Updated: 2025/Nov/16
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FSCK_LFS(8) System Manager's Manual FSCK_LFS(8)
NAME
fsck_lfs - Log-structured File System consistency check and interactive
repair
SYNOPSIS
fsck_lfs [-adfpqU] [-b block] [-i idaddr] [-m mode] [-y | -n] filesystem
...
DESCRIPTION
fsck_lfs performs interactive file system consistency checks and repair
for each of the file systems specified on the command line. It is
normally invoked from fsck(8).
The design of LFS takes care that no file system inconsistencies can
happen unless hardware or software failures intervene. fsck_lfs will
report and optionally correct any such inconsistencies.
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_lfs 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_lfs will finish the file system checks, then
exit with an abnormal return status.
Without the -p option, fsck_lfs 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 some of the corrective
actions 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 fsck_lfs will default to a -n action.
The following flags are interpreted by fsck_lfs:
-a Do not report discrepancies in avail accounting.
-b block Use block as the super block for the file system.
-d Print debugging output.
-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_lfs will not check the
file system. This option forces fsck_lfs to check the file
system, regardless of the state of the clean flag.
-i idaddr Use the given disk address to locate the index file inode,
rather than looking in the superblock.
-m mode Use 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 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_lfs
except for `CONTINUE?', which is assumed to be affirmative;
do not open the file system for writing.
-p Specify "preen" mode. Currently, in this mode fsck_lfs does
nothing.
-q Quiet mode, do not output any messages for clean file
systems.
-U Resolve user ids to user names.
-y Assume a yes response to all questions asked by fsck_lfs;
this should be used with great caution as this is a free
license to continue after essentially unlimited trouble has
been encountered.
Inconsistencies checked are as follows:
1. Blocks claimed by more than one inode.
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. 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.
7. Super Block checks:
More blocks for inodes than there are in the file
system.
8. Index File checks:
"In use" inodes on free list, or free inodes not on free
list.
Segment block counts incorrect, or "clean" segments
containing live data.
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.
DIAGNOSTICS
The diagnostics produced by fsck_lfs are fully enumerated and explained
in Appendix A of Fsck - The UNIX File System Check Program.
SEE ALSO
fstab(5), fsck(8), newfs_lfs(8), reboot(8)
HISTORY
The fsck_lfs program was first made available in NetBSD 1.4.
AUTHORS
Most of the fsck_lfs program was taken from fsck_ffs(8); what was not was
written by Konrad Schroder <perseant@NetBSD.org>.
NetBSD 11.99 September 14, 2025 NetBSD 11.99