[lfs-support] Can't Mount Root Filesystem

Роберт Киммель robert.l.kimmel at live.ru
Wed Mar 18 04:07:20 PDT 2015

On 18/3/15 18:41, Richard Melville wrote:
> On 18 March 2015 at 09:47, Роберт Киммель <robert.l.kimmel at live.ru
> <mailto: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.

I've certainly had that error in the past, so I've checked it quite a
bit.  When I boot with the LFS 6.3 LiveCD, it comes up as /dev/sda2, or
(8,2).  I can mount this partition from the LiveCD system, look at the
files, etc.

So my working hypothesis is that the rootfs is in the wrong place
(specifically, nowhere), because the kernel isn't recognising the
hardware on which it resides.  But the debugging is a bit difficult when
you can't even get a shell going, and all these messages screech past my
on the screen, too fast to read, with no apparent way to capture them.

> 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.

There is a /proc/config.gz file when I boot from the LiveCD, so I'll try
this.  But I can't do it now, so I'll have to see how it is tomorrow.

> Richard

Many thanks,


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