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FSCK_FFS(8) NetBSD System Manager's Manual FSCK_FFS(8)
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fsck_ffs -- Fast File System consistency check and interactive repair
fsck_ffs [-adFfPpqUXz] [-B byteorder] [-b block] [-c level] [-m mode]
[-x snap-backup] [-y | -n] filesystem ...
fsck_ffs performs interactive file system consistency checks and repair
for each of the file systems specified on the command line. It is nor-
mally invoked from fsck(8).
The kernel takes care that only a restricted class of innocuous file sys-
tem inconsistencies can happen unless hardware or software failures
intervene. These are limited to the following:
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_ffs in ``preen'' mode (with
the -p option) will correct; if it encounters other inconsistencies, it
exits with an abnormal return status. For each corrected inconsistency
one or more lines will be printed identifying the file system on which
the correction will take place, and the nature of the correction. After
successfully correcting a file system, fsck_ffs will print the number of
files on that file system, the number of used and free blocks, and the
percentage of fragmentation.
If sent a QUIT signal, fsck_ffs will finish the file system checks, then
exit with an abnormal return status.
If fsck_ffs receives a SIGINFO signal (see the status argument for
stty(1)), a line will be written to the standard error output indicating
the name of the device currently being checked, the current phase number
and phase-specific progress information.
Without the -p option, fsck_ffs audits and interactively repairs incon-
sistent 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 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 diagnos-
tic 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 file system fsck_ffs will default to a -n
fsck_ffs has more consistency checks than its predecessors check, dcheck,
fcheck, and icheck combined.
The following flags are interpreted by fsck_ffs.
-a Interpret the filesystem as an Apple UFS filesys-
tem, even if there is no Apple UFS volume label
-B byteorder Convert the file system metadata to byteorder byte
order if needed. Valid byte orders are ``be'' and
``le''. If fsck_ffs is interrupted while swapping
the metadata byte order, the file system cannot be
recovered. fsck_ffs will print a message in inter-
active mode if the file system is not in host byte
-b block Use the block number block as the super block for
the file system. Block 32 is usually an alterna-
tive super block. The -b option of the scan_ffs(8)
utility can also be used to find the offset of
other super block backups in a file system.
-c level Convert the FFSv1 file system to the level level.
Note that the level of a file system can only be
raised. There are currently five levels defined:
0 The file system is in the old (static
1 The file system is in the new (dynamic
table) format. Such file systems are
made by using the -O 0 option to
2 The file system supports 32-bit UIDs and
GIDs, short symbolic links are stored in
the inode, and directories have an added
field showing the file type. This for-
mat was introduced in 4.4BSD.
3 If maxcontig is greater than one, build
the free segment maps to aid in finding
contiguous sets of blocks. If maxcontig
is equal to one, delete any existing
segment maps. This was the default
before NetBSD 2.0.
4 Rearrange the super block to the same
layout as FFSv2; disable the rotational
layout tables and per cylinder group
block totals. Such file systems are
made by using the -O 1 option to
Note that FFSv2 file systems always have the fea-
tures of FFSv1 level 4.
FFSv2 file systems have separate conversion
ea Convert the file system to the format
which supports extended attributes (and
access control lists). After this con-
version is performed, the file system
will no longer be recognized at all by
releases prior to NetBSD 10.0.
Convert the file system to the format
which does not support extended
attributes (or access control lists).
This will remove any existing extended
attributes, and the file system will
become recognizable to releases prior to
In interactive mode, fsck_ffs will list the conver-
sion to be made and ask whether the conversion
should be done. If a negative answer is given, no
further operations are done on the file system. In
preen mode, the conversion is listed and done if
possible without user interaction. Conversion in
preen mode is best used when all the file systems
are being converted at once.
The output of dumpfs(8) can be examined to deter-
mine the format of the file system (``format'' in
the second line) and the file system level
(``fslevel'' in the sixth line).
-d Print debugging output.
-F Indicates that filesystem is a file system image,
rather than a raw character device. filesystem
will be accessed `as-is', and no attempts will be
made to read a disklabel.
-f Force checking of file systems. Normally, if a
file system is cleanly unmounted, the kernel will
set a ``clean flag'' in the file system super
block, and fsck_ffs will not check the file system.
This option forces fsck_ffs to check the file sys-
tem, regardless of the state of the clean flag.
-m mode Use the octal value mode as the permission bits to
use when creating the lost+found directory rather
than the default 1700. In particular, systems 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.
-n Assume a no response to all questions asked by
fsck_ffs except for `CONTINUE?', which is assumed
to be affirmative; do not open the file system for
-P Display a progress meter for the file system check.
A new meter is displayed for each of the 5 file
system check passes, unless -p is specified, in
which case only one meter for overall progress is
displayed. Progress meters are disabled if the -d
option is specified.
-p Specify ``preen'' mode, described above.
-q Quiet mode, do not output any messages for clean
-U Resolve user ids to usernames.
-X Similar to -x but uses a file system internal snap-
shot on the file system to be checked.
-x snap-backup Use a snapshot with snap-backup as backup to check
a read-write mounted filesystem. Must be used with
-n. See fss(4) for more details. The point is to
check an internally-consistent version of the
filesystem to find out if it is damaged; on failure
one should unmount the filesystem and repair it.
-y Assume a yes response to all questions asked by
fsck_ffs; this should be used with great caution as
this is a free license to continue after essen-
tially unlimited trouble has been encountered.
-z Clear unused directory space. The cleared space
includes deleted file names and name padding.
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 file sys-
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 number.
8. Super Block checks:
More blocks for inodes than there are in the file sys-
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.
The diagnostics produced by fsck_ffs are fully enumerated and explained
in Appendix A of Fsck - The UNIX File System Check Program.
fss(4), fs(5), fstab(5), dumpfs(8), fsck(8), fsdb(8), newfs(8),
A fsck utility appeared in 4.0BSD. It was renamed to fsck_ffs in
NetBSD 1.3 with the introduction of a filesystem independent wrapper as
NetBSD 10.99 May 4, 2018 NetBSD 10.99