{
    "mode": "man",
    "parameter": "mkfs.msdos",
    "section": "8",
    "url": "https://www.chedong.com/phpMan.php/man/mkfs.msdos/8/json",
    "generated": "2026-06-02T21:27:07Z",
    "synopsis": "mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]",
    "sections": {
        "NAME": {
            "content": "mkfs.fat - create an MS-DOS FAT filesystem\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "mkfs.fat  is  used to create a FAT filesystem on a device or in an image file.  DEVICE is the\nspecial file corresponding to the device (e.g. /dev/sdXX) or the image file (which  does  not\nneed  to  exist when the option -C is given).  BLOCK-COUNT is the number of blocks on the de‐\nvice and size of one block is always 1024 bytes, independently of  the  sector  size  or  the\ncluster  size.  Therefore BLOCK-COUNT specifies size of filesystem in KiB unit and not in the\nnumber of sectors (like for all other mkfs.fat options).  If omitted, mkfs.fat  automatically\nchooses a filesystem size to fill the available space.\n\nTwo different variants of the FAT filesystem are supported.  Standard is the FAT12, FAT16 and\nFAT32 filesystems as defined by Microsoft and widely used on hard disks and  removable  media\nlike USB sticks and SD cards.  The other is the legacy Atari variant used on Atari ST.\n\nIn  Atari mode, if not directed otherwise by the user, mkfs.fat will always use 2 sectors per\ncluster, since GEMDOS doesn't like other values very much.  It will  also  obey  the  maximum\nnumber  of  sectors GEMDOS can handle.  Larger filesystems are managed by raising the logical\nsector size.  An Atari-compatible serial number for the filesystem is generated, and a 12 bit\nFAT  is used only for filesystems that have one of the usual floppy sizes (720k, 1.2M, 1.44M,\n2.88M), a 16 bit FAT otherwise.  This can be overridden with the -F option.  Some PC-specific\nboot sector fields aren't written, and a boot message (option -m) is ignored.\n",
            "subsections": []
        },
        "OPTIONS": {
            "content": "",
            "subsections": [
                {
                    "name": "-a",
                    "content": "structures to cluster size, to make sure that  as  long  as  the  partition  is  properly\naligned,  so will all the data structures in the filesystem.  This option disables align‐\nment; this may provide a handful of additional clusters of storage at the  expense  of  a\nsignificant performance degradation on RAIDs, flash media or large-sector hard disks.\n",
                    "flag": "-a"
                },
                {
                    "name": "-A",
                    "content": "erwise select standard FAT filesystem.  This is selected by default if mkfs.fat is run on\n68k Atari Linux.\n",
                    "flag": "-A"
                },
                {
                    "name": "-b",
                    "content": "Selects  the  location of the backup boot sector for FAT32.  Default depends on number of\nreserved sectors, but usually is sector 6.  If there is a free space available after  the\nbackup boot sector then backup of the FAT32 info sector is put after the backup boot sec‐\ntor, usually at sector 7.  The backup must be  within  the  range  of  reserved  sectors.\nValue 0 completely disables creating of backup boot and info FAT32 sectors.\n",
                    "flag": "-b"
                },
                {
                    "name": "-c",
                    "content": "",
                    "flag": "-c"
                },
                {
                    "name": "-C",
                    "content": "tem to it.  This can be used to create the new filesystem in a file instead of on a  real\ndevice, and to avoid using dd in advance to create a file of appropriate size.  With this\noption, the BLOCK-COUNT must be  given,  because  otherwise  the  intended  size  of  the\nfilesystem  wouldn't  be  known.   The file created is a sparse file, which actually only\ncontains the meta-data areas (boot sector, FATs, and root directory).  The data  portions\nwon't  be  stored on the disk, but the file nevertheless will have the correct size.  The\nresulting file can be copied later to a floppy disk or other device, or mounted through a\nloop device.\n",
                    "flag": "-C"
                },
                {
                    "name": "-D",
                    "content": "Specify  the  BIOS  drive number to be stored in the FAT boot sector.  For hard disks and\nremovable medias it is usually 0x80–0xFF (0x80 is first hard disk C:, 0x81 is second hard\ndisk  D:,  ...),  for  floppy devices or partitions to be used for floppy emulation it is\n0x00–0x7F (0x00 is first floppy A:, 0x01 is second floppy B:).\n",
