[lfs-support] Can't Mount Root Filesystem

Richard Melville richard.melville69 at googlemail.com
Wed Mar 18 03:41:55 PDT 2015


On 18 March 2015 at 09:47, Роберт Киммель <robert.l.kimmel at live.ru> wrote:

> On 18/3/15 17:14, Pierre Labastie wrote:
> > Le 18/03/2015 09:11, Роберт Киммель a écrit :
> >> Greetings All,
> >>
> >> I've been building LFS systems on and off for more than a decade, but
> >> I've been struggling with this one for a while now.
> >>
> >> I have my 7.6 system installed, and when I boot, it seems like the
> >> kernel loads, and everything goes as it should for a while.  But, when
> >> it comes time to remount the root file system (which is the one where
> >> the kernel was in the first place), it can't find it, kernel panic.
> >>
> >> I've checked all the relevant /etc and /boot files, and they seem OK, so
> >> I suspect this is a matter of some kernel setting which is needed for
> >> this particular hard disk, but which is not set properly.  All my
> >> previous LFS systems were on what I'll call more "consumer" grade
> >> hardware, but this one is a more up-market server platform.  So I think
> >> probably I need to enable some option, some hardware driver, which I
> >> never needed before.  However, I have tried a bunch of things, and
> >> nothing works so far.
> >>
> >> My LFS 6.3 LiveCD boots on the same hardware no problem, and I can mount
> >> the hard disk Linux partition, and do all the things one would normally
> >> do to a hard disk, no problem.  So my thought was, maybe I can start
> >> with the LFS 6.3 kernel settings, do a "make oldconfig" or something
> >> similar on the kernel used in 7.6, and see if I can get the 7.6 system
> >> to work that way.
> >>
> >> But I can't find the kernel settings for the LiveCD.  Are they on the CD
> >> somewhere?
> >>
> >> Also, if anyone can think of a way to approach this problem which is
> >> different than the one I'm pursuing, I'd appreciate any advice.
> >>
> >>
> > I am not sure exactly when the panic occurs. Is it after init start
> > (message 'INIT: version 2.88 booting') or before?
> > If it is after, it means it is not a kernel issue, since it was able
> > to load init. If it is before, I guess your approch is OK. You could
> > try to install a modern distro, instead of the old LIve CD, and see
> > what kernel modules are loaded once the system is started.
> >
> > Pierre
> >
>
> I can't capture the output, because the system is non-functional.  But,
> what I can see on the screen is a bunch of messages, all beginning with
> [   1.07XXXX], where XXXX is an increasing sequence.  The first message
> (not literally the first one, but the first one at the top of the screen
> after the whole process grinds to a halt) says "Hardware name: Dell
> Inc.  Precision WorkStation T7500   /06FW8P BIOS A05 04/12/2010".
>
> The next three consist entirely of hex numbers, I guess some kind of
> memory dump.
>
> After that, there is a "Call Trace:", which has a bunch of sub-messages
> below it, with things like "dump_stack", "panic", "mount_block_root",
> and a bunch of others.
>
> Next to last message is "Kernel Offset: 0x0 from 0xc1000000 (relocation
> range: 0xc0000000-0xf7ffdfff)"
>
> Then the final message is "---[ end Kernel panic - not syncing: VFS:
> Unable to mount roof fs on unknown-block(8,2)"
>
> I can't vouch for perfect accuracy above, because I'm reading messages
> from one computer's screen and typing them on another computer's
> keyboard.  I don't see the "INIT" message which you reference, but the
> screen scrolls so quickly I can't read the messages before these, and I
> don't know how to capture them, if that's even possible.
>
> I think this is the point where the kernel is trying to mount the
> filesystem for the first time though - does that sound correct?
>

Yes.

You say that you've "checked all the relevant /etc and /boot files, and
they seem OK", but it looks to me that the kernel panic is resulting from
the rootfs being listed in the wrong place.

Regarding your .config file: the best way to capture the kernel .config of
a running system, and to load it into your new kernel, is to run zcat
/proc/config.gz > linux-x.x.x/.config, providing, of course, that the
running kernel has been set up to save a copy of .config to /proc.

Richard
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