how to boot or access problem file system

PJ af.gourmet at
Fri Jul 31 19:12:22 UTC 2009

Roland Smith wrote:
> On Thu, Jul 30, 2009 at 03:20:55PM -0400, PJ wrote:
>> Roland Smith wrote:
>>> 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?
> I forgot to mention that your boot sector is fine. If it were screwed
> up, you wouldn't get to the boot prompt.
> Since the boot code cannot locate your kernel, there are several things
> that could have gone wrong. See below.
> <snip>
>>>> The /usr files should be ok but how to access?   
>>> Use fsck_ffs to try and repair the filesystem.
>> how can I use it if I can't boot or access the file system?
> Use a livefs cd or use the Fixit option in the main menu of sysinstall
> on an install disk. That should get you a shell where you can run
> fsck_ffs on your disk partitions.
> If you have booted from CD, list the disk devices with e.g. 'ls
> /dev/ad*'. If you have SCSI drives, use 'da' instead of 'ad'.
> What does that command list? On my machine, I'll get
> something like this:
> /dev/ad4         /dev/ad4s1d      /dev/ad6         /dev/ad6s1d
> /dev/ad4s1       /dev/ad4s1e      /dev/ad6s1       /dev/ad6s1e
> /dev/ad4s1a      /dev/ad4s1f      /dev/ad6s1a      /dev/ad6s1f
> /dev/ad4s1b      /dev/ad4s1g      /dev/ad6s1b      /dev/ad6s1g
> /dev/ad4s1c      /dev/ad4s1g.eli  /dev/ad6s1c      /dev/ad6s1g.eli
> If you only see e.g. /dev/ad4 and /dev/ad6, your slice table has been
> overwritten (with fdisk) and your data is lost. If you see /dev/ad4s1
> but not /dev/ad4s1a-g, the BSD partitions have been removed and your
> data is lost as well.
> Since there is only one slice on both ad4 and ad6 (otherwise you'd see
> /dev/ad4s2x) The next step is to examine the disk labels:
> bsdlabel /dev/ad4s1
> # /dev/ad4s1:
> 8 partitions:
> #        size   offset    fstype   [fsize bsize bps/cpg]
>   a:  1024000       16    4.2BSD     2048 16384 64008 
>   b: 16777216  1024016      swap                    
>   c: 976768002        0    unused        0     0         # "raw" part, don't edit
>   d:  4194304 17801232    4.2BSD     2048 16384 28528 
>   e: 104857600 21995536    4.2BSD     2048 16384 28528 
>   f: 41943040 126853136    4.2BSD     2048 16384 28528 
>   g: 807971826 168796176    4.2BSD     2048 16384     0
> This tells us that the a, d, e, f and g partition are carrying a BSD
> filesystem, and should be checked with fsck_ffs.
> Try these steps and report back what you find.
>>>> 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.
>> Maybe the real problem is that the manual is too screwed up (why are
>> there so many problems being brought up on the mailing lists? we can't
>> all be that stupid.)
> It is a mailing list for questions. Ipso facto you'll see questions and
> problems on this list. People who are not having problems will not be
> posting very much. :-) 
> As to the handbook, this is by necessity written by people who are
> knowledgeable on the subject they write on. Unfortunately this sometimes
> lead to really basic steps/assumptions being skipped because they are
> self-evident for the writer. If you gain enough knowledge about a
> subject it becomes really hard to write for people new to the system
> because you've internalized a lot of stuff by then.
> If you have specific questions about parts of the handbook, ask.
> Roland
I get the impression that my disks have all been overwritten; it's
rather strange that in the instructions to upgrade it says to not change
anything on the Newfs... and that files would not be overwritten... is
that at fact?
If that is true, then surely it should be possible to recover files in
the /usr /var and /tmp directories. If the disks have not been
overwritten... I think there was a huge misinformation gap here if this
is not so...
If we're upgrading a file system, there is no reason to either format or
overwrite those directories and/or slices that are not involved. Anyway,
I'm waiting to hear if there is any hoope here or do I just go ahead an
reinstall everything?

Hervé Kempf: "Pour sauver la planète, sortez du capitalisme."
Phil Jourdan --- pj at

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