Name

mkfs − construct a file system

Syntax

/etc/mkfs [ -N ] special size [ nsect ] [ ntrack ] [ blksize ]
[ fragsize ] [ ncpg ] [ minfree] [ rps ] [ nbpi ] [ opt ]

Description

File systems are normally created with the newfs() command.

The -N option is used to run mkfs in no update mode.  In this mode, mkfs will not write to special.

The mkfs command constructs a file system by writing on the special file special.  The numeric size specifies the number of sectors in the file system.  The mkfs command builds a file system with a root directory and a lost+found directory.  For further information, see fsck(.). The number of i-nodes is calculated as a function of the file system size. No boot program is initialized by mkfs. For further information, see newfs(.).

When the on-disks inodes of the file system are written, each contains a unique number in its generation number field.  This number uniquely identifies each inode in a file system. 

The optional arguments allow fine tune control over the parameters of the file system.  The nsect argument specifies the number of sectors per track on the disk.  The ntrack argument specifies the number of tracks per cylinder on the disk.  The blksize argument gives the primary block size for files on the file system.  It must be a power of two, currently selected from 4096 or 8192.  The fragsize argument gives the fragment size for files on the file system.  The fragsize argument represents the smallest amount of disk space that will be allocated to a file.  It must be a power of two currently selected from the range 512 to 8192.  The ncpg argument specifies the number of disk cylinders per cylinder group.  This number must be in the range 1 to 32.  The minfree argument specifies the minimum percentage of free disk space allowed.  Once the file system capacity reaches this threshold, only the superuser is allowed to allocate disk blocks.  The default value is 10%.  If a disk does not revolve at 60 revolutions per second, the rps parameter may be specified.  Users with special demands for their file systems are referred to “A Fast File System for UNIX” in the ULTRIX Supplementary Documents, Volume 3: System Manager for a discussion of the tradeoffs in using different configurations.  The nbpi argument specifies the number (ratio) of bytes per inode.  The default is 2048 bytes.  The opt argument is used to indicate the whether the file system should optimize for space or time.  The opt argument can be assigned a value of s or t. 

Restrictions

If /bin/mkfs is invoked without arguments, the RISC machines dump core instead of returning an error.

If the user-specified value for nbpi exceeds the maximum value allowed, the user is not notified by mkfs (or by newfs ).

See Also

dir(5), fs(5), fsck(8), newfs(8), tunefs(8)
"A Fast File System for UNIX", Supplementary Documents, Volume 3: System Manager