mkdosfs(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 and size of one block is always 1024 bytes,
       independently of the sector size or the cluster size.  Therefore
       BLOCK-COUNT specifies size of filesystem in KiB unit and not in
       the number of sectors (like for all other mkfs.fat options).  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 Linux.

           Selects the location of the backup boot sector for FAT32.
           Default depends on number of reserved sectors, but usually is
           sector 6.  If there is a free space available after the
           backup boot sector then backup of the FAT32 info sector is
           put after the backup boot sector, usually at sector 7.  The
           backup must be within the range of reserved sectors.  Value 0
           completely disables creating of backup boot and info FAT32

       -c  Check the device for bad blocks before creating the

       -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.  For hard disks and removable media it is usually
           0x80–0xFF (0x80 is first hard disk C:, 0x81 is second hard
           disk D:, ...), for floppy devices or partitions to be used
           for floppy emulation it is 0x00–0x7F (0x00 is first floppy
           A:, 0x01 is second floppy B:).

       -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 HEADS and SECTORS-PER-TRACK numbers which represents
           disk geometry of DEVICE.  Both numbers are stored into the
           FAT boot sector.  Number SECTORS-PER-TRACK is used also for
           aligning the total count of FAT sectors.  By default disk
           geometry is read from DEVICE itself.  If it is not available
           then LBA-Assist Translation and translation table from the SD
           Card Part 2 File System Specification based on total number
           of disk sectors is used.

           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

       -I  Ignore and disable safety checks.  By default mkfs.fat
           refuses to create a filesystem on a device with partitions or
           virtual mapping.  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 emulation.

           Fill (fake) MBR table with disk signature one partition which
           starts at sector 0 (includes MBR itself) and spans whole disk
           device.  It is needed only for non-removable disks used on
           Microsoft Windows systems and only when formatting whole
           unpartitioned disk.  Location of the disk signature and
           partition table overlaps with the end of the first FAT sector
           (boot code location), therefore there is no additional space
           usage.  Default is auto mode in which mkfs.fat put MBR table
           only for non-removable disks when formatting whole
           unpartitioned disk.

       -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 minimal number of entries available in the root
           directory.  The default is 112 or 224 for floppies and 512
           for hard disks.  Note that this is minimal number and it may
           be increased by mkfs.fat due to alignment of structures.  See
           also mkfs.fat option -a.

           Select the minimal 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).  Note
           that this is minimal number and it may be increased by
           mkfs.fat due to alignment of structures.  See also mkfs.fat
           option -a.

           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 filesystem 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 filesystem specification and
           may not work everywhere.  Some operating systems have
           requirement that filesystem sector size must match logical
           disk device sector size. So default value is logical disk
           sector size.

       -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

       --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
       ⟨⟩, Roman Hodek ⟨Roman.Hodek@⟩, and others.  Current maintainers are
       Andreas Bombe ⟨⟩ and Pali Rohár ⟨pali.rohar@⟩.

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 2024-06-14.
       (At that time, the date of the most recent commit that was found
       in the repository was 2023-10-10.)  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 4.2+git             2021-01-31                    MKFS.FAT(8)

Pages that refer to this page: mkfs(8)