








        FFsscckk__ffffss -- TThhee UUNNIIXX[[++]] FFiillee SSyysstteemm CChheecckk PPrrooggrraamm


                     _M_a_r_s_h_a_l_l _K_i_r_k _M_c_K_u_s_i_c_k
                 Computer Systems Research Group
                    Computer Science Division
    Department of Electrical Engineering and Computer Science
               University of California, Berkeley
                       Berkeley, CA  94720

                         _T_. _J_. _K_o_w_a_l_s_k_i
                        Bell Laboratories
                  Murray Hill, New Jersey 07974


                            _A_B_S_T_R_A_C_T

          This  document  reflects  the use of _f_s_c_k___f_f_s with
     the 4.2BSD and 4.3BSD file system  organization.   This
     is  a  revision  of the original paper written by T. J.
     Kowalski.

          File System Check Program (_f_s_c_k___f_f_s) is an  inter-
     active  file system check and repair program.  _F_s_c_k___f_f_s
     uses the redundant structural information in  the  UNIX
     file  system to perform several consistency checks.  If
     an inconsistency is detected, it  is  reported  to  the
     operator, who may elect to fix or ignore each inconsis-
     tency.  These inconsistencies result from the permanent
     interruption of the file system updates, which are per-
     formed every time a file is modified.  Unless there has
     been  a  hardware  failure,  _f_s_c_k___f_f_s is able to repair
     corrupted file systems using procedures based upon  the
     order  in  which  UNIX  honors these file system update
     requests.

          The purpose of this document is  to  describe  the
     normal updating of the file system, to discuss the pos-
     sible causes of file system corruption, and to  present
     the  corrective  actions implemented by _f_s_c_k___f_f_s_.  Both
     the program and the interaction between the program and
     the operator are described.


-----------
[+]UNIX is a trademark of Bell Laboratories.
This work was done under grants from the National Sci-
ence  Foundation  under  grant  MCS80-05144,  and  the
Defense  Advance  Research Projects Agency (DoD) under
Arpa Order No. 4031 monitored by Naval Electronic Sys-
tem Command under Contract No. N00039-82-C-0235.









SMM:3-2                        The UNIX File System Check Program


     Revised July 16, 1985






























































The UNIX File System Check Program                        SMM:3-3


                        TTAABBLLEE OOFF CCOONNTTEENNTTSS


11..  IInnttrroodduuccttiioonn

22..  OOvveerrvviieeww ooff tthhee ffiillee ssyysstteemm
2.1.    Superblock
2.2.    Summary Information
2.3.    Cylinder groups
2.4.    Fragments
2.5.    Updates to the file system

33..  FFiixxiinngg ccoorrrruupptteedd ffiillee ssyysstteemmss
3.1.    Detecting and correcting corruption
3.2.    Super block checking
3.3.    Free block checking
3.4.    Checking the inode state
3.5.    Inode links
3.6.    Inode data size
3.7.    Checking the data associated with an inode
3.8.    File system connectivity

AAcckknnoowwlleeddggeemmeennttss

RReeffeerreenncceess

44..  AAppppeennddiixx AA
4.1.     Conventions
4.2.     Initialization
4.3.     Phase 1 - Check Blocks and Sizes
4.4.     Phase 1b - Rescan for more Dups
4.5.     Phase 2 - Check Pathnames
4.6.     Phase 3 - Check Connectivity
4.7.     Phase 4 - Check Reference Counts
4.8.     Phase 5 - Check Cyl groups
4.9.     Cleanup



























SMM:3-4                        The UNIX File System Check Program


11..  IInnttrroodduuccttiioonn

     This  document  reflects the use of _f_s_c_k___f_f_s with the 4.2BSD
and 4.3BSD file system organization.  This is a revision  of  the
original paper written by T. J. Kowalski.

     When  a  UNIX  operating system is brought up, a consistency
check of the file systems should always be performed.  This  pre-
cautionary  measure  helps  to  insure a reliable environment for
file storage on disk.  If an inconsistency is discovered, correc-
tive action must be taken.  _F_s_c_k___f_f_s runs in two modes.  Normally
it is run non-interactively by the system after  a  normal  boot.
When  running in this mode, it will only make changes to the file
system that are known to always be  correct.   If  an  unexpected
inconsistency  is  found  _f_s_c_k___f_f_s will exit with a non-zero exit
status, leaving the system running  single-user.   Typically  the
operator  then runs _f_s_c_k___f_f_s interactively.  When running in this
mode, each problem is listed followed by a  suggested  corrective
action.   The  operator  must decide whether or not the suggested
correction should be made.

     The purpose of this memo is to dispel the mystique surround-
ing file system inconsistencies.  It first describes the updating
of the file system (the calm before the storm) and then describes
file  system  corruption (the storm).  Finally, the set of deter-
ministic corrective actions used by _f_s_c_k___f_f_s (the Coast Guard  to
the rescue) is presented.

22..  OOvveerrvviieeww ooff tthhee ffiillee ssyysstteemm

     The file system is discussed in detail in [Mckusick84]; this
section gives a brief overview.

22..11..  SSuuppeerrbblloocckk

     A file system is described by its _s_u_p_e_r_-_b_l_o_c_k.   The  super-
block  is  built  when  the file system is created (_n_e_w_f_s(8)) and
never changes.  The super-block contains the basic parameters  of
the  file  system,  such as the number of data blocks it contains
and a count of the maximum number of files.  Because  the  super-
block  contains  critical  data,  _n_e_w_f_s  replicates it to protect
against  catastrophic  loss.   The  _d_e_f_a_u_l_t  _s_u_p_e_r  _b_l_o_c_k  always
resides at a fixed offset from the beginning of the file system's
disk partition.  The _r_e_d_u_n_d_a_n_t _s_u_p_e_r _b_l_o_c_k_s  are  not  referenced
unless  a  head crash or other hard disk error causes the default
super-block to be unusable.  The redundant blocks  are  sprinkled
throughout the disk partition.

     Within the file system are files.  Certain files are distin-
guished as directories and contain  collections  of  pointers  to
files  that  may  themselves  be  directories.   Every file has a
descriptor associated with it called an _i_n_o_d_e.   The  inode  con-
tains  information  describing ownership of the file, time stamps
indicating modification and access times for  the  file,  and  an









The UNIX File System Check Program                        SMM:3-5


array  of  indices  pointing to the data blocks for the file.  In
this section, we assume that the first 12 blocks of the file  are
directly  referenced  by  values  stored  in  the inode structure
itself[+].   The  inode  structure may also contain references to
indirect blocks containing further data block indices.  In a file
system  with a 4096 byte block size, a singly indirect block con-
tains 1024 further block addresses, a doubly indirect block  con-
tains  1024  addresses  of  further single indirect blocks, and a
triply indirect block contains 1024 addresses of  further  doubly
indirect  blocks  (the  triple  indirect block is never needed in
practice).

     In order to create files with up to 2^32 bytes,  using  only
two  levels  of  indirection,  the  minimum size of a file system
block is 4096 bytes.  The size of file system blocks can  be  any
power  of  two  greater than or equal to 4096.  The block size of
the file system is maintained in the super-block, so it is possi-
ble  for  file  systems of different block sizes to be accessible
simultaneously on the  same  system.   The  block  size  must  be
decided when _n_e_w_f_s creates the file system; the block size cannot
be subsequently changed without rebuilding the file system.

22..22..  SSuummmmaarryy iinnffoorrmmaattiioonn

     Associated with the super block is  non  replicated  _s_u_m_m_a_r_y
_i_n_f_o_r_m_a_t_i_o_n.   The summary information changes as the file system
is modified.  The summary  information  contains  the  number  of
blocks, fragments, inodes and directories in the file system.

22..33..  CCyylliinnddeerr ggrroouuppss

     The  file  system partitions the disk into one or more areas
called _c_y_l_i_n_d_e_r _g_r_o_u_p_s.  A cylinder group is comprised of one  or
more  consecutive  cylinders  on  a  disk.   Each  cylinder group
includes inode slots for files, a _b_l_o_c_k _m_a_p describing  available
blocks  in the cylinder group, and summary information describing
the usage of data blocks within the cylinder group.  A fixed num-
ber  of inodes is allocated for each cylinder group when the file
system is created.  The current policy is to allocate  one  inode
for  each  2048  bytes  of disk space; this is expected to be far
more inodes than will ever be needed.

     All the cylinder  group  bookkeeping  information  could  be
placed  at the beginning of each cylinder group.  However if this
approach were used, all the redundant information would be on the
top  platter.   A  single hardware failure that destroyed the top
platter could cause the loss  of  all  copies  of  the  redundant
super-blocks.   Thus  the  cylinder group bookkeeping information
begins at a floating offset from the beginning  of  the  cylinder
group.   The  offset  for  the  _i_+_1st cylinder group is about one
track further from the beginning of the cylinder  group  than  it
-----------
[+]The actual number may vary from system  to  system,
but is usually in the range 5-13.









SMM:3-6                        The UNIX File System Check Program


was  for  the  _ith  cylinder  group.   In this way, the redundant
information spirals down into the pack; any single track,  cylin-
der,  or  platter  can  be  lost without losing all copies of the
super-blocks.  Except for the first  cylinder  group,  the  space
between  the beginning of the cylinder group and the beginning of
the cylinder group information stores data.

