KVM¶

this is for a vanilla CentOS 8 minimal installation,
largely based on kvm_virtualization_in_rhel_7_made_easy.pdf

good information is also found at http://virtuallyhyper.com/2013/06/migrate-from-libvirt-kvm-to-virtualbox/

basic updates/installs¶

yum update
yum install wget
yum install vim
reboot

check machine capability¶

grep -E 'svm|vmx' /proc/cpuinfo

vmx ... Intel
svm ... AMD

install KVM on CentOS minimal¶

yum install qemu-kvm libvirt libguestfs-tools virt-install
systemctl enable libvirtd && systemctl start libvirtd

verify the following kernel modules are loaded

lsmod | grep kvm

kvm
kvm_intel

kvm
kvm_amd

h2. setup networking

add to the network controller configuration file /etc/sysconfig/network-scripts/ifcfg-em1

...
BRIDGE=br0

add following new file /etc/sysconfig/network-scripts/ifcfg-br0

DEVICE="br0" 
# BOOTPROTO is up to you. If you prefer “static”, you will need to
# specify the IP address, netmask, gateway and DNS information.
BOOTPROTO="dhcp" 
IPV6INIT="yes" 
IPV6_AUTOCONF="yes" 
ONBOOT="yes" 
TYPE="Bridge" 
DELAY="0" 

enable network forwarding /etc/sysctl.conf

...
net.ipv4.ip_forward = 1

read the file and restart NetworkManager

sysctl -p /etc/sysctl.conf
systemctl restart NetworkManager

can KVM and Virtualbox coexist¶

http://www.dedoimedo.com/computers/kvm-virtualbox.html

convert Virtualbox to KVM¶

uninstall Virtualbox-guest-additions¶

opt/[VboxAddonsFolder]/uninstall.sh

some people had to remove /etc/X11/xorg.conf

convert image from Virtualbox to KWM¶

VBoxManage clonehd --format RAW Virt_Image.vdi Virt_Image.img

RAW-Datei nach qcow konvertieren

qemu-img convert -f raw Virt_Image.img -O qcow2 Virt_Image.qcow

automatic start/shutdown of VMs with Host¶

taken from https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Administration_Guide/sub-sect-Shutting_down_rebooting_and_force_shutdown_of_a_guest_virtual_machine-Manipulating_the_libvirt_guests_configuration_settings.html

enable libvirt-guests service

systemctl enable libvirt-guests
systemctl start libvirt-guests

all settings are to be done in /etc/sysconfig/libvirt-guests

install¶

yum install virt-manager

usermod -a -G libvirt username

rename KVM-guest¶

taken from http://www.taitclarridge.com/techlog/2011/01/rename-kvm-virtual-machine-with-virsh.html

Power off the virtual machine and export the machine's XML configuration file:

virsh dumpxml name_of_vm > name_of_vm.xml

Next, edit the XML file and change the name between the <name></name> tags (should be right near the top). As an added step you could also rename the disk file to reflect the change of the name and change the name of it in the <devices> section under <source file='/path/to/name_of_vm.img'>.

Save the XML file and undefine the old VM name with:

virsh undefine name_of_vm

Now just import the edited XML file to define the VM:

virsh define name_of_vm.xml

And that should be it! You can now start up your vm either in the Virtual Machine Manager or with virsh using:

virsh start name_of_vm

set fixed IP-adr via DHCP (default-network)¶

taken from https://wiki.libvirt.org/page/Networking

virsh edit <guest>

where <guest> is the name or uuid of the guest. Add the following snippet of XML to the config file:

<interface type='network'>
  <source network='default'/>
  <mac address='00:16:3e:1a:b3:4a'/>
</interface>

Applying modifications to the network

Sometimes, one needs to edit the network definition and apply the changes on the fly. The most common scenario for this is adding new static MAC+IP mappings for the network's DHCP server. If you edit the network with "virsh net-edit", any changes you make won't take effect until the network is destroyed and re-started, which unfortunately will cause a all guests to lose network connectivity with the host until their network interfaces are explicitly re-attached.
virsh net-update

Fortunately, many changes to the network configuration (including the aforementioned addition of a static MAC+IP mapping for DHCP) can be done with "virsh net-update", which can be told to enact the changes immediately. For example, to add a DHCP static host entry to the network named "default" mapping MAC address 53:54:00:00:01 to IP address 192.168.122.45 and hostname "bob", you could use this command:

virsh net-update default add ip-dhcp-host \
          "<host mac='52:54:00:00:00:01' \
           name='bob' ip='192.168.122.45' />" \
           --live --config

forwarding incoming connections¶

taken from https://wiki.libvirt.org/page/Networking

By default, guests that are connected via a virtual network with <forward mode='nat'/> can make any outgoing network connection they like. Incoming connections are allowed from the host, and from other guests connected to the same libvirt network, but all other incoming connections are blocked by iptables rules.

