Editing Kernel-based Virtual Machine (KVM)

[[wikipedia:Kernel-based_Virtual_Machine|Kernel-based Virtual Machine]] (KVM) ([[2007]]) is a [[virtualization]] module in the Linux kernel that allows the kernel to function as a hypervisor. KVM support dynamic memory management<ref>https://www.linux-kvm.org/page/FAQ#Is_dynamic_memory_management_for_guests_supported.3F</ref> and [[Live Migration]]<ref>https://www.linux-kvm.org/page/Migration</ref> since [[2007]] ([[Linux Kernel changelog|kernel version 2.6.20]]), 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 [[Red Hat Virtualization|RHV]] with unlimited VM.<ref>https://www.redhat.com/en/topics/virtualization/what-is-KVM</ref> 

<code>[[systemd-cgtop]]</code> can be used for showing [[control group]]s resource utilization.

== Basic KVM commands ==


=== Config files and directories ===
* <code>/etc/[[libvirt]]/[[qemu]]</code>
* <code>/etc/[[libvirt]]/[[qemu.conf]]</code>
* <code>/etc/libvirt/[[virtlogd.conf]]</code>
* <code>/var/lib/libvirt/images/</code>

=== Information ===
* Show information by pool: <code>[[virsh pool-info]] YOUR_POOL_NAME</code>
* <code>[[virsh pool-list]]</code>
* <code>[[virsh guestinfo]]</code>

=== Operations ===
* Editing Virtual Machine configuration: <code>[[virsh edit]] $VM_ID</code>
* Create VM_MACHINE: <code>[[virsh define]] [[MY_XML_VM_DEFINITION.XML]]</code><ref>https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/virtualization_administration_guide/section-libvirt-dom-xml-example</ref>
* Modifying [[CPU]]s: <code>virsh setvcpus $VM_NAME ([--maximum] [[--config] [--live] | [--current]])</code>  // Can be live or offline in the next reboot <ref>http://wiki.stoney-cloud.org/wiki/VM_CPU_Hotplug</ref>
** To check vcpu info: <code>[[virsh vcpuinfo]] $VM_NAME</code>
* Modifying Memory: <code>[[virsh setmem]] <vm_name> <memsize></code>
* Connection by console: <code>virsh console VM_NAME</code>. See also: <code>[[virt-manager]]</code>
* Clone a virtual machine: <code>virt-clone</code>
* Create image: <code>[[qemu-img]] create</code>
* Resize image: <code>[[qemu-img]] resize</code>
* Create domain/virtual machine: <code>[[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</code>
* <code>[[virsh migrate]]</code>

=== Monitoring ===
* <code>[[virsh domstate]]</code>
* <code>[[virsh domstats]]</code>

=== [[KVM Networking]] ===
* <code>[[virsh net-list]]</code>
* <code>[[virsh net-info]] YOUR_NET_NAME</code>
* <code>virsh net-destroy YOUR_NET_NAME</code>
See also: [[MacVTap]], virbr0, ovirtmgmt, [[virtio]]<ref>https://wiki.libvirt.org/page/Virtio</ref> and <code>[[brctl]]</code>. 

==== Activities ====
# Read KVM Network Performance - Best Practices and Tuning Recommendations <ref>https://www.ibm.com/support/knowledgecenter/en/linuxonibm/liaag/wkvm/l0wkvm00_2016.htm</ref>
# 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:
::<code>[[virsh pool-list]]</code><ref>http://manpages.ubuntu.com/manpages/precise/man1/virsh.1.html#storage%20pool%20commands</ref>
::<code>virsh pool-list --all</code>
* Show information by pool: <code>[[virsh pool-info]] YOUR_POOL_NAME</code>
* List Volumes from a pool: <code>[[virsh vol-list]] YOUR_POOL_NAME</code>
* Create pool:(RHEL 6 documentation <ref>https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/virtualization_administration_guide/sect-virtualization-storage_pools-creating-local_directories-virsh</ref>)
<pre>
    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
</pre>
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
::<code>virsh vol-create-as --format qcow2 --capacity VM_DISK_SIZE --pool VM_STORAGE_POOL_NAME --name VM_SERVER_NAME.qcow2</code>