22..44..  FFrraaggmmeennttss

     To avoid waste in storing small files, the file system space
allocator  divides  a  single  file system block into one or more
_f_r_a_g_m_e_n_t_s.  The fragmentation of the  file  system  is  specified
when  the  file  system is created; each file system block can be
optionally broken into 2, 4, or  8  addressable  fragments.   The
lower  bound on the size of these fragments is constrained by the
disk sector size; typically 512 bytes is the lower bound on frag-
ment  size.   The  block  map associated with each cylinder group
records the space availability at the  fragment  level.   Aligned
fragments are examined to determine block availability.

     On a file system with a block size of 4096 bytes and a frag-
ment size of 1024 bytes, a file is represented by  zero  or  more
4096 byte blocks of data, and possibly a single fragmented block.
If a file system block must be fragmented to obtain space  for  a
small  amount  of data, the remainder of the block is made avail-
able for allocation to other files.   For  example,  consider  an
11000  byte  file  stored  on a 4096/1024 byte file system.  This
file uses two full size blocks and a 3072 byte fragment.   If  no
fragments with at least 3072 bytes are available when the file is
created, a full size block is split yielding the  necessary  3072
byte  fragment  and an unused 1024 byte fragment.  This remaining
fragment can be allocated to another file, as needed.

22..55..  UUppddaatteess ttoo tthhee ffiillee ssyysstteemm

     Every working day hundreds of files are  created,  modified,
and removed.  Every time a file is modified, the operating system
performs a series of file system updates.   These  updates,  when
written on disk, yield a consistent file system.  The file system
stages all modifications of  critical  information;  modification
can  either  be  completed  or  cleanly backed out after a crash.
Knowing the information that is first written to the file system,
deterministic  procedures  can be developed to repair a corrupted
file system.  To understand this  process,  the  order  that  the
update requests were being honored must first be understood.

     When  a  user  program  does an operation to change the file
system, such as a _w_r_i_t_e, the data to be written is copied into an
internal _i_n_-_c_o_r_e buffer in the kernel.  Normally, the disk update
is handled asynchronously; the user process is allowed to proceed
even  though  the data has not yet been written to the disk.  The
data, along with the inode information reflecting the change,  is
eventually written out to disk.  The real disk write may not hap-
pen until long after the _w_r_i_t_e system call has returned.  Thus at









The UNIX File System Check Program                        SMM:3-7


any  given time, the file system, as it resides on the disk, lags
the state of the file system represented by the in-core  informa-
tion.

     The  disk  information  is  updated  to  reflect the in-core
information when the buffer is required for another use,  when  a
_s_y_n_c(2) is done (at 30 second intervals) by _/_e_t_c_/_u_p_d_a_t_e(8), or by
manual operator intervention with the _s_y_n_c(8)  command.   If  the
system is halted without writing out the in-core information, the
file system on the disk will be in an inconsistent state.

     If all updates  are  done  asynchronously,  several  serious
inconsistencies can arise.  One inconsistency is that a block may
be claimed by two inodes.  Such an inconsistency can  occur  when
the  system  is halted before the pointer to the block in the old
inode has been cleared in the copy of the old inode on the  disk,
and  after  the  pointer  to  the block in the new inode has been
written out to the copy of the new  inode  on  the  disk.   Here,
there  is no deterministic method for deciding which inode should
really claim the block.  A similar problem can arise with a  mul-
tiply claimed inode.

     The  problem  with asynchronous inode updates can be avoided
by doing all inode  deallocations  synchronously.   Consequently,
inodes  and indirect blocks are written to the disk synchronously
(_i_._e_. the process blocks until the information is really  written
to  disk)  when they are being deallocated.  Similarly inodes are
kept consistent by synchronously deleting,  adding,  or  changing
directory entries.

33..  FFiixxiinngg ccoorrrruupptteedd ffiillee ssyysstteemmss

     A  file  system  can  become corrupted in several ways.  The
most common of these ways are improper  shutdown  procedures  and
hardware failures.

     File  systems  may  become corrupted during an _u_n_c_l_e_a_n _h_a_l_t.
This happens when proper shutdown procedures  are  not  observed,
physically  write-protecting  a mounted file system, or a mounted
file system is taken off-line.  The most common  operator  proce-
dural failure is forgetting to _s_y_n_c the system before halting the
CPU.

     File systems may become further corrupted if proper  startup
procedures are not observed, e.g., not checking a file system for
inconsistencies, and not repairing inconsistencies.   Allowing  a
corrupted  file system to be used (and, thus, to be modified fur-
ther) can be disastrous.

     Any piece of hardware can fail at any time.  Failures can be
as  subtle as a bad block on a disk pack, or as blatant as a non-
functional disk-controller.











SMM:3-8                        The UNIX File System Check Program


33..11..  DDeetteeccttiinngg aanndd ccoorrrreeccttiinngg ccoorrrruuppttiioonn

     Normally _f_s_c_k___f_f_s is run non-interactively.  In this mode it
will  only  fix  corruptions  that  are expected to occur from an
unclean halt.  These actions are a proper subset of  the  actions
that  _f_s_c_k___f_f_s  will  take  when  it  is  running  interactively.
Throughout this paper we assume that _f_s_c_k___f_f_s is being run inter-
actively,  and  all  possible errors can be encountered.  When an
inconsistency is discovered in this mode,  _f_s_c_k___f_f_s  reports  the
inconsistency for the operator to chose a corrective action.

     A  quiescent[++]  file  system may be checked for structural
integrity by performing consistency checks on the redundant  data
intrinsic  to  a  file system.  The redundant data is either read
from the file system, or computed from other known  values.   The
file  system  mmuusstt  be in a quiescent state when _f_s_c_k___f_f_s is run,
since _f_s_c_k___f_f_s is a multi-pass program.

     In the following sections, we discuss  methods  to  discover
inconsistencies  and possible corrective actions for the cylinder
group blocks, the inodes,  the  indirect  blocks,  and  the  data
blocks containing directory entries.

33..22..  SSuuppeerr--bblloocckk cchheecckkiinngg

     The  most  commonly  corrupted  item in a file system is the
summary information associated with the super-block.  The summary
information  is  prone  to corruption because it is modified with
every change to the file system's blocks or inodes, and  is  usu-
ally corrupted after an unclean halt.

     The  super-block  is  checked  for inconsistencies involving
file-system size, number of inodes,  free-block  count,  and  the
free-inode  count.   The file-system size must be larger than the
number of blocks used by the super-block and the number of blocks
used  by  the  list  of  inodes.  The file-system size and layout
information are the  most  critical  pieces  of  information  for
_f_s_c_k___f_f_s.   While  there is no way to actually check these sizes,
since they are statically determined by _n_e_w_f_s, _f_s_c_k___f_f_s can check
that  these  sizes  are within reasonable bounds.  All other file
system checks require that these sizes be correct.   If  _f_s_c_k___f_f_s
detects corruption in the static parameters of the default super-
block, _f_s_c_k___f_f_s requests the operator to specify the location  of
an alternate super-block.

33..33..  FFrreeee bblloocckk cchheecckkiinngg

     _F_s_c_k___f_f_s  checks  that  all the blocks marked as free in the
cylinder group block maps are not claimed by any files.  When all
the  blocks  have  been  initially accounted for, _f_s_c_k___f_f_s checks
that the number of free blocks plus the number of blocks  claimed
by  the  inodes  equals  the  total  number of blocks in the file
-----------
[++] I.e., unmounted and not being written on.









The UNIX File System Check Program                        SMM:3-9


system.

     If  anything  is  wrong  with  the  block  allocation  maps,
_f_s_c_k___f_f_s  will rebuild them, based on the list it has computed of
allocated blocks.

     The summary  information  associated  with  the  super-block
counts  the  total  number of free blocks within the file system.
_F_s_c_k___f_f_s compares this count to the  number  of  free  blocks  it
found  within  the  file system.  If the two counts do not agree,
then _f_s_c_k___f_f_s replaces the incorrect count in the summary  infor-
mation by the actual free-block count.

     The  summary  information  counts  the  total number of free
inodes within the file system.  _F_s_c_k___f_f_s compares this  count  to
the  number  of  free inodes it found within the file system.  If
the two counts do not agree, then _f_s_c_k___f_f_s replaces the incorrect
count  in the summary information by the actual free-inode count.

33..44..  CChheecckkiinngg tthhee iinnooddee ssttaattee

     An individual inode is not as likely to be corrupted as  the
allocation  information.  However, because of the great number of
active inodes, a few of the inodes are usually corrupted.

     The list of inodes in the file  system  is  checked  sequen-
tially  starting with inode 2 (inode 0 marks unused inodes; inode
1 is saved for future generations) and  progressing  through  the
last  inode  in  the  file  system.   The  state of each inode is
checked for  inconsistencies  involving  format  and  type,  link
count, duplicate blocks, bad blocks, and inode size.

     Each  inode  contains a mode word.  This mode word describes
the type and state of the inode.   Inodes  must  be  one  of  six
types:  regular inode, directory inode, symbolic link inode, spe-
cial block inode,  special  character  inode,  or  socket  inode.
Inodes  may  be  found in one of three allocation states: unallo-
cated, allocated, and neither unallocated  nor  allocated.   This
last  state suggests an incorrectly formated inode.  An inode can
get in this state if bad data is written  into  the  inode  list.
The  only  possible corrective action is for _f_s_c_k___f_f_s is to clear
the inode.

