KVM: Explanation & Insights

Kernel-based Virtual Machine (KVM) is a full hardware virtualization solution which allows you to turn your Linux server into a hypervisor, enabling it to host multiple, isolated virtual machines (VMs). It integrates with the Linux kernel and leverages the hardware virtualization features included in many modern CPUs.

How KVM Works

KVM consists of a loadable kernel module that provides the core virtualization infrastructure and a processor-specific module. Once loaded, the KVM module turns the Linux kernel into a hypervisor, an underpinning technology that allows multiple operating systems to share a single hardware host. A user space program, QEMU, works alongside KVM to run multiple operating systems and their applications as if they were standalone machines, isolated from each other.

Importance of KVM

KVM allows for greater efficiency in computing resource usage by creating multiple virtual servers on a single physical server. This leads to cost savings, as fewer physical servers are required, and it enhances the flexibility of system resources, allowing you to allocate as needed.

Typical Problems with KVM

While KVM has many advantages, it isn't without its challenges. Users may face issues with VM network configurations, or difficulties setting up bridged networking. Additionally, getting VMs to use hardware directly can be tricky.

Linux Commands for KVM

Several Linux commands are used when working with KVM. The virt-install command is used to create new VMs, while virsh is a utility for managing and monitoring VMs. The virt-viewer command is used to display the graphical console for a VM. For example:

sudo virt-install \
--name test_vm \
--ram 1024 \
--disk path=/var/lib/libvirt/images/test_vm.img,size=8 \
--vcpus 1 \
--os-type linux \
--network bridge:virbr0 \
--graphics none \
--console pty,target_type=serial \
--location 'http://us.archive.ubuntu.com/ubuntu/dists/xenial/main/installer-amd64/' \
--extra-args 'console=ttyS0,115200n8 serial'

This command will create a new VM with 1GB of RAM, one CPU, and 8GB of storage.

Bash Examples for KVM

To list all the running VMs, you can use the virsh list command:

virsh list --all

If you want to start a VM, use the virsh start command followed by the VM name:

virsh start test_vm

Conclusion

KVM is a powerful tool for managing virtual machines on a Linux server. It provides a high degree of control and flexibility, allowing you to make the most of your server resources.