Date: Thu, 27 Sep 2001 04:03:33 +0200 From: Piet Delport <siberiyan@mweb.co.za> To: freebsd-stable@freebsd.org Subject: "fixlabel: invalid magic" while dd'ing to /dev/ad4s1 Message-ID: <20010927040332.C96979@athalon.homenet>
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Hi stable people,
Some verbose background (hurried folks can skip to "end background"):
A while back, while i was installing FreeBSD onto a free slice on this
box, i accidentally overwrote the start of my first slice (which
contains a Winders 98 installation) with the FreeBSD boot loader,
instead of installing it in the MBR.
The result is that said Win98 slice is now unbootable (FreeBSD gets
booted instead when i try) and unmountable (both from FreeBSD and a DOS
boot floppy). Not too big a deal, as my most important data is
elsewhere, and the Windows installation is expendable, but there's still
one or two non-backed-up files on the Win98 slice that i'd like to
recover. Which is what i set out to do, in the name of Knowledge,
Prosperity, and Copious Free Time.
Initial investigation revealed that only the first 8K of /dev/ad4s1 (the
Windows boot slice) differed from a normal FAT32 filesystem header, a
convenient example of which exists in the form of /dev/ad4s5, my other
FAT32 slice. So, by restoring the first 8K of ad4s1 from ad4s5, i am
hoping to make ad4s1 usable again, at least enough so that i can recover
my files.
[end background]
I tried the following:
# dd if=/dev/ad4s5 of=/dev/ad4s1 bs=512 count=16
but dd replied with:
| dd: /dev/ad4s1: Read-only file system
| 2+0 records in
| 1+0 records out
| 512 bytes transferred in 0.022429 secs (22828 bytes/sec)
Note that the first 512 bytes were indeed written to ad4s1, but nothing
more was.
Additionally, the kernel reported:
| dscheck(#ad/0x20022): fixlabel: invalid magic
| fixlabel: invalid magic
For what it's worth, 0x20022 seems to be the minor device number of
/dev/ad4s1:
$ ls -l /dev | grep 20022
crw-r----- 2 root operator 116, 0x00020022 Sep 27 01:47 ad4s1
crw-r----- 2 root operator 116, 0x00020022 Sep 27 01:47 rad4s1
$
Searching various manpages didn't shed any light on the error messages,
so i grepped the FreeBSD source tree for "fixlabel: invalid magic" and
found (the only) match in sys/kern/subr_diskslice.c:
| /* These errors "can't happen" so don't bother reporting details. */
| if (lp->d_magic != DISKMAGIC || lp->d_magic2 != DISKMAGIC)
| return ("fixlabel: invalid magic");
| if (dkcksum(lp) != 0)
| return ("fixlabel: invalid checksum");
Unfortunately, my non-existent kernel-fu precluded me from gleaning
anything meaningful from the code, other than that this probably
shouldn't happen.
I should also mention that i tried:
# disklabel -W ad4s1
after reading about it in disklabel(8), but i still got the same error
message. I also tried dd'ing to/from /dev/rad4s? instead of /dev/ad4s?,
with no success.
Am i doing something wrong here, is this a bug, or what?
Thanks in advance for any replies,
--
Piet Delport <siberiyan@mweb.co.za>
Today's subliminal thought is:
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