Re: Booting uncompressed kernel images
On Mon, Feb 1, 2016 at 12:03 AM, Tiago Ilieve <tiago.myhro@gmail.com> wrote:
> Hi,
>
> I have a scenario[1] where the default Linux kernel compressed with XZ
> (from Jessie and up) cannot be booted. The first thing that I've tried
> was to uncompress it using "extract-linux"[2] and it didn't worked by
> the time, so I decided to rebuild the entire "linux-image-*" package
> changing "CONFIG_KERNEL_XZ=y" to "CONFIG_KERNEL_GZIP=y". This, of
> course, implies that it would be needed to recompile the kernel every
> time a new version of the package is released, which is an overkill
> for a such simple requirement.
Does the kernel boot after after you rebuild it with GZIP=y?
>
> Yesterday, Ben Hutchings itself suggested[3] me to write a hook that
> decompresses the kernel at package installation time, something which
> I find a great idea. The problem is that, again, I couldn't boot a
> machine (tried on VirtualBox and Xen) after uncompressing its
> "/boot/vmlinuz-*" using "extract-linux".
The script is not without its issues, apparently, but you can modify
xxx[1] in script if that is causing your hang.
> I can generate an initrd file
> from this uncompressed image, "update-grub" detects it fine, but if I
> reboot it the following error appears:
>
> Loading Linux 3.16.0-4-amd64 ...
> error: invalid magic number.
> Loading initial ramdisk ...
> error: you need to load the kernel first.
>
> The same error happens if this uncompressed image is compressed again
> with "gzip", for instance.
>
> Given this situation, I have two questions:
>
> - If a kernel is configured to be compressed at build time, it can't
> be booted if uncompressed later? I have some doubts about this,
> because there is more than one report of successfully booting
> uncompressed kernels[4][5].
> - Is "extract-linux" stripping some essential information (the script
> looks for an offset to start the decompression process) from the
> kernel image that is needed to boot it later? If so, is there a way to
> recover and insert it on the uncompressed image?
In Google Cloud Engine (GCE) I have not experienced those issues as I
have created several images in Jessie and Stretch -- manually at the
moment. They are Debian vanilla except for Reiser4 -patched kernel and
root (/) Reiser4 -formatted.
Best Professional Regards.
PS I have also found binwalk [2] useful when examining contents of
compressed kernel
apt-get install binwalk
Was not aware that Oracle had such an outdated cloud infrastructure ;-)
[1] http://stackoverflow.com/questions/12002315/extract-vmlinux-from-vmlinuz-or-bzimage
[2] http://unix.stackexchange.com/questions/163346/why-is-it-that-my-initrd-only-has-one-directory-namely-kernel
--
Jose R R
http://metztli.it
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