Note that you need the qemu command, which is provided on wheezy by the qemu-system package.

• Start the VM

  • with a 64-bit CPU that supports PAE

    qemu -enable-kvm -cpu Nehalem -cdrom tails.iso -m 5120 -no-reboot -no-shutdown
    

  • with a 32-bit CPU that does not support PAE

    qemu -enable-kvm -cpu 486 -cdrom tails.iso -m 5120 -no-reboot -no-shutdown
    

• Open the qemu console (CTRL-ALT-2).

• Save physical memory to the tails.dump file (length is an integer, max size for one dump is 4G = 0xF0000000):

    pmemsave <start address> <length> <filename>
  

  e.g for 5G one has to do two dumps:

    pmemsave 0 0xFFFFFFFF tails14.dump
    pmemsave 0x100000000 0x40000000 tails5.dump