A usable Qemu image

Qemu is nice and highly configurable. Compared to other virtual environments, it is much more flexible, offering a lot of potential. However, it can sometimes be daunting to use due to the overwhelming number of options.

Fortunately, the community has developed a user-friendly UI interface for Qemu, which aids in the configuration and setup process. This is known as the Virtual Machine Manager, or virt-manager (Ref. 1).

Some preparatory work

First check if the virtual machine is enabled in your machine:

egrep -c '(vmx|svm)' /proc/cpuinfo

This counts the occurrences of the vmx/svm features supported by your CPU. The result should be a number equal to the number of cores in your machine.

If the number received from that command is '0', it means that the virtualization feature needs to be enabled in the BIOS.

Ensure that the following packages are installed on your PC, or install them if necessary:

sudo apt install qemu-system-x86 libvirt-daemon bridge-utils virt-manager

The bridge-utils will come at handy next in this page.

Add the user to the virtualization groups:

sudo usermod -aG libvirt andi
sudo usermod -aG kvm andi

Ensure the libvirt daemon is enabled at boot time and restart it with the following commands:

sudo systemctl enable libvirtd
sudo systemctl start libvirtd

At this point, we are ready to start our virt-manager.

This part is largely inspired by Veronica's vlog, which I found to be very neat and clear, devoid of the usual extra fluff found in blogs. If you encounter any issues setting up virt-manager, check out her video (Ref. 2).

Network bridge

While setting up the virtual machine in the previous section, you were asked about the network interface to use. For this we will setup an ad-hoc bridge that will connect our Virtual OS to the network.

A network bridge is a virtual network that forwards packets to our physical interface.

In the picture eno1 represent the physical ethernet interface. We need to create a br0 virtual interface where to which the Virtual Machines will be connected. All their traffic will be routed by the bridge to eno1, enabling our virtual machines to connect to the network.

Let's start by creating the bridge:

ip link add name br0 type bridge

Enable the interface:

ip link set dev br0 up

Let's assign it the address 192.168.1.201. It needs to be in the same network domain of the network where the PC is connected, in order to be able to be routed outside:

ip address add 192.168.1.201/24 dev br0

Now we set up the default gateway:

ip route append default via 192.168.1.1 dev br0

And finally we link the virtual interface br0 with the physical interface eno1:

ip link set eno1 master br0

Now the network on the Virtual Devices should be up and running and they can be assigned their own address through dhcp.

Reference

1. The official Virtual Machine Manager website
2. QEMU/KVM for absolute beginners -- a Vlog from "Veronica explains" with a very basic summary of what needs to be done in order to run a virt-manager.
3. Network bridge, by Arch Linux Wiki.