33..55..  IInnooddee lliinnkkss

     Each inode counts the  total  number  of  directory  entries
linked  to  the  inode.  _F_s_c_k___f_f_s verifies the link count of each
inode by starting at the root of the file system, and  descending
through  the directory structure.  The actual link count for each
inode is calculated during the descent.

     If the stored link count is non-zero  and  the  actual  link
count is zero, then no directory entry appears for the inode.  If
this happens, _f_s_c_k___f_f_s will place the disconnected  file  in  the









SMM:3-10                       The UNIX File System Check Program


_l_o_s_t_+_f_o_u_n_d  directory.   If the stored and actual link counts are
non-zero and unequal, a directory entry may have  been  added  or
removed  without  the  inode  being  updated.   If  this happens,
_f_s_c_k___f_f_s replaces the incorrect stored link count by  the  actual
link count.

     Each  inode  contains a list, or pointers to lists (indirect
blocks), of all the blocks claimed by the inode.  Since  indirect
blocks  are owned by an inode, inconsistencies in indirect blocks
directly affect the inode that owns it.

     _F_s_c_k___f_f_s compares each block  number  claimed  by  an  inode
against  a  list  of  already allocated blocks.  If another inode
already claims a block number, then the block number is added  to
a  list  of  _d_u_p_l_i_c_a_t_e  _b_l_o_c_k_s.  Otherwise, the list of allocated
blocks is updated to include the block number.

     If there are any duplicate blocks, _f_s_c_k___f_f_s will  perform  a
partial  second pass over the inode list to find the inode of the
duplicated block.  The second pass is needed, since without exam-
ining the files associated with these inodes for correct content,
not enough information is available to determine which  inode  is
corrupted  and  should  be cleared.  If this condition does arise
(only hardware failure will cause it), then the  inode  with  the
earliest modify time is usually incorrect, and should be cleared.
If this happens, _f_s_c_k___f_f_s prompts  the  operator  to  clear  both
inodes.   The  operator  must decide which one should be kept and
which one should be cleared.

     _F_s_c_k___f_f_s checks the range of each block number claimed by an
inode.  If the block number is lower than the first data block in
the file system, or greater than the last data  block,  then  the
block  number is a _b_a_d _b_l_o_c_k _n_u_m_b_e_r.  Many bad blocks in an inode
are usually caused by an indirect block that was not  written  to
the  file  system,  a condition which can only occur if there has
been a hardware failure.  If an inode contains bad block numbers,
_f_s_c_k___f_f_s prompts the operator to clear it.

33..66..  IInnooddee ddaattaa ssiizzee

     Each  inode  contains  a  count of the number of data blocks
that it contains.  The number of actual data blocks is the sum of
the allocated data blocks and the indirect blocks.  _F_s_c_k___f_f_s com-
putes the actual number of data blocks and  compares  that  block
count  against  the actual number of blocks the inode claims.  If
an inode contains an incorrect count _f_s_c_k___f_f_s prompts the  opera-
tor to fix it.

     Each  inode  contains a thirty-two bit size field.  The size
is the number of data bytes  in  the  file  associated  with  the
inode.  The consistency of the byte size field is roughly checked
by computing from the size field the  maximum  number  of  blocks
that  should  be  associated  with  the inode, and comparing that
expected block count against the  actual  number  of  blocks  the









The UNIX File System Check Program                       SMM:3-11


inode claims.

33..77..  CChheecckkiinngg tthhee ddaattaa aassssoocciiaatteedd wwiitthh aann iinnooddee

     An inode can directly or indirectly reference three kinds of
data blocks.  All referenced blocks must be the same  kind.   The
three  types of data blocks are: plain data blocks, symbolic link
data blocks, and directory data blocks.  Plain data  blocks  con-
tain  the information stored in a file; symbolic link data blocks
contain the path name stored in a link.   Directory  data  blocks
contain  directory entries.  _F_s_c_k___f_f_s can only check the validity
of directory data blocks.

     Each directory data block is checked for  several  types  of
inconsistencies.   These  inconsistencies include directory inode
numbers pointing to unallocated inodes, directory  inode  numbers
that  are  greater  than the number of inodes in the file system,
incorrect directory inode  numbers  for  ``..''  and  ``....'',  and
directories  that  are  not  attached to the file system.  If the
inode number in a directory data block references an  unallocated
inode,  then  _f_s_c_k___f_f_s  will remove that directory entry.  Again,
this condition can only arise when  there  has  been  a  hardware
failure.

     _F_s_c_k  also  checks  for  directories with unallocated blocks
(holes).  Such directories should never be created.  When  found,
_f_s_c_k  will  prompt the user to adjust the length of the offending
directory which is done by shortening the size of  the  directory
to  the  end  of  the  last  allocated  block preceding the hole.
Unfortunately, this means that another Phase  1  run  has  to  be
done.   _F_s_c_k will remind the user to rerun fsck after repairing a
directory containing an unallocated block.

     If a directory entry inode  number  references  outside  the
inode list, then _f_s_c_k___f_f_s will remove that directory entry.  This
condition occurs if bad data is written  into  a  directory  data
block.

     The  directory  inode  number  entry  for ``..''  must be the
first entry in the directory data block.  The  inode  number  for
``..''   must reference itself; e.g., it must equal the inode num-
ber for the directory data block.   The  directory  inode  number
entry  for  ``....'' must be the second entry in the directory data
block.  Its value must equal the inode number for the  parent  of
the  directory  entry  (or the inode number of the directory data
block if the directory is the root directory).  If the  directory
inode  numbers are incorrect, _f_s_c_k___f_f_s will replace them with the
correct values.  If there are multiple hard links to a directory,
the  first one encountered is considered the real parent to which
``....'' should point; _f_s_c_k___f_f_s recommends deletion for the  subse-
quently discovered names.












SMM:3-12                       The UNIX File System Check Program


33..88..  FFiillee ssyysstteemm ccoonnnneeccttiivviittyy

     _F_s_c_k___f_f_s checks the general connectivity of the file system.
If directories are not linked into the file system, then _f_s_c_k___f_f_s
links  the  directory back into the file system in the _l_o_s_t_+_f_o_u_n_d
directory.  This condition only occurs  when  there  has  been  a
hardware failure.

AAcckknnoowwlleeddggeemmeennttss

     I thank Bill Joy, Sam Leffler, Robert Elz and Dennis Ritchie
for their suggestions and help in implementing the new file  sys-
tem.   Thanks also to Robert Henry for his editorial input to get
this document together.   Finally  we  thank  our  sponsors,  the
National  Science  Foundation  under  grant  MCS80-05144, and the
Defense Advance Research Projects Agency (DoD) under  Arpa  Order
No.  4031 monitored by Naval Electronic System Command under Con-
tract No. N00039-82-C-0235. (Kirk McKusick, July 1983)

     I would like to thank Larry A. Wehr for advice that lead  to
the  first  version  of  _f_s_c_k___f_f_s and Rick B. Brandt for adapting
_f_s_c_k___f_f_s to UNIX/TS. (T. Kowalski, July 1979)



RReeffeerreenncceess


[Dolotta78]         Dolotta, T. A., and Olsson, S. B. eds.,  _U_N_I_X
                    _U_s_e_r_'_s _M_a_n_u_a_l_, _E_d_i_t_i_o_n _1_._1, January 1978.

[Joy83]             Joy,  W., Cooper, E., Fabry, R., Leffler, S.,
                    McKusick, M., and Mosher, D.   4.2BSD  System
                    Manual, _U_n_i_v_e_r_s_i_t_y _o_f _C_a_l_i_f_o_r_n_i_a _a_t _B_e_r_k_e_l_e_y,
                    _C_o_m_p_u_t_e_r  _S_y_s_t_e_m_s  _R_e_s_e_a_r_c_h  _G_r_o_u_p  _T_e_c_h_n_i_c_a_l
                    _R_e_p_o_r_t #4, 1982.

[McKusick84]        McKusick,  M.,  Joy,  W.,  Leffler,  S.,  and
                    Fabry, R.  A Fast File System for  UNIX,  _A_C_M
                    _T_r_a_n_s_a_c_t_i_o_n_s  _o_n  _C_o_m_p_u_t_e_r _S_y_s_t_e_m_s _2, 3.  pp.
                    181-197, August 1984.

[Ritchie78]         Ritchie, D. M., and Thompson,  K.,  The  UNIX
                    Time-Sharing  System, _T_h_e _B_e_l_l _S_y_s_t_e_m _T_e_c_h_n_i_-
                    _c_a_l _J_o_u_r_n_a_l 5577, 6 (July-August 1978, Part 2),
                    pp. 1905-29.

[Thompson78]        Thompson,  K.,  UNIX Implementation, _T_h_e _B_e_l_l
                    _S_y_s_t_e_m _T_e_c_h_n_i_c_a_l _J_o_u_r_n_a_l 5577,  6  (July-August
                    1978, Part 2), pp. 1931-46.













