Automate KVM on Arch Linux

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Introduction

This is a tutorial on how to automate the setup of VMs using KVM on Arch Linux. This tutorial uses QEMU as a back-end for KVM and libvirt, Packer and Vagrant.

This tutorial is meant as a supplement to my OVH: Custom Installation tutorial

Installation

Before getting started there are a few packages that will be needed to set all of this up.

# pacaur -S libvirt openssl-1.0 packer-io qemu-headless qemu-headless-arch-extra vagrant

vagrant-libvirt

The libvirt plugin installation for vagrant requires some cleanup first.

# sudo mv /opt/vagrant/embedded/lib/libcurl.so{,.backup} # sudo mv /opt/vagrant/embedded/lib/libcurl.so.4{,.backup} # sudo mv /opt/vagrant/embedded/lib/libcurl.so.4.4.0{,.backup} # sudo mv /opt/vagrant/embedded/lib/pkgconfig/libcurl.pc{,backup}

Then build the plugin.

# vagrant plugin install vagrant-libvirt

Hugepages

Enabling hugepages can improve the performance of virtual machines. First add an entry to the fstab, make sure to first check what the group id of the group kvm is.

# grep kvm /etc/group # sudoedit /etc/fstab

filename: /etc/fstab

hugetlbfs /dev/hugepages hugetlbfs mode=1770,gid=999 0 0

Instead of rebooting, remount instead.

# sudo umount /dev/hugepages # mount /dev/hugepages

This can then be verified.

# sudo mount | grep huge # ls -FalG /dev/ | grep huge

Now to set the number of hugepages to use. For this one has to do a bit of math, for each gigabyte of the system RAM that you want to use for VMs you divide the size in megabytes by two.

On my setup I will dedicated 12GB out of the 16GB of system RAM to VMs. This means (12 * 1024) / 2 or 6144

Set the number of hugepages.

# echo 6144 | sudo tee /proc/sys/vm/nr_hugepages

Also set this permanently by adding a file to /etc/sysctl.d.

filename: /etc/sysctl.d/40-hugepages.conf

vm.nr_hugepages = 6144

Again verify the changes.

# grep HugePages_Total /proc/meminfo

KVM User

Finally create a user for KVM.

# sudo useradd -g kvm -s /usr/bin/nologin kvm

Then modify the libvirt QEMU config to reflect this.

filename: /etc/libvirt/qemu.conf

user = "kvm" group = "kvm"