If you would like to make a service that is on a guest behind a NATed virtual network publicly available, you can setup libvirt's "hook" script for qemu to install the necessary iptables rules to forward incoming connections to the host on any given port HP to port GP on the guest GNAME:

1) Determine a) the name of the guest "G" (as defined in the libvirt domain XML), b) the IP address of the guest "I", c) the port on the guest that will receive the connections "GP", and d) the port on the host that will be forwarded to the guest "HP".

(To assure that the guest's IP address remains unchanged, you can either configure the guest OS with static ip information, or add a <host> element inside the <dhcp> element of the network that is used by your guest. See the libvirt network XML documentation address section for defails and an example.)

2) Stop the guest if it's running.

3) Create the file /etc/libvirt/hooks/qemu (or add the following to an already existing hook script), with contents similar to the following (replace GNAME, IP, GP, and HP appropriately for your setup):

Use the basic script below or see an "advanced" version, which can handle several different machines and port mappings here (improvements are welcome) or here's a python script which does a similar thing and is easy to understand and configure (improvements are welcome):

#!/bin/bash
# used some from advanced script to have multiple ports: use an equal number of guest and host ports

# Update the following variables to fit your setup
Guest_name=GUEST_NAME
Guest_ipaddr=GUEST_IP
Host_ipaddr=HOST_IP
Host_port=(  'HOST_PORT1' 'HOST_PORT2' )
Guest_port=( 'GUEST_PORT1' 'GUEST_PORT2' )

length=$(( ${#Host_port[@]} - 1 ))
if [ "${1}" = "${Guest_name}" ]; then
   if [ "${2}" = "stopped" ] || [ "${2}" = "reconnect" ]; then
       for i in `seq 0 $length`; do
               iptables -t nat -D PREROUTING -d ${Host_ipaddr} -p tcp --dport ${Host_port[$i]} -j DNAT --to ${Guest_ipaddr}:${Guest_port[$i]}
               iptables -D FORWARD -d ${Guest_ipaddr}/32 -p tcp -m state --state NEW -m tcp --dport ${Guest_port[$i]} -j ACCEPT
       done
   fi
   if [ "${2}" = "start" ] || [ "${2}" = "reconnect" ]; then
       for i in `seq 0 $length`; do
               iptables -t nat -A PREROUTING -d ${Host_ipaddr} -p tcp --dport ${Host_port[$i]} -j DNAT --to ${Guest_ipaddr}:${Guest_port[$i]}
               iptables -I FORWARD -d ${Guest_ipaddr}/32 -p tcp -m state --state NEW -m tcp --dport ${Guest_port[$i]} -j ACCEPT
       done
   fi
fi

4) chmod +x /etc/libvirt/hooks/qemu

5) Restart the libvirtd service.

6) Start the guest.

(NB: This method is a hack, and has one annoying flaw in versions of libvirt prior to 0.9.13 - if libvirtd is restarted while the guest is running, all of the standard iptables rules to support virtual networks that were added by libvirtd will be reloaded, thus changing the order of the above FORWARD rule relative to a reject rule for the network, hence rendering this setup non-working until the guest is stopped and restarted. Thanks to the new "reconnect" hook in libvirt-0.9.13 and newer (which is used by the above script if available), this flaw is not present in newer versions of libvirt (however, this hook script should still be considered a hack).

wrapper script for virsh¶

#! /bin/sh
# kvm_control   Startup script for KVM Virtual Machines
#
# description: Manages KVM VMs
# processname: kvm_control.sh
#
# pidfile: /var/run/kvm_control/kvm_control.pid
#
### BEGIN INIT INFO
#
### END INIT INFO
#
# Version 20171103 by Jeremias Keihsler added ionice prio 'idle'
# Version 20161228 by Jeremias Keihsler based on:
# virsh-specific parts are taken from:
#  https://github.com/kumina/shutdown-kvm-guests/blob/master/shutdown-kvm-guests.sh
# Version 20110509 by Jeremias Keihsler (vboxcontrol) based on:
# Version 20090301 by Kevin Swanson <kswan.info> based on:
# Version 2008051100 by Jochem Kossen <jochem.kossen@gmail.com>
# http://farfewertoes.com
#
# Released in the public domain
#
# This file came with a README file containing the instructions on how
# to use this script.
# 
# this is no more to be used as an init.d-script (vboxcontrol was an init.d-script)
#

