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

NAME
     fsck -- filesystem consistency check and interactive repair

SYNOPSIS
     fsck -p [-f]
     fsck [-l maxparallel] [-q] [-y] [-n] [-d]

DESCRIPTION
     The first form of fsck preens a standard set of filesystems or the speci-
     fied filesystems.  It is normally used in the script /etc/rc during auto-
     matic 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.  Filesys-
     tems are marked clean when they are unmounted, when they have been
     mounted read-only, or when fsck runs on them successfully.

     It should be noted that fsck is now essentially a wrapper that invokes
     other fsck_XXX utilities as needed.  Currently, fsck can invoke fsck_hfs,
     fsck_apfs, fsck_msdos, fsck_exfat, and fsck_udf.  If this underlying
     process that fsck invokes encounters serious inconsistencies or the
     filesystem type is not one of the above, it exits with an abnormal return
     status and an automatic reboot will then fail.  For each corrected incon-
     sistency one or more lines will be printed identifying the filesystem on
     which the correction will take place, and the nature of the correction.

     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.  It should be noted that some of the correc-
     tive 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 deter-
     mined from the diagnostic output.  If the operator does not have write
     permission on the filesystem fsck will default to a -n action.

     The following flags are interpreted by fsck and passed along to the
     underlying tool that it spawns.

     -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 num-
                 ber of disks, running one process per disk.  If a smaller
                 limit is given, the disks are checked round-robin, one
                 filesystem at a time.

     -R          Specify a particular passno number for which fsck is to
                 check.  You may only specify 1 or 2.  Only those filesystems
                 matching that particular passno entry (if using fstab) will
                 be checked.  For more information on the passno field, see
                 fstab(5).

     -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 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 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).

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

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

4th Berkeley Distribution        May 18, 2010        4th Berkeley Distribution