KVM manual

This document shows and describes the most important commands for a KVM environment.

Before you can start with any virtual machine, you have to install the following packages first:

dnf -y install virt-install libvirt-daemon-kvm qemu-kvm libvirt-client qemu libvirt-daemon

It’s not a bad idea, to check, if your host system is virtualisation capable.

virt-host-validate
  QEMU: Checking for hardware virtualization                                 : PASS
  QEMU: Checking if device /dev/kvm exists                                   : PASS
  QEMU: Checking if device /dev/kvm is accessible                            : PASS
  QEMU: Checking if device /dev/vhost-net exists                             : PASS
  QEMU: Checking if device /dev/net/tun exists                               : PASS
  QEMU: Checking for cgroup 'memory' controller support                      : PASS
  QEMU: Checking for cgroup 'memory' controller mount-point                  : PASS
  QEMU: Checking for cgroup 'cpu' controller support                         : PASS
  QEMU: Checking for cgroup 'cpu' controller mount-point                     : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support                     : PASS
  QEMU: Checking for cgroup 'cpuacct' controller mount-point                 : PASS
  QEMU: Checking for cgroup 'cpuset' controller support                      : PASS
  QEMU: Checking for cgroup 'cpuset' controller mount-point                  : PASS
  QEMU: Checking for cgroup 'devices' controller support                     : PASS
  QEMU: Checking for cgroup 'devices' controller mount-point                 : PASS
  QEMU: Checking for cgroup 'blkio' controller support                       : PASS
  QEMU: Checking for cgroup 'blkio' controller mount-point                   : PASS
  QEMU: Checking for device assignment IOMMU support                         : PASS
  QEMU: Checking if IOMMU is enabled by kernel                               : WARN (IOMMU appears to be disabled in kernel. Add intel_iommu=on to kernel cmdline arguments)
   LXC: Checking for Linux >= 2.6.26                                         : PASS
   LXC: Checking for namespace ipc                                           : PASS
   LXC: Checking for namespace mnt                                           : PASS
   LXC: Checking for namespace pid                                           : PASS
   LXC: Checking for namespace uts                                           : PASS
   LXC: Checking for namespace net                                           : PASS
   LXC: Checking for namespace user                                          : PASS
   LXC: Checking for cgroup 'memory' controller support                      : PASS
   LXC: Checking for cgroup 'memory' controller mount-point                  : PASS
   LXC: Checking for cgroup 'cpu' controller support                         : PASS
   LXC: Checking for cgroup 'cpu' controller mount-point                     : PASS
   LXC: Checking for cgroup 'cpuacct' controller support                     : PASS
   LXC: Checking for cgroup 'cpuacct' controller mount-point                 : PASS
   LXC: Checking for cgroup 'cpuset' controller support                      : PASS
   LXC: Checking for cgroup 'cpuset' controller mount-point                  : PASS
   LXC: Checking for cgroup 'devices' controller support                     : PASS
   LXC: Checking for cgroup 'devices' controller mount-point                 : PASS
   LXC: Checking for cgroup 'blkio' controller support                       : PASS
   LXC: Checking for cgroup 'blkio' controller mount-point                   : PASS

curl -O http://192.168.122.1/fedora/27/os/
curl -O http://192.168.122.1/centos/7.4/os/

virsh dumpxml <domain name> > <outputfile>.xml

virsh create <outputfile>.xml

• Completely delete a VM:

  virsh --connect qemu:///system destroy fedora27
  virsh --connect qemu:///system undefine fedora27

  | Note: | This does not delete the data on the disk (Logical Volume or image)! |

• Unordered List ItemEdit/configure the settings of a virtual machine (domain):

  virsh edit <domain name>

• Unordered List ItemList all (also not started VM's):

  virsh --connect qemu:///system list --all
   Id    Name                           State
  ----------------------------------------------------
   4     cc                             running
   9     centos7                        running
   -     fedora27                       shut off

• Start a console session for a VM:

  virsh --connect qemu:///system console centos7

• Setup autostart (when booting the KVM server) for a VM:

  virsh --connect qemu:///system autostart centos7

If you want to add a second network interface, you should add it after the kickstart installation. If there are two or more interfaces configured, the installer (dracut) does not find the network based installation files. Here two example domains, one is a Fedora server and one is a CentOS server.

