How it works...

We take advantage of the functionality that the nbd kernel module provides by allowing us to associate a raw image file to a block device using the qemu-nbd utility. To get more information about the kernel module run the following code:

root@kvm:~# modinfo nbd
filename: /lib/modules/4.4.0-62-generic/kernel/drivers/block/nbd.ko
license: GPL
description: Network Block Device
srcversion: C67096AF2AE3C738DBE0B7E
depends:
intree: Y
vermagic: 4.4.0-62-generic SMP mod_unload modversions
parm: nbds_max:number of network block devices to initialize (default: 16) (int)
parm: max_part:number of partitions per device (default: 0) (int)
root@kvm:~#

We can examine the block device metadata created in step 2 by running the following command:

root@kvm:~# file -s /dev/nbd0
/dev/nbd0: x86 boot sector
root@kvm:~#

After creating the two new partitions in step 3, the type of the image file has changed. Let's examine it again:

root@kvm:~# file -s debian.img
debian.img: x86 boot sector
root@kvm:~#

Now that we have an image file that contains two partitions and a filesystem, we can proceed with installing the guest OS in the next recipe.