The UNIX File System Check Program                       SMM:3-13


44..  AAppppeennddiixx AA -- FFsscckk__ffffss EErrrroorr CCoonnddiittiioonnss

44..11..  CCoonnvveennttiioonnss

     _F_s_c_k___f_f_s  is  a  multi-pass file system check program.  Each
file system pass invokes a different Phase of the  _f_s_c_k___f_f_s  pro-
gram.   After  the  initial  setup,  _f_s_c_k___f_f_s performs successive
Phases over each file system, checking blocks  and  sizes,  path-
names,  connectivity,  reference  counts,  and  the  map  of free
blocks, (possibly rebuilding it), and performs some cleanup.

Normally _f_s_c_k___f_f_s is run non-interactively to _p_r_e_e_n the file sys-
tems  after  an  unclean halt.  While preen'ing a file system, it
will only fix corruptions that are  expected  to  occur  from  an
unclean  halt.   These actions are a proper subset of the actions
that  _f_s_c_k___f_f_s  will  take  when  it  is  running  interactively.
Throughout  this  appendix  many errors have several options that
the operator  can  take.   When  an  inconsistency  is  detected,
_f_s_c_k___f_f_s  reports  the  error  condition  to  the operator.  If a
response is required, _f_s_c_k___f_f_s prints a prompt message and  waits
for a response.  When preen'ing most errors are fatal.  For those
that are expected, the response taken is  noted.   This  appendix
explains  the  meaning  of  each  error  condition,  the possible
responses, and the related error conditions.

The error conditions are organized by the _P_h_a_s_e of  the  _f_s_c_k___f_f_s
program  in  which they can occur.  The error conditions that may
occur in more than one Phase will be discussed in initialization.

44..22..  IInniittiiaalliizzaattiioonn

     Before  a file system check can be performed, certain tables
have to be set up and certain files opened.   This  section  con-
cerns  itself with the opening of files and the initialization of
tables.  This section lists error conditions resulting from  com-
mand  line  options, memory requests, opening of files, status of
files, file system size checks, and creation of the scratch file.
All  the  initialization errors are fatal when the file system is
being preen'ed.


_C ooppttiioonn??
_C is not a legal option to _f_s_c_k___f_f_s; legal options  are  -b,  -c,
-y,  -n,  and  -p.   _F_s_c_k___f_f_s terminates on this error condition.
See the _f_s_c_k___f_f_s(8) manual entry for further detail.


ccaannnnoott aalllloocc NNNNNN bbyytteess ffoorr bblloocckkmmaapp
ccaannnnoott aalllloocc NNNNNN bbyytteess ffoorr ffrreeeemmaapp
ccaannnnoott aalllloocc NNNNNN bbyytteess ffoorr ssttaatteemmaapp
ccaannnnoott aalllloocc NNNNNN bbyytteess ffoorr llnnccnnttpp
_F_s_c_k___f_f_s's request for  memory  for  its  virtual  memory  tables
failed.   This  should never happen.  _F_s_c_k___f_f_s terminates on this
error condition.  See a guru.









SMM:3-14                       The UNIX File System Check Program


CCaann''tt ooppeenn cchheecckklliisstt ffiillee:: _F
The file system checklist file _F (usually _/_e_t_c_/_f_s_t_a_b) can not  be
opened for reading.  _F_s_c_k___f_f_s terminates on this error condition.
Check access modes of _F.


CCaann''tt ssttaatt rroooott
_F_s_c_k___f_f_s's request for statistics about the root directory  ``/''
failed.   This  should never happen.  _F_s_c_k___f_f_s terminates on this
error condition.  See a guru.


CCaann''tt ssttaatt _F
CCaann''tt mmaakkee sseennssee oouutt ooff nnaammee _F
_F_s_c_k___f_f_s's request for statistics about the file system _F failed.
When  running manually, it ignores this file system and continues
checking the next file system given.  Check access modes of _F.


CCaann''tt ooppeenn _F
_F_s_c_k___f_f_s's request attempt to open  the  file  system  _F  failed.
When  running manually, it ignores this file system and continues
checking the next file system given.  Check access modes of _F.


_F:: ((NNOO WWRRIITTEE))
Either the -n flag was specified or _f_s_c_k___f_f_s's  attempt  to  open
the file system _F for writing failed.  When running manually, all
the  diagnostics  are  printed  out,  but  no  modifications  are
attempted to fix them.


ffiillee iiss nnoott aa bblloocckk oorr cchhaarraacctteerr ddeevviiccee;; OOKK
You  have  given  _f_s_c_k___f_f_s a regular file name by mistake.  Check
the type of the file specified.

Possible responses to the OK prompt are:

YES  ignore this error condition.

NO   ignore this file system and continues checking the next file
     system given.


UUNNDDEEFFIINNEEDD OOPPTTIIMMIIZZAATTIIOONN IINN SSUUPPEERRBBLLOOCCKK ((SSEETT TTOO DDEEFFAAUULLTT))
The  superblock  optimization  parameter  is neither OPT_TIME nor
OPT_SPACE.

Possible responses to the SET TO DEFAULT prompt are:

YES  The superblock is set to request  optimization  to  minimize
     running  time  of  the system.  (If optimization to minimize
     disk space utilization is  desired,  it  can  be  set  using
     _t_u_n_e_f_s(8).)









The UNIX File System Check Program                       SMM:3-15


NO   ignore this error condition.


IIMMPPOOSSSSIIBBLLEE MMIINNFFRREEEE==_D IINN SSUUPPEERRBBLLOOCCKK ((SSEETT TTOO DDEEFFAAUULLTT))
The  superblock  minimum  space percentage is greater than 99% or
less than 0%.

Possible responses to the SET TO DEFAULT prompt are:

YES  The minfree parameter is set to 10%.  (If  some  other  per-
     centage is desired, it can be set using _t_u_n_e_f_s(8).)

NO   ignore this error condition.


IIMMPPOOSSSSIIBBLLEE IINNTTEERRLLEEAAVVEE==_D IINN SSUUPPEERRBBLLOOCCKK ((SSEETT TTOO DDEEFFAAUULLTT))
The file system interleave is less than or equal to zero.

Possible responses to the SET TO DEFAULT prompt are:

YES  The interleave parameter is set to 1.

NO   ignore this error condition.


IIMMPPOOSSSSIIBBLLEE NNPPSSEECCTT==_D IINN SSUUPPEERRBBLLOOCCKK ((SSEETT TTOO DDEEFFAAUULLTT))
The  number of physical sectors per track is less than the number
of usable sectors per track.

Possible responses to the SET TO DEFAULT prompt are:

YES  The npsect parameter is set to the number of usable  sectors
     per track.

NO   ignore this error condition.


One of the following messages will appear:
MMAAGGIICC NNUUMMBBEERR WWRROONNGG
NNCCGG OOUUTT OOFF RRAANNGGEE
CCPPGG OOUUTT OOFF RRAANNGGEE
NNCCYYLL DDOOEESS NNOOTT JJIIVVEE WWIITTHH NNCCGG**CCPPGG
SSIIZZEE PPRREEPPOOSSTTEERROOUUSSLLYY LLAARRGGEE
TTRRAASSHHEEDD VVAALLUUEESS IINN SSUUPPEERR BBLLOOCCKK
and will be followed by the message:
_F:: BBAADD SSUUPPEERR BBLLOOCCKK:: _B
UUSSEE --bb OOPPTTIIOONN TTOO FFSSCCKK__FFFFSS TTOO SSPPEECCIIFFYY LLOOCCAATTIIOONN OOFF AANN AALLTTEERRNNAATTEE
SSUUPPEERR--BBLLOOCCKK TTOO SSUUPPPPLLYY NNEEEEDDEEDD IINNFFOORRMMAATTIIOONN;; SSEEEE ffsscckk__ffffss((88))..
The  super  block has been corrupted.  An alternative super block
must be selected from among those listed by _n_e_w_f_s  (8)  when  the
file  system was created.  For file systems with a blocksize less
than 32K, specifying -b 32 is a good first choice.











SMM:3-16                       The UNIX File System Check Program


IINNTTEERRNNAALL IINNCCOONNSSIISSTTEENNCCYY:: _M
_F_s_c_k___f_f_s's has had an internal panic, whose message is  specified
as _M.  This should never happen.  See a guru.


CCAANN NNOOTT SSEEEEKK:: BBLLKK _B ((CCOONNTTIINNUUEE))
_F_s_c_k___f_f_s's  request  for  moving to a specified block number _B in
the file system failed.  This should never happen.  See a guru.

Possible responses to the CONTINUE prompt are:

YES  attempt to continue to run the file  system  check.   Often,
     however the problem will persist.  This error condition will
     not allow a complete check of the file system.  A second run
     of _f_s_c_k___f_f_s should be made to re-check this file system.  If
     the block was part  of  the  virtual  memory  buffer  cache,
     _f_s_c_k___f_f_s   will  terminate  with  the  message  ``Fatal  I/O
     error''.

NO   terminate the program.


CCAANN NNOOTT RREEAADD:: BBLLKK _B ((CCOONNTTIINNUUEE))
_F_s_c_k___f_f_s's request for reading a specified block number _B in  the
file system failed.  This should never happen.  See a guru.

