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Virtualization
with Qemu, Kqemu and KVM
This page presents:
Introduction
and Disclaimer :)
Disclaimer: I resume here what I have learned
about the virtualization with the QEMU/KQEMU/KVM
tools. I DO NOT assume any responsibility about rights and wrongs of what you
find
here. These are my understandings of the tool, they can be
right or
wrong, so if you are using the information, evaluate it by yourself first.
Other
thing is that, this is a "hands on" kind of tutorial, so if you are
searching why and how... maybe here is not the best place to search for
them,
sorry :(.
Qemu is
a virtualization tool that started, and is maintained by Fabrice Bellard, the main pages
are QEMU,
KQEMU
and KVM.
There are many, really many, information sources about these tools. I
think these tools became even MORE popular after the linux kernel
introduce support
for them (kvm) by default.
What we will discuss here are related to debian based distributions, what does include ubuntu. Attention that KVM will work ONLY if you have a newer processor with support to virtualization (e.g. Intel Core duo or AMD Athlon or Turion), other thing is that KVM is based in QEMU, but is an independent project. The basic difference, for the user point of view, between KVM, Kqemu and Qemu is the perceived speed but the procedures are basically the same.
Other good tutorials and information sources can be found at:
Conventions:
- host #> : denotes commands executed in
the real machine, the host machine
- virtual #>: denotes commands
executed in the virtual machine, the exemplified one
Installation
- At first add the repository to
/etc/apt/sources.list for edgy:
host #> cat >> /etc/apt/sources.list
deb http://ubuntu.tolero.org/ edgy main
deb-src http://ubuntu.tolero.org/ edgy main
Or that lines if you are running dapper:
host #> cat >> /etc/apt/sources.list
deb http://ubuntu.tolero.org/ dapper main
deb-src http://ubuntu.tolero.org/ dapper main
I, personally, prefer to do the installation from the console package manager, rather than with the graphical one (synaptic for instance). Ensure that you have also ubuntu universal repository is included to the sources.list. If so, cross your fingers and pass one by one to the console the next commands:
host #> sudo aptitude update
host #> sudo aptitude install kqemu-common kqemu-source
host #> sudo aptitude install module-assistant
host #> sudo m-a prepare
host #> sudo m-a build kqemu
host #> sudo m-a install kqemu
host #> sudo aptitude install qemu
host #> depmod -a
host #> modprobe kqemu
To see if every thing it is OK
host #> /sbin/lsmod|grep kqemu ##Comment## The kqemu should appear here.
Disk
Images
- To run Qemu you need first to
have an image of the system you want to run. You probably can find many
different images already made in the internet, or you can create your
own.
- To create a new image
host #> qemu-img create -f raw rtmk_linux-2.6.16.49.img 3G - Let me say you do have a iso of
the desired Linux distribution, let us call here of
"ubuntu-7.04-desktop-i386.iso", if you do not have you can download
from the distributor site or buy a CD.
host #> qemu -boot d -cdrom ubuntu-7.04-desktop-i386.iso rtmk_linux-2.6.16.49.img -m 400 - If you have problems with the
designed memory size
host #> umount /dev/shm
host #> mount -t tmpfs -o size=416m none /dev/shm
Well.... in truth, as much memory you have the better, but remember that you need to keep your own machine running ;) - To resize the image IF needed
- Ok you already have an image but it is start to
get really small, to resize it:
- The image people let at the QEMU website is
small, only 20MB, if I recall well, let me say we need to
resize it
host #> dd if=/dev/zero of=rt_linux-2.6.16.49.img seek=300 obs=1MB count=0
where 300 is new size to resize hdd.img in MB
host #> e2fsck rt_linux-2.6.16.49.img
host #> qemu-img info rt_linux-2.6.16.49.img
to see the new virtual size, in my case it was 286M
host #> resize2fs /root/rt_linux-2.6.16.49.img 286M - To Use with the image
host
#> modprobe
kqemu
host #> rm -rf /dev/kqemu
host #> mknod /dev/kqemu c
250 0
host #> /bin/chmod 666
/dev/kqemu ##Comment##
make it accessible to all users
host #> qemu -m
200 rtmk_linux-2.6.16.49.img&
Network Configuration
- Ok I don't think you will want to use the
virtual machine without network, so we need to setup it. There are many
different ways to do this we will use tap interfaces using a bridge.
host
#> tunctl -d
tap0
Set 'tap0' persistent
and owned by uid 1000
- To configure the nat
host
#> iptables
-t nat -A POSTROUTING -o eth0 -j MASQUERADE
host #> echo 1 >
/proc/sys/net/ipv4/ip_forward
- Create a file, for example qemu-ifup.sh
host
#> cat
> qemu-ifup.sh
#!/bin/sh
echo "Executing /etc/qemu-ifup"
echo "Bringing up $1 for bridged mode..."
sudo /sbin/ifconfig $1 0.0.0.0 promisc up
echo "Adding $1 to br0..."
sudo /usr/sbin/brctl addif br0 $1
#sleep 2
- To Start the Bridge
- # insert the tuntap module
host #> modprobe tun - insert the bridge module
host #> modprobe bridge - insert the kqemu module
host #> modprobe kqemu major=0 - To configure the
bridge :
host #> ifconfig eth0 down
host #> brctl addbr br0
host #> ifconfig eth0 up
host #> brctl addif br0 eth0
host #> ifconfig br0 192.168.12.102 up ##comment## Change for your bridge address
host #> ifconfig eth0 down
host #> ifconfig eth0 0.0.0.0 up
host #> route add default gw 192.168.12.100 ##comment## Change for your gateway - To start QEMU using the network
host #> qemu -m 200 -net nic,vlan=0 -net tap,vlan=0,ifname=tap0,script=qemu-ifup.sh YourImage.img&
Configuring the client
- Everything now happens INSIDE the virtual
machine
- Put insite
/etc/network/interfaces the following lines:
auto eth0
iface eth0 inet static
address 192.168.12.102 ##comment## Change for your bridge address
netmask 255.255.255.0
gateway 192.168.12.100 ##comment## Change for your gateway - To restart configurations
virtual #> /etc/init.d/networking restart
- To solve the names put in the /etc/resolv.conf
file
virtual #> cat > /etc/resolv.conf
nameserver 192.168.12.100 ##comment## Change for your real name server
For every day usage
If you are following this as a
step by step
tutorial, up to here it is one time only, you will need to do every
thing that
is below only once, here we will discuss the every day use, what you
need to do
daily make the thing work.
- To start the virtual machine using the network
host #> qemu -m 200 -net nic,vlan=0 -net tap,vlan=0,ifname=tap0,script=qemu-ifup.sh YourImage.img&
- If the kqemu doesn't work try
host #> modprobe kqemu
host #> rm -rf /dev/kqemu
host #> mknod /dev/kqemu c 250 0
host #> /bin/chmod 666 /dev/kqemu ##comment## to make it accessible to all users