mkfs.fat(8) — Linux manual page


MKFS.FAT(8)                System Manager's Manual               MKFS.FAT(8)

NAME         top

       mkfs.fat - create an MS-DOS FAT filesystem

SYNOPSIS         top

       mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]

DESCRIPTION         top

       mkfs.fat is used to create a FAT filesystem on a device or in an
       image file.  DEVICE is the special file corresponding to the device
       (e.g. /dev/sdXX) or the image file (which does not need to exist when
       the option -C is given).  BLOCK-COUNT is the number of blocks on the
       device.  If omitted, mkfs.fat automatically chooses a filesystem size
       to fill the available space.

       Two different variants of the FAT filesystem are supported.  Standard
       is the FAT12, FAT16 and FAT32 filesystems as defined by Microsoft and
       widely used on hard disks and removable media like USB sticks and SD
       cards.  The other is the legacy Atari variant used on Atari ST.

       In Atari mode, if not directed otherwise by the user, mkfs.fat will
       always use 2 sectors per cluster, since GEMDOS doesn't like other
       values very much.  It will also obey the maximum number of sectors
       GEMDOS can handle.  Larger filesystems are managed by raising the
       logical sector size.  An Atari-compatible serial number for the
       filesystem is generated, and a 12 bit FAT is used only for
       filesystems that have one of the usual floppy sizes (720k, 1.2M,
       1.44M, 2.88M), a 16 bit FAT otherwise.  This can be overridden with
       the -F option.  Some PC-specific boot sector fields aren't written,
       and a boot message (option -m) is ignored.

OPTIONS         top

       -a  Normally, for any filesystem except very small ones, mkfs.fat
           will align all the data structures to cluster size, to make sure
           that as long as the partition is properly aligned, so will all
           the data structures in the filesystem.  This option disables
           alignment; this may provide a handful of additional clusters of
           storage at the expense of a significant performance degradation
           on RAIDs, flash media or large-sector hard disks.

       -A  Select using the Atari variation of the FAT filesystem if that
           isn't active already, otherwise select standard FAT filesystem.
           This is selected by default if mkfs.fat is run on 68k Atari

           Selects the location of the backup boot sector for FAT32.
           Default depends on number of reserved sectors, but usually is
           sector 6.  The backup must be within the range of reserved

       -c  Check the device for bad blocks before creating the filesystem.

       -C  Create the file given as DEVICE on the command line, and write
           the to-be-created filesystem to it.  This can be used to create
           the new filesystem in a file instead of on a real device, and to
           avoid using dd in advance to create a file of appropriate size.
           With this option, the BLOCK-COUNT must be given, because
           otherwise the intended size of the filesystem wouldn't be known.
           The file created is a sparse file, which actually only contains
           the meta-data areas (boot sector, FATs, and root directory).  The
           data portions won't be stored on the disk, but the file
           nevertheless will have the correct size.  The resulting file can
           be copied later to a floppy disk or other device, or mounted
           through a loop device.

           Specify the BIOS drive number to be stored in the FAT boot
           sector.  This value is usually 0x80 for hard disks and 0x00 for
           floppy devices or partitions to be used for floppy emulation.

       -f NUMBER-OF-FATS
           Specify the number of file allocation tables in the filesystem.
           The default is 2.

       -F FAT-SIZE
           Specifies the type of file allocation tables used (12, 16 or 32
           bit).  If nothing is specified, mkfs.fat will automatically
           select between 12, 16 and 32 bit, whatever fits better for the
           filesystem size.

           Specify the number of so-called hidden sectors, as stored in the
           FAT boot sector: this number represents the beginning sector of
           the partition containing the file system. Normally this is an
           offset (in sectors) relative to the start of the disk, although
           for MBR logical volumes contained in an extended partition of
           type 0x05 (a non-LBA extended partition), a quirk in the MS-DOS
           implementation of FAT requires it to be relative to the
           partition's immediate containing Extended Boot Record. Boot code
           and other software handling FAT volumes may also rely on this
           field being set up correctly; most modern FAT implementations
           will ignore it.  By default, if the DEVICE is a partition block
           device, mkfs.fat uses the partition offset relative to disk
           start. Otherwise, mkfs.fat assumes zero. Use this option to
           override this behaviour.

