kernel panic

holocene · n00b Joined: 24 Jan 2011 Posts: 8

Greetings Gentoo gurus,

I am a new Gentoo user, and I have followed the amd64 handbook exactly AFAIK.

I am getting a kernel panic with this text:

VFS: Cannot open root device "(null)" or unknown-block(8,3)
Please append a correct "root=" boot option...
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,3)
pid: 1, comm: swapper Not tainted 2.6.36-gentoo-r5 #4

On a previous install attempt, I noticed a compile error (can't create bzImage) about lzma, so I did a emerge lzma-utils, which resulted in a compile with no lzma error this time.
Compile did complete with only warnings. No error at the end.
to the best of my understanding, the SATA drivers installed NOT as module (as per the generic config file, that is NOT from genkernel)

any ideas appreciated.
Steve.

My environment:
machine is amd64 dual processor
working from http://distfiles.gentoo.org/releases/amd64/autobuilds/current-iso/install-amd64-minimal-20110113.iso
stage: http://gentoo.mirrors.easynews.com/linux/gentoo/releases/amd64/autobuilds/20110120/stage3-amd64-20110120.tar.bz2
kernel source: gentoo-sources
kernel config: no changes made to config
compilation method: make && make modules_install
SATA drive: 1 only (sda1 boot sda2 swap sda3 /) just like handbook examples
grub installed to mbr using grub-install (hd0,0) just like handbook examples

DONAHUE · Posted: Tue Jan 25, 2011 2:05 pm Post subject:

boot the cd, mount the gentoo partitions, run

Jaglover · Posted: Tue Jan 25, 2011 2:09 pm Post subject:

GES · Posted: Tue Jan 25, 2011 2:49 pm Post subject: Re: kernel panic

holocene · n00b Joined: 24 Jan 2011 Posts: 8

holocene · n00b Joined: 24 Jan 2011 Posts: 8

holocene · n00b Joined: 24 Jan 2011 Posts: 8

NeddySeagoon · Posted: Tue Jan 25, 2011 6:52 pm Post subject:

holocene,

There are degrees of 'read'. The kernel can find the drive and read raw disk blocks but it cannot make any sense of what it reads.
That requires the file system driver. Without that, the kernel cannot find any files on the drive.

Follow this guide
Actually, its a part made kernel config file with instructions for completing it to suit your hardware.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

holocene · n00b Joined: 24 Jan 2011 Posts: 8

Jaglover · Posted: Tue Jan 25, 2011 8:19 pm Post subject:

Steve,

there are three ways to compress the kernel image, you have chosen lzma, to make it work you need to emerge lzma-utils. Or choose another compression method.
_________________
My Gentoo installation notes.
Please learn how to denote units correctly!

NeddySeagoon · Posted: Tue Jan 25, 2011 10:16 pm Post subject:

holocene,

A initrd is a temporary root filesystem, loaded into RAM by the boot loader that the kernel looks for at /dev/ram0
You need initrd support in the kernel for this.

The kernel runs a script to do whatever is needed, using this initrd to get the system in a state where it can mount the real root file system.
As no file system drivers are needed, kernel modules can be loaded from the initrd. You just need a script to tell what has to be done and in what order.
genkernel makes a fully modular kernel and an initrd so in theory it all just works. If you deviate from the handbook, genkernel may welll need a bit of help.

When you do not use an initrd, kernel modules are stored on disk, in the root filesystem. Its a bit difficult to load a module from disk, when you need the module you are trying to load to read the disk.
Thus when you choose not to use an initrd, everything needed to boot must be built into the kernel.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

holocene · n00b Joined: 24 Jan 2011 Posts: 8

The genkernel compile completed ok, installed grub, rebooted, choose my kernel from the menu, and it freaking WORKED!!

I think that when I tried the genkernel method previously, I might have used the grub from the non-genkernel.

I am going to back my system up using clonezilla so I have a good reference point to fall back to.

After that, I want to learn to compile the kernel "the right way". No genkernel.

I know I should keep my working kernel intact as a fall back, so my grub should have an entry pointing to it.

I assume that when I compile a new trial kernel, that will become another entry in grub.

If this is incorrect, please let me know.

Thanks to all for your patience.

holocene · n00b Joined: 24 Jan 2011 Posts: 8

Update on my progress:

I was able to compile a custom kernel that would boot on my machine.

Previously, the custom kernel would fail with a VFS error.

These are the changes to the stock .config file(each changed from M to *):

* turned on gzip kernel compression (was lzma but lzma is not present in a new vanilla install)
* AHCI SATA
* ATI PATA SUPPORT
*GENERIC PLATFORM DEVICE PATA SUPPORT
*GENERIC ATA SUPPORT

Question:
I did not emerge gentoo-sources after the prior kernel build. Instead, I just make menuconfig again. Is this the right way to do it?

Thanks to all.
Steve.

Jaglover · Posted: Wed Jan 26, 2011 12:57 pm Post subject:

You can have as many kernels in your /boot as you want, just add them to grub.conf.

You can re-use the sources, yes. You can run make clean on them to remove all stuff you built (should leave enough to build modules if needed). Running make mrproper will return the sources to the pristine condition, meaning all generated files and your .config will be removed, too.

http://www.gentoo.org/doc/en/kernel-upgrade.xml
http://www.gentoo.org/doc/en/articles/linux-kernel-compiling.xml
_________________
My Gentoo installation notes.
Please learn how to denote units correctly!

holocene · n00b Joined: 24 Jan 2011 Posts: 8