DOSFSCK(8) MAINTENANCE COMMANDS DOSFSCK(8)NAME
dosfsck - check and repair MS-DOS file systems
dosfsck [-aAflnrtvVwy] [-d path -d ...] [-u path -u ...] device
dosfsck verifies the consistency of MS-DOS file systems and optionally
tries to repair them. The following file system problems can be cor‐
rected (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 cor‐
rupt). The directory can be dropped.
- Files . and .. are non-directories. They can be dropped or
- Directories . and .. in root directory. They are dropped.
- Bad file names. They can be renamed.
- Duplicate directory entries. They can be dropped 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.
- Start cluster number of a file is invalid. The file is trun‐
- 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 file system 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.
Additionally, the following problems are detected, but not repaired:
- Invalid parameters in boot sector.
- Absence of . and .. entries in non-root directories
When dosfsck checks a file system, it accumulates all changes in memory
and performs them only after all checks are complete. This can be dis‐
abled with the -w option.
OPTIONS-a Automatically repair the file system. No user intervention is
necessary. Whenever there is more than one method to solve a
problem, the least destructive approach is used.
-A 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 dif‐
ferent. 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).
-d Drop the specified file. If more that one file with that name
exists, the first one is dropped.
-f Salvage unused cluster chains to files. By default, unused clus‐
ters are added to the free disk space except in auto mode (-a).
-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.
-r Interactively repair the file system. The user is asked for
advice whenever there is more than one approach to fix an incon‐
-t Mark unreadable clusters as bad.
-u 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.
-v Verbose mode. Generates slightly more output.
-V Perform a verification pass. The file system 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.
-w Write changes to disk immediately.
-y Same as -a (automatically repair filesystem) for compatibility
with other fsck tools.
If -a and -r are absent, the file system is only checked, but not
0 No recoverable errors have been detected.
1 Recoverable errors have been detected or dosfsck has discovered
an internal inconsistency.
2 Usage error. dosfsck did not access the file system.
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 algorithm.
Werner Almesberger <email@example.com> Extensions
(FAT32, VFAT) by and current maintainer: Roman Hodek <firstname.lastname@example.org>
Linux December 31 1997 DOSFSCK(8)