term% cat index.txt FSCK(8) System Manager's Manual 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 men‐
tioned in /etc/fstab) or the specified file systems. It is normally
called from /etc/rc during automatic reboot.
The file /etc/fstab defines the order in which disks are checked by as‐
signing 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 num‐
ber is 0 or it is not to be mounted.
Fsck with the -p option will repair only the following ailments:
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 re‐
turn status and the automatic reboot aborts. For each corrected incon‐
sistency 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 inconsis‐
tent conditions on file systems. If the file system is inconsistent
the operator is prompted for concurrence before each correction is at‐
tempted. The operator may require arcane knowledge to guide fsck
safely through repair of a badly damaged file system.
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 automati‐
cally 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 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 reconstructed unless the -n option is enabled.
The -sX option allows for creating an optimal free-list organiza‐
tion. The following forms of X are supported 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 cre‐
ated are used. If these values were not specified, 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 en‐
ables -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 be‐
ing 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.
Inconsistencies checked are as follows:
Blocks claimed by more than one inode or the free list.
Blocks claimed by an inode or the free list outside the range of the
file system.
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 system.
Bad free block list format.
Total free block and/or free inode count incorrect.
Orphaned files and directories (allocated but unreferenced) are recon‐
nected 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 sys‐
tems, 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.
FSCK(8)