fsck - perform file system consistency check

     fsck [-pfwcyn] [-l number] [filesystem ...]

     Fsck checks a file system's consistency after a crash  or  to  make  sure
     that an unknown file system may be safely mounted.

     Fsck is really a forerunner to fsck1 through  fsck2f,  see  fsck1(1)  for
     more details.

     This program is a kind of manager to the four real checkers, it will read
     /etc/fstab  (see  fstab(5)) to check all the file systems with a non-zero
     pass number if no arguments are given,  or  it  will  use  the  fstab  to
     translate the name of a mount point to the proper device, so you can type
     fsck /usr for instance.  It will know which program to call by looking at
     the superblock type.

  The clean flag
     Fsck is a bit more than just a forerunner, it will also  manage  the  so-
     called "file system clean flag".  This flag is cleared by the kernel when
     a file system is mounted, and set when it is unmounted or when the system
     is rebooted with reboot(8), but only if it was set to begin with.

     The clean flag will only be set  if  it  is  specifically  enabled  by  a
     special magic number in the superblock.  It should only be enabled if the
     file system is never ever used by a system that does not know  about  the
     clean  flag, because those systems will either choke on it (most likely),
     or not clear it on mount.

     Mkfs will enable the clean flag when making a flex file  system,  because
     no other system can use this file system type anyway.


     -p   Run  in  preen  mode  repairing  noncritical  errors  automatically.
          Errors  that  need  operator  intervention  are  only noted, but not
          repaired.  Even file systems that are mounted are  checked,  because
          the  root file system is mounted read-only at boot time.  You should
          reboot immediately if the root  file  system  had  to  be  repaired.
          Several  fsck's  should be run in parallel for file systems with the
          same pass number, but this is not yet implemented.  (The output from
          the different fsck's would make an unintelligible mess.)

     -l number
          Limit the number of fscks run in parallel in preen  mode.   (Useful,
          isn't it?)

     -f   Force checking even if the file system is marked clean.

     -w   Only check file systems from fstab that are normally  mounted  read-

     -c   Toggle the clean flag enable.  On a file system with a clean flag it
          will  disable  the  flag  and reset it, on a file system without the
          clean flag enabled it will  write  the  necessary  magic  number  to
          enable  it.   No  check  will  be  done,  all  other options will be

     -n   Assume 'no' to all questions asked, the file system will  be  opened
          read-only  and  only  a  report on all the errors will be generated.
          Fsck will automatically revert to this mode if the file system can't
          be opened read-write.

     -y   Assume 'yes' on all questions asked.  This is  a  dangerous  option,
          because  it  will allow repairs being made without user supervision.
          Better first run fsck -n to see what it is up to.


     /etc/fstab     Default list of file systems to check.

     /etc/mtab      To check if a file system is currently mounted.

     fsck1(1), fstab(5), mkfs(1), mount(1).


     0    Either there  were  no  errors,  or  all  errors  were  successfully

     2    A QUIT signal has been typed while  in  preen  mode.   The  fsck  is
          finished, but the reboot must be interrupted.

     4    Errors have been corrected on a mounted file system.

     8    There are serious errors that have not been fixed, or another severe

     12   An INTERRUPT signal stopped the fsck.

     The message you like to see at boot time: "/dev/hd3: is clean".

     Kees J. Bot (kjb@cs.vu.nl)