Most of us may have used virtualbox or vmware, they have friendly UI and are easily to use, they run under a host OS, just like a normal software. but xen is different, xen runs directly on hardware, it is loaded by the bootloader before OS, then it loads the first special VM(dom0), dom0 has access to hardware, xen-tools are installed on dom0 used to communicate with xen hypervisor and manage other VMs, other VMs can’t access the hardware directly. in this article, i will tell you how to install xen-4.8 on debian9 64bit, and install a windows guest OS.

Content:

1. Host OS preparation
    1.1 Install xen hypervisor
    1.2 Install xen tools
    1.3 Configuration network for guest OS
2. Guest OS installation
3. Optimize

Host OS preparation

Install xen hypervisor

To install xen hypervisor, all you need to do is:

    apt-get install xen-linux-system-amd64

After you install the xen hypervisor, the grub will automatically set xen hypervisor as default boot item. now you can reboot.

Install xen tools

Xen has many toolstack which can be used to create and manage VMs. xl is the default tools. to install xl-tools. type:

    apt-get install xen-tools

If you have already reboot in the previous step. now you can type:

    xl top

It will show the dom0 status.

Configuration network for guest OS

Now we have installed xen hypervisor and xen-tools. the next step is to configure the network for guest OS. unlike virtualbox or vmware, they can create virtual ethernet automatically for us, we need create it manually. first we need to install bridge utilities.

    apt-get install bridge-utils

Now we can specify network information through /etc/network/interfaces file.

    auto lo
    iface lo inet loopback

    auto eth0
    iface eth0 inet manual

    auto xenbr0
    iface xenbr0 inet dhcp
    bridge_ports eth0

Above we create a virtual ethernet xenbr0 and bridge it to eth0. Now restart networking:

    ifdown -a && ifup -a

Check to make sure it worked:

    brctl show

Guest OS installnation

To install a xen guest, we need to create a config file that can describe the hardware information about the guest OS. a sample windows_7.cfg:

    builder= 'hvm'
    memory = 2048
    vcpus=4

    name = "windows_7"
    vif = [ 'bridge=xenbr0' ]
    acpi=1
    apic=1
    disk = [ 'file:/home/windows_7/windows_7.img,hda,w', 'file:/home/windows_7/windows_7.iso,hdc:cdrom,r' ]
    
    device_model_version = 'qemu-xen'
    xen_platform_pci=1

    boot="dc"
    sdl=0
    vnc=1
    vnclisten=""
    vncpasswd=""
    serial='pty'

Pay special attention to the disk line, we have two disks, the first one is a .img file used for windows system intallation. you need to create it manually first, size more than 20GB is recommended, the second one is a ISO file, that is the windows installation ISO image which you can download from internet.
Now finnaly we can start the VM:

    xl create windows_7.cfg

After that, we can use vncviewer to connect to the guest OS and complete the OS installation.

    gvncviewer <dom0-ip-address>

Now you can enjoy it, but i recommend you to read the next section.

Optimize

Actually xen uses intel VT-x and AMD-V to boost its cpu and memory virtualization. for device IO, it uses qemu to emulate it, and it is very slow because it’s emulated. to gain better performace, we can use PV drivers to improve both disk and network performance. after install the windows guest, we can download PV drivers here and install it in the guest OS.

References:

https://wiki.xenproject.org/wiki/Xen_Project_Beginners_Guide