BAD SUPER BLOCK: string (Solaris Common Messages and Troubleshooting Guide)

Solaris Common Messages and Troubleshooting Guide

BAD SUPER BLOCK: `string`

Cause

This message from fsck(1M) indicates that a file system's super block is damaged beyond repair and must be replaced. At boot time (with the -p option) this message is prefaced by the file system's device name. After this message comes the actual damage recognized (see Action). Unfortunately, fsck(1M) does not print the number of the damaged super block.

Action

The most common cause of this error is overlapping disk partitions. Do not immediately rerun fsck(1M) as suggested by the lines that display after the error message. First, make sure that you have a recent backup of the file system involved; if not, try to back up the file system now using ufsdump(1M). Then, run the format(1M) command, select the disk involved, and print out the partition information.

# format
: N
> partition
> print

Note whether the overlap occurs at the beginning or end of the file system involved. Then, run newfs(1M) with the -N option to print out the file system parameters, including the location of backup super blocks.

# newfs -N /dev/dsk/device

Select a super block from a non-overlapping area of the disk, but note that in most cases you have only one chance to select the proper replacement super block, which fsck(1M) soon propagates to all the cylinders. If you select the wrong replacement super block, data corruption will probably occur, and you will have to restore from backup tapes. After you select a new super block, provide fsck(1M) with the new master super block number:

# fsck -o b=NNNN /dev/dsk/device

Technical Notes

Specific reasons for a damaged super block include: a wrong magic number, an out-of-range number of cylinder groups (NCG) or cylinders per group (CPG), the wrong number of cylinders, a preposterously large super block size, and trashed values in super block. These reasons are generally not meaningful, because a corrupt super block is usually extremely corrupt.