On Sun, 30 Mar 2008, Paul M Foster wrote:
> On Sun, Mar 30, 2008 at 10:33:43PM -0400, Donald E Haselwood wrote:
>
>> Can linux, e.g. Suse 10.3, copied and booted up on a partition with a
>> different filesystem from the one it was installed on? My experiments
>> suggest that this cannot be done, but maybe there is something I'm
>> overlooking.
>>
>> For example, I have Suse 10.3 installed on a partition with ext3. I copy the
>> whole system to a partition formatted with ext2. I fix fstab and grub. Boot
>> fails early, ending with "Loading ext3"; "Mount: unknown filesystem type
>> ext2"; then," kernel panic...". If I do the same copy/fix-up process to a
>> partition with ext3 it works fine.
>>
>> I also tried it on a machine with Suse 10.2 installed on an ext2 partition
>> and
>> copied to an ext3 partition. Boot fails with "unknown filesystem type ext3"
>> when the filesystem type on the copy is ext3; of course in this case the
>> filesystem types are reversed, i.e. "Loading ext2"; "Mount: unknown
>> filesystem type ext3." And again, it works fine if the partition filesystem
>> type for the copy is the same as the installed type, ext2.
>>
>> This suggests that something in the kernel/initrd images has the filesystem
>> type expected and fails when a different one is encountered. So far, I
>> haven't been able to turn up anything to confirm/refute this on the web.
>>
>
> Linux shouldn't care what filesystem it boots/runs on (within limits).
> As long as the driver for the file system it boots/runs from is loaded
> into the kernel.
>
> When you say you "copied" a SuSE installation from one filesystem to
> another, I'm not sure how you mean "copied". Using cp? Using dd? Using
> rsync? Could make a difference.
>
> An ext3 filesystem is essentially an ext2 filesystem with hidden
> journaling for fault-tolerance. However, there is something somewhere
> which tells the kernel what filesystem you're using. And it appears that
> whatever that is (grub? something in /etc?) is being copied over and
> telling your kernel the wrong filesystem type. I believe the bootloader
> has to know what type of filesystem to load (I don't believe it
> autodetects it), and it loads or tells the kernel to load the proper
> driver for it.
There's either a kernel flag for it supplied by the bootloader, or the
kernel expects / to be mounted when it's invoked, I can't figure out which.
/etc/fstab has an entry for / , but it must be dummy, since by that time /
is already mounted. The kernel needs support for /'s filesystem, either
modular (and in the initrd) or in the kernel. If the module to access / is
on /, you have a nice catch-22.
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