1MKFS.FAT(8) System Manager's Manual MKFS.FAT(8)
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6 mkfs.fat - create an MS-DOS FAT filesystem
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9 mkfs.fat [OPTIONS] DEVICE [BLOCK-COUNT]
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12 mkfs.fat is used to create a FAT filesystem on a device or in an image
13 file. DEVICE is the special file corresponding to the device (e.g.
14 /dev/sdXX) or the image file (which does not need to exist when the op‐
15 tion -C is given). BLOCK-COUNT is the number of blocks on the device
16 and size of one block is always 1024 bytes, independently of the sector
17 size or the cluster size. Therefore BLOCK-COUNT specifies size of
18 filesystem in KiB unit and not in the number of sectors (like for all
19 other mkfs.fat options). If omitted, mkfs.fat automatically chooses a
20 filesystem size to fill the available space.
21 Two different variants of the FAT filesystem are supported. Standard
23 is the FAT12, FAT16 and FAT32 filesystems as defined by Microsoft and
24 widely used on hard disks and removable media like USB sticks and SD
25 cards. The other is the legacy Atari variant used on Atari ST.
26 In Atari mode, if not directed otherwise by the user, mkfs.fat will al‐
28 ways use 2 sectors per cluster, since GEMDOS doesn't like other values
29 very much. It will also obey the maximum number of sectors GEMDOS can
30 handle. Larger filesystems are managed by raising the logical sector
31 size. An Atari-compatible serial number for the filesystem is gener‐
32 ated, and a 12 bit FAT is used only for filesystems that have one of
33 the usual floppy sizes (720k, 1.2M, 1.44M, 2.88M), a 16 bit FAT other‐
34 wise. This can be overridden with the -F option. Some PC-specific
35 boot sector fields aren't written, and a boot message (option -m) is
36 ignored.
37
39 -a Normally, for any filesystem except very small ones, mkfs.fat will
40 align all the data structures to cluster size, to make sure that as
41 long as the partition is properly aligned, so will all the data
42 structures in the filesystem. This option disables alignment; this
43 may provide a handful of additional clusters of storage at the ex‐
44 pense of a significant performance degradation on RAIDs, flash me‐
45 dia or large-sector hard disks.
46 -A Select using the Atari variation of the FAT filesystem if that
48 isn't active already, otherwise select standard FAT filesystem.
49 This is selected by default if mkfs.fat is run on 68k Atari Linux.
50 -b SECTOR-OF-BACKUP
52 Selects the location of the backup boot sector for FAT32. Default
53 depends on number of reserved sectors, but usually is sector 6. If
54 there is a free space available after the backup boot sector then
55 backup of the FAT32 info sector is put after the backup boot sec‐
56 tor, usually at sector 7. The backup must be within the range of
57 reserved sectors. Value 0 completely disables creating of backup
58 boot and info FAT32 sectors.
59 -c Check the device for bad blocks before creating the filesystem.
61 -C Create the file given as DEVICE on the command line, and write the
63 to-be-created filesystem to it. This can be used to create the new
64 filesystem in a file instead of on a real device, and to avoid us‐
65 ing dd in advance to create a file of appropriate size. With this
66 option, the BLOCK-COUNT must be given, because otherwise the in‐
67 tended size of the filesystem wouldn't be known. The file created
68 is a sparse file, which actually only contains the meta-data areas
69 (boot sector, FATs, and root directory). The data portions won't
70 be stored on the disk, but the file nevertheless will have the cor‐
71 rect size. The resulting file can be copied later to a floppy disk
72 or other device, or mounted through a loop device.
73 -D DRIVE-NUMBER
75 Specify the BIOS drive number to be stored in the FAT boot sector.
76 For hard disks and removable medias it is usually 0x80–0xFF (0x80
77 is first hard disk C:, 0x81 is second hard disk D:, ...), for
78 floppy devices or partitions to be used for floppy emulation it is
79 0x00–0x7F (0x00 is first floppy A:, 0x01 is second floppy B:).
80 -f NUMBER-OF-FATS
82 Specify the number of file allocation tables in the filesystem.
83 The default is 2.
84 -F FAT-SIZE
86 Specifies the type of file allocation tables used (12, 16 or 32
87 bit). If nothing is specified, mkfs.fat will automatically select
88 between 12, 16 and 32 bit, whatever fits better for the filesystem
89 size.
90 -g HEADS/SECTORS-PER-TRACK
92 Specify HEADS and SECTORS-PER-TRACK numbers which represents disk
93 geometry of DEVICE. Both numbers are stored into the FAT boot sec‐
94 tor. Number SECTORS-PER-TRACK is used also for aligning the total
95 count of FAT sectors. By default disk geometry is read from DEVICE
96 itself. If it is not available then LBA-Assist Translation and
97 translation table from the SD Card Part 2 File System Specification
98 based on total number of disk sectors is used.
99 -h NUMBER-OF-HIDDEN-SECTORS
101 Specify the number of so-called hidden sectors, as stored in the
102 FAT boot sector: this number represents the beginning sector of the
103 partition containing the file system. Normally this is an offset
104 (in sectors) relative to the start of the disk, although for MBR
105 logical volumes contained in an extended partition of type 0x05 (a
106 non-LBA extended partition), a quirk in the MS-DOS implementation
107 of FAT requires it to be relative to the partition's immediate con‐
108 taining Extended Boot Record. Boot code and other software han‐
109 dling FAT volumes may also rely on this field being set up cor‐
110 rectly; most modern FAT implementations will ignore it. By de‐
111 fault, if the DEVICE is a partition block device, mkfs.fat uses the
112 partition offset relative to disk start. Otherwise, mkfs.fat as‐
113 sumes zero. Use this option to override this behaviour.
