fsck_hfs(1M)

NAME

fsck_hfs: fsck — HFS file system consistency check and interactive repair

SYNOPSIS

/usr/sbin/fsck [-F hfs] [-m] [-i] [-s] [-V] [-b blocknum] [special]...

/usr/sbin/fsck [-F hfs] [-c size] [-f] [-i] [-p|-P] [-V] [-s] [special]...

/usr/sbin/fsck [-F hfs] [-b blocknum] [-c size] [-f] [-i] [-n|-N|-y|-Y] [-q] [-s] [-V] [special]...

DESCRIPTION

The fsck command audits and repairs inconsistent conditions for HFS file systems on mass storage device files identified by special. If the file system is consistent, the number of files on that file system and the number of used and free blocks are reported. If the file system is inconsistent, fsck provides a mechanism to fix these inconsistencies, depending on which form of the fsck command is used.

special represents a special device (for example, /dev/rdisk/disk8).

If the target device is a swap device, fsck does not continue to process. fsck also checks the target device to ensure a mounted file system is not being checked. If a mounted device is specified but the -f and -i options are omitted, fsck prompts the user for a response.

If the -p|-P option is used and special is not specified, fsck reads the pass numbers in /etc/fstab to determine which groups of disks to inspect in parallel, taking maximum advantage of I/O overlap to process the file systems as quickly as possible. The -p|-P option is normally used in the script /sbin/bcheckrc during automatic reboot.

Normally, the root file system is checked on pass 1, and other "root" (section 0) file systems on pass 2. Other small file systems are checked on separate passes (such as the section 4 file systems on pass 3 and the section 7 file systems on pass 4), and finally the large user file systems are checked on the last pass (for example, pass 5). A pass number of 0 in /etc/fstab causes a file system not to be checked. If the optional fields are not present on a line in /etc/fstab, fsck processes the file system on such lines sequentially after all eligible file systems with positive pass numbers have been processed.

The inconsistencies that fsck with the -p|-P option corrects are shown below. These are inconsistencies that are correctable without data loss. If it encounters other inconsistencies, it exits with an abnormal return status. For each corrected inconsistency, one or more lines are printed identifying the file system on which the correction will take place and the nature of the correction. Correctable inconsistencies are limited to the following:

Unreferenced inodes
Unreferenced continuation inodes
Unreferenced pipes and FIFOs
Link counts in inodes too large
Missing blocks in the free list
Blocks in the free list also in files
Counts in the superblock wrong.

The -P option operates in the same manner as the -p option except that cleanly unmounted file systems are not checked (see fsclean(1M)). This can greatly decrease the amount of time required to reboot a system that was brought down cleanly.

If the -p|-P option is not specified, the pass numbers are ignored and the file systems are checked interactively in the order they are listed in /etc/fstab.

Without the -p|-P option, fsck prompts for concurrence before each correction is attempted when the file system is inconsistent. It should be noted that some corrective actions result in a loss of data. The amount and severity of data loss can 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 defaults to a -n action.

Options

fsck recognizes the following options:

-F hfs: Specify the HFS file system.
-c size: Set the size of the buffer cache which fsck uses to cache disk blocks. size is the number of cache blocks, and is between 0 and 100 inclusive. The most common use of this option is -c 0 to disable all caches, thus reducing memory usage.
-b blocknum: Use the specified blocknum as the superblock for the file system. An alternate superblock can usually be found at block ((SBSIZE+BBSIZE)/DEV_BSIZE), typically block 16. DEV_BSIZE is defined in <sys/param.h>. You can also find a list of alternate superblocks in /var/adm/sbtab (see mkfs(1M)).
-f: Force fsck to check a mounted file system.
-i: Ignore (that is, do not check) mounted file systems. This option does not ask the user whether to check the mounted file systems or not. Instead it simply ignores the mounted file systems and does not check them. If the -i option is specified with the -f option, then the -i option takes precedence; that is, the fsck is skipped on mounted file systems in this case.
-m: Perform a sanity check only. Verify whether special is mounted, or needs additional checking. Refer to the RETURN VALUE section for more information.
-n|-N: Assume a no response to all questions asked by fsck about repairing a file system. Do not open the file system for writing.
-p: "Preen" the file system. Proceed to process and repair file systems without user interaction, as described above. Exit immediately if there is a problem requiring intervention.
-P: Same as -p except that cleanly unmounted file systems are not checked.
-q: Quiet. Do not print size-check messages in Phase 1. Unreferenced fifos are silently removed. If fsck requires it, counts in the superblock and cylinder groups are automatically fixed.
-s: Safe performance mode. To improve performance, a system wide sync() will not be issued.
-V: Echo the completed command line, but perform no other actions. The command line is generated by incorporating the user-specified options and other information derived from /etc/fstab. This option allows the user to verify the command line.
-y|-Y: Assume a yes response to all questions asked by fsck about repairing a file system. This should be used with great caution, because this is a free license to continue after essentially unlimited trouble has been encountered.

In all cases, fsck checks the following inconsistencies:

Blocks claimed by more than one inode or the free list.
Blocks claimed by an inode or the free list outside the range of the file system.
Incorrect link counts.
Size checks:
-
Directory size not of proper format.
Bad inode format.
Blocks not accounted for anywhere.
Directory checks:
-
File pointing to unallocated inode.
-
Inode number out of range.
Superblock checks:
-
More blocks for inodes than there are in the file system.
Bad free block list format.
Total free block and/or free inode count incorrect.
Invalid continuation inode number in a primary inode.

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 have empty slots in which entries can be made. This is accomplished by copying a number of files to the directory, then removing them before fsck is executed.

Unreferenced continuation inodes are removed with the -p option, since they do not refer back to the primary inode. When a primary inode contains an invalid continuation inode number, the continuation inode number should be cleared (that is, set to 0). This is not done automatically (with the -p option), because access control list information may have been lost and should be corrected.

After fsck has checked and fixed the file system, it stores the correct fs_clean flag in the superblock if it is not already there. For a nonroot file system, FS_CLEAN is stored there. For the root file system, which is mounted at the time of the fsck, no changes are required to the superblock if no problems were found and FS_OK was already set.

Checking the raw device is almost always faster.

RETURN VALUE

fsck returns the following values:

0: Either no errors were detected or all errors were corrected.
1: A syntax error or other operational error occurred when invoked with the -V option.
4: Root file system errors were corrected. The system must be rebooted.
8: Some uncorrected errors exist on one or more of the file systems checked, there was a syntax error, or some other operational error occurred.
12: A signal was caught during processing.
31: The open of the device file failed.
32: The file system is unmounted and needs additional checking.
33: The file system is mounted.
34: The file system is damaged.

WARNINGS

fsck should not be run on mounted file systems or on the root device. If you do run on mounted file systems, be sure the system is in single-user state (see shutdown(1M)).

The special case of the -c option, -c 0, will disable all internal caches, which will reduce memory usage but may impact performance.

The -F option, from prior releases, has been replaced by the -f option.

AUTHOR

fsck was developed by HP, AT&T, the University of California, Berkeley.

FILES

/etc/fstab: Default list of file systems to check.
/var/adm/sbtab: List of locations of the superblocks for file systems. The mkfs command appends entries to this file.

STANDARDS CONFORMANCE

fsck: SVID3