FSCK_FFS(8) BSD System Manager's Manual FSCK_FFS(8)NAME
fsck_ffs, fsck_ufs — file system consistency check and interactive repair
SYNOPSISfsck_ffs [-BFprfny] [-b block] [-c level] [-m mode] filesystem ...
The specified disk partitions and/or file systems are checked. In
"preen" or "check clean" mode the clean flag of each file system's
superblock is examined and only those file systems that are not marked
clean are checked. File systems are marked clean when they are
unmounted, when they have been mounted read-only, or when fsck_ffs runs
on them successfully. If the -f option is specified, the file systems
will be checked regardless of the state of their clean flag.
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 with the -p option will
correct; if it encounters other inconsistencies, it exits with an abnor‐
mal return status and an automatic reboot will then fail. For each cor‐
rected 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 that causes an automatic reboot to
fail. This is useful when you want to finish the file system checks dur‐
ing an automatic reboot, but do not want the machine to come up multiuser
after the checks complete.
If fsck_ffs receives a SIGINFO (see the “status” argument for stty(1))
signal, a line will be written to the standard 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
The following flags are interpreted by fsck_ffs:
-F Determine whether the file system needs to be cleaned immediately
in foreground, or if its cleaning can be deferred to background.
To be eligible for background cleaning it must have been running
with soft updates, not have been marked as needing a foreground
check, and be mounted and writable when the background check is
to be done. If these conditions are met, then fsck_ffs exits
with a zero exit status. Otherwise it exits with a non-zero exit
status. If the file system is clean, it will exit with a non-
zero exit status so that the clean status of the file system can
be verified and reported during the foreground checks. Note that
when invoked with the -F flag, no cleanups are done. The only
thing that fsck_ffs does is to determine whether a foreground or
background check is needed and exit with an appropriate status
-B A check is done on the specified and possibly active file system.
The set of corrections that can be done is limited to those done
when running in preen mode (see the -p flag). If unexpected
errors are found, the file system is marked as needing a fore‐
ground check and fsck_ffs exits without attempting any further
-b Use the block specified immediately after the flag as the super
block for the file system. An alternate super block is usually
located at block 32 for UFS1, and block 160 for UFS2.
-C Check if file system was dismounted cleanly. If so, skip file
system checks (like "preen"). However, if the file system was
not cleanly dismounted, do full checks, as if fsck_ffs was
invoked without -C.
-c 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:
0 The file system is in the old (static table) format.
1 The file system is in the new (dynamic table) format.
2 The file system supports 32-bit uid's and gid's, short
symbolic links are stored in the inode, and directories
have an added field showing the file type.
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
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 sys‐
tem. In preen mode, the conversion is listed and done if possi‐
ble 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 dumpfs(8).
This option implies the -f flag.
-f Force fsck_ffs to check ‘clean’ file systems when preening.
-m Use the mode specified in octal immediately after the flag as the
permission bits to use when creating the lost+found directory
rather than the default 1777. 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 writing.
-p Preen file systems (see above).
-r Free up excess unused inodes. Decreasing the number of preallo‐
cated inodes reduces the running time of future runs of fsck_ffs
and frees up space that can allocated to files. The -r option is
ignored when running in preen mode.
-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 essentially unlimited trouble has been encoun‐
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 system.
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.
Directories with unallocated blocks (holes).
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 system.
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.
The full foreground fsck_ffs checks for many more problems that may occur
after an unrecoverable disk write error. Thus, it is recommended that
you perform foreground fsck_ffs on your systems periodically and whenever
you encounter unrecoverable disk write errors or file-system-related pan‐
/etc/fstab contains default list of file systems to check.
The fsck_ffs utility exits 0 on success, and >0 if an error occurs.
If the option -F is used, fsck_ffs exits 7 if the file system is clean.
The diagnostics produced by fsck_ffs are fully enumerated and explained
in Appendix A of Fsck - The UNIX File System Check Program.
SEE ALSOfs(5), fstab(5), fsck(8), fsdb(8), newfs(8), reboot(8)BSD January 25, 2009 BSD