2.9BSD/usr/man/cat8/fsck.8

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

NAME
fsck - file system consistency check and interactive repair

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

DESCRIPTION
The first form of _f_s_c_k preens a standard set of file systems
or the specified file systems. It is normally used in the
script /_e_t_c/_r_c during automatic reboot. In this case _f_s_c_k
reads the table /_e_t_c/_f_s_t_a_b 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

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

These are the only inconsistencies which _f_s_c_k 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,
_f_s_c_k 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 and PDP-11 Unix kernels with the UCB_FSFIX
option have the appropriate modifications; the -p option
should not be used on other systems.

Without the -p option, _f_s_c_k 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
_f_s_c_k will default to a -n action.

_F_s_c_k has more consistency checks than its predecessors
_c_h_e_c_k, _d_c_h_e_c_k, _f_c_h_e_c_k, and _i_c_h_e_c_k combined.

The following flags are interpreted by _f_s_c_k.

-y Assume a yes response to all questions asked by _f_s_c_k;
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 _f_s_c_k;
do not open the file system for writing.

-s_X 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 -s_X option allows for creating an optimal free
list organization. The following forms of _X are

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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 _4_0_0:_9 is used.

-S_X Conditionally reconstruct the free list. This option
is like -s_X 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 _f_s_c_k. This option is useful for
forcing free list reorganization on uncontaminated
file systems.

-t If _f_s_c_k 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,
_f_s_c_k 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 _f_s_c_k
completes.

If no file systems are given to _f_s_c_k then a default list of
file systems is read from the file /_e_t_c/_f_s_t_a_b.

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

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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 _l_o_s_t+_f_o_u_n_d directory. The name assigned is the
inode number. The only restriction is that the directory
_l_o_s_t+_f_o_u_n_d 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
_l_o_s_t+_f_o_u_n_d, copying a number of files to the directory, and
then removing them (before _f_s_c_k is executed). _M_k_f_s(8) will
automatically create a _l_o_s_t+_f_o_u_n_ddirectory.

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 _f_s_c_k 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 (_f_s_c_k was
interrupted).

SEE ALSO
filsys(5), fstab(5), crash(8), mkfs(8), mklost+found(8),
reboot(8)
T. J. Kowalski, _F_S_C_K - _T_h_e _U_N_I_X _F_i_l_e _S_y_s_t_e_m _C_h_e_c_k _P_r_o_g_r_a_m

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

Printed 8/2/83 4