V8/usr/man/man8/fsck.8

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.TH FSCK 8
.SH NAME
fsck \- file system consistency check and interactive repair
.SH SYNOPSIS
.B /etc/fsck
.B \-p
[
filesystem ...
]
.br
.B /etc/fsck
[
.B \-y
] [
.B \-n
] [
.BR \-s X
] [
.BR \-S X
] [
.B \-t
filename
] [
filesystem 
] ...
.SH DESCRIPTION
The first form of
.I fsck
preens a standard set of filesystems
(those mentioned in
.IR /etc/fstab )
or the specified file systems.
It is normally called from
.I /etc/rc
during automatic reboot.
.PP
The file
.I /etc/fstab
defines the order in which disks are checked
by assigning each file system to a ``pass'' of
.IR fsck .
Normally, the root file system will be checked on pass 1,
and other files on later passes.
For
.IR 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.
.PP
.I Fsck
with the
.I \-p
option will repair only the following ailments:
.IP
unreferenced i-nodes;
.ns
.IP
wrong link counts in i-nodes;
.ns
.IP
missing blocks in the free list;
.ns
.IP
blocks in the free list also in files; and
.ns
.IP
counts wrong in the super-block.
.PP
If
.I 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,
.I fsck
will print the number of files on that file system and the number of
used and free blocks.
.PP
Without the
.B \-p
option,
.I 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
.I fsck
safely through repair of a badly damaged file system.
.PP
The following flags are interpreted by
.I fsck.
.TP 6
.B  \-y
Assume a yes response to all questions asked by 
.I fsck;
this should be used with great caution.
.TP 6
.B  \-n
Assume a no response to all questions asked by 
.I fsck;
do not open the file system for writing.
This option is enabled automatically if the file system is not writable.
.TP 6
.BR \-s \fIX
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
.IR filsys (5)),
the free list is always reconstructed unless the
.B \-n
option is enabled.
.IP
The
.BR \-s \fIX
option allows for creating an optimal free-list organization.
The following forms of
.I X
are supported for the following devices:
.sp
.nf
	\f3\-s3\fP (RP03)
	\f3\-s4\fP (RP04, RP05, RP06)
	\f3\-sB\fPlocks-per-cylinder\fB:\fPBlocks-to-skip (for anything else)
.fi
.IP "" 6
If 
.I X
is not given,
the values used when the filesystem was created
are used.
If these values were not specified, then the value
.I 400:9
is used.
.TP 6
.BR \-S \fIX
Conditionally reconstruct the free list. This option
is like
.BR \-s \fIX
above except that the free list is rebuilt only
if there were no discrepancies discovered in the
file system. The
.B \-S
option enables
.BR \-n .
.TP 6
.B \-t
If
.I 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,
.I 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
.I fsck
completes.
.PP
If no filesystems are given to 
.I fsck
then a default list of file systems is read from
the file
.IR /etc/fstab .
.PP
.ne 10
Inconsistencies checked are as follows:
.TP "" 6
Blocks claimed by more than one inode or the free list.
.br
.ns
.TP "" 6
Blocks claimed by an inode or the free list outside the range of the file system.
.br
.ns
.TP "" 6
Incorrect link counts.
.br
.ns
.TP "" 6
Size checks:
.br
.ns
.TP "" 12
Directory size not 16-byte aligned.
.br
.ns
.TP "" 6
Bad inode format.
.br
.ns
.TP "" 6
Blocks not accounted for anywhere.
.br
.ns
.TP "" 6
Directory checks:
.br
.ns
.TP "" 12
File pointing to unallocated inode.
.br
Inode number out of range.
.br
.ns
.TP "" 6
Super Block checks:
.br
.ns
.TP "" 12
More than 65536 inodes.
.br
More blocks for inodes than there are in the file system.
.br
.ns
.TP 6
Bad free block list format.
.br
.ns
.TP "" 6
Total free block and/or free inode count incorrect.
.PP
Orphaned files and directories (allocated but unreferenced) are
reconnected by
placing them in the 
.I lost+found
directory.
The name assigned is the inode number. The only restriction
is that the directory 
.I lost+found
must exist
in the root of the filesystem being checked and
must have empty slots in which entries can be made.
.PP
Checking the raw device is almost always faster for 1K-block file systems, but
bitmap file systems must be checked using the block device.
.SH FILES
.br
.ns
.TP 21
/etc/fstab
contains default list of file systems to check.
.SH "SEE ALSO"
fstab(5), filsys(5), crash(8), reboot(8)
.SH BUGS
Inode numbers for
.B .
and
.B .\|.
in each directory should be checked for validity.
.PP
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.