# mkfs.fat

## NAME



           mkfs.fat - create an MS-DOS FAT filesystem
    


## SYNOPSIS



           **mkfs.fat**[_OPTIONS_] _DEVICE_ [_BLOCK-COUNT_]
    


## DESCRIPTION



           **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



           **-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.  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 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.  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.
    
           **-g** _HEADS_ /_SECTORS-PER-TRACK_
               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.
    
           **-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** 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.
    
           **-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.
    
           **--mbr**[=_y_ |_yes_ |_n_ |_no_ |_a_ |_auto_]
               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.
    
           **--codepage** =_PAGE_
               Use DOS codepage _PAGE_ to encode label.  By default codepage
               850 is used.
    
           **-r** _ROOT-DIR-ENTRIES_
               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**.
    
           **-R** _NUMBER-OF-RESERVED-SECTORS_
               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**.
    
           **-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** _SECTOR-SIZE_
               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 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**.
    


## BUGS



           **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
           ;)
    


## HOMEPAGE



           The home for the **dosfstools** project is its GitHub project page 
           ⟨https://github.com/dosfstools/dosfstools⟩.
    


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