Setting Up Virtual Machines with KVM and QEMU on Debian

Introduction

Virtualization has become an essential tool for developers, system administrators, and tech enthusiasts. It allows you to run multiple operating systems on a single physical machine, providing flexibility, isolation, and efficient resource utilization. In this comprehensive guide, we'll explore how to set up and manage virtual machines using KVM (Kernel-based Virtual Machine) and QEMU on Debian Linux.

Prerequisites

Before we begin, make sure you have:

• A Debian-based system (this guide uses Debian 11 Bullseye)
• Root or sudo access
• Basic familiarity with the Linux command line

Installing KVM and QEMU

Let's start by installing the necessary packages:

sudo apt update
sudo apt dist-upgrade -y
sudo apt install qemu-system libvirt-clients libvirt-daemon-system

After installation, reboot your system to ensure all changes are applied:

sudo reboot

Setting Up Network Bridge

Creating a network bridge allows your virtual machines to communicate with the host system and the outside network. Here's how to set it up:

1. Edit the netplan configuration file:

sudo vim /etc/netplan/01-netcfg.yaml

2. Add the following configuration, adjusting the IP address and interface name as needed:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp1s0:
      dhcp4: no
  bridges:
    br0:
      interfaces: [enp1s0]
      addresses: [192.168.42.50/24]
      gateway4: 192.168.42.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]

3. Apply the changes:

sudo netplan apply

4. Verify the bridge is working:

ip addr show br0
ping -c 4 google.com

Configuring User Permissions

Add your user to the libvirt group to manage virtual machines without sudo:

sudo adduser $USER libvirt

Log out and back in for the changes to take effect.

Installing Additional Packages

Install these packages to enable UEFI support and provide additional utilities:

sudo apt install ovmf qemu-utils virt-install

Creating a Virtual Machine

Now, let's create a script to streamline the VM creation process:

1. Create a directory for scripts:

mkdir ~/scripts

2. Create and edit the VM creation script:

vim ~/scripts/create_vm.sh

3. Add the following content to the script:

#!/bin/bash

sudo virt-install \
  --virt-type kvm \
  --name bbtbvm \
  --location 'https://deb.debian.org/debian/dists/bullseye/main/installer-amd64/' \
  --os-variant debian11 \
  --disk path=/home/$USER/virtual_machines/bbtbvm.qcow2,size=5 \
  --memory 2048 \
  --vcpus 2 \
  --graphics none \
  --console pty,target_type=serial \
  --extra-args 'console=ttyS0,115200n8 serial' \
  --boot uefi \
  --filesystem source=/home/$USER/scripts,target=scripts,mode=mapped \
  --cpu host-passthrough,cache.mode=passthrough \
  --network bridge=br0

4. Make the script executable:

chmod +x ~/scripts/create_vm.sh

5. Create the virtual machines directory:

mkdir ~/virtual_machines

6. Run the script to create the VM:

~/scripts/create_vm.sh

The script will start the VM installation process. Follow the on-screen prompts to complete the Debian installation.

Managing Virtual Machines

Here are some useful commands for managing your virtual machines:

• List all VMs:

virsh list --all

- Start a VM:
```bash
virsh start bbtbvm

• Stop a VM:

virsh shutdown bbtbvm

- Force stop a VM:
```bash
virsh destroy bbtbvm

• Delete a VM:

virsh undefine bbtbvm --nvram

- Connect to a VM's console:
```bash
virsh console bbtbvm

Troubleshooting

If you encounter issues, here are some common troubleshooting steps:

1. Check libvirtd service status:

sudo systemctl status libvirtd

2. Verify KVM module is loaded:
```bash
lsmod | grep kvm

3. Check libvirt logs:

sudo journalctl -u libvirtd

4. Verify network bridge status:
```bash
ip addr show br0

Advanced Configuration

CPU Pinning

CPU pinning can improve performance by assigning specific host CPU cores to the VM:

1. Edit the VM's XML configuration:

virsh edit bbtbvm

2. Add the following within the `<vcpu>` section:
```xml
<vcpu placement='static'>2</vcpu>
<cputune>
<vcpupin vcpu='0' cpuset='2'/>
<vcpupin vcpu='1' cpuset='3'/>
</cputune>

Memory Ballooning

Memory ballooning allows dynamic allocation of host RAM to VMs:

1. Edit the VM's XML configuration:

virsh edit bbtbvm

2. Add the following within the `<devices>` section:
```xml
<memballoon model='virtio'>
<stats period='10'/>
</memballoon>

Storage I/O Tuning

Optimize storage performance with I/O tuning:

1. Edit the VM's XML configuration:

virsh edit bbtbvm

2. Modify the disk section:
```xml
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' cache='none' io='native'/>
<source file='/home/user/virtual_machines/bbtbvm.qcow2'/>
<target dev='vda' bus='virtio'/>
</disk>

Security Considerations

When working with virtual machines, keep these security practices in mind:

1. Keep the host system and all VMs updated regularly.
2. Use strong, unique passwords for each VM.
3. Implement network segmentation to isolate VMs from each other and the host.
4. Use SELinux or AppArmor for additional security layers.
5. Regularly backup both the host system and VMs.
6. Monitor VM resource usage and network traffic for anomalies.

Performance Optimization

To get the best performance out of your virtual machines:

1. Use virtio drivers for network and storage devices.
2. Enable CPU passthrough for near-native performance.
3. Allocate sufficient RAM to prevent swapping.
4. Use SSD storage for VM disks when possible.
5. Avoid overcommitting resources on the host system.

Backup and Recovery

Implement a robust backup strategy for your virtual machines:

1. Use virsh snapshot-create to create VM snapshots.
2. Regularly backup VM disk images using tools like rsync or duplicity.
3. Test your backups by restoring them to a separate host.
4. Document your VM configurations and keep backups of XML files.

Monitoring and Logging

Set up monitoring and logging for your virtual environment:

1. Use virt-top to monitor VM resource usage in real-time.
2. Configure libvirt logging for troubleshooting:

sudo vim /etc/libvirt/libvirtd.conf

Set `log_level = 3` for more verbose logging.
3. Use tools like Prometheus and Grafana for long-term performance monitoring.

## Scaling Your Virtual Environment

As your needs grow, consider these scaling strategies:

1. Implement a centralized storage solution like NFS or Ceph for VM disks.
2. Use configuration management tools like Ansible to automate VM provisioning.
3. Consider migrating to a clustered solution like Proxmox or oVirt for high availability.

## Conclusion

Setting up and managing virtual machines with KVM and QEMU on Debian provides a powerful and flexible virtualization solution. By following this guide, you've learned how to install the necessary components, create and manage VMs, and optimize their performance. As you become more comfortable with these tools, you'll be able to create complex virtual environments tailored to your specific needs.

Remember to stay updated with the latest developments in KVM and QEMU, as new features and optimizations are regularly introduced. Happy virtualizing!

Article created from: https://www.youtube.com/watch?v=Q2OHR-uJMcU