       -i VOLUME-ID
           Sets the volume ID of the newly created filesystem; VOLUME-ID is
           a 32-bit hexadecimal number (for example, 2e24ec82).  The default
           is a number which depends on the filesystem creation time.

       -I  It is typical for fixed disk devices to be partitioned so, by
           default, you are not permitted to create a filesystem across the
           entire device.  mkfs.fat will complain and tell you that it
           refuses to work.  This is different when using MO disks.  One
           doesn't always need partitions on MO disks.  The filesystem can
           go directly to the whole disk.  Under other OSes this is known as
           the 'superfloppy' format.  This switch will force mkfs.fat to
           work properly.

       -l FILENAME
           Read the bad blocks list from FILENAME.

       -m MESSAGE-FILE
           Sets the message the user receives on attempts to boot this
           filesystem without having properly installed an operating system.
           The message file must not exceed 418 bytes once line feeds have
           been converted to carriage return-line feed combinations, and
           tabs have been expanded.  If the filename is a hyphen (-), the
           text is taken from standard input.

           Specify the media type to be stored in the FAT boot sector.  This
           value is usually 0xF8 for hard disks and is 0xF0 or a value from
           0xF9 to 0xFF for floppies or partitions to be used for floppy

       -n VOLUME-NAME
           Sets the volume name (label) of the filesystem.  The volume name
           can be up to 11 characters long.  Supplying an empty string, a
           string consisting only of white space or the string "NO NAME" as
           VOLUME-NAME has the same effect as not giving the -n option.  The
           default is no label.

           Use DOS codepage PAGE to encode label.  By default codepage 850
           is used.

           Select the number of entries available in the root directory.
           The default is 112 or 224 for floppies and 512 for hard disks.

           Select the number of reserved sectors.  With FAT32 format at
           least 2 reserved sectors are needed, the default is 32.
           Otherwise the default is 1 (only the boot sector).

           Specify the number of disk sectors per cluster.  Must be a power
           of 2, i.e. 1, 2, 4, 8, ... 128.

           Specify the number of bytes per logical sector.  Must be a power
           of 2 and greater than or equal to 512, i.e. 512, 1024, 2048,
           4096, 8192, 16384, or 32768.  Values larger than 4096 are not
           conforming to the FAT file system specification and may not work

       -v  Verbose execution.

       --offset SECTOR
           Write the filesystem at a specific sector into the device file.
           This is useful for creating a filesystem in a partitioned disk
           image without having to set up a loop device.

       --variant TYPE
           Create a filesystem of variant TYPE.  Acceptable values are
           'standard' and 'atari' (in any combination of upper/lower case).
           See above under DESCRIPTION for the differences.

           Display option summary and exit.

           Use constants for normally randomly generated or time based data
           such as volume ID and creation time.  Multiple runs of mkfs.fat
           on the same device create identical results with this option.
           Its main purpose is testing mkfs.fat.

BUGS         top

       mkfs.fat can not create boot-able filesystems.  This isn't as easy as
       you might think at first glance for various reasons and has been
       discussed a lot already.  mkfs.fat simply will not support it ;)

SEE ALSO         top

       fatlabel(8), fsck.fat(8)

HOMEPAGE         top

       The home for the dosfstools project is its GitHub project page 

AUTHORS         top

       dosfstools were written by Werner Almesberger ⟨werner.almesberger@⟩, Roman Hodek ⟨Roman.Hodek@informatik.uni-⟩, and others.  The current maintainer is Andreas Bombe

COLOPHON         top

       This page is part of the dosfstools (Tools for making and checking
       MS-DOS FAT filesystems) project.  Information about the project can
       be found at ⟨⟩.  If you have
       a bug report for this manual page, see
       ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨⟩ on 2020-09-18.  (At
       that time, the date of the most recent commit that was found in the
       repository was 2020-02-14.)  If you discover any rendering problems
       in this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

dosfstools 4.1+git               2017-10-01                      MKFS.FAT(8)

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