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.\"	@(#)fsck.8	8.4 (Berkeley) 5/9/95
.\" $FreeBSD: src/sbin/fsck/fsck.8,v 1.14.2.3 2001/01/23 23:11:07 iedowse Exp $
.\"
.Dd September 29, 2016
.Dt FSCK 8
.Os
.Sh NAME
.Nm fsck
.Nd UFS filesystem consistency check and interactive repair
.Sh SYNOPSIS
.Nm
.Fl p
.Op Fl f
.Op Fl m Ar mode
.Op Ar filesystem
.Ar ...
.Nm
.Op Fl Lny
.Op Fl b Ar block#
.Op Fl c Ar level
.Op Fl l Ar maxparallel
.Op Fl m Ar mode
.Op Ar filesystem
.Ar ...
.Sh DESCRIPTION
The first form of
.Nm
preens a standard set of filesystems or the specified filesystems.
It is normally used in the script
.Pa /etc/rc
during automatic reboot.
Here
.Nm
reads the table
.Pa /etc/fstab
to determine which filesystems to check.
Only partitions in fstab that are mounted ``rw,'' ``rq'' or ``ro''
and that have non-zero pass number are checked.
Filesystems with pass number 1 (normally just the root filesystem)
are checked one at a time.
When pass 1 completes, all remaining filesystems are checked,
running one process per disk drive.
The disk drive containing each filesystem is inferred from the longest prefix
of the device name that ends in a digit; the remaining characters are assumed
to be the partition designator.
.Pp
In "preen" mode the clean flag of each filesystem's superblock is examined
and only those filesystems that
are not marked clean are checked.
Filesystems are marked clean when they are unmounted,
when they have been mounted read-only, or when
.Nm
runs on them successfully.
If the
.Fl f
option is specified, the filesystems
will be checked regardless of the state of their clean flag.
.Pp
The kernel takes care that only a restricted class of innocuous filesystem
inconsistencies can happen unless hardware or software failures intervene.
These are limited to the following:
.Pp
.Bl -item -compact -offset indent
.It
Unreferenced inodes
.It
Link counts in inodes too large
.It
Missing blocks in the free map
.It
Blocks in the free map also in files
.It
Counts in the super-block wrong
.El
.Pp
These are the only inconsistencies that
.Nm
with the
.Fl 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 filesystem on which the correction will take place,
and the nature of the correction.  After successfully correcting a filesystem,
.Nm
will print the number of files on that filesystem,
the number of used and free blocks,
and the percentage of fragmentation.
.Pp
If sent a
.Dv QUIT
signal,
.Nm
will finish the filesystem checks, then exit with an abnormal
return status that causes an automatic reboot to fail.
This is useful when you want to finish the filesystem checks during an
automatic reboot,
but do not want the machine to come up multiuser after the checks complete.
.Pp
If
.Nm
receives a
.Dv SIGINFO
(see the
.Dq status
argument for
.Xr stty 1 )
signal, a line will be written to the standard output indicating
the name of the device currently being checked, the current phase
number and phase-specific progress information.
.Pp
Without the
.Fl p
option,
.Nm
audits and interactively repairs inconsistent conditions for filesystems.
If the filesystem 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
correctable under the
.Fl 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 consistency correction
is to wait for the operator to respond
.Li yes
or
.Li no .
If the operator does not have write permission on the filesystem
.Nm
will default to a
.Fl n
action.
.Pp
.Nm Fsck
has more consistency checks than
its predecessors
.Em check , dcheck , fcheck ,
and
.Em icheck
combined.
.Pp
The following flags are interpreted by
.Nm .
.Bl -tag -width indent
.It Fl b
Use the block specified immediately after the flag as
the super block for the filesystem.  Block 32 is usually
an alternate super block.
.It Fl c
Convert the filesystem to the specified level.
Note that the level of a filesystem can only be raised.