=== Snapshots <ref>http://manpages.ubuntu.com/manpages/xenial/man1/virsh.1.html#snapshot%20commands</ref> ===
Snapshots can be offline or live and internal or external:
* RedHat recommend using external snapshots using <code>virsh snapshot-create-as</code> command. <ref>https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-managing_guests_with_the_virtual_machine_manager_virt_manager-managing_snapshots</ref>
* Live snapshot are not supported in [[Red Hat Enterprise Linux|RHEL]] 8<ref>https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/configuring_and_managing_virtualization/index</ref>

* List snapshots:<code>virsh snapshot-list $DOMAIN</code><ref>https://www.cyberciti.biz/faq/how-to-create-create-snapshot-in-linux-kvm-vmdomain/</ref>
* Create snapshot: <code>virsh snapshot-create-as --domain {VM-NAME} --name "{SNAPSHOT-NAME}"</code>
* Revert snapshot: <code>virsh snapshot-revert --domain YOUR_DOMAIN --snapshotname YOUR_SNAPSHOT_NAME --running</code>

* Snapshots with blockcommit<ref>https://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit</ref> and blockpull<ref>https://kashyapc.wordpress.com/2013/01/22/live-backup-with-external-disk-snapshots-and-libvirts-blockpull/</ref>

== Hybernate VM ==
* <code>[[virsh save]]</code>

== Performance ==
* <code>[[systemd-cgtop]]</code> can be used for showing control groups resource utilization.


== KVM [[timeline]] ==
* 2013 KVM virtual machine in [[ARM]] architecture [[Linux Kernel 3.9]] in April 2013
* [[2009]] [[RHV]]
* [[2007]] [[Live Migration]] support

== Activities ==
=== General ===
# [[Install KVM in an Ubuntu Server]] following https://help.ubuntu.com/community/KVM/Installation instructions.
# Connect to KVM using [[Virt Manager]] (<code>brew install [[virt-manager]]</code> <ref>https://help.ubuntu.com/community/KVM/VirtManager</ref>
# Create a KVM virtual machine with Ansible: [[ovirt-RHV module]]
# Read about raw files and [[qcow2]] differences: https://www.berrange.com/posts/2017/02/10/the-surprisingly-complicated-world-of-disk-image-sizes/
# Read StackOverflow most popular questions https://stackoverflow.com/questions/tagged/kvm?tab=Votes
* [[Virt-install Windows]]: [[Install virtio-win]]

=== 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<ref>https://www.berrange.com/posts/2016/05/12/analysis-of-techniques-for-ensuring-migration-completion-with-kvm/</ref>.
* [[Offline Migrate or move a virtual machine between two KVM servers without shared storage]]<ref>https://serverfault.com/questions/434064/correct-way-to-move-kvm-vm</ref>: <code>[[virsh dumpxml]]</code> and <code>[[virsh define]]</code>
* Recover a VM using <code>[[virt-rescue]]</code>


[[Backup]]:
* [[Create Live backups]] using <code>[[virsh blockcommit]]</code>
* Review [[Bacula]] Enterprise KVM plugin: http://www.bacula.lat/kvm-plugin-bacula-enterprise-quick-guide/?lang=en
* Review [[Bacula]] solution with <code>bpipe</code>: http://www.bacula.lat/kvm-hot-online-virtual-machines-backup-with-bacula-bpipe/?lang=en
* Review Veritas [[Netbackup]] support for [[Red Hat Virtualization|RHV]]

== Related terms ==
* [[Avi Kivity]]
* [[VM-Exits]]
* [[Amazon Firecracker]]
* [[MacVTap]] device driver
* [[Ansible]] [[ovirt-RHV module]] (ovirt_vm)
* [[KubeVirt]]
* [[QEMU Logs]]
* [[OVirt]] and [[RHV]]
* [[/dev/kvm]]
* [[vhost_net]] kernel module

== See also ==
* {{virtinst}}
* {{virt}}
* {{virt-manager}}
* {{libvirtd}}
* {{QEMU}}
* {{KVM}}
* {{Virtualization}}




[[Category:Virtualization]]

{{CC license}} 
Source: https://en.wikiversity.org/wiki/KVM