File System consistency check and interactive repair
performs interactive file system
consistency checks and repairs the file system specified. It is normally
invoked from fsck(8)
The kernel takes care that only a restricted class of innocuous file system
inconsistencies can happen unless hardware or software failures intervene.
These are limited to the following:
- Unreferenced inodes
- Link counts in inodes too
- Missing blocks in the free
- Blocks in the free map also in
- Counts in the super-block
These are the only inconsistencies that fsck_ffs
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 along with 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
will finish the file system checks, then
exit with an abnormal return status that causes an automatic reboot to fail.
This is useful when you want to finish the file system checks during an
automatic reboot, but do not want the machine to come up multiuser after the
If sent an
will print a line to standard error
indicating the name of the device currently being checked, the current phase
number, and phase-specific progress information.
Without the -p
audits and interactively repairs
inconsistent conditions for the filesystem. 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 diagnostic output. The default action for each consistency correction
is to wait for the operator to respond “yes” or “no”.
If the operator does not have write permission on the file system,
will default to a
has more consistency checks than its
The following flags are interpreted by fsck_ffs
- Use the block# specified
as the super block for the file system. If the primary superblock is
corrupted fsck_ffs tries to find a valid
alternate superblock based on the information in the disklabel. If that
fails, a number printed by newfs (using
-N combined with the original flags used to
create the filesystem) can be used as a value to this argument.
- Convert the file system to the specified
level. Note that the level of a file
system can only be raised. There are currently four levels defined:
- The file system is in the old (static table)
- The file system is in the new (dynamic table)
- 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.
- 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.
- Force checking of the filesystem. Normally, if a file
system is cleanly unmounted, the kernel will set a “clean
flag” in the file system superblock and
fsck_ffs will not check the file system. This
option forces fsck_ffs to check the file
system, regardless of the state of the clean flag.
- Use the mode specified in
octal as the permission bits to use when creating the
lost+found directory rather than the default
1700. In particular, systems that wish to have lost files accessible by
all users on the system should use a less restrictive set of permissions
such as 755.
- Assume a “no” response to all questions asked
by fsck_ffs except for
“CONTINUE?”, which is assumed to be affirmative. The
filesystem will not be opened for writing. This is the default for file
systems to be checked that are concurrently mounted writable.
- Enter preen mode: fsck_ffs
will check the filesystem on the special (raw) device listed on the
command line and will make minor repairs without human intervention. Any
major problems will cause fsck_ffs to exit
with a non-zero exit code, so as to alert any invoking program or script
that human intervention is required.
- 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 essentially unlimited
trouble has been encountered.
If neither of the -y
options are specified, the user may force
to assume an answer of “yes”
to all the remaining questions by replying to a question with a value of
In interactive mode, fsck_ffs
will list the
conversion 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 format of a file system can be determined
from the first line of output from
Inconsistencies checked are as follows:
- Blocks claimed more than once
by inodes or the free map.
- Blocks claimed by an inode
outside the range of the file system.
- Incorrect link counts.
- Size checks:
- Directory size not a
- Partially truncated
- Bad inode format.
- Blocks not accounted for
- Directory checks:
- File pointing to
- Inode number out of
- Dot or dot-dot not the
first two entries of a directory or having the wrong inode
- Super Block checks:
- More blocks for inodes
than there are in the file system.
- Bad free block map
- 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
directory. The name assigned is the
inode number. If the lost+found
not exist, it is created. If there is insufficient space its size is
Because of inconsistencies between the block device and the buffer cache, the
raw device should always be used.
The diagnostics produced by fsck_ffs
enumerated and explained in Appendix A of
Fsck_ffs - The UNIX File System