How to create a Virtual Machine using KVM hypervisor
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Diogo Monteiro - 29 Jun, 2024
Before the advent of containers, resource encapsulation was primarily achieved using virtualization technology. Consequently, achieving high performance for encapsulated programs posed significant challenges. The development of Kernel-based Virtual Machines (KVM) marked a pivotal advancement, as it introduced the capability to bypass virtualization limitations and minimize performance losses associated with encapsulation. Due to its effectiveness, KVM has become one of the most widely used virtualization solutions, supported by a robust community.
This tutorial has been developed using Ubuntu 22.04.
Installing KVM
Firstly, update apt-get:
sudo apt-get update && sudo apt-get upgrade
Then, install the KVM packages:
sudo apt -y install bridge-utils cpu-checker libvirt-clients libvirt-daemon libvirt-daemon-system virtinst qemu qemu-kvm
Checking virtualization availability
First of all, you need to verify if your CPU supports virtualization. In this case, we are checking if your processor (Intel or AMD) indicates that it have virtualization technology (i.e. if its more than zero, it supports).
egrep -c '(vmx|svm)' /proc/cpuinfo
To make sure that KVM VM can run in the system:
kvm-ok
# Expected output: INFO: /dev/kvm exists \ KVM acceleration can be used
Adjusting KVM to work
Add your user to the libvirtand kvmgroups:
sudo usermod -aG libvirt $USER
sudo usermod -aG kvm $USER
Start libvirtdservice:
sudo systemctl enable --now libvirtd
Creating a Ubuntu 22.04 VM
Create the repository where the VM’s images will be stored:
sudo mkdir -p /var/kvm/images
Create the VM, changing specifications as demanded:
sudo virt-install \
--name vm_name \
--ram 2048 \
--disk path=/var/kvm/images/vm_name.img,size=30 \
--vcpus 2 \
--os-variant ubuntu22.04 \
--network network=default \
--graphics none \
--console pty,target_type=serial \
--location /home/ubuntu-22.04-live-server-amd64.iso,kernel=casper/vmlinuz,initrd=casper/initrd \
--extra-args 'console=ttyS0,115200n8'
[NOTE:] To other values to
os-variantinstalllibosinfo-binand execute:osinfo-query os
Now, if all is correct you should be able to see VM here.
sudo virsh list --all
Useful commands
sudo virsh <command> <vm_name>
Available commands:
- start: Starts VM
- shutdown: Turns off VM
- destroy: Force VM to shutoff
- undefine: deletes VM’s domain
- console: Access VM’s console (just one session allowed)
- edit: Allows to modify VM’s yaml file
Virtual network commands
The same commands work for the virtual network, adding “net-” before command, just like the follow:
sudo virsh net-<command> <net_name>
You can also use net-list to list all available networks.
sudo virsh net-list
Creating a new disk
Creates a new disk:
qemu-img create -f qcow2 /path/to/new/disk.qcow2 10G
Attributes the disk to the virtual machine:
virsh attach-disk <vm_name> /path/to/new/disk.qcow2 vdb --cache none --subdriver qcow2 --persistent
Creating a new interface
To list VM network interfaces:
sudo virsh domiflist <vm_name>
To create a new interface:
sudo virsh attach-interface --domain <vm_name> --type bridge --source br0 --model virtio --config --live
Here is a an example of a interface in the VM file:
<interface type='bridge'>
<mac address='52:54:00:3f:b9:0a'/>
<source bridge='br-mgmt'/>
<target dev='vnet0'/>
<model type='virtio'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</interface>
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