MKFS(8) System Manager's Manual MKFS(8)
mkfs - construct a file system
/usr/etc/mkfs [ -N ] special size [ nsect ] [ ntrack ]
[ blksize ] [ fragsize ] [ ncpg ] [ minfree ]
[ rps ] [ nbpi ] [ opt ] [ apc ] [ rot ] [ nrpos ] [ maxcontig ]
Note: file systems are normally created with the newfs(8) command.
mkfs constructs a file system by writing on the special file special
unless the -N flag has been specified. special must be specified as a
raw device and disk partition. For example, to create a file system on
sd0, specify /dev/rsd0[a-h], where a-h is the disk partition.
The numeric size specifies the number of sectors in the file system.
mkfs builds a file system with a root directory and a lost+found direc-
tory (see fsck(8)). The number of inodes is calculated as a function
of the file system size. No boot program is initialized by mkfs (see
You must be super-user to use this command.
-N Print out the file system parameters without actually creating
the file system.
The following arguments allow fine tune control over the parameters of
the file system.
nsect The number of sectors per track on the disk. The default is 32.
ntrack The number of tracks per cylinder on the disk. The default is
The primary block size for files on the file system. It must be
a power of two, currently selected from 4096 or 8192 (the
The fragment size for files on the file system. The fragsize
represents the smallest amount of disk space that will be allo-
cated to a file. It must be a power of two currently selected
from the range 512 to 8192. The default is 1024.
ncpg The number of disk cylinders per cylinder group. The default is
The minimum percentage of free disk space allowed. Once the
file system capacity reaches this threshold, only the super-user
is allowed to allocate disk blocks. The default value is 10%.
rps The rotational speed of the disk, in revolutions per second.
The default is 60.
nbpi The number of bytes for which one inode block is allocated.
This parameter is currently set at one inode block for every
opt Space or time optimization preference; s specifies optimization
for space, t specifies optimization for time. The default is t.
apc The number of alternates per cylinder (SCSI devices only). The
default is 0.
rot The expected time (in milliseconds) to service a transfer com-
pletion interrupt and initiate a new transfer on the same disk.
It is used to decide how much rotational spacing to place
between successive blocks in a file. The default is 1.
Note: in earlier releases mkfs tried to guess what the right
value for this parameter by querying the controller type. Since
mkfs is a more primitive interface, this query has been moved
into newfs. mkfs now does exactly what you tell it to do.
nrpos The number of distinguished rotational positions. The default
The maximum number of blocks that will be allocated contiguously
before inserting a rotational delay. The default is 1.
Note: This parameter also controls clustering. Regardless of
the value of rotdelay, clustering is enabled only when maxcontig
is greater than 1. Clustering allows higher I/O rates for
sequential I/O and is described in tunefs(8).
Users with special demands for their file systems are referred to the
paper cited below for a discussion of the tradeoffs in using different
dir(5), fs(5), fsck(8), newfs(8), tunefs(8)
McKusick, Joy, Leffler; A Fast File System for UNIX
newfs(8) is preferred for most routine uses.
5 July 1990 MKFS(8)