Re: [Qemu-discuss] how configure network into backing file without using vnc

[Jakob Bohm]

On 7/19/2012 12:17 PM, Simon Poulleau wrote:
> Hello,
>
> I am currently developing a Bash script which aims to provide users 
> several virtual machines. These machines must be reachable through the 
> network.
>
> After preparing and installing a first virtual machine, I create 
> several backing files in order to start several identical virtual 
> machines.
>
> The problem: I want my virtual machines to be reachable on the 
> network. But when they have completed their boot, no network interface 
> is configured with the exception of the loopback.
There are 4 things you can do:

A) configure the base image to use DHCP and to not insist on having the 
same MAC address each time

B) loop mount each image (if the image is not in raw format, there are 
qemu tools to mount it anyway), change appropriate config files and 
unmount it.  This can be done from a bash script running as root

C) mount each image as the "second hard disk" of an "automatic editing" 
virtual machine, which mounts it, changes appropriate config files, 
unmounts it and shuts itself down.  This can be done with bash scripts 
without being root on the host machine, only on the virtual "automatic 
editing" virtual machine.

D) In the base image install a private bash script in /etc/init.d which 
configures the virtual machine on first boot.  Clear/Set whatever flags 
your script uses to determine if this is the first boot just before 
saving the base image, thus ensuring it is run once in each copied image.

> I tried to start my virtual machines using the user network, but I 
> succeed in configuring only one virtual machine based on backing file. 
> Others have only the loopback interface configured.
>
> Hence my questions:
> Is it possible to assign IP address to virtual machine based on 
> backing file ? (Having conducted tests through vnc I would say yes)

The important thing to remember is to use qemu options to give each 
virtual machine a different MAC address for its virtual network card.  
If you set that MAC address based on the name/location of the virtual 
hard drive in a systematic manner, you can then configure your DHCP 
server to hand out specific IP address, computer name etc. corresponding 
to what you want for each virtual machine.

> Is it possible to mount a backing file image to create a file enabling 
> to configure the network via dhcp when virtual machine is booting (eg: 
> ifcfg-eth0) ?
> Are there any other way from a Bash script to configure the network of 
> a virtual machine run from a backing file.
>
> I hope I was clear on the problem I have, do not hesitate to ask me 
> for details.
Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark.  Direct +45 31 13 16 10
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