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FSCK_FFS(8) OpenBSD System Manager's Manual FSCK_FFS(8)
fsck_ffs, fsck - Fast File System consistency check and interactive re-
fsck_ffs -p [-f] [-m mode]
fsck_ffs [-f] [-b block#] [-c level] [-y] [-n] [-m mode] [filesystem] ...
The first form of fsck_ffs preens a standard set of filesystems or the
specified filesystems. It is normally used in the script /etc/rc during
automatic reboot. Here fsck_ffs reads the table /etc/fstab to determine
which filesystems to check. Only partitions in fstab that are mounted
``rw,'' ``rq'' or ``ro'' and that have non-zero pass number are checked.
Filesystems with pass number 1 (normally just the root filesystem) are
checked one at a time. When pass 1 completes, all remaining filesystems
are checked, running one process per disk drive. The disk drive contain-
ing each filesystem is inferred from the longest prefix of the device
name that ends in a digit; the remaining characters are assumed to be the
The kernel takes care that only a restricted class of innocuous filesys-
tem inconsistencies can happen unless hardware or software failures in-
tervene. 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
filesystem on which the correction will take place, and the nature of the
correction. After successfully correcting a filesystem, fsck_ffs will
print the number of files on that filesystem, the number of used and free
blocks, and the percentage of fragmentation.
If sent a QUIT signal, fsck_ffs will finish the filesystem checks, then
exit with an abnormal return status that causes an automatic reboot to
fail. This is useful when you want to finish the filesystem checks dur-
ing an automatic reboot, but do not want the machine to come up multiuser
after the checks complete.
Without the -p option, fsck_ffs audits and interactively repairs incon-
sistent conditions for filesystems. If the filesystem is inconsistent
the operator is prompted for concurrence before each correction is at-
tempted. 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 filesystem fsck_ffs will default to a -n action.
Fsck has more consistency checks than its predecessors check, dcheck,
fcheck, and icheck combined.
The following flags are interpreted by fsck_ffs.
-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 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.
-b Use the block specified immediately after the flag as the super
block for the filesystem. Block 32 is usually an alternate super
-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 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.
-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-
-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 filesystem for writing.
-c Convert the filesystem to the specified level. Note that the
level of a filesystem can only be raised. There are currently
four levels defined:
0 The filesystem is in the old (static table) format.
1 The filesystem is in the new (dynamic table) format.
2 The filesystem 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 an-
swer is given, no further operations are done on the filesystem.
In preen mode, the conversion is listed and done if possible
without user interaction. Conversion in preen mode is best used
when all the filesystems are being converted at once. The format
of a filesystem can be determined from the first line of output
If no filesystems are given to fsck_ffs then a default list of filesys-
tems is read from the file /etc/fstab.
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 filesystem.
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 filesystem.
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 di-
rectory. The name assigned is the inode number. If the lost+found di-
rectory 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.
/etc/fstab contains default list of filesystems to check.
The diagnostics produced by fsck_ffs are fully enumerated and explained
in Appendix A of Fsck - The UNIX File System Check Program.
fstab(5), fs(5), fsdb(8), newfs(8), mkfs(8), reboot(8)
4th Berkeley Distribution November 29, 1994 3
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
OpenBSD sources for fsck_ffs(8)
Up to: File System Operations - Operations for entire file-systems (quotas, configuration, consistency, mount, unmount, et al)
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