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FSCK(8) 										  FSCK(8)

NAME
       fsck - file system consistency check and interactive repair

SYNOPSIS
       fsck -p[ # ] [ filesystem ...  ]
       fsck [ -y ] [ -n ] [ -sX ] [ -SX ] [ -t filename ] [ filesystem ] ...

DESCRIPTION
       The  first  form  of fsck preens a standard set of file systems or the specified file sys-
       tems.  It is normally used in the script /etc/rc during automatic reboot.   In  this  case
       fsck  reads  the  table	/etc/fstab to determine which file systems to check.  It uses the
       information there to inspect groups of disks in parallel taking maximum advantage  of  i/o
       overlap	to check the file systems as quickly as possible.  Normally, the root file system
       will be checked on pass 1, other ``root'' (``a'' partition) file systems on pass 2,  other
       small file systems on separate passes (e.g. the ``d'' file systems on pass 3 and the ``e''
       file systems on pass 4), and finally the large user file systems on the	last  pass,  e.g.
       pass  5.  Only one file system from each disk should be checked in each pass.  A pass num-
       ber of 0 in fstab causes a disk to not be checked;  similarly  partitions  which  are  not
       shown as to be mounted ``rw'' or ``ro'' are not checked.  A number or range of numbers may
       be given after the -p to start or end the check at a specified pass number.  A single num-
       ber  specifies  the  starting  pass (e.g. -p2 or -p2-); a range specifies the starting and
       endig passes (-p2-4).  A missing start means to start with pass 1 (-p-2).   These  can  be
       used  to  stop fsck to mount a temporary file system before continuing the check on larger
       file systems requiring scratch files.

       The system normally takes care that only a restricted class of  innocuous  inconsistencies
       can  happen unless hardware or software failures intervene.  These are limited to the fol-
       lowing:

	      Unreferenced inodes

	      Link counts in inodes too large

	      Missing blocks in the free list

	      Blocks in the free list also in files

	      Counts in the superblock wrong

	      Allocated inodes in the free inode list

       These are the only inconsistencies which fsck with the  -p  option  will  correct;  if  it
       encounters other inconsistencies, it exits with an abnormal return status and an automatic
       reboot will then fail.  For each corrected inconsistency one or more lines will be printed
       identifying the file system on which the correction will take place, and the nature of the
       correction.  After successfully correcting a file system, fsck will print  the  number  of
       files on that file system and the number of used and free blocks.  Warning: kernel changes
       are required to limit the types of inconsistencies, and fsck -p	makes  assumptions  about
       the  kernel's actions in repairing these.  Vmunix, PDP-11 2.9BSD with the UCB_FSFIX option
       and PDP-11 2.10BSD Unix kernels have the appropriate modifications; the -p  option  should
       not be used on other systems.

       Without	the  -p option, fsck audits and interactively repairs inconsistent conditions for
       file systems.  If the file system is inconsistent the operator is prompted for concurrence
       before  each  correction is attempted.  It should be noted that a number of the corrective
       actions which are not fixable under the -p option will result in some loss of  data.   The
       amount  and  severity  of  data	lost  may  be determined from the diagnostic output.  The
       default action for each consistency correction is to wait for the operator to respond  yes
       or no.  If the operator does not have write permission fsck will default to a -n action.

       Fsck  has  more consistency checks than its predecessors check, dcheck, fcheck, and icheck
       combined.

       The following flags are interpreted by fsck.

       -y    Assume a yes response to all questions asked by fsck; this should be used with great
	     caution  as  this	is a free license to continue after essentially unlimited trouble
	     has been encountered.

       -n    Assume a no response to all questions asked by fsck; do not open the file system for
	     writing.

       -sX   Ignore the actual free list and (unconditionally) reconstruct a new one by rewriting
	     the superblock of the file system.  The file system should be unmounted  while  this
	     is  done; if this is not possible, care should be taken that the system is quiescent
	     and that it is rebooted immediately afterwards.  This  precaution	is  necessary  so
	     that  the	old, bad, in-core copy of the superblock will not continue to be used, or
	     written on the file system.

	     The -sX option allows for creating an optimal free list organization.  The following
	     forms of X are supported for the following devices:

		  -s3 (RP03)
		  -s4 (RP04, RP05, RP06)
		  -sBlocks-per-cylinder:Blocks-to-skip (for anything else)

	     If  X  is	not given, the values used when the file system was created are used.  If
	     these values were not specified, then the value 400:9 is used.

       -SX   Conditionally reconstruct the free list. This option is like -sX above  except  that
	     the  free list is rebuilt only if there were no discrepancies discovered in the file
	     system. Using -S will force a no response to all  questions  asked  by  fsck.   This
	     option  is  useful  for forcing free list reorganization on uncontaminated file sys-
	     tems.

       -t    If fsck cannot obtain enough memory to keep its tables, it uses a scratch	file.  If
	     the  -t  option  is  specified,  the  file named in the next argument is used as the
	     scratch file, if needed. Without the -t flag, fsck will prompt the operator for  the
	     name  of  the  scratch  file. The file chosen should not be on the file system being
	     checked, and if it is not a special file or did not already  exist,  it  is  removed
	     when fsck completes.

       If  no file systems are given to fsck then a default list of file systems is read from the
       file /etc/fstab.

       Inconsistencies checked are as follows:

       1.    Blocks claimed by more than one inode or the free list.
       2.    Blocks claimed by an inode or the free list outside the range of the file system.
       3.    Incorrect link counts.
       4.    Size checks:
		   Directory size not 16-byte aligned.
       5.    Bad inode format.
       6.    Blocks not accounted for anywhere.
       7.    Directory checks:
		   File pointing to unallocated inode.
		   Inode number out of range.
       8.    Super Block checks:
		   More than 65536 inodes.
		   More blocks for inodes than there are in the file system.
       9.    Bad free block list format.
       10.   Total free block and/or free inode count incorrect.
       11.   Allocated inodes on the free inode list in the superblock.

       Orphaned files and directories (allocated but unreferenced) are, with the operator's  con-
       currence,  reconnected  by placing them in the lost+found directory.  The name assigned is
       the inode number. The only restriction is that the directory lost+found must  preexist  in
       the  root  of the file system being checked and must have empty slots in which entries can
       be made.  This can be accomplished manually by making  lost+found,  copying  a  number  of
       files  to  the  directory, and then removing them (before fsck is executed).  Mkfs(8) will
       automatically create a lost+found directory.

       Checking the raw device is almost always faster.  The root device should  not  be  checked
       using the raw device, however, since it cannot be unmounted.

FILES
       /etc/fstab	   default list of file systems to check

DIAGNOSTICS
       The diagnostics produced by fsck are intended to be self-explanatory.  The exit codes with
       the -p option are 0 (no problems that weren't fixed), 4 (root file system was modified), 8
       (problems that couldn't be fixed) and 12 (fsck was interrupted).

SEE ALSO
       filsys(5), fstab(5), crash(8), mkfs(8), mklost+found(8), reboot(8)
       T. J. Kowalski, FSCK - The UNIX File System Check Program

BUGS
       Inode numbers for .  and ..  in each directory should be checked for validity.

3rd Berkeley Distribution								  FSCK(8)
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