Possible responses to the CONTINUE prompt are:

YES  attempt  to  continue to run the file system check.  It will
     retry the read and print out the message:
     TTHHEE FFOOLLLLOOWWIINNGG SSEECCTTOORRSS CCOOUULLDD NNOOTT BBEE RREEAADD:: _N
     where _N indicates the sectors that could not  be  read.   If
     _f_s_c_k___f_f_s ever tries to write back one of the blocks on which
     the read failed it will print the message:
     WWRRIITTIINNGG ZZEERROO''EEDD BBLLOOCCKK _N TTOO DDIISSKK
     where _N indicates the sector that was written  with  zero's.
     If  the  disk is experiencing hardware problems, the problem
     will persist.  This error condition will not  allow  a  com-
     plete  check  of  the file system.  A second run of _f_s_c_k___f_f_s
     should be made to re-check this file system.  If  the  block
     was  part  of the virtual memory buffer cache, _f_s_c_k___f_f_s will
     terminate with the message ``Fatal I/O error''.

NO   terminate the program.


CCAANN NNOOTT WWRRIITTEE:: BBLLKK _B ((CCOONNTTIINNUUEE))
_F_s_c_k___f_f_s's request for writing a specified block number _B in  the
file system failed.  The disk is write-protected; check the write
protect lock on the drive.  If that is not  the  problem,  see  a
guru.

Possible responses to the CONTINUE prompt are:










The UNIX File System Check Program                       SMM:3-17


YES  attempt to continue to run the file system check.  The write
     operation will be retried with the failed  blocks  indicated
     by the message:
     TTHHEE FFOOLLLLOOWWIINNGG SSEECCTTOORRSS CCOOUULLDD NNOOTT BBEE WWRRIITTTTEENN:: _N
     where _N indicates the sectors that could not be written.  If
     the disk is experiencing hardware problems, the problem will
     persist.   This  error  condition  will not allow a complete
     check of the file system.  A second run of  _f_s_c_k___f_f_s  should
     be made to re-check this file system.  If the block was part
     of the virtual memory buffer cache, _f_s_c_k___f_f_s will  terminate
     with the message ``Fatal I/O error''.

NO   terminate the program.


bbaadd iinnooddee nnuummbbeerr DDDDDD ttoo ggiinnooddee
An  internal  error has attempted to read non-existent inode _D_D_D.
This error causes _f_s_c_k___f_f_s to exit.  See a guru.

44..33..  PPhhaassee 11 -- CChheecckk BBlloocckkss aanndd SSiizzeess

     This phase concerns itself with the inode list.   This  sec-
tion  lists error conditions resulting from checking inode types,
setting up the zero-link-count table, examining inode block  num-
bers for bad or duplicate blocks, checking inode size, and check-
ing inode format.  All errors  in  this  phase  except  IINNCCOORRRREECCTT
BBLLOOCCKK  CCOOUUNNTT  and PPAARRTTIIAALLLLYY TTRRUUNNCCAATTEEDD IINNOODDEE are fatal if the file
system is being preen'ed.


UUNNKKNNOOWWNN FFIILLEE TTYYPPEE II==_I ((CCLLEEAARR))
The mode word of the inode _I indicates that the inode  is  not  a
special block inode, special character inode, socket inode, regu-
lar inode, symbolic link, or directory inode.

Possible responses to the CLEAR prompt are:

YES  de-allocate inode _I by  zeroing  its  contents.   This  will
     always invoke the UNALLOCATED error condition in Phase 2 for
     each directory entry pointing to this inode.

NO   ignore this error condition.


PPAARRTTIIAALLLLYY TTRRUUNNCCAATTEEDD IINNOODDEE II==_I ((SSAALLVVAAGGEE))
_F_s_c_k___f_f_s has found inode _I whose size is shorter than the  number
of  blocks  allocated to it.  This condition should only occur if
the system crashes while in the midst of truncating a file.  When
preen'ing  the  file system, _f_s_c_k___f_f_s completes the truncation to
the specified size.

Possible responses to SALVAGE are:











SMM:3-18                       The UNIX File System Check Program


YES  complete the truncation to the size specified in the  inode.

NO   ignore this error condition.


LLIINNKK CCOOUUNNTT TTAABBLLEE OOVVEERRFFLLOOWW ((CCOONNTTIINNUUEE))
An internal table for _f_s_c_k___f_f_s containing allocated inodes with a
link count of zero cannot allocate  more  memory.   Increase  the
virtual memory for _f_s_c_k___f_f_s.

Possible responses to the CONTINUE prompt are:

YES  continue  with  the  program.  This error condition will not
     allow a complete check of the file system.  A second run  of
     _f_s_c_k___f_f_s  should  be  made to re-check this file system.  If
     another allocated inode with a zero  link  count  is  found,
     this error condition is repeated.

NO   terminate the program.


_B BBAADD II==_I
Inode _I contains block number _B with a number lower than the num-
ber of the first data block in the file system  or  greater  than
the number of the last block in the file system.  This error con-
dition may invoke the EEXXCCEESSSSIIVVEE BBAADD BBLLKKSS error condition in Phase
1 (see next paragraph) if inode _I has too many block numbers out-
side the file system range.  This  error  condition  will  always
invoke the BBAADD//DDUUPP error condition in Phase 2 and Phase 4.


EEXXCCEESSSSIIVVEE BBAADD BBLLKKSS II==_I ((CCOONNTTIINNUUEE))
There is more than a tolerable number (usually 10) of blocks with
a number lower than the number of the first  data  block  in  the
file  system or greater than the number of last block in the file
system associated with inode _I.

Possible responses to the CONTINUE prompt are:

YES  ignore the rest of the blocks in  this  inode  and  continue
     checking with the next inode in the file system.  This error
     condition will not allow a complete check of the  file  sys-
     tem.   A  second  run of _f_s_c_k___f_f_s should be made to re-check
     this file system.

NO   terminate the program.


BBAADD SSTTAATTEE DDDDDD TTOO BBLLKKEERRRR
An internal error has scrambled _f_s_c_k___f_f_s's state map to have  the
impossible value _D_D_D.  _F_s_c_k___f_f_s exits immediately.  See a guru.












The UNIX File System Check Program                       SMM:3-19


_B DDUUPP II==_I
Inode  _I  contains  block  number  _B  that  is already claimed by
another inode.  This error condition may invoke the EEXXCCEESSSSIIVVEE DDUUPP
BBLLKKSS  error  condition  in  Phase 1 if inode _I has too many block
numbers claimed by  other  inodes.   This  error  condition  will
always invoke Phase 1b and the BBAADD//DDUUPP error condition in Phase 2
and Phase 4.


EEXXCCEESSSSIIVVEE DDUUPP BBLLKKSS II==_I ((CCOONNTTIINNUUEE))
There is more than a tolerable  number  (usually  10)  of  blocks
claimed by other inodes.

Possible responses to the CONTINUE prompt are:

YES  ignore  the  rest  of  the blocks in this inode and continue
     checking with the next inode in the file system.  This error
     condition  will  not allow a complete check of the file sys-
     tem.  A second run of _f_s_c_k___f_f_s should be  made  to  re-check
     this file system.

NO   terminate the program.


DDUUPP TTAABBLLEE OOVVEERRFFLLOOWW ((CCOONNTTIINNUUEE))
An  internal table in _f_s_c_k___f_f_s containing duplicate block numbers
cannot allocate any more space.  Increase the amount  of  virtual
memory available to _f_s_c_k___f_f_s.

Possible responses to the CONTINUE prompt are:

YES  continue  with  the  program.  This error condition will not
     allow a complete check of the file system.  A second run  of
     _f_s_c_k___f_f_s  should  be  made to re-check this file system.  If
     another duplicate block is found, this error condition  will
     repeat.

NO   terminate the program.


PPAARRTTIIAALLLLYY AALLLLOOCCAATTEEDD IINNOODDEE II==_I ((CCLLEEAARR))
Inode _I is neither allocated nor unallocated.

Possible responses to the CLEAR prompt are:

YES  de-allocate inode _I by zeroing its contents.

NO   ignore this error condition.


IINNCCOORRRREECCTT BBLLOOCCKK CCOOUUNNTT II==_I ((_X sshhoouulldd bbee _Y)) ((CCOORRRREECCTT))
The  block count for inode _I is _X blocks, but should be _Y blocks.
When preen'ing the count is corrected.










SMM:3-20                       The UNIX File System Check Program


Possible responses to the CORRECT prompt are:

YES  replace the block count of inode _I with _Y.

NO   ignore this error condition.

44..44..  PPhhaassee 11BB:: RReessccaann ffoorr MMoorree DDuuppss

     When a duplicate block is found in the file system, the file
system  is  rescanned  to  find the inode that previously claimed
that block.  This section lists  the  error  condition  when  the
duplicate block is found.


_B DDUUPP II==_I
Inode  _I  contains  block  number  _B  that  is already claimed by
another inode.  This  error  condition  will  always  invoke  the
BBAADD//DDUUPP  error  condition  in  Phase  2.  You can determine which
inodes have overlapping blocks by examining this error  condition
and the DUP error condition in Phase 1.

44..55..  PPhhaassee 22 -- CChheecckk PPaatthhnnaammeess

     This  phase  concerns itself with removing directory entries
pointing to error conditioned inodes from Phase 1 and  Phase  1b.
This  section  lists  error  conditions resulting from root inode
mode and status, directory inode pointers in range, and directory
entries  pointing  to bad inodes, and directory integrity checks.
All errors in this phase are fatal if the file  system  is  being
preen'ed,  except  for  directories  not  being a multiple of the
blocks size and extraneous hard links.