################################################################################
# INITIAL CONFIGURATION

export PATH="${PATH:+$PATH:}/bin:/usr/bin:/usr/sbin:/sbin" 

VIRSH=/usr/bin/virsh
TIMEOUT=300

declare -i VM_isrunning

################################################################################
# FUNCTIONS

log_failure_msg() {
echo $1
}

log_action_msg() {
echo $1
}

# list running domains
list_running_domains() {
  $VIRSH list | grep running | awk '{ print $2}'
}

# Check for running machines every few seconds; return when all machines are
# down
wait_for_closing_machines() {
RUNNING_MACHINES=`list_running_domains | wc -l`
if [ $RUNNING_MACHINES != 0 ]; then
  log_action_msg "machines running: "$RUNNING_MACHINES
  sleep 2

  wait_for_closing_machines
fi
}

################################################################################
# RUN
case "$1" in
  start)
    if [ -f /etc/kvm_box/machines_enabled_start ]; then

      cat /etc/kvm_box/machines_enabled_start | while read VM; do
        log_action_msg "Starting VM: $VM ..." 
        $VIRSH start $VM
        sleep 20
        RETVAL=$?
      done
      touch /tmp/kvm_control
    fi
  ;;
  stop)
    # NOTE: this stops first the listed VMs in the given order
    # and later all running VM's. 
    # After the defined timeout all remaining VMs are killed

    # Create some sort of semaphore.
    touch /tmp/shutdown-kvm-guests

    echo "Try to cleanly shut down all listed KVM domains..." 
    # Try to shutdown each listed domain, one by one.
    if [ -f /etc/kvm_box/machines_enabled_stop ]; then
      cat /etc/kvm_box/machines_enabled_stop | while read VM; do
        log_action_msg "Shutting down VM: $VM ..." 
        $VIRSH shutdown $VM --mode acpi
        sleep 10
        RETVAL=$?
      done
    fi
    sleep 10

    echo "give still running machines some more time..." 
    # wait 20s per still running machine
    list_running_domains | while read VM; do
      log_action_msg "waiting 20s ... for: $VM ..." 
      sleep 20
    done

    echo "Try to cleanly shut down all running KVM domains..." 
    # Try to shutdown each remaining domain, one by one.
    list_running_domains | while read VM; do
      log_action_msg "Shutting down VM: $VM ..." 
      $VIRSH shutdown $VM --mode acpi
      sleep 10
    done

    # Wait until all domains are shut down or timeout has reached.
    END_TIME=$(date -d "$TIMEOUT seconds" +%s)

    while [ $(date +%s) -lt $END_TIME ]; do
      # Break while loop when no domains are left.
      test -z "$(list_running_domains)" && break
      # Wait a litte, we don't want to DoS libvirt.
      sleep 2
    done

    # Clean up left over domains, one by one.
    list_running_domains | while read DOMAIN; do
      # Try to shutdown given domain.
      $VIRSH destroy $DOMAIN
      # Give libvirt some time for killing off the domain.
      sleep 10
    done

    wait_for_closing_machines
    rm -f /tmp/shutdown-kvm-guests
    rm -f /tmp/kvm_control
  ;;
  export)
    JKE_DATE=$(date +%F)
    if [ -f /etc/kvm_box/machines_enabled_export ]; then
      cat /etc/kvm_box/machines_enabled_export  | while read VM; do
        rm -f /tmp/kvm_control_VM_isrunning
        VM_isrunning=0
        list_running_domains | while read RVM; do
          #echo "VM list -$VM- : -$RVM-" 
          if [[ "$VM" ==  "$RVM" ]]; then
            #echo "VM found running..." 
            touch /tmp/kvm_control_VM_isrunning
            VM_isrunning=1
            #echo "$VM_isrunning" 
            break
          fi
          #echo "$VM_isrunning" 
        done

        # took me a while to figure out that the above 'while'-loop 
        # runs in a separate process ... let's use the 'file' as a 
        # kind of interprocess-communication :-) JKE 20161229
        if [ -f /tmp/kvm_control_VM_isrunning ]; then
          VM_isrunning=1
        fi
        rm -f /tmp/kvm_control_VM_isrunning

