After upgrading my laptop to Windows 8.1 I realized that one cannot easily run VirtualBox and HyperV in parallel. Unfortunately I was not able to find a working CentOs box for HyperV. This post shows how to create one from scratch.

The instructions given in this post were the starting point for my adjusted configuration. Source code can be found in my github repository. It contains the kickstart config and powershell scripts to automate large parts of the process.

Creating a basic CentOS VM

You should have enabled HyperV and set up a virtual switch for the VMs, called "vm-network". Download the latest CentOs6 release image. At the time of writing, that is version 6.6, which comes with HyperV support built-in.

Create the virtual machine

Use the wizard to create a bare vm. Make sure to select the correct virtual switch and set the path to the install .iso in the installation options. My settings were:

• Name: dev.centos6
• Generation: Generation 1
• Memory: 1024MB
• Network: shared hyperv switch
• Disk size: 32GB
• Operating System: path/to/centos-install.iso

You can increase the cpu count in the VM settings. Assigned memory and cpu count can also be changed later by Vagrant.

Install CentOs 6.6

I recommend using this [kickstart script][https://github.com/pyranja/vbox-centos6-hyperv/blob/master/ks.cfg] to automate the installation, but you can of course perform a manual installation, detailed instructions are available here. Set the root password to "vagrant", if you want to publish the box later.

To provide some guidance I will explain the most important settings and post-installation steps.

Kickstart settings

selinux --permissive

Change this to --enforced, if security is a concern.

bootloader --location=mbr --driveorder=sda --append="crashkernel=auto rhgb quiet elevator=noop"

The elevator=noop kernel parameter is added, which may improve performance as described here.

%packages
@core
@server-policy
openssh-clients
hyperv-daemons
%end

core and server-policy are the default setting for a minimal installation. openssh-clients is required for vagrant's shell provisioner and hyperv-daemons to let the virtual machine report its IP-Address to Vagrant.

services --enabled hypervkvpd

This service reports the IP-Address (among other properties) to the HyperV container. Vagrant won't be able to connect to the box if it is not enabled.

Post-installation steps

# adjust security
sed --in-place --expression='s/^Defaults\s*requiretty/# &/' /etc/sudoers
# vagrant user
VAGRANT_USER="vagrant"
VAGRANT_HOME="/home/${VAGRANT_USER}"
useradd --user-group --create-home "${VAGRANT_USER}"
echo "${VAGRANT_USER}:${VAGRANT_USER}" | chpasswd
mkdir --mode 0700 --parents "${VAGRANT_HOME}/.ssh"
curl https://raw.githubusercontent.com/mitchellh/vagrant/master/keys/vagrant.pub >> "${VAGRANT_HOME}/.ssh/authorized_keys"
chmod 600 "${VAGRANT_HOME}/.ssh/authorized_keys"
chown --recursive "${VAGRANT_USER}:${VAGRANT_USER}" "${VAGRANT_HOME}/.ssh"
echo "${VAGRANT_USER} ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers

Add the vagrant user and the default public ssh keys for login. Vagrant also needs passwordless sudo to initialize the vm.

# networking
cat <<EOF > /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
TYPE="Ethernet"
BOOTPROTO="dhcp"
ONBOOT="yes"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
NM_CONTROLLED="no"
EOF

sed --in-place --expression='s/ATTR{address}=="[a-zA-Z0-9:]*", //' /etc/udev/rules.d/70-persistent-net.rules

When starting a new VM, HyperV assigns a randomized MAC address to eth0. Therefore delete the fixed MAC address - set while installing - from the interface configuration and also prevent the udev rule from rewriting it again.

yum clean all
rm -rf /tmp/*
rm -f /var/log/wtmp /var/log/btmp
history -c
dd if=/dev/zero of=/EMPTY bs=1M
rm -f /EMPTY
sync

At last clean up and prepare virtual disk optimization. The last three commands first fill all remaining space on the virtual disk with a single zero file, then delete that file. This is necessary to allow compaction of the disk image. Obviously you are in trouble if you had set the maximum size of the virtual disk too high! The VM is now configured, shut it down and compact the disk with the HyperV wizard at Settings -> Hard Drive -> Edit. Finally export it, this may take some time.

Package as Vagrant box

Almost done! Open the directory, where you exported the vm to, Snapshots may be deleted. Add a metadata.json containing { "provider": "hyperv" } and zip it together with the Virtual Hard Drive and Virtual Machines directory.

Scripted build

The repository contains three powershell scripts, which automate large parts of the box creation. They require the 7-Zip command line tool 7z.exe and mkisofs.exe from the CDRTools to be available in the path.

Prepare-Iso.ps1 downloads a CentOs network installation image if necessary and injects the kickstart configuration into it. After stage/centos-netinstall-ks.iso has been created, run Create-VM.ps1 to create a new virtual machine, mount the .iso and connect to it. Installation will start automatically from the embedded kickstart script. When installation succeeded, invoke Pack-VM.ps1 to export the virtual machine and package it in the vagrant box format - a zip file including the metadata.json. The script uses the highest available compression level, therefore it may take a while to complete.

Use the box

The created box can now be added to vagrant:

vagrant box add my-box dev.centos6.box

I have added a box created this way to Atlas: pyranja/centos6