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.\" @(#)newfs.8 8.3 (Berkeley) 3/27/94
.Nd construct a new file system
the disk must be labeled using
builds a file system on the specified special device
basing its defaults on the information in the disk label.
Typically the defaults are reasonable, however
has numerous options to allow the defaults to be selectively overridden.
is used to build a file system in virtual memory and then mount it
exits and the contents of the file system are lost
when the file system is unmounted.
is sent a signal while running,
for example during system shutdown,
it will attempt to unmount its
corresponding file system.
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.
The following options define the general layout policies.
Causes the file system parameters to be printed out
without really creating the file system.
Creates a 4.3BSD format filesystem.
This options is primarily used to build root filesystems
that can be understood by older boot ROMs.
This specifies the maximum number of contiguous blocks that will be
laid out before forcing a rotational delay (see the
The default value is one.
for more details on how to set this option.
The block size of the file system, in bytes.
.It Fl c Ar #cylinders/group
The number of cylinders per cylinder group in a file system.
This specifies the expected time (in milliseconds) to service a transfer
completion interrupt and initiate a new transfer on the same disk.
The default is 4 milliseconds.
for more details on how to set this option.
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 default is about one quarter of the total blocks in a cylinder group.
for more details on how to set this option.
The fragment size of the file system in bytes.
.It Fl i Ar number of bytes per inode
This specifies the density of inodes in the file system.
The default is to create an inode for each 2048 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.
.It Fl m Ar free space \&%
The percentage of space reserved from normal users; the minimum free
The default value used is 10%.
for more details on how to set this option.
.It Fl o Ar optimization\ preference
.Pq ``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.
If the value of minfree (see above) is less than 10%,
the default is to optimize for space;
if the value of minfree is greater than or equal to 10%,
the default is to optimize for time.
for more details on how to set this option.
The size of the file system in sectors.
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
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
to find the alternate superblocks if the standard superblock is lost.
The size of a sector in bytes (almost never anything but 512).
.It Fl k Ar sector \&0 skew , per track
Used to describe perturbations in the media format to compensate for
Track skew is the offset of sector 0 on track N relative to sector 0
on track N-1 on the same cylinder.
.It Fl l Ar hardware sector interleave
Used to describe perturbations in the media format to compensate for
Interleave is physical sector interleave on each track,
specified as the denominator of the ratio:
.Dl sectors read/sectors passed over
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.
.It Fl p Ar 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
since they are not available to the file system for data allocation.
.It Fl r Ar revolutions/minute
The speed of the disk in revolutions per minute.
.It Fl t Ar #tracks/cylinder
The number of tracks/cylinder available for data allocation by the file
.It Fl u Ar sectors/track
The number of sectors per track available for data allocation by the file
This does not include sectors reserved at the end of each track for bad
block replacement (see the
.It Fl x Ar 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
of the last track of each cylinder since they are not available to the file
system for data allocation.
command are as described for the
That option is as follows:
Options are specified with a
flag followed by a comma separated string of options.
man page for possible options and their meanings.
.%T A Fast File System for UNIX ,
.%J ACM Transactions on Computer Systems 2
.%O (reprinted in the BSD System Manager's Manual)