FSCK(8) System Manager's Manual FSCK(8)
fsck - file system consistency check and interactive repair
/etc/fsck -p [ filesystem ... ]
/etc/fsck [ -b block# ] [ -y ] [ -n ] [ filesystem ] ...
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 dur-
ing 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 sys-
tems on pass 4), and finally the large user file systems on the last
pass, e.g. pass 5. A pass number of 0 in fstab causes a disk to not be
checked; similarly partitions which are not shown as to be mounted
``rw'' or ``ro'' are not checked.
The system takes care that only a restricted class of innocuous incon-
sistencies can happen unless hardware or software failures intervene.
These are limited to the following:
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 which 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 identi-
fying 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 and the number
of used and free blocks.
Without the -p option, fsck audits and interactively repairs inconsis-
tent 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 a number of the corrective actions
which are not fixable 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 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 always an alternate super
-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. The only
restriction is that the directory lost+found must preexist in the root
of the filesystem being checked and must have empty slots in which
entries can be made. This is accomplished by making lost+found, copy-
ing a number of files to the directory, and then removing them (before
fsck is executed).
Checking the raw device is almost always faster.
/etc/fstab contains default list of file systems to check.
The diagnostics produced by fsck are intended to be self-explanatory.
fstab(5), fs(5), newfs(8), mkfs(8), crash(8V), reboot(8)
Inode numbers for . and .. in each directory should be checked for
There should be some way to start a fsck -p at pass n.
4th Berkeley Distribution 4 February 1983 FSCK(8)