From Linux Man Pages
dosfsck - check and repair MS-DOS file systems
dosfsck [-aAflnrtvVwy] [-d path -d ...] [-u path -u ...] device
DESCRIPTION
dosfsck verifies the consistency of MS-DOS file systems and optionally tries to repair them. The following file
system 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 dropped.
- Files . and .. are non-directories. They can be dropped or renamed.
- 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 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 file system check is restarted after trunca-
tion.
- 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 disabled 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
different. Under MS-DOS 0xfff8 is used for EOF and Atari employs 0xffff by default, but both systems rec-
ognize 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 clusters 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 inconsistency.
-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 repaired.
EXIT STATUS
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.
BUGS
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.
CATEGORY