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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | BUGS | SEE ALSO | HOMEPAGE | AUTHORS | COLOPHON |
MKFS.FAT(8) System Manager's Manual MKFS.FAT(8)
mkfs.fat - create an MS-DOS FAT filesystem
mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]
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.
-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.
-b SECTOR-OF-BACKUP
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
sectors.
-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.
-D DRIVE-NUMBER
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.
-h NUMBER-OF-HIDDEN-SECTORS
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.
-M FAT-MEDIA-TYPE
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.
-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.
--codepage=PAGE
Use DOS codepage PAGE to encode label. By default codepage 850
is used.
-r ROOT-DIR-ENTRIES
Select the number of entries available in the root directory.
The default is 112 or 224 for floppies and 512 for hard disks.
-R NUMBER-OF-RESERVED-SECTORS
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).
-s SECTORS-PER-CLUSTER
Specify the number of disk sectors per cluster. Must be a power
of 2, i.e. 1, 2, 4, 8, ... 128.
-S LOGICAL-SECTOR-SIZE
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
everywhere.
-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.
--help
Display option summary and exit.
--invariant
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.
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 ;)
fatlabel(8), fsck.fat(8)
The home for the dosfstools project is its GitHub project page
⟨https://github.com/dosfstools/dosfstools⟩.
dosfstools were written by Werner Almesberger ⟨werner.almesberger@
lrc.di.epfl.ch⟩, Roman Hodek ⟨Roman.Hodek@informatik.uni-
erlangen.de⟩, and others. The current maintainer is Andreas Bombe
⟨aeb@debian.org⟩.
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 ⟨https://github.com/dosfstools/dosfstools⟩. If you have
a bug report for this manual page, see
⟨https://github.com/dosfstools/dosfstools/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/dosfstools/dosfstools.git⟩ on 2020-08-13. (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
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dosfstools 4.1+git 2017-10-01 MKFS.FAT(8)
Pages that refer to this page: mkfs(8)