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Windows VM in KVM/QEMU on headless Ubuntu server

without using libvirt

install kvm

apt-get install kvm qemu

now create a disk image

qemu-img create -f raw /vm/windows.img 100G

(note: creating a raw image has severale advantages: if your filesystem supports sparse files, it only uses the actually used space of your virtual disk on your physical disk.. all journalling filesystems that use inodes support that, so ext4 for example works fine. second you can easily mount it using mount -o loop <imgfile> <mountpoint> at any time. however, it does not support snapshots, use qcow2 if you need snapsots or if your filesystem does not support sparse files)

in my case i had a windows 7 cd that i installed from.. if your server dos not have a cd rom you can also us an iso image instead.

since I want to use virtio for fast hdd emulation, we also need the virtio drivers

cd /vm

run qemu and install windows. access the display via VNC

qemu-system-x86_64 -enable-kvm -k de-ch -name windows -vnc :1 -cdrom /dev/cdrom -boot d -drive file=/vm/windows.img,if=virtio,format=raw,index=0 -m 4096

now connect with your favourite vnc client to the ip of your server and install windows. you need to load the derivers from the second cdrom that is emulated. make sure you choose the correct virtio storage driver for your windows version. it may load the wrong one if you just select the root directory and let the installer search for it, resulting in an unstable windows vm

autostart on boot / init script

once the installation is done, shut down your windows vm. it is now time to make it autostart upon boot of your linux machine.. in order to do that i used Thomas Martin's kvm-simple-init of which i keep a local copy (dated 2016-01-23)

this script will also send a shutdown command to all vms once the server shuts down, so no need to manually do that in order to gracefully shutdown your vm's

bridged network

by default qemu uses nat-ed network, so that the vm is in its own network and the vm host acts as a nat router. if you want your vm to be part of your network like any physical machine you have connected to your swich you can use a bridged connection..

you need to install bridge-utils to be able to create a bridge network device

 apt-get install bridge-utils 

now change your /etc/network/scripts file and basically replace eth0 with br0 and then add three lines for the bridge config. here the end result on mine:

auto br0
iface br0 inet static 
	bridge_ports eth0
	bridge_stp off
	bridge_maxwait 5

Notice: you won't need any block for eth0 after you defined the bridge interface. 

now either reboot your machine or try to get your eth0 down using ''ifconfig'' and then get br0 up using ''ifup'' however be careful when you are doing this all remoetely!! in that case make really really sure you got your config right or even better, setup a backdoor, make sure your remote management module is accessible, whatever.. and then reboot your server.. and hope :) 

now in your qemu command line you ened to add the parameters 
<code>-net nic -net tap

the default qemu-ifup script in /etc/ will do the rest for you.

example config

here is an example configuration for a windows 7 machine using the above mentioned init script.. if you use another init script or run kvm manually you can simply use all the cli options listed below as an example of what you might want to pass on to qemu.. also take a look at the man page it is very informative and helpful!

# Should be unique among all VMs

# Not mandatory, but useful to keep it in a distinct variable

# KVM parameters
-enable-kvm \
-k de-ch \
-name windows \
-drive file=/vm/windows.img,if=virtio,format=raw,index=0 \
-m 4096 \
-net nic \
-net tap \
-vnc :$VNC_DISPLAY \
-monitor tcp:$MONITOR_PORT,server,nowait \
-monitor vc \
-daemonize \

Windows 10 upgrade

I had a windows 7 license laying around so i used that but wanted to upgrade to win 10. unfortunately the update crashed with error

0xC1900101 - 0x20017 The installation failed in the SAFE_OS phase with an error during BOOT operation

this was easily fixed by temporarily adding a

-cpu core2duo

to my options in the above config file. keep in mind you need to stop your VM and start it again for this change to be activated.. after the update the setting can be removed and the cpu can be reverted to kvm, the default.