RROOOOTT IINNOODDEE UUNNAALLLLOOCCAATTEEDD ((AALLLLOOCCAATTEE))
The root inode (usually inode number  2)  has  no  allocate  mode
bits.  This should never happen.

Possible responses to the ALLOCATE prompt are:

YES  allocate  inode 2 as the root inode.  The files and directo-
     ries usually found in the root will be recovered in Phase  3
     and  put  into  _l_o_s_t_+_f_o_u_n_d.   If the attempt to allocate the
     root fails, _f_s_c_k___f_f_s will exit with the message:
     CCAANNNNOOTT AALLLLOOCCAATTEE RROOOOTT IINNOODDEE.

NO   _f_s_c_k___f_f_s will exit.


RROOOOTT IINNOODDEE NNOOTT DDIIRREECCTTOORRYY ((RREEAALLLLOOCCAATTEE))
The root inode (usually inode number 2) is  not  directory  inode
type.

Possible responses to the REALLOCATE prompt are:










The UNIX File System Check Program                       SMM:3-21


YES  clear the existing contents of the root inode and reallocate
     it.  The files and directories usually  found  in  the  root
     will  be  recovered  in Phase 3 and put into _l_o_s_t_+_f_o_u_n_d.  If
     the attempt to allocate the root fails, _f_s_c_k___f_f_s  will  exit
     with the message:
     CCAANNNNOOTT AALLLLOOCCAATTEE RROOOOTT IINNOODDEE.

NO   _f_s_c_k___f_f_s will then prompt with FFIIXX

Possible responses to the FIX prompt are:

YES  replace  the  root  inode's  type to be a directory.  If the
     root inode's data blocks  are  not  directory  blocks,  many
     error conditions will be produced.

NO   terminate the program.


DDUUPPSS//BBAADD IINN RROOOOTT IINNOODDEE ((RREEAALLLLOOCCAATTEE))
Phase  1 or Phase 1b have found duplicate blocks or bad blocks in
the root inode (usually inode number 2) for the file system.

Possible responses to the REALLOCATE prompt are:

YES  clear the existing contents of the root inode and reallocate
     it.   The  files  and  directories usually found in the root
     will be recovered in Phase 3 and put  into  _l_o_s_t_+_f_o_u_n_d.   If
     the  attempt  to allocate the root fails, _f_s_c_k___f_f_s will exit
     with the message:
     CCAANNNNOOTT AALLLLOOCCAATTEE RROOOOTT IINNOODDEE.

NO   _f_s_c_k___f_f_s will then prompt with CCOONNTTIINNUUEE.

Possible responses to the CONTINUE prompt are:

YES  ignore the DDUUPPSS//BBAADD error condition in the  root  inode  and
     attempt  to  continue  to run the file system check.  If the
     root inode is not correct, then  this  may  result  in  many
     other error conditions.

NO   terminate the program.


NNAAMMEE TTOOOO LLOONNGG _F
An excessively long path name has been found.  This usually indi-
cates loops in the file system name space.  This can occur if the
super user has made circular links to directories.  The offending
links must be removed (by a guru).


II OOUUTT OOFF RRAANNGGEE II==_I NNAAMMEE==_F ((RREEMMOOVVEE))
A directory entry _F has an inode number _I that  is  greater  than
the end of the inode list.










SMM:3-22                       The UNIX File System Check Program


Possible responses to the REMOVE prompt are:

YES  the directory entry _F is removed.

NO   ignore this error condition.


UUNNAALLLLOOCCAATTEEDD II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T _t_y_p_e==_F ((RREEMMOOVVEE))
A  directory  or  file  entry _F points to an unallocated inode _I.
The owner _O, mode _M, size _S,  modify  time  _T,  and  name  _F  are
printed.

Possible responses to the REMOVE prompt are:

YES  the directory entry _F is removed.

NO   ignore this error condition.


DDUUPP//BBAADD II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T _t_y_p_e==_F ((RREEMMOOVVEE))
Phase  1  or  Phase  1b have found duplicate blocks or bad blocks
associated with directory or file entry _F, inode _I.  The owner _O,
mode  _M, size _S, modify time _T, and directory name _F are printed.

Possible responses to the REMOVE prompt are:

YES  the directory entry _F is removed.

NO   ignore this error condition.


ZZEERROO LLEENNGGTTHH DDIIRREECCTTOORRYY II==_I OOWWNNEERR==_O  MMOODDEE==_M  SSIIZZEE==_S  MMTTIIMMEE==_T  DDIIRR==_F
((RREEMMOOVVEE))
A directory entry _F has a size _S that is zero.  The owner _O, mode
_M, size _S, modify time _T, and directory name _F are printed.

Possible responses to the REMOVE prompt are:

YES  the directory entry _F is removed; this  will  always  invoke
     the BAD/DUP error condition in Phase 4.

NO   ignore this error condition.


DDIIRREECCTTOORRYY TTOOOO SSHHOORRTT II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((FFIIXX))
A directory _F has been found whose size _S is less than the  mini-
mum  size directory.  The owner _O, mode _M, size _S, modify time _T,
and directory name _F are printed.

Possible responses to the FIX prompt are:

YES  increase the size of the directory to the minimum  directory
     size.










The UNIX File System Check Program                       SMM:3-23


NO   ignore this directory.


DDIIRREECCTTOORRYY _F LLEENNGGTTHH _S NNOOTT MMUULLTTIIPPLLEE OOFF _B ((AADDJJUUSSTT))
A  directory  _F has been found with size _S that is not a multiple
of the directory blocksize _B.

Possible responses to the ADJUST prompt are:

YES  the length is rounded up  to  the  appropriate  block  size.
     This  error  can  occur  on  4.2BSD file systems.  Thus when
     preen'ing the file system only a warning is printed and  the
     directory is adjusted.

NO   ignore the error condition.


DDIIRREECCTTOORRYY CCOORRRRUUPPTTEEDD II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((SSAALL--
VVAAGGEE))
A directory with an inconsistent internal state has been found.

Possible responses to the FIX prompt are:

YES  throw away all entries up to  the  next  directory  boundary
     (usually  512-byte) boundary.  This drastic action can throw
     away up to 42 entries, and should be taken only after  other
     recovery efforts have failed.

NO   skip  up  to the next directory boundary and resume reading,
     but do not modify the directory.


BBAADD IINNOODDEE NNUUMMBBEERR FFOORR ``..'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T  DDIIRR==_F
((FFIIXX))
A directory _I has been found whose inode number for `.' does does
not equal _I.

Possible responses to the FIX prompt are:

YES  change the inode number for `.' to be equal to _I.

NO   leave the inode number for `.' unchanged.


MMIISSSSIINNGG ``..'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((FFIIXX))
A directory _I has been found whose first entry is unallocated.

Possible responses to the FIX prompt are:

YES  build an entry for `.' with inode number equal to _I.

NO   leave the directory unchanged.











SMM:3-24                       The UNIX File System Check Program


MMIISSSSIINNGG ``..'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F
CCAANNNNOOTT FFIIXX,, FFIIRRSSTT EENNTTRRYY IINN DDIIRREECCTTOORRYY CCOONNTTAAIINNSS _F
A directory _I has been found whose first entry  is  _F.   _F_s_c_k___f_f_s
cannot  resolve  this problem.  The file system should be mounted
and the offending entry  _F  moved  elsewhere.   The  file  system
should then be unmounted and _f_s_c_k___f_f_s should be run again.


MMIISSSSIINNGG ``..'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F
CCAANNNNOOTT FFIIXX,, IINNSSUUFFFFIICCIIEENNTT SSPPAACCEE TTOO AADDDD ``..''
A  directory  _I  has  been  found  whose  first entry is not `.'.
_F_s_c_k___f_f_s cannot resolve this problem as it should  never  happen.
See a guru.


EEXXTTRRAA ``..'' EENNTTRRYY II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((FFIIXX))
A  directory  _I  has  been found that has more than one entry for
`.'.

Possible responses to the FIX prompt are:

YES  remove the extra entry for `.'.

NO   leave the directory unchanged.


BBAADD IINNOODDEE NNUUMMBBEERR FFOORR ``....'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F
((FFIIXX))
A  directory  _I  has  been found whose inode number for `..' does
does not equal the parent of _I.

Possible responses to the FIX prompt are:

YES  change the inode number for `..' to be equal to  the  parent
     of _I (``....'' in the root inode points to itself).

NO   leave the inode number for `..' unchanged.


MMIISSSSIINNGG ``....'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((FFIIXX))
A directory _I has been found whose second entry is unallocated.

Possible responses to the FIX prompt are:

YES  build  an entry for `..' with inode number equal to the par-
     ent of _I (``....'' in the root inode points to itself).

NO   leave the directory unchanged.


MMIISSSSIINNGG ``....'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F
CCAANNNNOOTT FFIIXX,, SSEECCOONNDD EENNTTRRYY IINN DDIIRREECCTTOORRYY CCOONNTTAAIINNSS _F
A directory _I has been found whose second entry is  _F.   _F_s_c_k___f_f_s
cannot  resolve  this problem.  The file system should be mounted









The UNIX File System Check Program                       SMM:3-25


and the offending entry  _F  moved  elsewhere.   The  file  system
should then be unmounted and _f_s_c_k___f_f_s should be run again.