114 -i VOLUME-ID
116 Sets the volume ID of the newly created filesystem; VOLUME-ID is a
117 32-bit hexadecimal number (for example, 2e24ec82). The default is
118 a number which depends on the filesystem creation time.
119 -I Ignore and disable safety checks. By default mkfs.fat refuses to
121 create a filesystem on a device with partitions or virtual mapping.
122 mkfs.fat will complain and tell you that it refuses to work. This
123 is different when using MO disks. One doesn't always need parti‐
124 tions on MO disks. The filesystem can go directly to the whole
125 disk. Under other OSes this is known as the superfloppy format.
126 This switch will force mkfs.fat to work properly.
127 -l FILENAME
129 Read the bad blocks list from FILENAME.
130 -m MESSAGE-FILE
132 Sets the message the user receives on attempts to boot this
133 filesystem without having properly installed an operating system.
134 The message file must not exceed 418 bytes once line feeds have
135 been converted to carriage return-line feed combinations, and tabs
136 have been expanded. If the filename is a hyphen (-), the text is
137 taken from standard input.
138 -M FAT-MEDIA-TYPE
140 Specify the media type to be stored in the FAT boot sector. This
141 value is usually 0xF8 for hard disks and is 0xF0 or a value from
142 0xF9 to 0xFF for floppies or partitions to be used for floppy emu‐
143 lation.
144 --mbr[=y|yes|n|no|a|auto]
146 Fill (fake) MBR table with disk signature one partition which
147 starts at sector 0 (includes MBR itself) and spans whole disk de‐
148 vice. It is needed only for non-removable disks used on Microsoft
149 Windows systems and only when formatting whole unpartitioned disk.
150 Location of the disk signature and partition table overlaps with
151 the end of the first FAT sector (boot code location), therefore
152 there is no additional space usage. Default is auto mode in which
153 mkfs.fat put MBR table only for non-removable disks when formatting
154 whole unpartitioned disk.
155 -n VOLUME-NAME
157 Sets the volume name (label) of the filesystem. The volume name
158 can be up to 11 characters long. Supplying an empty string, a
159 string consisting only of white space or the string "NO NAME" as
160 VOLUME-NAME has the same effect as not giving the -n option. The
161 default is no label.
162 --codepage=PAGE
164 Use DOS codepage PAGE to encode label. By default codepage 850 is
165 used.
166 -r ROOT-DIR-ENTRIES
168 Select the minimal number of entries available in the root direc‐
169 tory. The default is 112 or 224 for floppies and 512 for hard
170 disks. Note that this is minimal number and it may be increased by
171 mkfs.fat due to alignment of structures. See also mkfs.fat option
172 -a.
173 -R NUMBER-OF-RESERVED-SECTORS
175 Select the minimal number of reserved sectors. With FAT32 format
176 at least 2 reserved sectors are needed, the default is 32. Other‐
177 wise the default is 1 (only the boot sector). Note that this is
178 minimal number and it may be increased by mkfs.fat due to alignment
179 of structures. See also mkfs.fat option -a.
180 -s SECTORS-PER-CLUSTER
182 Specify the number of disk sectors per cluster. Must be a power of
183 2, i.e. 1, 2, 4, 8, ... 128.
184 -S LOGICAL-SECTOR-SIZE
186 Specify the number of bytes per logical sector. Must be a power of
187 2 and greater than or equal to 512, i.e. 512, 1024, 2048, 4096,
188 8192, 16384, or 32768. Values larger than 4096 are not conforming
189 to the FAT file system specification and may not work everywhere.
190 -v Verbose execution.
192 --offset SECTOR
194 Write the filesystem at a specific sector into the device file.
195 This is useful for creating a filesystem in a partitioned disk im‐
196 age without having to set up a loop device.
197 --variant TYPE
199 Create a filesystem of variant TYPE. Acceptable values are stan‐
200 dard and atari (in any combination of upper/lower case). See above
201 under DESCRIPTION for the differences.
202 --help
204 Display option summary and exit.
205 --invariant
207 Use constants for normally randomly generated or time based data
208 such as volume ID and creation time. Multiple runs of mkfs.fat on
209 the same device create identical results with this option. Its
210 main purpose is testing mkfs.fat.
211
213 mkfs.fat can not create boot-able filesystems. This isn't as easy as
214 you might think at first glance for various reasons and has been dis‐
215 cussed a lot already. mkfs.fat simply will not support it ;)
216
218 fatlabel(8), fsck.fat(8)
219
221 The home for the dosfstools project is its GitHub project page
222 ⟨https://github.com/dosfstools/dosfstools⟩.
223
225 dosfstools were written by Werner Almesberger ⟨werner.almesberger@
226 lrc.di.epfl.ch⟩, Roman Hodek ⟨Roman.Hodek@informatik.uni-erlangen.de⟩,
227 and others. Current maintainers are Andreas Bombe ⟨aeb@debian.org⟩ and
228 Pali Rohár ⟨pali.rohar@gmail.com⟩.
229dosfstools 4.2 2021-01-31 MKFS.FAT(8)