[SOLVED]Waiting for 10 second for device /dev/disk/by-uuid/ error message during boot

I just upgraded to update pack 2014-07-31.
But i cannot boot the system properly now.
I got error as the subject “Waiting for 10 seconds for device /dev/disk/by-uuid/ error message during boot”.
I saw “Error: Unable to find root device”
Then landed at recovery shell.

If i can remember, something strange outputted when updating the kernel.
But cannot really remember the exact text.

My system is a laptop with SSD and HDD and i’m using LVM.
The root is inside the SSD.
I have two kernels installed 3.14 and 3.15, both cannot boot properly,

What should i do and what extra info should i provide?

Thank you.

You will need to fix grub, here is the wiki page on how to do this:

Thanks for the hint.
After chroot-ed it. I managed to fix this problem by adding ‘lvm2’ to HOOKS in mkinitcpio.conf
Then run

mkinitcpio -p linux315

I wonder why the lvm2 missing.

There must have been a change to the system that needed that file to be replaced, look for a mkinitcpio.conf.pacorigial in your /etc folder, if it is there you will need compare it with the new one and decide what to merge. This is probably what you thought was an error when the update ran, but in all actuality it was just a reminder that this and maybe other files needed to be looked at,