MMIISSSSIINNGG ``....'' II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F
CCAANNNNOOTT FFIIXX,, IINNSSUUFFFFIICCIIEENNTT SSPPAACCEE TTOO AADDDD ``....''
A  directory  _I  has  been  found whose second entry is not `..'.
_F_s_c_k___f_f_s cannot resolve this problem.  The file system should  be
mounted  and  the  second entry in the directory moved elsewhere.
The file system should then be unmounted and _f_s_c_k___f_f_s  should  be
run again.


EEXXTTRRAA ``....'' EENNTTRRYY II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T DDIIRR==_F ((FFIIXX))
A  directory  _I  has  been found that has more than one entry for
`..'.

Possible responses to the FIX prompt are:

YES  remove the extra entry for `..'.

NO   leave the directory unchanged.


_N IISS AANN EEXXTTRRAANNEEOOUUSS HHAARRDD LLIINNKK TTOO AA DDIIRREECCTTOORRYY _D ((RREEMMOOVVEE))
_F_s_c_k___f_f_s has found a hard link,  _N,  to  a  directory,  _D.   When
preen'ing the extraneous links are ignored.

Possible responses to the REMOVE prompt are:

YES  delete the extraneous entry, _N.

NO   ignore the error condition.


BBAADD IINNOODDEE _S TTOO DDEESSCCEENNDD
An  internal  error has caused an impossible state _S to be passed
to the routine that descends the file system directory structure.
_F_s_c_k___f_f_s exits.  See a guru.


BBAADD RREETTUURRNN SSTTAATTEE _S FFRROOMM DDEESSCCEENNDD
An internal error has caused an impossible state _S to be returned
from the routine that descends the file system  directory  struc-
ture.  _F_s_c_k___f_f_s exits.  See a guru.


BBAADD SSTTAATTEE _S FFOORR RROOOOTT IINNOODDEE
An internal error has caused an impossible state _S to be assigned
to the root inode.  _F_s_c_k___f_f_s exits.  See a guru.













SMM:3-26                       The UNIX File System Check Program


44..66..  PPhhaassee 33 -- CChheecckk CCoonnnneeccttiivviittyy

     This phase concerns itself with the  directory  connectivity
seen  in  Phase 2.  This section lists error conditions resulting
from unreferenced directories, and  missing  or  full  _l_o_s_t_+_f_o_u_n_d
directories.


UUNNRREEFF DDIIRR II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T ((RREECCOONNNNEECCTT))
The directory inode _I was not connected to a directory entry when
the file system was traversed.  The owner _O, mode _M, size _S,  and
modify  time _T of directory inode _I are printed.  When preen'ing,
the directory is reconnected if its size is  non-zero,  otherwise
it is cleared.

Possible responses to the RECONNECT prompt are:

YES  reconnect directory inode _I to the file system in the direc-
     tory for lost files (usually _l_o_s_t_+_f_o_u_n_d).  This  may  invoke
     the _l_o_s_t_+_f_o_u_n_d error condition in Phase 3 if there are prob-
     lems connecting directory inode _I to _l_o_s_t_+_f_o_u_n_d.   This  may
     also  invoke the CONNECTED error condition in Phase 3 if the
     link was successful.

NO   ignore this error condition.  This will  always  invoke  the
     UNREF error condition in Phase 4.


NNOO lloosstt++ffoouunndd DDIIRREECCTTOORRYY ((CCRREEAATTEE))
There  is  no  _l_o_s_t_+_f_o_u_n_d  directory in the root directory of the
file system; When preen'ing _f_s_c_k___f_f_s tries to create a _l_o_s_t_+_f_o_u_n_d
directory.

Possible responses to the CREATE prompt are:

YES  create  a  _l_o_s_t_+_f_o_u_n_d directory in the root of the file sys-
     tem.  This may raise the message:
     NNOO SSPPAACCEE LLEEFFTT IINN // ((EEXXPPAANNDD))
     See below for the possible responses.  Inability to create a
     _l_o_s_t_+_f_o_u_n_d directory generates the message:
     SSOORRRRYY.. CCAANNNNOOTT CCRREEAATTEE lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and  aborts the attempt to linkup the lost inode.  This will
     always invoke the UNREF error condition in Phase 4.

NO   abort the attempt to  linkup  the  lost  inode.   This  will
     always invoke the UNREF error condition in Phase 4.


lloosstt++ffoouunndd IISS NNOOTT AA DDIIRREECCTTOORRYY ((RREEAALLLLOOCCAATTEE))
The entry for _l_o_s_t_+_f_o_u_n_d is not a directory.

Possible responses to the REALLOCATE prompt are:











The UNIX File System Check Program                       SMM:3-27


YES  allocate  a directory inode, and change _l_o_s_t_+_f_o_u_n_d to refer-
     ence it.  The previous inode  reference  by  the  _l_o_s_t_+_f_o_u_n_d
     name is not cleared.  Thus it will either be reclaimed as an
     UNREF'ed inode or have its link  count  ADJUST'ed  later  in
     this Phase.  Inability to create a _l_o_s_t_+_f_o_u_n_d directory gen-
     erates the message:
     SSOORRRRYY.. CCAANNNNOOTT CCRREEAATTEE lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and aborts the attempt to linkup the lost inode.  This  will
     always invoke the UNREF error condition in Phase 4.

NO   abort  the  attempt  to  linkup  the  lost inode.  This will
     always invoke the UNREF error condition in Phase 4.


NNOO SSPPAACCEE LLEEFFTT IINN //lloosstt++ffoouunndd ((EEXXPPAANNDD))
There is no space to add another entry to the  _l_o_s_t_+_f_o_u_n_d  direc-
tory  in  the  root directory of the file system.  When preen'ing
the _l_o_s_t_+_f_o_u_n_d directory is expanded.

Possible responses to the EXPAND prompt are:

YES  the _l_o_s_t_+_f_o_u_n_d directory is expanded to make  room  for  the
     new entry.  If the attempted expansion fails _f_s_c_k___f_f_s prints
     the message:
     SSOORRRRYY.. NNOO SSPPAACCEE IINN lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and aborts the attempt to linkup the lost inode.  This  will
     always  invoke  the UNREF error condition in Phase 4.  Clean
     out unnecessary entries in _l_o_s_t_+_f_o_u_n_d.  This error is  fatal
     if the file system is being preen'ed.

NO   abort  the  attempt  to  linkup  the  lost inode.  This will
     always invoke the UNREF error condition in Phase 4.


DDIIRR II==_I_1 CCOONNNNEECCTTEEDD.. PPAARREENNTT WWAASS II==_I_2
This is an advisory message indicating a directory inode  _I_1  was
successfully  connected  to the _l_o_s_t_+_f_o_u_n_d directory.  The parent
inode _I_2 of the directory inode _I_1 is replaced by the inode  num-
ber of the _l_o_s_t_+_f_o_u_n_d directory.


DDIIRREECCTTOORRYY _F LLEENNGGTTHH _S NNOOTT MMUULLTTIIPPLLEE OOFF _B ((AADDJJUUSSTT))
A  directory  _F has been found with size _S that is not a multiple
of the directory blocksize _B (this can reoccur in Phase 3  if  it
is not adjusted in Phase 2).

Possible responses to the ADJUST prompt are:

YES  the  length  is  rounded  up  to the appropriate block size.
     This error can occur on  4.2BSD  file  systems.   Thus  when
     preen'ing  the file system only a warning is printed and the
     directory is adjusted.











SMM:3-28                       The UNIX File System Check Program


NO   ignore the error condition.


BBAADD IINNOODDEE _S TTOO DDEESSCCEENNDD
An internal error has caused an impossible state _S to  be  passed
to the routine that descends the file system directory structure.
_F_s_c_k___f_f_s exits.  See a guru.

44..77..  PPhhaassee 44 -- CChheecckk RReeffeerreennccee CCoouunnttss

     This phase concerns itself with the link  count  information
seen in Phase 2 and Phase 3.  This section lists error conditions
resulting from unreferenced files,  missing  or  full  _l_o_s_t_+_f_o_u_n_d
directory, incorrect link counts for files, directories, symbolic
links, or special files, unreferenced files, symbolic links,  and
directories,  and  bad  or  duplicate  blocks  in files, symbolic
links, and directories.  All errors in this phase are correctable
if  the file system is being preen'ed except running out of space
in the _l_o_s_t_+_f_o_u_n_d directory.


UUNNRREEFF FFIILLEE II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T ((RREECCOONNNNEECCTT))
Inode _I was not connected to a directory entry when the file sys-
tem  was traversed.  The owner _O, mode _M, size _S, and modify time
_T of inode _I are printed.  When preen'ing the file is cleared  if
either its size or its link count is zero, otherwise it is recon-
nected.

Possible responses to the RECONNECT prompt are:

YES  reconnect inode _I to the file system in  the  directory  for
     lost  files  (usually  _l_o_s_t_+_f_o_u_n_d).   This  may  invoke  the
     _l_o_s_t_+_f_o_u_n_d error condition in Phase 4 if there are  problems
     connecting inode _I to _l_o_s_t_+_f_o_u_n_d.