                    "flag": "-D"
                },
                {
                    "name": "-f",
                    "content": "Specify the number of file allocation tables in the filesystem.  The default is 2.\n",
                    "flag": "-f"
                },
                {
                    "name": "-F",
                    "content": "Specifies the type of file allocation tables used (12, 16 or  32  bit).   If  nothing  is\nspecified,  mkfs.fat  will  automatically select between 12, 16 and 32 bit, whatever fits\nbetter for the filesystem size.\n",
                    "flag": "-F"
                },
                {
                    "name": "-g",
                    "content": "Specify HEADS and SECTORS-PER-TRACK numbers which represents  disk  geometry  of  DEVICE.\nBoth  numbers are stored into the FAT boot sector.  Number SECTORS-PER-TRACK is used also\nfor aligning the total count of FAT sectors.  By default disk geometry is read  from  DE‐\nVICE  itself.   If  it is not available then LBA-Assist Translation and translation table\nfrom the SD Card Part 2 File System Specification based on total number of  disk  sectors\nis used.\n",
                    "flag": "-g"
                },
                {
                    "name": "-h",
                    "content": "Specify  the  number  of so-called hidden sectors, as stored in the FAT boot sector: this\nnumber represents the beginning sector of the partition containing the file system.  Nor‐\nmally  this is an offset (in sectors) relative to the start of the disk, although for MBR\nlogical volumes contained in an extended partition of type 0x05 (a non-LBA extended  par‐\ntition),  a  quirk  in the MS-DOS implementation of FAT requires it to be relative to the\npartition's immediate containing Extended Boot Record.  Boot code and other software han‐\ndling FAT volumes may also rely on this field being set up correctly; most modern FAT im‐\nplementations will ignore it.  By default, if the DEVICE is  a  partition  block  device,\nmkfs.fat  uses  the partition offset relative to disk start.  Otherwise, mkfs.fat assumes\nzero.  Use this option to override this behaviour.\n",
                    "flag": "-h"
                },
                {
                    "name": "-i",
                    "content": "Sets the volume ID of the newly created filesystem; VOLUME-ID  is  a  32-bit  hexadecimal\nnumber  (for example, 2e24ec82).  The default is a number which depends on the filesystem\ncreation time.\n",
                    "flag": "-i"
                },
                {
                    "name": "-I",
                    "content": "a device with partitions or virtual mapping.  mkfs.fat will complain and tell you that it\nrefuses to work.  This is different when using MO disks.  One doesn't always need  parti‐\ntions  on  MO disks.  The filesystem can go directly to the whole disk.  Under other OSes\nthis is known as the superfloppy format.  This switch will force mkfs.fat to  work  prop‐\nerly.\n",
                    "flag": "-I"
                },
                {
                    "name": "-l",
                    "content": "Read the bad blocks list from FILENAME.\n",
                    "flag": "-l"
                },
                {
                    "name": "-m",
                    "content": "Sets  the  message  the  user receives on attempts to boot this filesystem without having\nproperly installed an operating system.  The message file must not exceed 418 bytes  once\nline  feeds  have been converted to carriage return-line feed combinations, and tabs have\nbeen expanded.  If the filename is a hyphen (-), the text is taken from standard input.\n",
                    "flag": "-m"
                },
                {
                    "name": "-M",
                    "content": "Specify the media type to be stored in the FAT boot sector.  This value is  usually  0xF8\nfor  hard disks and is 0xF0 or a value from 0xF9 to 0xFF for floppies or partitions to be\nused for floppy emulation.\n\n--mbr[=y|yes|n|no|a|auto]\nFill (fake) MBR table with disk signature one partition which starts  at  sector  0  (in‐\ncludes  MBR  itself)  and  spans  whole disk device.  It is needed only for non-removable\ndisks used on Microsoft Windows systems and  only  when  formatting  whole  unpartitioned\ndisk.   Location  of  the disk signature and partition table overlaps with the end of the\nfirst FAT sector (boot code location), therefore there is no additional space usage.  De‐\nfault is auto mode in which mkfs.fat put MBR table only for non-removable disks when for‐\nmatting whole unpartitioned disk.\n",
