NAME

fsck − file system consistency check and interactive repair

SYNOPSIS

/etc/fsck [ −y ] [ −n ] [ −sX ] [ −SX ] [ −t file ] [ file-system ] ... 

DESCRIPTION

Fsck audits and interactively repairs inconsistent conditions for UNIX file systems.  If the file system is consistent then the number of files, number of blocks used, and number of blocks free are reported.  If the file system is inconsistent the operator is prompted for concurrence before each correction is attempted.  It should be noted that most corrective actions 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.

−y Assume a yes response to all questions asked by fsck.

−n Assume a no response to all questions asked by fsck; do not open the file system for writing.

−sX 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. 

The −sX option allows for creating an optimal free-list organization.  The following forms of X are supported for the following devices:

−s3 (RP03)
−s4 (RP04, RP05, RP06)
−sBlocks-per-cylinder:Blocks-to-skip (for anything else)

If X is not given, the values used when the file system was created are used.  If these values were not specified, then the value 400:9 is used. 

−SX Conditionally reconstruct the free list. This option is like −sX above except that the free list is rebuilt only if there were no discrepancies discovered in the file system. Using −S will force a no response to all questions asked by fsck. This option is useful for forcing free list reorganization on uncontaminated file systems.

−t If 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, fsck will prompt the operator for the name of the scratch file. The file chosen should not be on the file system being checked, and if it is not a special file or did not already exist, it is removed when fsck completes. 

If no file-systems are specified, fsck will read a list of default file systems from the file /etc/checklist. 

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:

Incorrect number of blocks. 
Directory size not 16-byte aligned.

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 than 65536 inodes. 
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 file system being checked and must have empty slots in which entries can be made.  This is accomplished by making lost+found, copying a number of files to the directory, and then removing them (before fsck is executed). 

Checking the raw device is almost always faster. 

FILES

/etc/checklist contains default list of file systems to check. 

DIAGNOSTICS

The diagnostics produced by fsck are intended to be self-explanatory. 

SEE ALSO

checklist(5), fs(5), crash(8).

BUGS

Inode numbers for .  and ..  in each directory should be checked for validity. 

−g and −b options from check should be available in fsck.

May 16, 1980