.Pp
There are currently four levels defined:
.Bl -tag -width indent
.It 0
The filesystem is in the old (static table) format.
.It 1
The filesystem is in the new (dynamic table) format.
.It 2
The filesystem supports 32-bit uid's and gid's,
short symbolic links are stored in the inode,
and directories have an added field showing the file type.
.It 3
If maxcontig is greater than one,
build the free segment maps to aid in finding contiguous sets of blocks.
If maxcontig is equal to one, delete any existing segment maps.
.El
.Pp
In interactive mode,
.Nm
will list the conversion to be made
and ask whether the conversion should be done.
If a negative answer is given,
no further operations are done on the filesystem.
In preen mode,
the conversion is listed and done if
possible without user interaction.
Conversion in preen mode is best used when all the filesystems
are being converted at once.
The format of a filesystem can be determined from the
first line of output from
.Xr dumpfs 8 .
.It Fl f
Force
.Nm
to check
.Sq clean
filesystems when preening.
.It Fl l
Limit the number of parallel checks to the number specified in the following
argument.
By default, the limit is the number of disks, running one process per disk.
If a smaller limit is given, the disks are checked round-robin, one filesystem
at a time.
.It Fl L
Just print the "last mounted on" information and exit, do no other checking.
.It Fl m
Use the mode specified in octal immediately after the flag as the
permission bits to use when creating the
.Pa lost+found
directory rather than the default 1777.
In particular, systems that do not wish to have lost files accessible
by all users on the system should use a more restrictive
set of permissions such as 700.
.It Fl n
Assume a no response to all questions asked by
.Nm
except for
.Ql CONTINUE? ,
which is assumed to be affirmative;
do not open the filesystem for writing.
.It Fl p
Preen filesystems (see above).
.It Fl y
Assume a yes response to all questions asked by
.Nm ;
this should be used with great caution as this is a free license
to continue after essentially unlimited trouble has been encountered.
.El
.Pp
If no filesystems are given to
.Nm
then a default list of filesystems is read from
the file
.Pa /etc/fstab .
.Pp
Inconsistencies checked are as follows:
.Bl -enum -compact
.It
Blocks claimed by more than one inode or the free map.
.It
Blocks claimed by an inode outside the range of the filesystem.
.It
Incorrect link counts.
.It
Size checks:
.Bl -item -offset indent -compact
.It
Directory size not a multiple of DIRBLKSIZ.
.It
Partially truncated file.
.El
.It
Bad inode format.
.It
Blocks not accounted for anywhere.
.It
Directory checks:
.Bl -item -offset indent -compact
.It
File pointing to unallocated inode.
.It
Inode number out of range.
.It
Directories with unallocated blocks (holes).
.It
Dot or dot-dot not the first two entries of a directory
or having the wrong inode number.
.El
.It
Super Block checks:
.Bl -item -offset indent -compact
.It
More blocks for inodes than there are in the filesystem.
.It
Bad free block map format.
.It
Total free block and/or free inode count incorrect.
.El
.El
.Pp
Orphaned files and directories (allocated but unreferenced) are,
with the operator's concurrence, reconnected by
placing them in the
.Pa lost+found
directory.
The name assigned is the inode number.
If the
.Pa lost+found
directory does not exist, it is created.
If there is insufficient space its size is increased.
.Pp
Because of inconsistencies between the block device and the buffer cache,
the raw device should always be used.
.Sh FILES
.Bl -tag -width /etc/fstab -compact
.It Pa /etc/fstab
contains default list of filesystems to check.
.El
.Sh DIAGNOSTICS
The diagnostics produced by
.Nm
are fully enumerated and explained in Appendix A of
.Rs
.%T "Fsck \- The UNIX File System Check Program"
.Re
.Sh SEE ALSO
.Xr fs 5 ,
.Xr fstab 5 ,
.Xr UFS 5 ,
.Xr fsdb 8 ,
.Xr newfs 8 ,
.Xr reboot 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.0 .