissions. The permissions argument can be in
any of the mode formats recognized by chmod(1). If symbolic
permissions are specified, the operation characters "+" and "-"
are interpreted relative to the initial permissions of "a=rwx".
-S Do not enable soft-updates on the file system.
-s size
Specify the size of the disk to create. This only makes sense if
-F is not specified. That is, this will work when the backing
storage is some form of memory, as opposed to a fixed-size file.
The size may include the usual SI suffixes (k, m, g, t, p). A
number without a suffix is interpreted as a count of 512-byte
sectors.
-t Turn on the TRIM enable flag for newfs(8). When used with a file
system that issue BIO_DELETE bio requests, md(4) returns deleted
blocks to the system memory pool.
-T fstype
Specify a file system type for a vnode-backed memory disk. Any
file system supported by mount(8) command can be specified. This
option only makes sense when -F and -P are used.
-U Enable soft-updates on the file system. This is the default, and
is accepted only for compatibility. It is only really useful to
negate the -S flag, should such a need occur.
-v version
Specify the UFS version number for use on the file system; it may
be either 1 or 2. The default is derived from the default of the
newfs(8) command.
-w user:group
Set the owner and group to user and group, respectively. The
arguments have the same semantics as with chown(8), but
specifying just a user or just a group is not supported.
-X Print what command will be run before running it, and other
assorted debugging information.
The -F and -s options are passed to mdconfig(8) as -f and -s,
respectively. The -a, -b, -c, -d, -e, -f, -i, -m and -n options are
passed to newfs(8) with the same letter. The -O option is passed to
newfs(8) as -o. The -o option is passed to mount(8) with the same
letter. The -T option is passed to mount(8) as -t. For information on
semantics, refer to the documentation of the programs that the options
are passed to.
EXAMPLES
Create and mount a 32 megabyte swap-backed file system on /tmp:
mdmfs -s 32m md /tmp
The same file system created as an entry in /etc/fstab:
md /tmp mfs rw,-s32m 2 0
Create and mount a 16 megabyte malloc-backed file system on /tmp using
the /dev/md1 device; furthermore, do not use soft-updates on it and mount
it async:
mdmfs -M -S -o async -s 16m md1 /tmp
Create and mount a geom_uzip(4) based compressed disk image:
mdmfs -P -F foo.uzip -oro md.uzip /tmp/
Mount the same image, specifying the /dev/md1 device:
mdmfs -P -F foo.uzip -oro md1.uzip /tmp/
Configure a vnode-backed file system and mount its first partition, using
automatic device numbering:
mdmfs -P -F foo.img mds1a /tmp/
Mount a vnode-backed cd9660 file system using automatic device numbering:
mdmfs -T cd9660 -P -F foo.iso md /tmp
COMPATIBILITY
The mdmfs utility, while designed to be compatible with mount_mfs(8), can
be useful by itself. Since mount_mfs(8) had some silly defaults, a
"compatibility" mode is provided for the case where bug-to-bug
compatibility is desired.
Compatibility is enabled by starting mdmfs with the name mount_mfs or mfs
(as returned by getprogname(3)). In this mode, the following behavior,
as done by mount_mfs(8), is duplicated:
• The file mode of mount-point is set by default to 01777 as if
-p 1777 was given on the command line.
SEE ALSO
md(4), fstab(5), tmpfs(5), mdconfig(8), mount(8), newfs(8)
HISTORY
The mdmfs utility appeared in FreeBSD 5.0.
AUTHORS
Dima Dorfman
FreeBSD 13.1-RELEASE-p6 October 31, 2019 FreeBSD 13.1-RELEASE-p6
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