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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | FILES | SECURITY CONSIDERATIONS | BUGS | SEE ALSO | HOMEPAGE | AUTHORS | COLOPHON |
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FSCK.FAT(8) System Manager's Manual FSCK.FAT(8)
fsck.fat - check and repair MS-DOS FAT filesystems
fsck.fat [OPTIONS] DEVICE
fsck.fat verifies the consistency of MS-DOS filesystems and
optionally tries to repair them.
The following filesystem problems can be corrected (in this
order):
• FAT contains invalid cluster numbers. Cluster is changed to
EOF.
• File's cluster chain contains a loop. The loop is broken.
• Bad clusters (read errors). The clusters are marked bad and
they are removed from files owning them. This check is
optional.
• Directories with a large number of bad entries (probably
corrupt). The directory can be deleted.
• Files . and .. are non-directories. They can be deleted or
renamed.
• Directories . and .. in root directory. They are deleted.
• Bad filenames. They can be renamed.
• Duplicate directory entries. They can be deleted or renamed.
• Directories with non-zero size field. Size is set to zero.
• Directory . does not point to parent directory. The start
pointer is adjusted.
• Directory .. does not point to parent of parent directory.
The start pointer is adjusted.
• . and .. are not the two first entries in a non-root
directory. The entries are created, moving occupied slots if
necessary.
• Start cluster number of a file is invalid. The file is
truncated.
• File contains bad or free clusters. The file is truncated.
• File's cluster chain is longer than indicated by the size
fields. The file is truncated.
• Two or more files share the same cluster(s). All but one of
the files are truncated. If the file being truncated is a
directory file that has already been read, the filesystem
check is restarted after truncation.
• File's cluster chain is shorter than indicated by the size
fields. The file is truncated.
• Volume label in root directory or label in boot sector is
invalid. Invalid labels are removed.
• Volume label in root directory and label in boot sector are
different. Volume label from root directory is copied to
boot sector.
• Clusters are marked as used but are not owned by a file.
They are marked as free.
Additionally, the following problems are detected, but not
repaired:
• Invalid parameters in boot sector
When fsck.fat checks a filesystem, it accumulates all changes in
memory and performs them only after all checks are complete.
This can be disabled with the -w option.
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.
There are some minor differences in Atari format: Some boot
sector fields are interpreted slightly different, and the special
FAT entries for end-of-file and bad cluster can be different.
Under MS-DOS 0xfff8 is used for EOF and Atari employs 0xffff by
default, but both systems recognize all values from 0xfff8–0xffff
as end-of-file. MS-DOS uses only 0xfff7 for bad clusters, where
on Atari values 0xfff0–0xfff7 are for this purpose (but the
standard value is still 0xfff7).
-a Automatically repair the filesystem. No user intervention is
necessary. Whenever there is more than one method to solve a
problem, the least destructive approach is used.
-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 Make read-only boot sector check.
-c PAGE
Use DOS codepage PAGE to decode short file names. By default
codepage 850 is used.
-d PATH
Delete the specified file. If more than one file with that
name exist, the first one is deleted. This option can be
given more than once.
-f Salvage unused cluster chains to files. By default, unused
clusters are added to the free disk space except in auto mode
(-a).
-F NUM
Specify FAT table NUM for filesystem access. By default
value 0 is assumed and then the first uncorrupted FAT table
is chosen. Uncorrupted means that FAT table has valid first
cluster. If default value 0 is used and all FAT tables are
corrupted then fsck.fat gives up and does not try to repair
FAT filesystem. If non-zero NUM value is specified then
fsck.fat uses FAT table NUM for repairing FAT filesystem. If
FAT table NUM has corrupted first cluster then fsck.fat will
repair it. In any case, if FAT filesystem has more FAT
tables then repaired content of chosen FAT table is copied to
other FAT tables. To repair corrupted first cluster it is
required to call fsck.fat with non-zero NUM value.
-l List path names of files being processed.
-n No-operation mode: non-interactively check for errors, but
don't write anything to the filesystem.
-p Same as -a, for compatibility with other *fsck.
