check and repair MS-DOS filesystems
see also :
dosfslabel - mkdosfs
[-aAflnrtvVwy] [-d PATH
-d ...] [-u PATH
-u ...] DEVICE
add an example, a script, a trick and tips
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verifies the consistency of MS-DOS filesystems and
optionally tries to repair them.
filesystem problems can be corrected (in this order):
FAT contains invalid cluster numbers. Cluster is changed
File’s cluster chain contains a loop. The loop is
Bad clusters (read errors). The clusters are marked bad
and they are removed from files owning them. This check is
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
Bad filenames. They can be renamed.
Duplicate directory entries. They can be deleted or
Directories with non-zero size field. Size is set
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.
Start cluster number of a file is invalid. The file is
File contains bad or free clusters. The file is
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.
Clusters are marked as used but are not owned by a file.
They are marked as free.
the following problems are detected, but not repaired:
Invalid parameters in boot
Absence of . and .. entries in non-root
dosfsck 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
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.
Use Atari variation of the MS-DOS filesystem. This
is default if dosfsck is run on an Atari, then this
option turns off Atari format. 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).
Make read-only boot sector check.
Delete the specified file. If more that one file with
that name exists, the first one is deleted.
Salvage unused cluster chains to files. By default,
unused clusters are added to the free disk space except in
auto mode (-a).
List path names of files being processed.
No-operation mode: non-interactively check
for errors, but don’t write anything to the
Interactively repair the filesystem. The user is asked
for advice whenever there is more than one approach to fix
Mark unreadable clusters as bad.
Try to undelete the specified file. dosfsck tries
to allocate a chain of contiguous unallocated clusters
beginning with the start cluster of the undeleted file.
Verbose mode. Generates slightly more output.
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.
Write changes to disk immediately.
Same as -a (automatically repair
filesystem) for compatibility with other fsck tools.
-a and -r are absent, the
filesystem is only checked, but not repaired.
No recoverable errors have been detected.
Recoverable errors have been detected or dosfsck has
discovered an internal inconsistency.
Usage error. dosfsck did not access the filesystem.
fsck0000.rec, fsck0001.rec, ...
When recovering from a corrupted filesystem, dosfsck dumps
recovered data into files named ’fsckNNNN.rec’ in the
top level directory of the filesystem.
More information about dosfsck and dosfstools can
be found at
Does not create
. and .. files where necessary. Does not remove entirely
empty directories. Should give more diagnostic messages.
Undeleting files should use a more sophisticated
were written by Werner Almesberger
and others. The current maintainer is Daniel Baumann