Kernel-based Virtual Machine (KVM)

Kernel-based Virtual Machine (KVM) is a virtualization module in the Linux kernel that allows the kernel to function as a hypervisor. KVM support dynamic memory management and Live Migration since 2007 among other features.

KVM is included in all mayor distribution including Ubuntu and RHEL (RedHat), RedHat provides 2 version of KVM, the one included with RHEL which allows to run up to 4 VM or the one included with RHV with unlimited VM.

systemd-cgtop can be used for showing control groups resource utilization.

Basic KVM commands

Config files and directories

/etc/libvirt/qemu

Information

• Show information by pool: virsh pool-info YOUR_POOL_NAME
• virsh pool-list
• virsh guestinfo

Operations

• Editing Virtual Machine configuration: virsh edit $VM_ID
• Create VM_MACHINE: virsh define /MY_XML_VM_DEFINITION.XML/
• Modifying CPUs: virsh setvcpus $VM_NAME ([--maximum] [[--config] [--live] | [--current]]) // Can be live or offline in the next reboot
  • To check vcpu info: virsh vcpuinfo $VM_NAME
• Modifying Memory: virsh setmem <vm_name> <memsize>
• Connection by console: virsh console VM_NAME. See also: virt-manager
• Clone a virtual machine: virt-clone
• Create image: qemu-img create
• Resize image: qemu-img resize
• Create domain/virtual machine: virt-install --autostart --check all=on --name VM_DOMAIN_NAME --memory VM_MEMORY_SIZE --vcpus VM_VCPUs --os-variant ubuntu18.04 --cdrom VM_INSTALLATION_MEDIA --disk /path/to/VM_STORAGE_POOL_NAME/VM_DOMAIN_NAME.qcow2 --noautoconsole --wait VM_CREATION_WAIT_TIME --network VM_NETWORK_SETTINGS
• virsh migrate

Monitoring

• virsh domstate
• virsh domstats

KVM Networking

• virsh net-list
• virsh net-info YOUR_NET_NAME
• virsh net-destroy YOUR_NET_NAME

See also: MacVTap, virbr0, ovirtmgmt, virtio and brctl.

Activities

1. Read KVM Network Performance - Best Practices and Tuning Recommendations
2. Learn about KVM Host Networking Configuration Choices https://www.ibm.com/support/knowledgecenter/en/linuxonibm/liaag/wkvm/wkvm_c_net.htm

Storage

File based (raw or qcow2) or block based.

• List Storage pools:

virsh pool-list

virsh pool-list --all

• Show information by pool: virsh pool-info YOUR_POOL_NAME
• List Volumes from a pool: virsh vol-list YOUR_POOL_NAME
• Create pool:(RHEL 6 documentation )

    virsh pool-define-as --name YOUR_POOL_NAME --type dir --target /your/path/YOUR_POOL_NAME/ 
    virsh pool-build YOUR_POOL_NAME
    virsh pool-start YOUR_POOL_NAME
    virsh pool-autostart YOUR_POOL_NAME

See also: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-managing_guest_virtual_machines_with_virsh-storage_pool_commands

• Create volume

virsh vol-create-as --format qcow2 --capacity VM_DISK_SIZE --pool VM_STORAGE_POOL_NAME --name VM_SERVER_NAME.qcow2

Snapshots

Snapshots can be offline or live and internal or external:

• RedHat recommend using external snapshots using virsh snapshot-create-as command.
• Live snapshot are not supported in RHEL 8

• List snapshots:virsh snapshot-list $DOMAIN
• Create snapshot: virsh snapshot-create-as --domain {VM-NAME} --name "{SNAPSHOT-NAME}"
• Revert snapshot: virsh snapshot-revert --domain YOUR_DOMAIN --snapshotname YOUR_SNAPSHOT_NAME --running

• Snapshots with blockcommit and blockpull

Hybernate VM

• virsh save

Performance

• systemd-cgtop can be used for showing control groups resource utilization.

Activities

General

1. Install KVM in an Ubuntu Server following https://help.ubuntu.com/community/KVM/Installation instructions.
2. Connect to KVM using Virt Manager (brew install virt-manager
3. Create a KVM virtual machine with Ansible: DevOps/Ansible/ovirt-RHV module
4. Read about raw files and qcow2 differences: https://www.berrange.com/posts/2017/02/10/the-surprisingly-complicated-world-of-disk-image-sizes/

Snapshots

• Read KVM virsh external vs internal snapshots: https://rentry.co/644h6
• Read RedHat recommendations: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-Troubleshooting-Workaround_for_creating_external_snapshots_with_libvirt
• Read this guide about handling snapshots: https://www.cyberciti.biz/faq/how-to-create-create-snapshot-in-linux-kvm-vmdomain/

Advanced

• Extend LVM on qcow2 images: https://www.technomenace.com/2014/08/how-to-extend-lvm-on-qcow2-images/
• Live Migrate a machine between two servers.
• Offline Migrate or move a virtual machine between two KVM servers without shared storage: virsh dumpxml and virsh define

Backup:

• Create Live backups using virsh blockcommit
• Review Bacula Enterprise KVM plugin: http://www.bacula.lat/kvm-plugin-bacula-enterprise-quick-guide/?lang=en
• Review Bacula solution with bpipe: http://www.bacula.lat/kvm-hot-online-virtual-machines-backup-with-bacula-bpipe/?lang=en
• Review Veritas Netbackup support for RHV

See also

• virtinst (package): virt-install, virt-clone, virt-convert and virt-xml
• libguestfs-tools: virt-sysprep, virt-clone, virt-builder, virt-customize, virt-resize, virt-rescue, virt-sparsify, guestmount, guestfish, virt-inspector, virt-cat, virt-log, virt-df, virt-ls, virt-filesystems, virt-list-filesystems, virt-edit
• virt-manager (virsh console VM_NAME)
• MacVTap device driver
• virt-sysprep
• Ansible ovirt-RHV module (ovirt_vm)

https://docs.ansible.com/ansible/latest/modules/ovirt_vm_module.html#ovirt-vm-module

• Amazon Firecracker
• QEMU: qemu-img, qemu-ga, qemu.conf, virsh qemu, QEMU guest agent (qemu-ga), qcow2, qemu-nbd, qemu-img map, qemu-io, /etc/libvirt/qemu.conf, QEMU releases, VENOM, qemu-nbd --help, qemu-system
• KVM, Installation, QEMU, virsh, virtinst, libguestfs-tools, libvirt, qemu, Red Hat Virtualization (RHV), MacVTap, Virtio, oVirt, KVM services, KVM networking, KVM graphics, CPU, KVM on ARM
• Virtualization: KVM, VirtualBox, multipass, containers, Vagrant, Packer, Hyper-V, VMware, Parallels, Bhyve, Virtual machine
• Kata containers
• KVM services

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Source: https://en.wikiversity.org/wiki/KVM