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man : mount_mfs(8)
NEWFS(8) OpenBSD System Manager's Manual NEWFS(8)
NAME
newfs, mount_mfs - construct a new file system
SYNOPSIS
newfs [-Nq] [-b block-size] [-c fragments-per-cylinder-group] [-e maxbpg]
[-f frag-size] [-g avgfilesize] [-h avgfpdir] [-i bytes]
[-m free-space] [-O filesystem-format] [-o optimization]
[-S sector-size] [-s size] [-T disktype] [-t fstype] special
mount_mfs [-b block-size] [-c fragments-per-cylinder-group] [-e maxbpg]
[-f frag-size] [-i bytes] [-m free-space] [-o options] [-P file]
[-s size] special node
DESCRIPTION
Before running newfs or mount_mfs, the disk must be labeled using
disklabel(8). newfs builds a file system on the specified special de-
vice, basing its defaults on the information in the disk label. Typical-
ly the defaults are reasonable, although newfs has numerous options to
allow the defaults to be selectively overridden.
The special file should be a raw device, for example /dev/rsd0a; if a
relative path like sd0a is specified, the corresponding raw device is
used.
mount_mfs is used to build a file system in virtual memory and then mount
it on a specified node. mount_mfs exits and the contents of the file
system are lost when the file system is unmounted. If mount_mfs is sent
a signal while running, for example during system shutdown, it will at-
tempt to unmount its corresponding file system. The parameters to
mount_mfs are the same as those to newfs. The special file is only used
to read the disk label which provides a set of configuration parameters
for the memory based file system. The special file is typically that of
the primary swap area, since that is where the file system will be backed
up when free memory gets low and the memory supporting the file system
has to be paged. If the keyword ``swap'' is used instead of a special
file name, default configuration parameters will be used. (This option
is useful when trying to use mount_mfs on a machine without any disks.)
Both newfs and mount_mfs now have the functionality of fsirand(8) built
in, so it is not necessary to run fsirand(8) manually unless you wish to
re-randomize the file system (or list the inode generation numbers).
The options to newfs are as follows:
-b block-size
The block size of the file system, in bytes. The default is
16KB.
-c fragments-per-cylinder-group
The number of fragments per cylinder group in a file system.
The default is to compute the maximum allowed by the other
parameters. This value is dependent on a number of other pa-
rameters, in particular the block size and the number of
bytes per inode.
-e maxbpg This indicates 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. The de-
fault is about one quarter of the total blocks in a cylinder
group. See tunefs(8) for more details on how to set this op-
tion.
-f frag-size
The fragment size of the file system in bytes. The default
is 2048.
-g avgfilesize
The expected average file size for the file system in bytes.
-h avgfpdir
The expected average number of files per directory on the
file system.
-i bytes This specifies the density of inodes in the file system. The
default is to create an inode for each 8192 bytes of data
space. If fewer inodes are desired, a larger number should
be used; to create more inodes a smaller number should be
given.
-m free-space
The percentage of space reserved from normal users; the mini-
mum free space threshold. The default value used is 5%. See
tunefs(8) for more details on how to set this option.
-N Causes the file system parameters to be printed out without
really creating the file system.
-O filesystem-format
Select the filesystem format:
0 4.3BSD format file system. This option is primar-
ily used to build root file systems that can be
understood by older boot ROMs.
1 Fast File System (the default).
2 Enhanced Fast File System (FFS2).
-o optimization
space or time. The file system can either be instructed to
try to minimize the time spent allocating blocks, or to try
to minimize the space fragmentation on the disk. Unless an
optimization has been specified, if the value of minfree (see
above) is less than 5%, the default is to optimize for space;
if the value of minfree is greater than or equal to 5%, the
default is to optimize for time. See tunefs(8) for more de-
tails on how to set this option.
-q Operate in quiet mode. With this option, newfs will not
print extraneous information like superblock backups.
-S sector-size
The size of a sector in bytes (almost never anything but
512). Changing this is useful only when using newfs to build
a file system whose raw image will eventually be used on a
different type of disk than the one on which it is initially
created (for example on a write-once disk). Note that chang-
ing this from its default will make it impossible for fsck(8)
to find the alternate superblocks if the standard superblock
is lost.
-s size The size of the file system in sectors. The maximum size of
a Fast File System is 2,147,483,647 (2^31 - 1) sectors, which
is slightly less than 1TB, assuming a sector size of 512
bytes. FFS2 file systems can be as large as the maximum par-
tition size supported. Note however that for mount_mfs the
practical limit is based on datasize in login.conf(5), and
ultimately depends on the per-arch MAXDSIZ limit.
-T disktype
Uses information for the specified disk from disktab(5) in-
stead of trying to get the information from the disklabel(5).
-t fstype Set the file system type of which file system you wish to
create. newfs will be smart enough to run the alternate
newfs_XXX program instead.
The options to mount_mfs are as described for newfs, except for the -o
and -P options.
Those options are as follows:
-o options
Options are specified with a -o flag followed by a comma separat-
ed string of options. See the mount(8) man page for possible op-
tions and their meanings.
-P file
If file is a directory, populate the created mfs file system with
the contents of the directory. If file is a block device, popu-
late the created mfs file system with the contents of the FFS
file system contained on the device.
If the -P file option is not used, the owner and mode of the created mfs
file system will be the same as the owner and mode of the mount point.
ENVIRONMENT
TMPDIR Directory in which to create temporary mount points for use by
mount_mfs -P instead of /tmp.
SEE ALSO
disktab(5), fs(5), disklabel(8), dumpfs(8), fsck(8), fsirand(8),
growfs(8), mount(8), tunefs(8)
M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for
UNIX", ACM Transactions on Computer Systems 2, 3, pp 181-197, August
1984, (reprinted in the BSD System Manager's Manual).
M. McKusick, M. Karels, and K. Bostic, "A Pageable Memory Based
Filesystem", USENIX Summer Conference Proceedings, 1990.
HISTORY
The newfs command appeared in 4.2BSD.
OpenBSD 4.5 August 3, 2008 3
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