View Full Version : Server 14.04 cannot find root after kernel upgrade

November 26th, 2014, 07:12 PM
Greetings All,

I am running Ubuntu Server 14.04 on two identical computers that I am about to deploy into a production environment. Recently I've run into an issue with the last two upgrades of the Ubuntu kernel which are preventing the servers from booting, requiring a roll-back to the previous version. I'm stumped as to what the issue may be. Obviously I can't deploy until I understand what is happening here.

The issue most recently cropped up today with an upgrade to 3.13.0-40-generic #66 from -39. I have two machines running on ASUS Z87-Plus motherboards with single SATA hard drives, configured using the default Ubuntu partitioning and unencrypted LVM. I did not specifically update the kernel, but do have automatic security updates turned on. One of the servers acts as an rsync clone of the master and reboots nightly... hence, I catch the error in the morning when the back-up server has failed to reboot. As the main server has also downloaded the new version of the kernel, it also fails when doing a manual reboot. Both machines can be brought up again if I roll back to the previous kernel.

In the boot sequence, the first indication of a problem is:

ata8: SATA link down (SStatus 0 SControl 300)
Begin: Running /scripts/init-premount... done
Begin: Mounting root file system...
Begin: Running /scripts/local-top ... done
system-udevd[156]: renamed network interface eth0 to em1
Gave up waiting for root device. Common problems:
- Boot args (cat /proc/cmdline)
ALERT! /dev/mapper/avh--server--20--vg-root does not exist. Dropping to a shell!

It then drops to a BusyBox shell with an (initramfs) prompt.

When I interrupt grub and examine the command sequence, I can see no difference between that for the successfully-booting -39 kernel and the failed -40. Both grub sequences specify the root in the same way - as an identical UUID number. All of the -40 kernel files exist in /boot and look to be reasonable sizes.

I would normally attribute this non-booting behavior to a bad download and corrupted kernel files, but the same thing ocurred when upgrading from -32 to -39. I resolved that issue only by eventually reinstalling Ubuntu on both servers and regenerating data files from a backup. Also, if this were only occurring on the backup server, I would think that I'm rsyncing something over from the master that I should not be, but the fact that it occurs on both the master and the backup make me think that there is something else going on.

I believe that this error only first appeared with -39, and now with -40. Previous kernel upgrades caused no problems on either machine. Has a module been removed in these kernels that I need?

Thanks in advance for any thoughts.

Sam Longiaru
Kamloops, BC Canada

November 26th, 2014, 09:12 PM
what happens if you switch the SATA cable with a new one?

had something similar happen in windows. turns otu it was a bad cable (poor contact).

cause it looks like it can't find the root device.

November 26th, 2014, 09:47 PM
Yes, it suggests that it is unable to find the root device, but it can find it when I direct grub to use the older kernel... and the behavior is identical on both machines. That would tend to suggest either a software problem or an introduced incompatibility between the boot software and the existing hardware. That's why I was wondering about any required modules.

For the installation of Ubuntu, I accepted the default to install using LVM. I don't normally use LVM, but decided to accept it here to help with future expansion. The fstab for avh-server-20 is as follows:

/dev/mapper/avh--server--20--vg-root / ext4 errors=remount-ro 0 1
#/boot was on /dev/sda1 during installation
UUID=2523c...932 /boot ext2 defaults 0 2
/dev/mapper/avh--server--20-vg-swap_1 none swap sw 0 0

and the grub boot command for -40 (fails by not finding boot device) is as fololows:

setparams 'Ubuntu'
gfxmode $linux_gfx_mode
insmod gzio
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 2523c...932
search --no-floppy --fs-uuid --set=root 2523c...932
linux /vmlinuz-3.13.0-40-generic root=/dev/mapper/avh--server--20--vg-root ro splash xvga=1024x768x24 $vt_handoff
initrd /initrd.img-3.13.0-40-generic

The grub boot for -39 (which works) is identical save for the following:

setparams 'Ubuntu, with Linux 3.13.0-39-generic'

and all references as above to -40-generic are set to -39-generic. Other than that... nothing different.

So this makes me think that it is not grub itself or the way the system is being loaded. -40 seems to be missing the ability to properly map the root device.

Does that provide any aditional clues to anyone?



November 30th, 2014, 09:36 PM
I didn't see this as solved, so... still need help?

Is it 64 bit server? Is it on MBR disks or GPT?

If you can boot that server from a Secure Boot remix LiveCD disk? Please post the results of:

sudo blkid
sudo fdisk -l
sudo pvdisplay

From those results, I can tell you how to mount an LVM filesystem and chroot into it, to diagnose, or to make repairs.

EDIT-- Warning: If you run boot repair from that disk... use it just to post a report to postbin, not to fix it. It sometimes thinks that an LVM filesystem is erroneously using mdadm (linux RAID) when it was not.