In this example the new virtual machine or domain (fedora27) will be installed using kickstart. Following features are given:

• The disk is a logical volume (/dev/mapper/sysvg-fedora27)
• The VM has two CPU’s and 2GB of RAM
• The VM has two network interfaces, one for internal guest/host comunication (the default network), and one for external connections via macvtap protocol
• The installation tree lifes on a webserver ( http://dangiga.danlocal.net/fedora/27/os/ )

virt-install --connect qemu:///system --name fedora27 \
    --disk path=/dev/mapper/sysvg-fedora27 --graphics spice \
    --vcpus 2 --ram=2048 --network bridge=virbr0 --os-type=linux \
    --os-variant=fedora26 --accelerate --noautoconsole --hvm \
    --location=http://dangiga.danlocal.net/fedora/27/os/ \
    --extra-args ks=http://dangiga.danlocal.net/ks/def-fedora27.ks console=ttyS0
virsh attach-interface --domain fedora27 --type direct --source enp0s31f6 --model virtio --config
virsh --connect qemu:///system console fedora27

In this example the new virtual machine or domain (centos7) will be installed using kickstart. Following features are given:

• The disk is a logical volume (/dev/mapper/sysvg-centos7)
• The VM has two CPU’s and 2GB of RAM
• The VM has one network interfaces for internal guest/host comunication (the default network) only
• The installation tree lifes on a webserver ( http://dangiga.danlocal.net/centos/7.4/os/ )

virt-install --connect qemu:///system --name centos7 \
    --disk path=/dev/mapper/sysvg-centos7 --graphics spice --vcpus 2 \
    --ram=2048 --network bridge=virbr0 --os-type=linux \
    --os-variant=centos7.0 --accelerate --noautoconsole --hvm \
    --location=http://dangiga.danlocal.net/centos/7.4/os/ \
    --extra-args "ks=http://dangiga.danlocal.net/ks/def-centos7.ks console=ttyS0"
virsh --connect qemu:///system console centos7

• List all networks:

  virsh net-list --all

• Attach a network interface to a virtual machine (domain):

  virsh attach-interface --domain <vm name> --type bridge --source virbr0 --model virtio --config --live

  virsh attach-interface --domain <vm name> --type direct --source enp0s31f6 --model virtio --config --live

• Unordered List ItemIf you want to figure out the IP addresss of one or more VM’s, you can use the following command executed on the KVM host:

  vm=fedora27
  for mac in `virsh domiflist $vm |grep -o -E "([0-9a-f]{2}:){5}([0-9a-f]{2})"` ; do
      arp -e |grep $mac  |grep -o -P "^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}"
  done

• Unordered List ItemThe virsh command also provides a editor for a network configuration. In this example the default network is edited.

  virsh net-edit default

• Show the network configuration of a network (here default net):

  virsh net-dumpxml default

  Output:

  <network>
    <name>default</name>
    <uuid>fffdb071-f34b-4672-b8c5-48ee04d7ab4b</uuid>
    <forward mode='nat'>
      <nat>
        <port start='1024' end='65535'/>
      </nat>
    </forward>
    <bridge name='virbr0' stp='on' delay='0'/>
    <mac address='52:54:00:65:80:59'/>
    <ip address='192.168.xxx.1' netmask='255.255.255.0'> (1)
      <dhcp>
        <range start='192.168.122.40' end='192.168.xxx.254'/>
        <host mac='52:54:00:f3:30:0f' ip='192.168.xxx.xx'/> (2)
        <host mac='52:54:00:f3:30:1f' ip='192.168.xxx.xx'/>
        <host mac='52:54:00:f3:30:2f' ip='192.168.xxx.xx'/>
      </dhcp>
    </ip>
  </network>

• Unordered List ItemAfter changing anything, you must activate the changed configuration, you have to reload the network:

  virsh net-destroy default && virsh net-start default

• Delete a vm (host) in a network (here default net):

  virsh net-update default delete ip-dhcp-host "<host mac='52:54:00:f3:30:2f' name='hostname' ip='192.168.xxx.xxx'/>" --live --config

• Add a network configuration (host) live:

  virsh net-update default add ip-dhcp-host "<host mac='52:54:00:43:56:84' name='hostname' ip='192.168.xxx.xxx'/>" --live --config

It’s also possible to add a disk to a running VM. The disk can be a disk image or a LVM volume. It’s possible to resize the disk, but, you have to reboot the client or relaod the kernel disk table (partx, only CentOS >=7).

• Add (persistent) a disk to a VM:

  virsh attach-disk ds --source /dev/sysvg/ds_test --target vdb --persistent

  
  This adds a new disk to the ds VM as /dev/vdb persistently.

• First increase size of the LV on KVM host:

  lvresize -G <size>G /dev/sysvg/<lv name>

• Configure the size of that domain and disk using virsh:

  virsh blockresize <domain> /dev/sysvg/<lv name> --size <size>G

  
  Now, you can resize the disk on the domain (VM).