how to boot or access problem file system

Roland Smith rsmith at
Thu Jul 30 19:05:02 UTC 2009

On Thu, Jul 30, 2009 at 01:40:58PM -0400, PJ wrote:
> What can be done to access a file system that seems to have the boot
> sector screwed up?

Do you mean the filesystem's superblock? Or the slice table (partitions
in PC parlance) or the freebsd partitions (disk labels)? Because the
boot sector is not part of any filesystem. 

The best way to try repairs is to make a complete copy of the partition
with dd(1), and experiment on the copy. That way you cannot further screw
up the original!

To check a UFS filesystem, use fsck_ffs(8). First, try if the preen
option '-p' is sufficient to fix the filesystem. If the superblock is
corrupt, try using the -b option to specify an alternate superblock. See
the manual page.

> The /usr files should be ok but how to access?

Use fsck_ffs to try and repair the filesystem.

> I get errors that the file system is full and I have no idea of how to
> deal with the boot up - the help message is no help!
> Boot says it cannot find a kernel... surely there must be some kind of
> recovery process even if nothing has been backed up. Surely FreeBSD must
> be have something that functions like certain software does on MS ?

Maybe the sleuth kit (sysutils/sleuthkit) can help you recover files. 

> I don't have a problem with irrecoverable files, I would just finally
> understand how things work and what can be done on FBSD.

Make regular backups. Especially before big upgrades.

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