NAME
newfs
, mount_mfs
— construct a new UFS file
system
SYNOPSIS
newfs |
[-L volname]
[-NCEOU ] [-S
sector-size] [-T
disktype] [-a
maxcontig] [-b
block-size] [-c
cylinders] [-d
rotdelay] [-e
maxbpg] [-f
frag-size] [-g
avgfilesize] [-h
avfpdir] [-i
bytes] [-k
skew] [-l
interleave] [-m
free space] [-n
rotational positions] [-o
optimization] [-p
sectors] [-r
revolutions] [-s
size] [-t
tracks] [-u
sectors] [-v ]
[-x sectors]
special |
mount_mfs |
[-NU ] [-F
file] [-T
disktype] [-a
maxcontig] [-b
block-size] [-c
cylinders] [-d
rotdelay] [-e
maxbpg] [-f
frag-size] [-i
bytes] [-m
free space] [-n
rotational positions] [-o
options] [-s
size] [-v ]
special node |
DESCRIPTION
Newfs
is used to initialize and clear filesystems before
first use. Before running newfs
or
mount_mfs
, the disk must be labeled using
disklabel(8). Newfs
builds a file
system on the specified special file. (We often refer to the “special
file” as the “disk”, although the special file need not
be a physical disk. In fact, it need not even be special.) Typically the
defaults are reasonable, however newfs
has numerous
options to allow the defaults to be selectively overridden.
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 attempt to unmount its corresponding
file system. The parameters to mount_mfs
are the
same as those to newfs
. If the
-T
flag is specified (see below), the special file
is unused. Otherwise, it 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.
mount_mfs
creates the raw character device
/dev/mfs<PID> to represent the backing store
while the mount is active. This device may be read but not written and
allows swap-based MFS filesystems to be dumped if desired.
The following options define the general layout policies:
-T
disktype- For backward compatibility and for
mount_mfs
. -E
- Use TRIM to erase the device's data before creating the file system. The underlying device must have the TRIM sysctl enabled. Only devices that support TRIM will have such a sysctl option (kern.cam.da.X.trim_enabled).
-F
fileMount_mfs
will use this file for the image of the filesystem. Whenmount_mfs
exits, this file will be left behind.-C
- Tell
Mount_mfs
to copy the underlying filesystem into the MFS mount being created over it. -L
volname- Add a volume label to the new file system.
-N
- Cause the file system parameters to be printed out without really creating the file system.
-O
- Create a 4.3BSD format filesystem. This options is primarily used to build root filesystems that can be understood by older boot ROMs.
-T
- Use information for the specified disk from /etc/disktab instead of trying to get geometry information from the storage device.
-U
- Enables soft updates on the new filesystem.
-a
maxcontig- Specify the maximum number of contiguous blocks that will be laid out
before forcing a rotational delay (see the
-d
option). The default value is 1. See tunefs(8) for more details on how to set this option. -b
block-size- The block size of the file system, in bytes. It must be a power of 2. The default size is 16384 bytes, and the smallest allowable size is 4096 bytes. The optimal block:fragment ratio is 8:1. Other ratios are possible, but are not recommended, and may produce unpredictable results.
-c
#cylinders/group- The number of cylinders 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 parameters, in particular the block size and the number of bytes per inode.
-d
rotdelay- This parameter once specified the minimum time in milliseconds required to initiate another disk transfer on the same cylinder. It was used in determining the rotationally optimal layout for disk blocks within a file. Modern disks with read/write-behind achieve higher performance with this feature disabled, so this value should be left at the default value of 0 milliseconds. See tunefs(8) for more details on how to set this option.
-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. The default is about one quarter of the total blocks in a cylinder group. See tunefs(8) for more details on how to set this option.
-f
frag-size- The fragment size of the file system in bytes. It must be a power of two ranging in value between blocksize/8 and blocksize. The default is 2048 bytes.
-g
avgfilesize- The expected average file size for the file system.
-h
avgfpdir- The expected average number of files per directory on the file system.
-i
number of bytes per inode- Specify the density of inodes in the file system. The default is to create an inode for every (4 * frag-size) 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. One inode is required for each distinct file, so this value effectively specifies the average file size on the file system.
