QEMU/KVM Cheatsheet

Create KVM image with virt-build

cd /var/lib/libvirt/qemu/

sudo virt-builder fedora-26 \
--arch x86_64 \
--size 20G \
-m 8192 \
--root-password password:{some_password} \
--format raw

sudo virt-install --name fedora26 \
--ram 8192 ]
--vcpus=4 \
--disk path=/var/lib/libvirt/qemu/fedora-26.img \
--rng /dev/urandom \
--import

Create KVM template

Run default virt-sysprep

sudo virt-sysprep -d {your_vm}

To change default operations:

First list available operations

sudo virt-sysprep --list-operations

Output:
abrt-data * Remove the crash data generated by ABRT
bash-history * Remove the bash history in the guest
blkid-tab * Remove blkid tab in the guest
ca-certificates   Remove CA certificates in the guest
...

Than specify the operations, in this case only bash_history and blkid will run

sudo virt-sysprep --operations bash_history,blkid-tab -d {your_vm}

Rename vm

sudo virsh domrename old_name_vm new_name_vm

Clonning KVM image from template

sudo virt-clone -o template_vm -n your_new_vm_name -f /var/lib/libvirt/qemu/your_new_vm_name.img

sudo virsh list --all (you should see)

Id    Name                           State
---------------------------------------------
-     your_new_vm_name               shut off

Edit KVM image

sudo virsh edit your_vm

<domain type='kvm'>
  <name>fedora26-vm1</name>
...
</domain>

Example: Change KVM img path

we have

sudo ls -la /var/lib/libvirt/your_vm.img

rw-------.  1 qemu qemu  21474836480 Aug 29 17:33 your_vm.img

we want to move img to var/lib/libvirt/qemu/your_vm.img

Shutdown vm to edit

sudo virsh shutdown your_vm

Enter

sudo virsh edit your_vm

Edit old: new:

  old:
  
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/your_vm.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    ...
  </devices>
  
  new:
  
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/qemu/your_vm.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    ...
  </devices>

Start vm

sudo virsh start your_vm

Setup KVM image after clonning (RHEL based for testing)

Log to KVM console:

sudo virsh console {your newly created KVM VM} - e.g. sudo virsh console centos7.3-vm1

Note: to escape press Ctrl+]

Stop(as root):

systemctl stop firewalld.service
systemctl disable firewalld.service

systemctl stop NetworkManager.service
systemctl disable NetworkManager.service

Edit:

vi /etc/sysconfig/network-scripts/ifcfg-etho0

HWADDR="{ get HW address from ip a}

read !ip a

then

systemctl start network.service
systemctl enable network.service

KVM change default pool for libvirt

Backup existing one

virsh pool-dumpxml default > default.xml

virsh pool-destroy default
virsh pool-undefine default

Links:

[how-to-change-the-default-storage-pool-from-libvirt] (https://serverfault.com/questions/840519/how-to-change-the-default-storage-pool-from-libvirt)
[linux-kvm-change-libvirt-vm-image-store-path] (https://www.unixarena.com/2015/12/linux-kvm-change-libvirt-vm-image-store-path.html/)

KVM snapshots

List KVM image snapshots

your_vm_name - e.g. centos7

sudo virsh snapshot-list your_vm_name

 Name                 Creation Time             State
------------------------------------------------------------
 base                 2017-05-15 22:50:43 +0200 shutoff
 base-upgrade         2017-05-16 08:34:53 +0200 shutoff
 some-next-tag        2017-05-21 22:15:00 +0200 shutoff

Create KVM image snapshot with custom parameters

sudo virsh snapshot-create-as your_vm_name --name "{name}" --description "{description}" --atomic

list to verify

sudo virsh snapshot-list your_vm_name

 Name                 Creation Time             State
------------------------------------------------------------
 {name}               2017-05-15 22:50:43 +0200 shutoff

Revert to previous KVM image snapshot

sudo virsh snapshot-revert your_vm_name --snapshotname "{snapshot}"

KVM convert raw image to VirtualBox VDI format

your_vm_name - e.g. centos7.4

sudo qemu-img convert -O vdi {your_vm_name}.img {your_vm_name}.vdi

Libvirt Networking

Get network address for running domain

Example:

sudo virsh domifaddr your_vm

Output:

 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:00:41:24:c8    ipv4         192.168.122.28/24