                    "flag": "-M"
                },
                {
                    "name": "-n",
                    "content": "Sets the volume name (label) of the filesystem.  The volume name can be up to 11  charac‐\nters  long.   Supplying  an  empty string, a string consisting only of white space or the\nstring \"NO NAME\" as VOLUME-NAME has the same effect as not giving the -n option.  The de‐\nfault is no label.\n\n--codepage=PAGE\nUse DOS codepage PAGE to encode label.  By default codepage 850 is used.\n",
                    "flag": "-n"
                },
                {
                    "name": "-r",
                    "content": "Select the minimal number of entries available in the root directory.  The default is 112\nor 224 for floppies and 512 for hard disks.  Note that this is minimal number and it  may\nbe increased by mkfs.fat due to alignment of structures.  See also mkfs.fat option -a.\n",
                    "flag": "-r"
                },
                {
                    "name": "-R",
                    "content": "Select  the  minimal  number  of reserved sectors.  With FAT32 format at least 2 reserved\nsectors are needed, the default is 32.  Otherwise the default is 1 (only  the  boot  sec‐\ntor).  Note that this is minimal number and it may be increased by mkfs.fat due to align‐\nment of structures.  See also mkfs.fat option -a.\n",
                    "flag": "-R"
                },
                {
                    "name": "-s",
                    "content": "Specify the number of disk sectors per cluster.  Must be a power of 2, i.e. 1, 2,  4,  8,\n... 128.\n",
                    "flag": "-s"
                },
                {
                    "name": "-S",
                    "content": "Specify the number of bytes per logical sector.  Must be a power of 2 and greater than or\nequal to 512, i.e. 512, 1024, 2048, 4096, 8192, 16384, or 32768.  Values larger than 4096\nare not conforming to the FAT file system specification and may not work everywhere.\n",
                    "flag": "-S"
                },
                {
                    "name": "-v",
                    "content": "--offset SECTOR\nWrite  the filesystem at a specific sector into the device file.  This is useful for cre‐\nating a filesystem in a partitioned disk image without having to set up a loop device.\n\n--variant TYPE\nCreate a filesystem of variant TYPE.  Acceptable values are standard and  atari  (in  any\ncombination of upper/lower case).  See above under DESCRIPTION for the differences.\n",
                    "flag": "-v"
                },
                {
                    "name": "--help",
                    "content": "Display option summary and exit.\n",
                    "long": "--help"
                },
                {
                    "name": "--invariant",
                    "content": "Use  constants  for  normally randomly generated or time based data such as volume ID and\ncreation time.  Multiple runs of mkfs.fat on the same  device  create  identical  results\nwith this option.  Its main purpose is testing mkfs.fat.\n",
                    "long": "--invariant"
                }
            ]
        },
        "BUGS": {
            "content": "mkfs.fat  can  not  create  boot-able  filesystems.  This isn't as easy as you might think at\nfirst glance for various reasons and has been discussed a lot already.  mkfs.fat simply  will\nnot support it ;)\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "fatlabel(8), fsck.fat(8)\n",
            "subsections": []
        },
        "HOMEPAGE": {
            "content": "The     home    for    the    dosfstools    project    is    its    GitHub    project    page\n⟨https://github.com/dosfstools/dosfstools⟩.\n",
            "subsections": []
        },
        "AUTHORS": {
            "content": "dosfstools were written  by  Werner  Almesberger  ⟨werner.almesberger@lrc.di.epfl.ch⟩,  Roman\nHodek  ⟨Roman.Hodek@informatik.uni-erlangen.de⟩, and others.  Current maintainers are Andreas\nBombe ⟨aeb@debian.org⟩ and Pali Rohár ⟨pali.rohar@gmail.com⟩.\n\n\n\ndosfstools 4.2                               2021-01-31                                  MKFS.FAT(8)",
            "subsections": []
        }
    },
    "summary": "mkfs.fat - create an MS-DOS FAT filesystem",
    "flags": [
        {
            "flag": "-a",
            "long": null,
            "arg": null,
            "description": "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 align‐ ment; 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."