NO   ignore  this  error  condition.  This will always invoke the
     CLEAR error condition in Phase 4.


((CCLLEEAARR))
The inode mentioned in the immediately previous  error  condition
can  not be reconnected.  This cannot occur if the file system is
being preen'ed, since lack of space to reconnect files is a fatal
error.

Possible responses to the CLEAR prompt are:

YES  de-allocate  the inode mentioned in the immediately previous
     error condition by zeroing its contents.

NO   ignore this error condition.












The UNIX File System Check Program                       SMM:3-29


NNOO lloosstt++ffoouunndd DDIIRREECCTTOORRYY ((CCRREEAATTEE))
There is no _l_o_s_t_+_f_o_u_n_d directory in the  root  directory  of  the
file system; When preen'ing _f_s_c_k___f_f_s tries to create a _l_o_s_t_+_f_o_u_n_d
directory.

Possible responses to the CREATE prompt are:

YES  create a _l_o_s_t_+_f_o_u_n_d directory in the root of the  file  sys-
     tem.  This may raise the message:
     NNOO SSPPAACCEE LLEEFFTT IINN // ((EEXXPPAANNDD))
     See below for the possible responses.  Inability to create a
     _l_o_s_t_+_f_o_u_n_d directory generates the message:
     SSOORRRRYY.. CCAANNNNOOTT CCRREEAATTEE lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and aborts the attempt to linkup the lost inode.  This  will
     always invoke the UNREF error condition in Phase 4.

NO   abort  the  attempt  to  linkup  the  lost inode.  This will
     always invoke the UNREF error condition in Phase 4.


lloosstt++ffoouunndd IISS NNOOTT AA DDIIRREECCTTOORRYY ((RREEAALLLLOOCCAATTEE))
The entry for _l_o_s_t_+_f_o_u_n_d is not a directory.

Possible responses to the REALLOCATE prompt are:

YES  allocate a directory inode, and change _l_o_s_t_+_f_o_u_n_d to  refer-
     ence  it.   The  previous  inode reference by the _l_o_s_t_+_f_o_u_n_d
     name is not cleared.  Thus it will either be reclaimed as an
     UNREF'ed  inode  or  have  its link count ADJUST'ed later in
     this Phase.  Inability to create a _l_o_s_t_+_f_o_u_n_d directory gen-
     erates the message:
     SSOORRRRYY.. CCAANNNNOOTT CCRREEAATTEE lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and  aborts the attempt to linkup the lost inode.  This will
     always invoke the UNREF error condition in Phase 4.

NO   abort the attempt to  linkup  the  lost  inode.   This  will
     always invoke the UNREF error condition in Phase 4.


NNOO SSPPAACCEE LLEEFFTT IINN //lloosstt++ffoouunndd ((EEXXPPAANNDD))
There  is  no space to add another entry to the _l_o_s_t_+_f_o_u_n_d direc-
tory in the root directory of the file  system.   When  preen'ing
the _l_o_s_t_+_f_o_u_n_d directory is expanded.

Possible responses to the EXPAND prompt are:

YES  the  _l_o_s_t_+_f_o_u_n_d  directory  is expanded to make room for the
     new entry.  If the attempted expansion fails _f_s_c_k___f_f_s prints
     the message:
     SSOORRRRYY.. NNOO SSPPAACCEE IINN lloosstt++ffoouunndd DDIIRREECCTTOORRYY
     and  aborts the attempt to linkup the lost inode.  This will
     always invoke the UNREF error condition in Phase  4.   Clean
     out  unnecessary entries in _l_o_s_t_+_f_o_u_n_d.  This error is fatal
     if the file system is being preen'ed.









SMM:3-30                       The UNIX File System Check Program


NO   abort the attempt to  linkup  the  lost  inode.   This  will
     always invoke the UNREF error condition in Phase 4.


LLIINNKK  CCOOUUNNTT _t_y_p_e II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T CCOOUUNNTT==_X SSHHOOUULLDD
BBEE _Y ((AADDJJUUSSTT))
The link count for inode _I, is _X but should be _Y.  The  owner  _O,
mode  _M,  size  _S, and modify time _T are printed.  When preen'ing
the link count is adjusted unless the  number  of  references  is
increasing,  a  condition that should never occur unless precipi-
tated by a hardware failure.  When the number  of  references  is
increasing under preen mode, _f_s_c_k___f_f_s exits with the message:
LLIINNKK CCOOUUNNTT IINNCCRREEAASSIINNGG

Possible responses to the ADJUST prompt are:

YES  replace the link count of file inode _I with _Y.

NO   ignore this error condition.


UUNNRREEFF _t_y_p_e II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T ((CCLLEEAARR))
Inode  _I,  was  not  connected to a directory entry when the file
system was traversed.  The owner _O, mode _M, size  _S,  and  modify
time  _T  of  inode _I are printed.  When preen'ing, this is a file
that was not connected because its size or link count  was  zero,
hence it is cleared.

Possible responses to the CLEAR prompt are:

YES  de-allocate inode _I by zeroing its contents.

NO   ignore this error condition.


BBAADD//DDUUPP _t_y_p_e II==_I OOWWNNEERR==_O MMOODDEE==_M SSIIZZEE==_S MMTTIIMMEE==_T ((CCLLEEAARR))
Phase  1  or  Phase  1b have found duplicate blocks or bad blocks
associated with inode _I.  The owner _O, mode _M, size _S, and modify
time  _T of inode _I are printed.  This error cannot arise when the
file system is being preen'ed, as it would have  caused  a  fatal
error earlier.

Possible responses to the CLEAR prompt are:

YES  de-allocate inode _I by zeroing its contents.

NO   ignore this error condition.

44..88..  PPhhaassee 55 -- CChheecckk CCyyll ggrroouuppss

     This  phase  concerns  itself  with the free-block and used-
inode maps.  This section lists error conditions  resulting  from
allocated blocks in the free-block maps, free blocks missing from
free-block maps, and the total free-block  count  incorrect.   It









The UNIX File System Check Program                       SMM:3-31


also  lists  error  conditions  resulting from free inodes in the
used-inode maps, allocated inodes missing from  used-inode  maps,
and the total used-inode count incorrect.


CCGG _C:: BBAADD MMAAGGIICC NNUUMMBBEERR
The  magic  number  of  cylinder  group _C is wrong.  This usually
indicates that the cylinder group maps have been destroyed.  When
running  manually  the  cylinder group is marked as needing to be
reconstructed.  This error is fatal if the file system  is  being
preen'ed.


BBLLKK((SS)) MMIISSSSIINNGG IINN BBIITT MMAAPPSS ((SSAALLVVAAGGEE))
A  cylinder  group block map is missing some free blocks.  During
preen'ing the maps are reconstructed.

Possible responses to the SALVAGE prompt are:

YES  reconstruct the free block map.

NO   ignore this error condition.


SSUUMMMMAARRYY IINNFFOORRMMAATTIIOONN BBAADD ((SSAALLVVAAGGEE))
The  summary  information  was  found  to  be  incorrect.    When
preen'ing, the summary information is recomputed.

Possible responses to the SALVAGE prompt are:

YES  reconstruct the summary information.

NO   ignore this error condition.


FFRREEEE BBLLKK CCOOUUNNTT((SS)) WWRROONNGG IINN SSUUPPEERRBBLLOOCCKK ((SSAALLVVAAGGEE))
The  superblock free block information was found to be incorrect.
When preen'ing, the superblock free block information  is  recom-
puted.

Possible responses to the SALVAGE prompt are:

YES  reconstruct the superblock free block information.

NO   ignore this error condition.

44..99..  CClleeaannuupp

     Once a file system has been checked, a few cleanup functions
are performed.  This section lists advisory  messages  about  the
file system and modify status of the file system.












SMM:3-32                       The UNIX File System Check Program


_V ffiilleess,, _W uusseedd,, _X ffrreeee ((_Y ffrraaggss,, _Z bblloocckkss))
This  is  an  advisory  message  indicating  that the file system
checked contained _V files using _W fragment sized blocks leaving _X
fragment  sized  blocks  free in the file system.  The numbers in
parenthesis breaks the free count down into _Y free fragments  and
_Z free full sized blocks.


********** RREEBBOOOOTT UUNNIIXX **********
This  is an advisory message indicating that the root file system
has been modified by _f_s_c_k___f_f_s_.  If UNIX is not  rebooted  immedi-
ately,  the  work  done  by _f_s_c_k___f_f_s may be undone by the in-core
copies of tables UNIX keeps.  When preen'ing, _f_s_c_k___f_f_s will  exit
with  a  code  of 4.  The standard auto-reboot script distributed
with 4.3BSD interprets an exit code of 4 by issuing a reboot sys-
tem call.


********** FFIILLEE SSYYSSTTEEMM WWAASS MMOODDIIFFIIEEDD **********
This is an advisory message indicating that the current file sys-
tem was modified by _f_s_c_k___f_f_s_.  If this file system is mounted  or
is  the  current  root file system, _f_s_c_k___f_f_s should be halted and
UNIX rebooted.  If UNIX is not  rebooted  immediately,  the  work
done  by  _f_s_c_k___f_f_s  may be undone by the in-core copies of tables
UNIX keeps.



































