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Solaris Common Messages and Troubleshooting Guide

BAD SUPER BLOCK: string

Cause

This message from fsck(1M) indicates that a filesystem's super-block is damaged beyond repair and must be replaced. At boot time (with the -p option) this message is prefaced by the filesystem'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 filesystem involved; if not, try to back up the filesystem 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 filesystem involved. Then run newfs(1M) with the -N option to print out the filesystem 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, out of range NCG (number of cylinder groups) or CPG (cylinders per group), 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.

See Also

For more information on bad superblocks, see the sections on restoring bad superblocks in the System Administration Guide, Volume I. If you are using the AnswerBook, "superblock" is a good search string.