        },
        {
            "flag": "-A",
            "long": null,
            "arg": null,
            "description": "erwise select standard FAT filesystem. This is selected by default if mkfs.fat is run on 68k Atari Linux."
        },
        {
            "flag": "-b",
            "long": null,
            "arg": null,
            "description": "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 sec‐ tor, 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."
        },
        {
            "flag": "-c",
            "long": null,
            "arg": null,
            "description": ""
        },
        {
            "flag": "-C",
            "long": null,
            "arg": null,
            "description": "tem 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."
        },
        {
            "flag": "-D",
            "long": null,
            "arg": null,
            "description": "Specify the BIOS drive number to be stored in the FAT boot sector. For hard disks and removable medias 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:)."
        },
        {
            "flag": "-f",
            "long": null,
            "arg": null,
            "description": "Specify the number of file allocation tables in the filesystem. The default is 2."
        },
        {
            "flag": "-F",
            "long": null,
            "arg": null,
            "description": "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."
        },
        {
            "flag": "-g",
            "long": null,
            "arg": null,
            "description": "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 DE‐ VICE 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."
        },
        {
            "flag": "-h",
            "long": null,
            "arg": null,
            "description": "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. Nor‐ mally 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 par‐ tition), 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 han‐ dling FAT volumes may also rely on this field being set up correctly; most modern FAT im‐ plementations 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."
        },
        {
            "flag": "-i",
            "long": null,
            "arg": null,
            "description": "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."
        },
        {
            "flag": "-I",
            "long": null,
            "arg": null,
            "description": "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 parti‐ tions 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 prop‐ erly."
        },
        {
            "flag": "-l",
            "long": null,
            "arg": null,
            "description": "Read the bad blocks list from FILENAME."
        },
        {
            "flag": "-m",
            "long": null,
            "arg": null,
            "description": "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."
        },
        {
            "flag": "-M",
            "long": null,
            "arg": null,
            "description": "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 (in‐ cludes 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. De‐ fault is auto mode in which mkfs.fat put MBR table only for non-removable disks when for‐ matting whole unpartitioned disk."
        },
        {
            "flag": "-n",
            "long": null,
            "arg": null,
            "description": "Sets the volume name (label) of the filesystem. The volume name can be up to 11 charac‐ ters 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 de‐ fault is no label. --codepage=PAGE Use DOS codepage PAGE to encode label. By default codepage 850 is used."
        },
        {
            "flag": "-r",
            "long": null,
            "arg": null,
            "description": "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."
        },
        {
            "flag": "-R",
            "long": null,
            "arg": null,
            "description": "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 sec‐ tor). Note that this is minimal number and it may be increased by mkfs.fat due to align‐ ment of structures. See also mkfs.fat option -a."
        },
        {
            "flag": "-s",
            "long": null,
            "arg": null,
            "description": "Specify the number of disk sectors per cluster. Must be a power of 2, i.e. 1, 2, 4, 8, ... 128."
        },
        {
            "flag": "-S",
            "long": null,
            "arg": null,
            "description": "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."
        },
        {
            "flag": "-v",
            "long": null,
            "arg": null,
            "description": "--offset SECTOR Write the filesystem at a specific sector into the device file. This is useful for cre‐ ating 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."
        },
        {
            "flag": "",
            "long": "--help",
            "arg": null,
            "description": "Display option summary and exit."
        },
        {
            "flag": "",
            "long": "--invariant",
            "arg": null,
            "description": "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."
        }
    ],
    "examples": [],
    "see_also": [
        {
            "name": "fatlabel",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/fatlabel/8/json"
        },
        {
            "name": "fsck.fat",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/fsck.fat/8/json"
        }
    ]
}