FSCK(8) FSCK(8)
NAME
fsck - file system consistency check and interactive repair
SYNOPSIS
/etc/fsck -p [ filesystem ... ]
/etc/fsck [ -y ] [ -n ] [ -sX ] [ -SX ] [ -t filename ] [
filesystem ] ...
DESCRIPTION
The first form of fsck preens a standard set of filesystems
(those mentioned in /etc/fstab) or the specified file sys-
tems. It is normally called from /etc/rc during automatic
reboot.
The file /etc/fstab defines the order in which disks are
checked by assigning each file system to a ``pass'' of fsck.
Normally, the root file system will be checked on pass 1,
and other files on later passes. For savecore(8) to work,
no more than three large file systems should be checked on
each pass. A file system is not checked if its pass number
is 0 or it is not to be mounted.
Fsck with the -p option will repair only the following ail-
ments:
unreferenced i-nodes;
wrong link counts in i-nodes;
missing blocks in the free list;
blocks in the free list also in files; and
counts wrong in the super-block.
If fsck encounters other inconsistencies, it exits with an
abnormal return status and the automatic reboot aborts. For
each corrected inconsistency one or more lines will be
printed identifying the file system and the nature of the
correction. After successfully preening a file system, fsck
will print the number of files on that file system and the
number of used and free blocks.
Without the -p option, fsck audits and interactively repairs
inconsistent conditions on file systems. If the file system
is inconsistent the operator is prompted for concurrence
before each correction is attempted. The operator may
require arcane knowledge to guide fsck safely through repair
of a badly damaged file system.
FSCK(8) FSCK(8)
The following flags are interpreted by fsck.
-y Assume a yes response to all questions asked by fsck;
this should be used with great caution.
-n Assume a no response to all questions asked by fsck;
do not open the file system for writing. This option
is enabled automatically if the file system is not
writable.
-sX Ignore the actual free list and (unconditionally)
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 precau-
tion 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 reconstructed unless the -n option is enabled.
The -sX option allows for creating an optimal free-
list organization. The following forms of X are sup-
ported for the following devices:
-s3 (RP03)
-s4 (RP04, RP05, RP06)
-sBlocks-per-cylinder:Blocks-to-skip (for anything else)
If X is not given, the values used when the filesystem
was created are used. If these values were not speci-
fied, then the value 400:9 is used.
-SX Conditionally reconstruct the free list. This option
is like -sX above except that the free list is rebuilt
only if there were no discrepancies discovered in the
file system. The -S option enables -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 the -t flag,
fsck will prompt the operator for the name of the
scratch file. The file chosen should not be on the
filesystem being checked, and if it is not a special
file or did not already exist, it is removed when fsck
completes.
If no filesystems are given to fsck then a default list of
file systems is read from the file /etc/fstab.
FSCK(8) FSCK(8)
Inconsistencies checked are as follows:
Blocks claimed by more than one inode or the free list.
the file system.
Blocks claimed by an inode or the free list outside the range of
Incorrect link counts.
Size checks:
Directory size not 16-byte aligned.
Bad inode format.
Blocks not accounted for anywhere.
Directory checks:
File pointing to unallocated inode.
Inode number out of range.
Super Block checks:
More than 65536 inodes.
More blocks for inodes than there are in the file sys-
tem.
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 lost+found directory.
The name assigned is the inode number. The only restriction
is that the directory lost+found must exist in the root of
the filesystem being checked and must have empty slots in
which entries can be made.
Checking the raw device is almost always faster for 1K-block
file systems, but bitmap file systems must be checked using
the block device.
FILES
/etc/fstab contains default list of file systems
to check.
SEE ALSO
fstab(5), filsys(5), crash(8), reboot(8)
BUGS
Inode numbers for . and .. in each directory should be
checked for validity.
The `three large filesystems' rule assumes a system with 4
megabytes of memory and a 20 megabyte swap area. Your
mileage may vary. The goal is to avoid overwriting the part
of the swap area where the dump lives.