||System Manager's Manual
mkfs.fat - create an MS-DOS filesystem under Linux
mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]
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
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 ;)
- 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
- 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 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
- -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.
- Check the device for bad blocks before creating the filesystem.
- 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
- 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 filesystem creation time.
- 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. 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. Values larger than 4096 are not conforming to the FAT file system
specification and may not work everywhere.
- Verbose execution.
- 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
- Display option summary and exit.