FSCK(8) FSCK(8)
NAME
fsck - file system consistency check and interactive repair
SYNOPSIS
/etc/fsck -p [ special ... ]
/etc/fsck [ -y ] [ -n ] [ -sX ] [ -SX ] [ -t filename ] [
special ... ]
DESCRIPTION
Fsck inspects the disk filesystems in the named special
files and repairs inconsistencies. If no files are named,
every file system listed in fstab(5) with type 0 and a
nonzero pass number is checked.
Under option -p, fsck runs without intervention, repairing
minor inconsistencies and aborting on major ones. This form
is usually called from rc(8). If no special files are named,
file systems in fstab are checked in parallel passes: all
file systems with pass number 1 are checked simultaneously,
then all file systems with pass number 2, and so on until
fstab is exhausted.
Here are the minor ailments repaired automatically under -p:
unreferenced inodes;
wrong link counts in inodes;
missing blocks in the free list;
blocks in the free list also in files; and
counts wrong in the super-block.
Other inconsistencies cause fsck to abandon the inconsistent
file system, and exit with a nonzero status when the current
pass finishes.
Without the -p option, fsck inspects one file system at a
time, interactively. Each inconsistency causes fsck to
print a message and ask permission to fix the problem. The
operator may require arcane knowledge to guide fsck safely
through repair of a badly damaged file system.
Here are the remaining options. They are allowed only if -p
is absent.
-y Assume a yes response to all questions. This should be
used with great caution.
-n Assume a no response to all questions; do not open the
file system for writing. This option is assumed if the
file system cannot be opened for writing.
-sX Ignore the actual free list and (unconditionally)
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reconstruct a new one by rewriting the super-block of
the file system. The file system should be unmounted
while this is done; if this is not possible, care
should be taken that the system is quiescent and that
it is rebooted immediately afterwards. This precaution
is necessary so that the old, bad, in-core copy of the
superblock will not continue to be used, or written on
the file system. If the file system has a bitmap free
list (see filsys(5)), the free list is always recon-
structed unless the -n option is enabled.
Parameter X allows free-list parameters to be speci-
fied: -sblocks-per-cylinder:blocks-to-skip. If X is
not given, the values used when the file system was
created are used; see mkfs(8). If these values were not
specified, X is assumed to be 400:9.
-SX Conditionally reconstruct the free list. This option
is like -sX except that the free list is rebuilt only
if no discrepancies were found. -S implies -n.
-t If fsck cannot obtain enough memory to keep its tables,
it uses a scratch file. If the -t option is specified,
the file named in the next argument is used as the
scratch file, if needed. Without -t, fsck will prompt
the operator for the name of the scratch file. The
file chosen should not be on the file system being
checked. If it did not already exist, it is removed
when fsck completes.
Inconsistencies checked are:
Blocks claimed more than once.
Blocks designated outside the file system.
Incorrect link counts.
Directory size not 16-byte aligned.
Bad inode format.
Blocks not accounted for anywhere.
Directory entry pointing to unallocated inode.
Inode number out of range.
More than 65536 inodes.
More blocks for inodes than there are in the file system.
Bad free block list format.
Total free block and/or free inode count incorrect.
Orphaned files and directories (allocated but unreferenced)
are reconnected by placing them in the directory in the root
of the file system being checked. The name assigned is the
inode number, prefixed by `#'.
Checking the raw device is almost always faster, but fsck
distinguishes bitmapped from non-bitmapped file systems by
FSCK(8) FSCK(8)
examining the minor device number, so the block device is
safer.
FILES
SEE ALSO
fstab(5), filsys(5), mkfs(8), reboot(8)
T. J. Kowalski, `Fsck-the UNIX File System Check Program',
this manual, Volume 2
BUGS
Inode numbers for . and .. in each directory should be
checked for validity.
Some systems save core images after a crash in the swap
area; on such machines, checking many large file systems in
parallel may cause swapping, overwriting the crash dump. It
is best just to write crash dumps in a a safer place. If
disk space for dumps and swapping is scarce, avoid checking
more than three 120-megabyte file systems in parallel on a
machine with four megabytes of physical memory.
Examining the minor device number is a botch; there should
be an explicit flag somewhere.
Fsck does not have supernatural powers.