Virtualization With KVM On A CentOS 5.2 Server

This guide explains how you can install and use KVM for creating and running virtual machines on a CentOS 5.2 server. I will show how to create image-based virtual machines and also virtual machines that use a logical volume (LVM). KVM is short for Kernel-based Virtual Machine and makes use of hardware virtualization, i.e., you need a CPU that supports hardware virtualization, e.g. Intel VT or AMD-V.

I do not issue any guarantee that this will work for you!


1 Preliminary Note

I'm using a CentOS 5.2 server with the hostname server1.example.com and the IP address 192.168.0.100 here as my KVM host.

We also need a desktop system where we install virt-manager so that we can connect to the graphical console of the virtual machines that we install. I'm using an Ubuntu 8.10 desktop here.


2 Installing KVM

CentOS 5.2 KVM Host:

Run

system-config-securitylevel

and set SELinux to Permissive (virt-install will not work if you set SELinux to Disabled).

Then check if your CPU supports hardware virtualization - if this is the case, the command

egrep '(vmx|svm)' --color=always /proc/cpuinfo

should display something, e.g. like this:

[root@server1 ~]# egrep '(vmx|svm)' --color=always /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall
 nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy misalignsse
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall
 nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy misalignsse
[root@server1 ~]#

If nothing is displayed, then your processor doesn't support hardware virtualization, and you must stop here.

Now we import the GPG keys for software packages:

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*

To install KVM and virtinst (a tool to create virtual machines), we run

yum install kvm kmod-kvm qemu libvirt python-virtinst

Then reboot the system:

reboot

After the reboot, the KVM kernel module should be loaded:

lsmod | grep kvm

[root@server1 ~]# lsmod | grep kvm
kvm_amd                50452  0
kvm                   109264  1 kvm_amd
[root@server1 ~]#

(This output is from a system with an AMD-V processor. If your system uses an Intel VT CPU, it should display something like kvm_intel.)

To check if KVM has successfully been installed, run

virsh -c qemu:///system list

It should display something like this:

[root@server1 ~]# virsh -c qemu:///system list
 Id Name                 State
----------------------------------

[root@server1 ~]#

If it displays an error instead, then something went wrong.

Next we need to set up a network bridge on our server so that our virtual machines can be accessed from other hosts as if they were physical systems in the network.

To do this, we install the package bridge-utils...

yum install bridge-utils

... and configure a bridge. Create the file /etc/sysconfig/network-scripts/ifcfg-br0 (please use the BOOTPROTO, BROADCAST, IPADDR, NETMASK and NETWORK values from the /etc/sysconfig/network-scripts/ifcfg-eth0 file):

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

DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
BROADCAST=192.168.0.255
IPADDR=192.168.0.100
NETMASK=255.255.255.0
NETWORK=192.168.0.0
ONBOOT=yes

Modify /etc/sysconfig/network-scripts/ifcfg-eth0 as follows (comment out BOOTPROTO, BROADCAST, IPADDR, NETMASK, and NETWORK and add BRIDGE=br0):

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

# Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+
DEVICE=eth0
#BOOTPROTO=static
#BROADCAST=192.168.0.255
HWADDR=00:10:A7:05:AF:EB
#IPADDR=192.168.0.100
#NETMASK=255.255.255.0
#NETWORK=192.168.0.0
ONBOOT=yes
BRIDGE=br0

Restart the network...

/etc/init.d/network restart

... and run

ifconfig

It should now show the network bridge (br0):

[root@server1 ~]# ifconfig
br0       Link encap:Ethernet  HWaddr 00:10:A7:05:AF:EB
          inet addr:192.168.0.100  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::210:a7ff:fe05:afeb/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17 errors:0 dropped:0 overruns:0 frame:0
          TX packets:53 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1160 (1.1 KiB)  TX bytes:14875 (14.5 KiB)

eth0      Link encap:Ethernet  HWaddr 00:10:A7:05:AF:EB
          inet6 addr: fe80::210:a7ff:fe05:afeb/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:13662 errors:7 dropped:160 overruns:4 frame:0
          TX packets:11646 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:15144608 (14.4 MiB)  TX bytes:1379942 (1.3 MiB)
          Interrupt:74 Base address:0xcc00

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:38 errors:0 dropped:0 overruns:0 frame:0
          TX packets:38 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:4308 (4.2 KiB)  TX bytes:4308 (4.2 KiB)

virbr0    Link encap:Ethernet  HWaddr 00:00:00:00:00:00
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:35 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:9987 (9.7 KiB)

[root@server1 ~]#


3 Installing virt-viewer Or virt-manager On Your Ubuntu 8.10 Desktop

Ubuntu 8.10 Desktop:

We need a means of connecting to the graphical console of our guests - we can use virt-manager (see KVM Guest Management With Virt-Manager On Ubuntu 8.10) for this. I'm assuming that you're using an Ubuntu 8.10 desktop.

Run

sudo aptitude install virt-manager

to install virt-manager.

(If you're using a Fedora 10 desktop, you can install virt-manager as follows:

Become root...

su

... and run

yum install virt-manager

)