Sunday, 12 August 2012

Physical Machine to Virtual Machine converting – Linux P2V (Unable to access resume device)


Unable to access resume device 
mount: could not find file system /dev/root
setuproot : error mounting /proc: No such file or directory
Kernel panic - not syncing: attempted to kill init!


Convert Linux Physical Machine to Virtual machine (vmware  and Virtualbox). Same procedure is working on vmware and virtual box


A fine morning started with a new question in mind, what if I could convert our Linux physical server to vm. This lead me to finishing the task and documenting it.


The  complete migration process of Linux physical machine to virtual machine. The following steps have been tested on oracle enterprise Linux 5. I will be sticking to OEL 5 during complete process.

The process comprises of taking a backup of physical machine and restoring it on a virtual machine


Back up the physical server

Startup a terminal on the physical server and change to maintenance mode

shutdown -y -g1 (in 1 minutes system will go to single user mode)






Unmount all partitions that you don’t want to include in the backup, in our case we are going to backup only root file system



tar cvpf  - --exclude=/proc --exclude=/lost+found --exclude=/bkp.tar.gz --exclude=/mnt --exclude=/sys / | gzip > /bkp.tar.gz

or

tar cvpzf  /u01/bkp.tar.gz --exclude=/proc --exclude=/lost+found --exclude=/u01/bkp.tar.gz --exclude=/mnt --exclude=/sys / 




--exclude :- use this option to exclude any file/directory from backup

Tar with z option is using absolute path in this example

Note:
make sure you have excluded the current backup file name using exclude option

copy the tar file and save at a location which we can access when restoring.

Creating Virtual Machine of Physical Server (Restoring)

Create a virtual machine and start it with Oracle Enterprise Linux 5 bootable media(cd/iso)

Type linux rescue in the prompt




During the boot up process in rescue mode system prompts you to configure network if you want  to copy files  from network configure network here,

Note:
By default vm is in NAT so don’t forget to change it to bridge if you are copying from a network


Partition the hard disk.

fdisk /dev/sda
                       
use n to create new partition

use t to change partition id to swap(82)

use a to toggle bootable flag

/dev/sda1 is our root partition(/)
/dev/sda2 is our swap partition(swap)


create file system

mkfs.ext3 /dev/sda1

this is going to be our root partition for new server

mount the partition under a new directory

mkdir a

mount /dev/sda1 /a


now copy the backup files from the media (copy over network or any other way you prefer)

I am going to copy from an external hard drive which is connected to the vm during startup

mount the external hard drive with backup files

mkdir backup
mount /dev/sdb1 /backup

copy the backup files to /a

cd /a

cp bkp.tar.gz /a or extract files to root directory directly (/a)

gzip -dc /backup/bkp.tar.gz | tar xzpvf -

or

tar xvpzf /backup/bkp.tar.gz

chroot /a

create the following directories
mkdir proc sys mnt


edit /etc/fstab to remove or comment automatically loaded partitions
and add the new entries for our new root partition and swap

/dev/sda1 / ext3  defaults 1 1     
/dev/sda2   swap  swap     0 0




Edit the grub.con file to modify the root partition related info




install grub

Either install it or reconfigure. To install just issue grub-install /dev/sda

Or setup as follows

grub
find /boot/grub/stage1
root (hd0,0)
setup (hd0)
            

at this stage restart the vm in rescue mode again. during the rescue startup system will ask to mount the Linux partitions automatically say yes and let system mount the already created Linux partition for you




system will mount it under /mnt/sysimage

now issue chroot /mnt/sysimage to change root to our newly recovered partition

configure the swap partition

mkswap /dev/sda2
swapon /dev/sda2

swapon –s :- will show you swap partition details if you did it skipping the auto mount option this is not going to give you swap details

Note:
if you manually mount the partition yourself without letting the system to do it for you and chroot to manually mounted root partition to configure the above swap setup, this is also resulting in kernel panic error. So let system mount it for you before you start configuring swap space. if you don’t do this way even after creating new ramdisk system will stop and booting with kernel panic screen







 now create new ramdisk image

backup the existing one

cp /boot/initrd-2.6.18-274.el5.img  initrd-2.6.18-274.el5.img.bkp

uname -r  to see your current kernel

ls /lib/modules     will list you all the kernel modules you have

I am using the default kernel as the other kernel is having errors while creating ramdisk. As base kernel is listed second in the grub.conf file you will have to make it default in grub.conf or select this kernel while booting up the system


mkinitrd -v /boot/initrd-2.6.18-274.el5.img  2.6.18-274.el5




exit
poweroff
remove bootable cd

Note:
don’t forget to select the base kernel 2.6.18-274.el5 while booting up if you have already not configured it to boot to base kernel.

After booting up system will fail to start xserver and asks you to reconfigure with new xserver setup say yes and system will automatically start xserver.




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