KVM: Difference between revisions

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[https://www.linux-kvm.org/page/Main_Page KVM] is an open source virtualization solution in a kernel module. KVM can virtualize x86, PowerPC, and S390 guests.
[https://www.linux-kvm.org/page/Main_Page KVM] is an free and open source virtualization solution in a kernel module. Although it is often simply referred to as KVM, the actual hypervisor is [https://www.qemu.org QEMU]. QEMU runs from user-space, but can integrate with KVM, providing better performance by leveraging the hardware from kernel-space. QEMU can virtualize x86, PowerPC, and S390 guests, amongst others. [https://libvirt.org Libvirt] is a management framework that integrates with QEMU/KVM, [https://wiki.alpinelinux.org/wiki/LXC LXC], [https://wiki.alpinelinux.org/wiki/Xen_Dom0 Xen] and others.


== Installation ==
The following commands provide '''libvirt''' as well as '''QEMU with emulation for x86_64''' and '''qemu-img''', a necessary component for using various disk formats such as qcow2. Without qemu-img, only raw disks are available. It can also convert images between several formats like vhdx and vmdk.
{{Cmd|<nowiki># apk add libvirt-daemon qemu-img qemu-system-x86_64
# rc-update add libvirtd</nowiki>}}


= Installing KVM =
== Networking ==
It is possible to install just qemu and libvirt for local management, but most users will probably want libvirt-deamon and/or virt-manager for a GUI.  
By default, libvirt uses NAT for VM connectivity. If you want to use the default configuration, you need to load the tun module.
{{Cmd|sudo apk add qemu-system-x86_64 libvirt
{{Cmd|# modprobe tun}}
sudo apk add libvirt-daemon dbus}}


Enable the KVM kernel module
If you prefer bridging a guest over your Ethernet interface, you need to make a [https://wiki.alpinelinux.org/wiki/Bridge#Configuration_file bridge].
{{Cmd|sudo modprobe kvm-intel}}
or
{{Cmd|sudo modprobe kvm-amd}}


It's quite common to use bridges with KVM environments but when IPv6 is used, Alpine will assign itself a link-local address as well as an SLAAC address in case there's a router sending Router Advertisements. You don't want this because you don't want to have the KVM host an IP address in every network it serves to guests. Unfortunately you cannot just disable IPv6 for the bridge via sysctl because it might not be up at boottime when sysctl fires. There's a workaround though which is to put a post-up hook into the /etc/network/interfaces file like this:
auto brlan
iface brlan inet manual
        bridge-ports eth1.5
        bridge-stp 0
        post-up ip -6 a flush dev brlan; sysctl -w net.ipv6.conf.brlan.disable_ipv6=1


Add your user to the follwing groups so you can mange the vms
== Management ==
{{Cmd|sudo addgroup user kvm
For (non-root) management, you will need to add your user to the libvirt group.
sudo addgroup user qemu
{{Cmd|# addgroup user libvirt}}
sudo addgroup user libvirt}}


You can use libvirt's virsh on the CLI. It can execute commands as well as run as an interactive shell. Read its manual page and/or use the "help" command for more info. Some basic commands are:
{{Cmd|<nowiki>virsh help
virsh list --all
virsh start $domain
virsh shutdown $domain</nowiki>
}}
The libvirt project provides a GUI for managing hosts, called virt-manager. It handles local systems as well as remote ones via SSH.
{{Cmd|<nowiki># apk add dbus polkit virt-manager
# rc-update add dbus</nowiki>}}
In order to use libvirtd to remotely control KVM over ssh PolicyKit needs a .pkla informing it that this is allowed.
Write the following file to /etc/polkit-1/localauthority/50-local.d/50-libvirt-ssh-remote-access-policy.pkla
{{Cmd|<nowiki>[Remote libvirt SSH access]
Identity=unix-group:libvirt
Action=org.libvirt.unix.manage
ResultAny=yes
ResultInactive=yes
ResultActive=yes</nowiki>
}}


[[Category:Virtualization]]
[[Category:Virtualization]]

Revision as of 11:09, 2 March 2020

KVM is an free and open source virtualization solution in a kernel module. Although it is often simply referred to as KVM, the actual hypervisor is QEMU. QEMU runs from user-space, but can integrate with KVM, providing better performance by leveraging the hardware from kernel-space. QEMU can virtualize x86, PowerPC, and S390 guests, amongst others. Libvirt is a management framework that integrates with QEMU/KVM, LXC, Xen and others.

Installation

The following commands provide libvirt as well as QEMU with emulation for x86_64 and qemu-img, a necessary component for using various disk formats such as qcow2. Without qemu-img, only raw disks are available. It can also convert images between several formats like vhdx and vmdk.

# apk add libvirt-daemon qemu-img qemu-system-x86_64 # rc-update add libvirtd

Networking

By default, libvirt uses NAT for VM connectivity. If you want to use the default configuration, you need to load the tun module.

# modprobe tun

If you prefer bridging a guest over your Ethernet interface, you need to make a bridge.

It's quite common to use bridges with KVM environments but when IPv6 is used, Alpine will assign itself a link-local address as well as an SLAAC address in case there's a router sending Router Advertisements. You don't want this because you don't want to have the KVM host an IP address in every network it serves to guests. Unfortunately you cannot just disable IPv6 for the bridge via sysctl because it might not be up at boottime when sysctl fires. There's a workaround though which is to put a post-up hook into the /etc/network/interfaces file like this:

auto brlan
iface brlan inet manual
       bridge-ports eth1.5
       bridge-stp 0
       post-up ip -6 a flush dev brlan; sysctl -w net.ipv6.conf.brlan.disable_ipv6=1

Management

For (non-root) management, you will need to add your user to the libvirt group.

# addgroup user libvirt

You can use libvirt's virsh on the CLI. It can execute commands as well as run as an interactive shell. Read its manual page and/or use the "help" command for more info. Some basic commands are:

virsh help virsh list --all virsh start $domain virsh shutdown $domain

The libvirt project provides a GUI for managing hosts, called virt-manager. It handles local systems as well as remote ones via SSH.

# apk add dbus polkit virt-manager # rc-update add dbus

In order to use libvirtd to remotely control KVM over ssh PolicyKit needs a .pkla informing it that this is allowed. Write the following file to /etc/polkit-1/localauthority/50-local.d/50-libvirt-ssh-remote-access-policy.pkla

[Remote libvirt SSH access] Identity=unix-group:libvirt Action=org.libvirt.unix.manage ResultAny=yes ResultInactive=yes ResultActive=yes