Importing server using initramfs shell

When all you have is a remote KVM (this, not this), management console doesn’t have image import/export feature, and you need to migrate a VPS.

Fortunately, during usual Linux boot process, there is a stage when it is not dependent on the OS partition because we’re running from RAM - logically enough it is called initramfs. Let’s use it to import the image!

On donor:

• open port on firewall, ideally only to acceptor’s IP.

• freeze all filesystems mounted on local disk:

  • mount / -o remount,ro - do for each partition
  • or
  • echo u > /proc/sysrq-trigger

• start fake HTTP server:

  • (printf 'HTTP/1.0 200 OK\r\n\r\n'; cat /dev/sda) | pv | nc -l -p 1234

On acceptor:

• in /etc/default/grub change GRUB_TIMEOUT to 10

• update-grub

• note ip address, netmask, gateway

• reboot

• open KVM console

• enter bootloader, edit options, add break=premount to command line and boot

• manually add ip address, netmask, gateway (ip…)

• but initramfs in Ubuntu doesn’t have netcat, so…

• wget -O /dev/sda http://DONOR:1234

• reboot

should work

Security considerations:

if doing it between VPSes in the same server room and everything is in well-protected network, then nothing to worry about, as VPS provider has access to all the content of the disk anyway.

Otherwise: verify sha512sum before reboot, revoke & regenerate keypairs, or don’t use this method at all if disk content is confidential