Stupid KVM Tricks

virt-install ubuntu16.04

Create the disk image

qemu-img create -f qcow2 /var/lib/libvirt/images/xenial.qcow2 20G

Command to run the install

virt-install \
    --name xenial \
    --ram 4096 \
    --disk path=/var/lib/libvirt/images/xenial.qcow2,size=20 \
    --vcpus 4 \
    --os-type linux \
    --os-variant ubuntu16.04 \
    --network bridge=br0 \
    --graphics none \
    --console pty,target_type=serial \
    --location ./ubuntu-16.04.3-server-amd64.iso \
    --extra-args 'console=ttyS0,115200n8 serial'

Change the Network Interface

br0 gets addresses from the network router, but what if you want your vm to have be on the virbr0 192.168.122.0/24 subnet?

virsh edit xenial

And then 'J' all the way down to the bottom, change the interface name from br0 to virbr0,

virsh start xenial

and then look for the machine with nmap

nmap -sn 192.168.122.0/24

Clone the VM

In this case we don't have to pre-allocate the disk image because virt-clone will do that for us.

virt-clone --original xenial --name xenial-clone \
    --file /var/lib/libvirt/images/xenial-clone.qcow2

Clone the VM to another Machine

First dump the xml that defines the virtual machine.

virsh dumpxml xenial > xenial.xml

Then copy both xenial.xml and xenial.qcow2 to the new host machine. On the new kvm host you'll want to at least make sure your vm has the correct CPU architecture. The command to get a list of supported kvm cpu architectures is:

virsh cpu-models <arch>
# i.e.
virsh cpu-models x86_64

After you edit xenial.xml and update the correct cpu architecture, mv xenial.qcow2 to /var/lib/libvirt/images/, clone it. virt-clone will handle generating new mac addresses for the network interfaces.

  <cpu mode='custom' match='exact'>
    <model fallback='allow'>Haswell-noTSX</model>
  </cpu>
# i.e. change to above to
  <cpu mode='custom' match='exact'>
    <model fallback='allow'>SandyBridge</model>
  </cpu>

virt-clone --original-xml xenial.xml --name xenial-clone \
    --file /var/lib/libvirt/images/xenial-clone.qcow2

What is the os-type and os-variant type names?

osinfo-query os

misc

Start the vm virsh start xenial
List all the vms virsh list --all
Stop the vm virsh destroy xenial
Delete the vm virsh undefine xenial

virsh help

The virsh help command returns a long chart of help information. But each section has a keyword.

Take for instance the command virsh help monitor. From this we see the domiflist subcommand (among others). Unfortunately domifaddr doesn't seem to work on the Ubuntu:16.04 host, but there are other ways to find the ip address of a virtual machine.

So now if you want to see what host interface the vm xenial is attached to, type.

virsh domiflist xenial

which returns:

Interface  Type       Source     Model       MAC
-------------------------------------------------------
vnet1      bridge     virbr0     virtio      52:54:00:58:bf:75

So now we can find the address of virbr0 on the host machine.

ifconfig virbr0

which returns:

virbr0    Link encap:Ethernet  HWaddr 52:54:00:38:87:38  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1351 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3037 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:232346 (232.3 KB)  TX bytes:502916 (502.9 KB)

and thus we know what subnet to scan with nmap to find the ip address of the vm

nmap -sn 192.168.122.0/24