Sometimes you need to proceed real installation process of some
GNU/Linux distribution due to run it using some virtualization software
afterwards. The simplest way to do it is to use QEMU emulation software
that is pretty easy to use. Sometimes networking is needy to have as
weel.

From this howto you will learn howto install Debian GNU/Linux using QEMU
to a virtual hard drive using network installation enabled installation
CD-ROM image of Debian GNU/Linux distribution (although this howto can
be used to any other GNU/Linux distribution as well and, perhaps, for
some other operational systems too).

You will also (and mainly) learn howto setup virtual TAP virtually
bridged networking too.



CREATING VIRTUAL BRIDGE INTERFACE

Prerequisities: bridge-utils, iproute2, iptables

Howto:

1. setup virtual bridge interface brg0
2. set the bridge up
3. add address on the bridge (example: 10.0.0.1/24)
4. setup masquerade

/sbin/brctl addbr brg0
/sbin/brctl setfd brg0 1
/sbin/brctl sethello brg0 1
/sbin/brctl stp brg0 off
/sbin/ip link set up dev brg0
/sbin/ip address add 10.0.0.1/24 brd + dev brg0
/sbin/iptables -t nat -I POSTROUTING -s 10.0.0.0/24 -j MASQUERADE

Note: instead of adding an specific address to the virtual bridge
interface you can setup DHCP daemon to listen on it.



DESTROYING VIRTUAL BRIDGE INTERFACE

Prerequisities: bridge-utils, iproute2, iptables

Howto:

1. delete masquerade
2. flush IP addresses from the bridge
3. set the bridge interface down
4. delete the bridge virtual interface brg0

/sbin/iptables -t nat -D POSTROUTING -s 10.0.0.0/24 -j MASQUERADE
/sbin/ip address flush dev brg0
/sbin/ip link set down dev brg0
/sbin/brctl delbr brg0



CREATE VIRTUAL TAP INTERFACE AND ADD IT TO A BRIDGE

Prerequisities: uml-utilities, iproute2, bridge-utils

Howto:

1. create virtual TAP interface tap0
2. set it up
3. add it to a bridge brg0

/sbin/tunctl -u username -t tap0
/sbin/ip link set up dev tap0
/sbin/brctl addif brg0 tap0



REMOVE VIRTUAL TAP INTERFACE FROM A BRIDGE AND DESTROY IT

Prerequisities: uml-utilities, iproute2, bridge-utils

Howto:

1. remove the virtual TAP interface from a bridge
2. set the virtual TAP interface down
2. destroy the virtual TAP interface tap0

/sbin/brctl delif brg0 tap0
/sbin/ip link set down dev tap0
/sbin/tunctl -d tap0



START QEMU USING NETWORK INSTALLATION CD

Prerequisities: qemu, dd, some GNU/Linux installation CD (Debian Etch)

Howto:

1. setup virtual hard drive space using dd utility
2. start QEMU with bridged TAP networking

dd if=/dev/zero of=debian.img bs=1M count=1 seek=4096

Next command will run QEMU with 256 Mb of shared RAM to use, debian.img
file as /dev/hda inside of the running system, debian-netinst.iso as
/dev/cdrom inside the running system, network interface eth0 connected
to the virtual TAP interface in the guest system and will boot from the
virtual CD-ROM device.

/usr/bin/qemu -m 256 -hda debian.img -cdrom debian-netinst.iso -localtime \
 -net nic,vlan=0 -net tap,vlan=0,ifname=tap0,script=/bin/true \
 -boot d