mkdosfs

MKFS.FAT(8) dosfstools MKFS.FAT(8)

NAME
mkfs.fat - create an MS-DOS filesystem under Linux

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

DESCRIPTION
mkfs.fat is used to create an MS-DOS filesystem under Linux on a device (usually a disk
partition). DEVICE is the special file corresponding to the device (e.g. /dev/sdXX).
BLOCK-COUNT is the number of blocks on the device. If omitted, mkfs.fat automatically
determines the filesystem size.

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 Use Atari variation of the MS-DOS filesystem. This is default if mkfs.fat is run on
an Atari, then this option turns off Atari format. There are some differences when
using Atari format: 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. Under Atari format, 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 oth‐
erwise. 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.

-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 usu‐
ally 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
Select the number of hidden sectors in the volume. Apparently some digital cameras
get indigestion if you feed them a CF card without such hidden sectors, this option
allows you to satisfy them.

-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 filesys‐
tem 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 parti‐
tions 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 char‐
acters long. The default is no label.

-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.

-v Verbose execution.

--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.

--help
Display option summary and exit.

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 ;)