-m
free space %- The percentage of space reserved from normal users; the minimum free space
threshold. The default value used is defined by
MINFREE
from<ufs/ffs/fs.h>
, currently 8%. See tunefs(8) for more details on how to set this option. -n
number of distinguished rotational positions- UFS(5) has the ability to keep track of the availability of blocks
at different rotational positions, so that it could lay out the data to be
picked up with minimum rotational latency. This parameter specifies the
default number of rotational positions to distinguish.
Nowadays this value should be set to 1 (which essentially disables the rotational position table) because modern drives with read-ahead and write-behind do better without the rotational position table.
-o
optimization preference- (
space
ortime
). 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. If the value of minfree (see above) is less than 8%, the default is to optimize forspace
; if the value of minfree is greater than or equal to 8%, the default is to optimize fortime
. See tunefs(8) for more details on how to set this option. -s
size- The size of the file system in sectors. This value defaults to the size of
the raw partition specified in special (in other
words,
newfs
will use the entire partition for the file system). -v
- Specify that the disk does not contain any partitions, and that
newfs
should build a file system on the whole disk. This option is useful for synthetic disks such asvinum
. It may also be used to allownewfs
to operate on regular files. When operating on a regular file,newfs
will synthesize a reasonable geometry for the filesystem.
The following options override the standard sizes for the disk
geometry. Their default values are taken from the disk label. Changing these
defaults 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 changing any of these values from their defaults
will make it impossible for
fsck(8) to find the alternate superblocks if the standard superblock
is lost.
-S
sector-size- The size of a sector in bytes (almost never anything but 512).
-k
sector 0 skew, per track- Used to describe perturbations in the media format to compensate for a slow controller. Track skew is the offset of sector 0 on track N relative to sector 0 on track N-1 on the same cylinder. This option is of historical importance only; modern controllers are always fast enough to handle operations back-to-back.
-l
hardware sector interleave- Used to describe perturbations in the media format to compensate for a
slow controller. Interleave is physical sector interleave on each track,
specified as the denominator of the ratio:
Thus an interleave of 1/1 implies contiguous layout, while 1/2 implies logical sector 0 is separated by one sector from logical sector 1. This option is of historical importance only; the physical sector layout of modern disks is not visible from outside.
sectors read/sectors passed over
-p
spare sectors per track- Spare sectors (bad sector replacements) are physical sectors that occupy
space at the end of each track. They are not counted as part of the
sectors/track (
-u
) since they are not available to the file system for data allocation. This option is of historical importance only. Modern disks perform their own bad sector allocation. -r
revolutions/minute- The speed of the disk in revolutions per minute. This value is no longer of interest, since all the parameters which depend on it are usually disabled.
-t
#tracks/cylinder- The number of tracks/cylinder available for data allocation by the file system. The default is 1. If zero is specified, the value from the device geometry will be used.
-u
sectors/track- The number of sectors per track available for data allocation by the file
system. The default is 4096. If zero is specified, the value from the
device geometry will be used. This does not include sectors reserved at
the end of each track for bad block replacement (see the
-p
option). -x
spare sectors per cylinder- Spare sectors (bad sector replacements) are physical sectors that occupy
space at the end of the last track in the cylinder. They are deducted from
the sectors/track (
-u
) of the last track of each cylinder since they are not available to the file system for data allocation. This option is of historical importance only. Modern disks perform their own bad sector allocation.
The options to the mount_mfs
command are
as described for the newfs
command, except for the
-o
option.
That option is as follows:
-o
- Options are specified with a
-o
flag followed by a comma separated string of options. See the mount(8) man page for possible options and their meanings.
EXAMPLES
newfs /dev/ad3s1a
Creates a new
UFS(5) file system on ad3s1a.
newfs
will use a block size of 16384 bytes, a
fragment size of 2048 bytes and the largest possible number of cylinders per
group. These values tend to produce better performance for most applications
than the historical defaults (8192 byte block size and 1024 byte fragment
size). This large fragment size may lead to large amounts of wasted space on
filesystems that contain a large number of small files.
mount_mfs -s 131072 -o
nosuid,nodev,nosymfollow /dev/da0s1b /tmp
Mount a 64 MB large memory file system on
/tmp, with
mount(8) options nosuid
,
nodev
, and nosymfollow
.
SEE ALSO
fdformat(1), disktab(5), fs(5), UFS(5), camcontrol(8), disklabel(8), dumpfs(8), fsck(8), makefs(8), mount(8), tunefs(8), vinum(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).
HISTORY
The newfs
command appeared in
4.2BSD. The mount_mfs
command appeared in 4.4BSD.