· virtualization openvswitch

Installing KVM & OVS on Ubuntu

KVM & OpenvSwitch are technologies I’ve wanted to learn for a while now. I think it’ll really help my understanding and knowledge of Linux and the underlying mechanics of virtualisation and how it interacts with the physical network.

Installing KVM is already well documented here, but for completeness here is my installation process:

First, update, and check your hardware can support virtualisation.

$ sudo apt-get -y update
$ egrep -c '(vmx|svm)' /proc/cpuinfo
$ kvm-ok
INFO: /dev/kvm exists
KVM acceleration can be used

egrep is like grep, a command that prints out any line with the given regular expression. So, here we’re searching the cpuinfo file for any lines containing vmx or svm. vmx is the flag that virtualisation is enabled in the BIOS for Intel CPUs & svm is the same for AMD CPUs. The -c option is for count, so here we only print out the number of lines that match, rather than the lines themselves. So, a result of 1 or more means virtualisation is enabled. Here, I’ve got 8 lines in the cpuinfo file matching vmx. If you do get a 0, reboot your computer, go into the BIOS menu and make sure you’ve got virtualisation enabled.

The kvm-ok program verifies whether your machine is able to run KVM virtual machines. It actually checks the cpuinfo file, like we did in the previous command. It also checks whether the kernel has detected the CPUs Virtualisation Technology (VT) capability, and looks to see if /dev/kvm exists.

The capabilities exist, so let’s install KVM.

$ sudo apt-get install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils virtinst

From the Ubuntu pages:

Ensure the user is added to the libvirtd & kvm groups.

$ sudo adduser `id -un` libvirtd && sudo adduser `id -un` kvm
The user `rob' is already a member of `libvirtd'.
The user `rob' is already a member of `kvm'.

I found it was good to do a reboot here, just to make sure this membership is in effect.

Verify the installation. When we get round to installing some VMs, they should show up in this list.

$ virsh -c qemu:///system list
Id Name State

And we’re all set.

On a separate machine, I’ve set up a Xubuntu VM, and installed Virtual Machine Manager (VMM), just to give me a visual understanding of my VMs if need be.

$ sudo apt-get install virt-manager

VMM is super simple and intuitive. I love using the command line, but I still find having visual cues really helps my understanding of a situation, too much time in Windows & vSphere perhaps!

For the OpenvSwitch installation I pretty faithfully followed Scott Lowe’s example, with a couple of differences.

Right, let’s get up-to-date, as per.

$ sudo apt-get -y update && sudo apt-get -y dist-upgrade

Make way for OVS by removing the default libvirt bridge.

$ sudo virsh net-destroy default
$ sudo virsh net-autostart --disable default

Remove ebtables, a Linux ethernet firewall.

$ sudo aptitude purge ebtables

Install OpenvSwitch.

$ sudo apt-get install openvswitch-controller openvswitch-switch openvswitch-datapath-source

The openvswitch-brcompat has apparently been removed now from OVS, so it can be ignored. Once that’s finished, try starting OVS, though I found it was already running.

$ sudo service openvswitch-switch start
start: Job is already running: openvswitch-switch

Run the OVS show command, you should just get an empty config.

$ sudo ovs-vsctl show
ovs_version: "2.0.2"

The ovs-vsctl command, according to the man page, is a “utility for querying and configuring ovs-vswitchd”. ovs-vswitchd is, again according to the man page, the daemon that manages and controls the OVS switch(es). As far as I understand it ovs-vsctl queries and configures ovsdb-server (which provides the interface to the OVS databases [man page] ), and ovs-vswitchd then implements the changes. To be honest I’m not entirely sure of this process, I need to spend some more time reading this I think. Anyway, ovs-vsctl show “Prints a brief overview of the database contents.” Of which, currently, we have none.

Now, the OVS bridge has to be created. When I was doing this I was SSH’d into the NIC I was configuring (em1), and creating the bridge brought the interface down. So, either make sure you have physical access to the machine, or SSH into another NIC.

$ sudo ovs-vsctl add-br br0
$ sudo ovs-vsctl add-port br0 em1

Run the show command again, and we should have a configuration.

$ sudo ovs-vsctl show
Bridge "br0"
Port "em1"
Interface "em1"
Port "br0"
Interface "br0"
type: internal
ovs_version: "2.0.2"

Now, the interfaces need to be configured.

$ sudo vim /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto em1
iface em1 inet static

# The OVS bridge interface
auto br0
iface br0 inet static
dns-search test.local
bridge_ports em1
bridge_fd 9
bridge_hello 2
bridge_maxage 12
bridge_stp off

This is just a copy of Scott’s configuration, with my network details in it. At this point I rebooted the server and ran ifconfig em1 up which brought my interface back up and I was able to SSH back into the machine.

Where the result of ifconfig was previously…

$ ifconfig
em1 Link encap:Ethernet HWaddr a4:ba:db:4d:0f:82
inet addr: Bcast: Mask:
RX packets:74620 errors:0 dropped:0 overruns:0 frame:0
TX packets:2094 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:7873976 (7.8 MB) TX bytes:216238 (216.2 KB)

is now…

$ ifconfig
br0 Link encap:Ethernet HWaddr a4:ba:db:4d:0f:82
inet addr: Bcast: Mask:
inet6 addr: fe80::a6ba:dbff:fe4d:f82/64 Scope:Link
RX packets:73075 errors:0 dropped:257 overruns:0 frame:0
TX packets:2101 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:6283264 (6.2 MB) TX bytes:199006 (199.0 KB)

em1 Link encap:Ethernet HWaddr a4:ba:db:4d:0f:82
RX packets:74620 errors:0 dropped:0 overruns:0 frame:0
TX packets:2094 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:7873976 (7.8 MB) TX bytes:216238 (216.2 KB)

So, I’m actually connecting to the bridge interface rather than the NIC.

Hopefully, this is just the beginning of an interesting adventure, in the meantime I’m going to read this again.

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