How it works...

A lot has happened in the previous section, so let's step through the commands and talk a little bit more about what exactly was performed and why.

In step 1, we mounted the root partition we created earlier on the /dev/nbd0p2 device to /mnt, so we can use it. Once mounted, in step 2, we installed an entire Debian distribution on that device using the mount-point as the target.

In order to install the GRUB boot loader on the root partition of the image, we bind and mounted the /dev directory from the host filesystem to the image filesystem in /mnt in step 4.

Then in step 6, we used the chroot tool to change our directory namespace to be /mnt, so we can perform operations, as we are directly on the new OS.

In step 8, we mounted the proc and sysfs virtual filesystems inside the image because the GRUB bootloader tool expect them.

In step 9, we proceeded to install the kernel source and GRUB tools in preparation of installing the bootloader on the boot partition and in step 10 we installed the bootloader.

In step 11, the GRUB configuration files were generated and the boot ramdisk image was updated.

In steps 12, 13, and 14, we changed the root password and ensured we get access to the pseudo Terminal, so we can log into the VM later and change the run-level from the default graphical interface to the multiuser.

Since the fstab file is empty right after installing the Debian OS on the image, we have to add the root mount point, or the VM will not be able to start. This was accomplished in step 15.

In steps 16 and 17, we performed some cleaning up by unmounting the filesystems we mounted earlier and exited the chroot environment.

Back on the host filesystem in step 18, we installed GRUB on the nbd0 device by specifying the mounted location of the image. 

In step 19, we updated the GRUB config device name to be sda2 because this is the name that will appear inside the virtual machine once we start it. The nbd0p2 name is only present while we have the association between the raw image and the network block device on the host OS. From the VM perspective, the second partition inside the image we created by is named sda2 by default.

And finally, in steps 20 and 21, we performed some cleaning by removing the mount point and disassociating the raw image from the network block device nbd0.