how to boot or access problem file system

[Roland Smith]

On Fri, Jul 31, 2009 at 03:12:21PM -0400, PJ wrote:
> 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.
> >
> I get the impression that my disks have all been overwritten; it's

Don't have impressions. Get the data. Boot from a livefs CD and start a
shell as explained in in some of my previous messages. Then use the commands
listed above to check your filesystems. *And report back wat you found*.

> 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?

What instructions are you referring to? Neither the handbook section
[http://www.freebsd.org/doc/en/books/handbook/updating-freebsdupdate.html]
nor the manual page for freebsd-update mention newfs at all! Nor should they.

> 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...

For an upgrade, the filesystems are not overwritten. Only a new install
creates new filesystems.

Please boot from a livefs CD and check the filesystems on the harddisk
as explained before and report the results.

Roland
-- 
R.F.Smith                                   http://www.xs4all.nl/~rsmith/
[plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated]
pgp: 1A2B 477F 9970 BA3C 2914  B7CE 1277 EFB0 C321 A725 (KeyID: C321A725)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 196 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-questions/attachments/20090731/d45f1b65/attachment.pgp