FSCK(8) FSCK(8)
NAME
fsck - file system consistency check and interactive
repair
SYNOPSIS
fsck -p [ -m mode ]
fsck [ -b block# ] [ -c ] [ -y ] [ -n ] [ -m mode ] [
filesystem ] ...
DESCRIPTION
The first form of fsck preens a standard set of filesys-
tems or the specified file systems. It is normally used
in the script /etc/rc during automatic reboot. Here fsck
reads the table /etc/fstab to determine which file systems
to check. Only partitions in fstab that are mounted
``rw,'' ``rq'' or ``ro'' and that have non-zero pass num-
ber 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 con-
taining each filesystem is inferred from the longest pre-
fix of the device name that ends in a digit; the remaining
characters are assumed to be the partition designator.
The system takes care that only a restricted class of
innocuous 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 map
Blocks in the free map 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 inconsisten-
cies, it exits with an abnormal return status and an auto-
matic reboot will then fail. For each corrected inconsis-
tency 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 correct-
ing 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 fragmentation.
If sent a QUIT signal, fsck will finish the file system
checks, then exit with an abnormal return status that
causes an automatic reboot to fail. This is useful when
to finish the file system checks during an automatic
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FSCK(8) FSCK(8)
reboot, but do not want the machine to come up multiuser
after the checks complete.
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 correctable 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 consistency 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.
-b Use the block specified immediately after the flag
as the super block for the file system. Block 32 is
usually an alternate super block.
-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 pro-
cess per disk. If a smaller limit is given, the
disks are checked round-robin, one filesystem at a
time.
-m Use the mode specified in octal immediately after
the flag as the permission bits to use when creating
the 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 sys-
tem should use a more restrictive set of permissions
such as 700.
-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
except for ``CONTINUE?'', which is assumed to be
affirmative; do not open the file system for writ-
ing.
-c If the file system is in the old (static table) for-
mat, convert it to the new (dynamic table) format.
If the file system is in the new format, convert it
to the old format provided the old format can
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support the filesystem configuration. In interac-
tive mode, fsck will list the direction the conver-
sion is 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 direction of the conversion is
listed and done if possible without user interac-
tion. Conversion in preen mode is best used when
all the file systems are being converted at once.
The format of a file system can be determined from
the first line of output from dumpfs(8).
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
map.
2. Blocks claimed by an inode outside the range of the
file system.
3. Incorrect link counts.
4. Size checks:
Directory size not of proper format.
Partially truncated file.
5. Bad inode format.
6. Blocks not accounted for anywhere.
7. Directory checks:
File pointing to unallocated inode.
Inode number out of range.
Dot or dot-dot not the first two entries of a
directory or having the wrong inode number.
8. Super Block checks:
More blocks for inodes than there are in the
file system.
9. Bad free block map format.
10. Total free block and/or free inode count incorrect.
Orphaned files and directories (allocated but unrefer-
enced) 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.
Because of inconsistencies between the block device and
the buffer cache, the raw device should always be used.
FILES
/etc/fstab contains default list of file systems
to check.
DIAGNOSTICS
The diagnostics produced by fsck are fully enumerated and
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FSCK(8) FSCK(8)
explained in Appendix A of ``Fsck - The UNIX File System
Check Program'' (SMM:5).
SEE ALSO
fstab(5), fs(5), fsdb(8), newfs(8), mkfs(8), reboot(8)
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