# 2.11BSD#431 - /usr/man/cat8/fsck.0

    FSCK(8)             UNIX Programmer's Manual		  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 systems.  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 number 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
         number 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

    Printed 11/26/99						1

    FSCK(8)             UNIX Programmer's Manual		  FSCK(8)

         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 modifica-
         tions; 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 fix-
         able 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 con-
         sistency 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 precau-
    	   tion 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

    Printed 11/26/99						2

    FSCK(8)             UNIX Programmer's Manual		  FSCK(8)

    	   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 sys-
    	   tem 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 systems.

         -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

    Printed 11/26/99						3

    FSCK(8)             UNIX Programmer's Manual		  FSCK(8)

    	   superblock.

         Orphaned files and directories (allocated but unreferenced)
         are, with the operator's concurrence, 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 modi-
         fied), 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.

    Printed 11/26/99						4

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