fsck_msdosfs —
    DOS/Windows (FAT) file system consistency
  checker
  
    | fsck_msdosfs | -p[-Cf]
      filesystem ... | 
  
    | fsck_msdosfs | [ -CMny] filesystem
      ... | 
The fsck_msdosfs utility verifies and
    repairs FAT file systems (more commonly known as DOS file systems).
The first form of fsck_msdosfs preens the
    specified file systems. It is normally started by
    fsck(8)
    run from /etc/rc during automatic reboot, when a FAT
    file system is detected. When preening file systems,
    fsck_msdosfs will fix common inconsistencies
    non-interactively. If more serious problems are found,
    fsck_msdosfs does not try to fix them, indicates
    that it was not successful, and exits.
The second form of fsck_msdosfs checks the
    specified file systems and tries to repair all detected inconsistencies,
    requesting confirmation before making any changes.
The options are as follows:
  - -C
- Compatibility with the corresponding
      fsck(8)
      option (skip check if clean), defined to no-op.
- -F
- Compatibility with the wrapper
      fsck(8)
      which seeks to determine whether the file system needs to be cleaned
      immediately in foreground, or if its cleaning can be deferred to
      background. FAT (MS-DOS) file systems must always be cleaned in the
      foreground. A non-zero exit code is always returned for this option.
- -M
- Causes fsck_msdosfsto not use
      mmap(2)
      when checking a FAT32 file system. This option is mainly for debugging
      purposes and is not normally necessary. Thefsck_msdosfsutility will automatically fall back
      to use a simple LRU cache of 4 MiB when it failed to perform
      mmap(2),
      or when-Mis specified.
- -f
- Force fsck_msdosfsto check “clean”
      file systems when preening.
- -n
- Causes fsck_msdosfsto assume
      “no” as the answer to all operator
      questions, except “CONTINUE?”.
- -p
- Preen the specified file systems.
- -y
- Causes fsck_msdosfsto assume
      “yes” as the answer to all operator
      questions.
The fsck_msdosfs utility appeared in
    NetBSD 1.2. fsck_msdosfs
    first appeared in FreeBSD 4.4.
The fsck_msdosfs utility is currently
    under development.