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.
- •
- 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
dosfstools were written by
Werner
Almesberger
Roman
Hodek and others. Current maintainers are
Andreas Bombe and
Pali
Rohár