-r Interactively repair the filesystem. The user is asked for
advice whenever there is more than one approach to fix an
inconsistency. This is the default mode and the option is
only retained for backwards compatibility.
-S Consider short (8.3) file names with spaces in the middle to
be invalid, like previous versions of this program did.
While such file names are not forbidden by the FAT
specification, and were never treated as errors by Microsoft
file system checking tools, many DOS programs are unable to
handle files with such names. Using this option can make
them accessible to these programs.
Short file names which start with a space are considered
invalid regardless of this option's setting.
Previous versions of this program exceptionally treated EA
DATA. SF and WP ROOT. SF as valid short names; using this
option does not preserve that exception.
-t Mark unreadable clusters as bad.
-u PATH
Try to undelete the specified file. fsck.fat tries to
allocate a chain of contiguous unallocated clusters beginning
with the start cluster of the undeleted file. This option
can be given more than once.
-U Consider lowercase volume and boot label as invalid and allow
only uppercase characters. Such labels are forbidden by the
FAT specification, but they are widely used by Linux tools.
Moreover MS-DOS and Windows systems do not have problems to
read them. Therefore volume and boot labels with lowercase
characters are by default permitted.
-v Verbose mode. Generates slightly more output.
-V Perform a verification pass. The filesystem check is
repeated after the first run. The second pass should never
report any fixable errors. It may take considerably longer
than the first pass, because the first pass may have
generated long list of modifications that have to be scanned
for each disk read.
--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.
-w Write changes to disk immediately.
-y Same as -a (automatically repair filesystem) for
compatibility with other fsck tools.
--help
Display help message describing usage and options then exit.
0 No recoverable errors have been detected.
1 Recoverable errors have been detected or fsck.fat has
discovered an internal inconsistency.
2 Usage error. fsck.fat did not access the filesystem.
fsck0000.rec, fsck0001.rec, ...
When recovering from a corrupted filesystem, fsck.fat dumps
recovered data into files named fsckNNNN.rec in the top level
directory of the filesystem.
When checking a filesystem with orphan (unconnected) cluster
chains, fsck.fat either marks these chains as free or, if the -f
or -a option is given, salvages (recovers) them into files. In
the latter case, since an exact data size of an orphan cluster
chain is unknown, it is set to include all bytes within the
cluster chain.
Some operating systems don't clean the space between the last
byte of a file and the end of its cluster chain, this space may
include deleted data (or even data that existed before the drive
was formatted to the FAT filesystem).
If such a file is deleted while open, and the filesystem is not
unmounted properly, its cluster chain becomes orphan. Salvaging
this chain into a file poses a security risk when unprivileged
users have access to the mountpoint of the filesystem, because
some amount of deleted data will be exposed to these users (the
salvaged file will be larger than the original one, including
remnant data after the original end-of-file position).
It is recommended that you never run fsck.fat with the -f or -a
option against a filesystem containing sensitive deleted data if
unprivileged users have access to its mountpoint.
• Does not remove entirely empty directories.
• Should give more diagnostic messages.
• Undeleting files should use a more sophisticated algorithm.
fatlabel(8), mkfs.fat(8)
The home for the dosfstools project is its GitHub project page
⟨https://github.com/dosfstools/dosfstools⟩.
dosfstools were written by Werner Almesberger
⟨[email protected]⟩, Roman Hodek ⟨Roman.Hodek@
informatik.uni-erlangen.de⟩, and others. Current maintainers are
Andreas Bombe ⟨[email protected]⟩ and Pali Rohár ⟨pali.rohar@
gmail.com⟩.
This page is part of the dosfstools (Tools for making and
checking MS-DOS FAT filesystems) project. Information about the
project can be found at
⟨https://github.com/dosfstools/dosfstools⟩. If you have a bug
report for this manual page, see
⟨https://github.com/dosfstools/dosfstools/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/dosfstools/dosfstools.git⟩ on 2024-06-14.
(At that time, the date of the most recent commit that was found
in the repository was 2023-10-10.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
dosfstools 4.2+git 2021-01-31 FSCK.FAT(8)
Pages that refer to this page: fsck(8@@e2fsprogs), fsck(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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