Kernel-based Virtual Machine (KVM)

Description: KVM is “a full virtualization solution for Linux on x86 hardware containing virtualization extensions.” (KVM Main Page) It can be run on the desktop with GUI managers or on a headless server.

Assumptions:

• Some Red Hat based distro is already installed. (CentOS, Scientific, RHEL, etc)
• This page was written using CentOS 6.6 with GNOME desktop (headless KVM is on the to do list!)

2015-02-13: These are rough notes and in progress as I learn KVM.

yum install qemu-kvm python-virtinst virt-top libvirt libvirt-client

CLI Package Explanations

• qemu-kvm ⇒ The main KVM package.
• python-virtinst ⇒ CLI tools and libraries for creating VMs.
• virt-top ⇒ CLI VM stats.
• libvirt ⇒ Toolkit for libvirtd service.
• libvirt-client ⇒ Toolkit for VM clients.

yum install virt-manager virt-viewer

GUI Package Explanations

• virt-manager ⇒ GUI VM administration tool.
• virt-viewer ⇒ GUI local console connection to VMs.

yum install bridge-utils dejavu-lgc-sans-fonts tigervnc xorg-x11-xauth

Packages Descriptions

• bridge-utils ⇒ network bridging to allow the VMs to use the host machine's physical interfaces as a bridge.
• dejavu-lgc-sans-fonts ⇒ Fonts for virt-manager (GUI VM manager)
• tigervnc ⇒ VNC to connect remotely to VM's GUI.
• xorg-x11-xauth ⇒ X11 forwarding through ssh. (Remote virt-manager for headless servers)

• Ensure that the KVM kernel module is loaded

[root@bash ~]# lsmod | grep kvm
kvm_intel              55496  0 
kvm                   337900  1 kvm_intel

• If it is not loaded, attempt to load the module:

modprobe -v kvm

• Start the libvirtd service

service libvirtd start

• Enable libvirtd on system boot

chkconfig libvirtd on

• Verify libvirtd is running successfully (Yes, 3 forward slashes)

service libvirtd status
virsh -c qemu:///system list

By default, VMs will be on a private network with no access to the outside world unless they use a physical host network interface as a bridge.

• Turn off NetworkManager, which does not play nice with bridging.

chkconfig NetworkManager off
service NetworkManager stop

• Ensure the network service is enabled and running.

chkconfig network on
service network start

• Create a bridge interface called “br0” that will use the physical interface “eth0” the easy way.

virsh iface-bridge eth0 br0

This will create the new file “ifcfg-br0” and modify “ifcfg-eth0” to look as follows:

/etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0"
HWADDR="00:04:4B:17:3C:FA"
ONBOOT="yes"
BRIDGE="br0"

/etc/sysconfig/network-scripts/ifcfg-br0

DEVICE="br0"
ONBOOT="yes"
TYPE="Bridge"
BOOTPROTO="dhcp"
STP="on"
DELAY="0"

br0 will be the interface with an IP address. To make it static, simply edit ifcfg-br0 and change it:

DEVICE="br0"
ONBOOT="yes"
TYPE="Bridge"
BOOTPROTO="none"
STP="on"
DELAY="0"
IPADDR="192.168.0.100"
NETMASK="255.255.255.0"
GATEWAY="192.168.0.1"
DNS1="208.67.222.222"
DNS2="208.67.220.220"

Note: Those DNS entries are for OpenDNS.

• Enable ip forwarding

Edit /etc/sysctl.conf

inet.ipv4.ip_forward = 1

• Apply settings

sysctl -p /etc/sysctl.conf

• Restart the network service

service network restart

If SELinux is on and in Enforcing mode, there is additional configuration if you change the default directory for VM images.

Check if SELinux is on/enabled

[bash]# sestatus
SELinux status:                 enabled
SELinuxfs mount:                /selinux
Current mode:                   enforcing

Default VM Image directory: /var/lib/libvirt/images/

• Create the directory

mkdir /vm-images

• Install the following package to enable use of the “semanage” utility.

yum install policycoreutils-python

• Set security context for the vm-images directory and everything that is created under it.

semanage fcontext -a -t virt_image_t "/vm-images(/.*)?"

• Restore the security context (I don't know why you have to do this yet…but you do)

restorecon -R /vm-images

• Verify

ls -Z /vm-images

VMs can be installed via a command line tool (virt-install) or a GUI (virt-manager).

virt-install has many options, see them with “virt-install –help”.

Common options:

General Options
--name=NAME  (Name of the guest)
--ram=MEMORY  (Memory in megabytes)
--vcpus=VCPUS  (Number of vcpus)
 
Installation Method
--cdrom=CDROM  (CD-ROM installation media, can be ISO or physical cd-rom drive)
--location=LOCATION  (Installation source via http, ftp, or nfs.)
--pxe  (Boot from network using PXE)
--extra-args "ks=http://myserver/mykickstartfile.ks"  (Path to kickstart file for automated installs)
 
Storage Configuration
--disk=DISKOPTS  (Storage with different options)
  --disk path=/my/existing/disk 
  --disk path=/my/new/disk,size=10 (in GB)
 
Network
--network bridge=br0  (Guest network interface)
 
Graphics
--graphics=GRAPHICS  (Guest display settings)
  --graphics vnc  (Default if DISPLAY environment variable is set)
  --graphics none  (Default if DISPLAY environment variable is not set)

Install a VM called “centos1”, create a 20GB hard drive, 1 CPU, 1GB ram, point it to the iso, have it use the network interface “br0”

virt-install \
--name=centos1 \
--disk path=/vm-images/centos1.img,size=20 \
--vcpus=1 --ram=1024 \
--cdrom=/vm-images/CentOS-6.6-x86_64-netinstall.iso \
--network bridge=br0

After the VM is created, if you are using the “–graphics vnc” option (either by default or explicitly), a console is opened up for interactive install.

If you close it, this is how you can connect back to the guest:

• Method 1: Connect directly to the guest console

Example connect to the guest named “centos1” (Yes, that is 3 slashes)

virt-viewer --connect qemu:///system centos1

• Method 2: Open virt-manager

Example open virt-manager and then the VM “centos1”

virt-manager

• Select the VM
• Click “Open”

Proceed with installation as normal.

Installing locally via a GUI.

• Open a terminal and type:

virt-manager

• The virt-manager GUI will open.
• Select the name of the host (probably “localhost (QEMU)”)
• Click the “Create a New Virtual Machine” button (the monitor with a play button on it)
  • Step 1 ⇒
    • Name: Name the virtual machine
    • Choose how to install: Select the install method
  • Step 2 ⇒
    • Browse for the media
    • OS Type/Version: Optionally, select the OS type and version
  • Step 3 ⇒
    • Memory/CPU: Select memory and CPU.
  • Step 4 ⇒
    • Storage: Create or use existing storage
  • Step 5 ⇒
    • Ready to install: Confirm settings, set advanced options such as Host network device.