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FSCK(8)                                  BSD System Manager's Manual                                 FSCK(8)

NAME
     fsck -- filesystem consistency check and interactive repair

SYNOPSIS
     fsck -p [-f] [-m mode]
     fsck [-b block#] [-l maxparallel] [-q] [-y] [-n] [-m mode] [filesystem] ...

DESCRIPTION
     The first form of fsck preens a standard set of filesystems or the specified filesystems.  It is nor-mally normally
     mally used in the script /etc/rc during automatic reboot.  Here fsck reads the filesystem descriptor
     table (using getfsent(3)) to determine which filesystems to check.  Only partitions that have ``rw,''
     ``rq'' or ``ro'' as options, and that have non-zero pass number are checked.  Filesystems with pass
     number 1 (normally just the root filesystem) are checked one at a time.  When pass 1 completes, all
     remaining filesystems are checked, running one process per disk drive.  The disk drive containing each
     filesystem is inferred from the shortest prefix of the device name that ends in one or more digits; the
     remaining characters are assumed to be the partition designator.  In preening mode, filesystems that
     are marked clean are skipped.  Filesystems are marked clean when they are unmounted, when they have
     been mounted read-only, or when fsck runs on them successfully.

     The kernel takes care that only a restricted class of innocuous filesystem inconsistencies can happen
     unless hardware or software failures intervene.  These are limited to the following:
           Unreferenced inodes
           Link counts in inodes too large
           Missing blocks in the free map
           Blocks in the free map also in files
           Counts in the super-block wrong

     These are the only inconsistencies that 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 filesystem on which the
     correction will take place, and the nature of the correction.  After successfully correcting a filesys-tem, filesystem,
     tem, fsck will print the number of files on that filesystem, the number of used and free blocks, and
     the percentage of fragmentation.

     If sent a QUIT signal, fsck will finish the filesystem checks, then exit with an abnormal return status
     that causes an automatic reboot to fail.  This is useful when you want to finish the filesystem checks
     during an automatic reboot, but do not want the machine to come up multiuser after the checks complete.

     Without the -p option, fsck audits and interactively repairs inconsistent conditions for filesystems.
     If the filesystem is inconsistent the operator is prompted for concurrence before each correction is
     attempted.  It should be noted that some of the corrective actions which are not correctable 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 on the filesystem 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.

     -b          Use the block specified immediately after the flag as the super block for the filesystem.
                 Block 32 is usually an alternate super block.

     -f          Force fsck to check `clean' filesystems when preening.

     -l          Limit the number of parallel checks to the number specified in the following argument.  By
                 default, the limit is the number of disks, running one process per disk.  If a smaller
                 limit is given, the disks are checked round-robin, one filesystem at a time.

     -m          Use the mode specified in octal immediately after the flag as the permission bits to use
                 when creating the lost+found directory rather than the default 1777.  In particular, sys-tems systems
                 tems that do not wish to have lost files accessible by all users on the system should use a
                 more restrictive set of permissions such as 700.

     -p          "Preen" mode, described above.

     -q          Do a quick check to determine if the filesystem was unmounted cleanly.

     -y          Assume a yes response to all questions asked by fsck; this should be used with great cau-tion caution
                 tion 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 except for `CONTINUE?', which is
                 assumed to be affirmative; do not open the filesystem for writing.

     If no filesystems are given to fsck then a default list of filesystems is read using getfsent(3).

           Inconsistencies checked are as follows:
           1.   Blocks claimed by more than one inode or the free map.
           2.   Blocks claimed by an inode outside the range of the filesystem.
           3.   Incorrect link counts.
           4.   Size checks:
                      Directory size not a multiple of DIRBLKSIZ.
                      Partially truncated file.
           5.   Bad inode format.
           6.   Blocks not accounted for anywhere.
           7.   Directory checks:
                      File pointing to unallocated inode.
                      Inode number out of range.
                      Dot or dot-dot not the first two entries of a directory or having the wrong inode num-ber. number.
                      ber.
           8.   Super Block checks:
                      More blocks for inodes than there are in the filesystem.
                      Bad free block map format.
                      Total free block and/or free inode count incorrect.

     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.  If
     the lost+found directory does not exist, it is created.  If there is insufficient space its size is
     increased.

     Because of inconsistencies between the block device and the buffer cache, the raw device should always
     be used.

DIAGNOSTICS
     The diagnostics produced by fsck are fully enumerated and explained in Appendix A of Fsck - The UNIX
     File System Check Program.

SEE ALSO
     fs(5), fsck_hfs(8), fsck_msdos(8), getfsent(3), newfs(8), reboot(8)

4th Berkeley Distribution                      March 20, 2008                      4th Berkeley Distribution