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2054_fsck_manpage.txt
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1995-10-13
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FSCK(8) UNIX Programmer's Manual FSCK(8)
NAME
fsck - file system consistency check and interactive repair
SYNOPSIS
/usr/etc/fsck -p [ filesystem ... ]
/usr/etc/fsck [ -P ] [ -b block# ] [ -y ] [ -n ] [ filesys-
tem ] ...
DESCRIPTION
The first form of fsck preens a standard set of filesystems
or the specified file systems. It is normally used in the
script /etc/rc during automatic reboot. In this case fsck
reads the table /etc/fstab to determine which file systems
to check. It uses the information there to inspect groups
of disks in parallel taking maximum advantage of i/o overlap
to check the file systems as quickly as possible. Normally,
the root file system will be checked on pass 1, other
``root'' (``a'' partition) file systems on pass 2, other
small file systems on separate passes (e.g. the ``d'' file
systems on pass 3 and the ``e'' file systems on pass 4), and
finally the large user file systems on the last pass, e.g.
pass 5. Only partitions in fstab that are mounted ``rw'' or
``rq'' and that have non-zero pass number are checked.
The system takes care that only a restricted class of inno-
cuous inconsistencies can happen unless hardware or software
failures intervene. These are limited to the following:
Unreferenced inodes
Link counts in inodes too large
Missing blocks in the free list
Blocks in the free list also in files
Counts in the super-block wrong
These are the only inconsistencies that fsck with the -p
option will correct; if it encounters other inconsistencies,
it exits with an abnormal return status and an automatic
reboot will then fail. 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 will print the number of files on that file system, the
number of used and free blocks, and the percentage of frag-
mentation.
If sent a QUIT signal, fsck will finish the file system
checks, then exit with an abnormal return status that causes
the automatic reboot to fail. This is useful when you wish
to finish the file system checks, but do not want the
machine to come up multiuser.
Without the -p option, fsck 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 which are not correct-
able under the -p option 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 con-
sistency 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 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.
-P This flag forces fsck to check the disk even if the
clean flag is set on the disk's superblock.
-b Use the block specified immediately after the flag as
the super block for the file system. Block 16 is
always an alternate super block.
-y Assume a yes response to all questions asked by fsck;
this should be used with great caution as this is a
free license to continue after essentially unlimited
trouble has been encountered.
-n Assume a no response to all questions asked by fsck;
do not open the file system for writing.
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:
1. Blocks claimed by more than one inode or the free
list.
2. Blocks claimed by an inode or the free list outside
the range of the file system.
3. Incorrect link counts.
4. Size checks:
Directory size not of proper format.
5. Bad inode format.
6. Blocks not accounted for anywhere.
7. Directory checks:
File pointing to unallocated inode.
Inode number out of range.
8. Super Block checks:
More blocks for inodes than there are in the
file system.
9. Bad free block list format.
10. 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 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.
Checking the raw device is almost always faster.
FILES
/etc/fstab contains default list of file systems
to check.
DIAGNOSTICS
The diagnostics produced by fsck are fully enumerated and
explained in Appendix A of ``Fsck - The UNIX File System
Check Program'' (SMM:5).
SEE ALSO
fstab(5), fs(5), newfs(8), mkfs(8), crash(8V), reboot(8)
BUGS
There should be some way to start a fsck -p at pass n.