        #echo "VM status $VM_isrunning" 
        if [ "$VM_isrunning" -ne 0 ]; then
          log_failure_msg "Exporting VM: $VM is not possible, it's running ..." 
        else
          log_action_msg "Exporting VM: $VM ..." 
          VM_BAK_DIR="$VM"_"$JKE_DATE" 
          mkdir "$VM_BAK_DIR" 
          $VIRSH dumpxml $VM > ./$VM_BAK_DIR/$VM.xml
          $VIRSH -q domblklist $VM | awk '{ print$2}' | while read VMHDD; do
            echo "$VM hdd=$VMHDD" 
            if [ -f "$VMHDD" ]; then
              ionice -c 3 rsync --progress $VMHDD ./$VM_BAK_DIR/`basename $VMHDD`
            else
              log_failure_msg "Exporting VM: $VM image-file $VMHDD not found ..." 
            fi
          done
        fi
      done
    else
      log_action_msg "export-list not found" 
    fi
  ;;
  start-vm)
    log_action_msg "Starting VM: $2 ..." 
    $VIRSH start $2
    RETVAL=$?
  ;;
  stop-vm)
    log_action_msg "Stopping VM: $2 ..." 
    $VIRSH shutdown $2 --mode acpi
    RETVAL=$?
  ;;
  poweroff-vm)
    log_action_msg "Powering off VM: $2 ..." 
    $VIRSH destroy $2
    RETVAL=$?
  ;;
  export-vm)
    # NOTE: this exports the given VM
    log_action_msg "Exporting VM: $2 ..." 
    rm -f /tmp/kvm_control_VM_isrunning
    VM_isrunning=0
    JKE_DATE=$(date +%F)
    list_running_domains | while read RVM; do
      #echo "VM list -$VM- : -$RVM-" 
      if [[ "$2" ==  "$RVM" ]]; then
        #echo "VM found running..." 
        touch /tmp/kvm_control_VM_isrunning
        VM_isrunning=1
        #echo "$VM_isrunning" 
        break
      fi
      #echo "$VM_isrunning" 
    done

    # took me a while to figure out that the above 'while'-loop 
    # runs in a separate process ... let's use the 'file' as a 
    # kind of interprocess-communication :-) JKE 20161229
    if [ -f /tmp/kvm_control_VM_isrunning ]; then
      VM_isrunning=1
    fi
    rm -f /tmp/kvm_control_VM_isrunning

    #echo "VM status $VM_isrunning" 
    if [ "$VM_isrunning" -ne 0 ]; then
      log_failure_msg "Exporting VM: $VM is not possible, it's running ..." 
    else
      log_action_msg "Exporting VM: $VM ..." 
      VM_BAK_DIR="$2"_"$JKE_DATE" 
      mkdir "$VM_BAK_DIR" 
      $VIRSH dumpxml $2 > ./$VM_BAK_DIR/$2.xml
      $VIRSH -q domblklist $2 | awk '{ print$2}' | while read VMHDD; do
        echo "$2 hdd=$VMHDD" 
        if [ -f "$VMHDD" ]; then
          ionice -c 3 rsync --progress $VMHDD ./$VM_BAK_DIR/`basename $VMHDD`
        else
          log_failure_msg "Exporting VM: $2 image-file $VMHDD not found ..." 
        fi
      done
    fi
  ;;
  status)
    echo "The following virtual machines are currently running:" 
    list_running_domains | while read VM; do
      echo -n "  $VM" 
      echo " ... is running" 
    done
  ;;

  *)
    echo "Usage: $0 {start|stop|status|export|start-vm <VM name>|stop-vm <VM name>|poweroff-vm <VM name>}|export-vm <VMname>" 
    echo "  start      start all VMs listed in '/etc/kvm_box/machines_enabled_start'" 
    echo "  stop       1st step: acpi-shutdown all VMs listed in '/etc/kvm_box/machines_enabled_stop'" 
    echo "             2nd step: wait 20s for each still running machine to give a chance to shut-down on their own" 
    echo "             3rd step: acpi-shutdown all running VMs" 
    echo "             4th step: wait for all machines shutdown or $TIMEOUT s" 
    echo "             5th step: destroy all sitting VMs" 
    echo "  status     list all running VMs" 
    echo "  export     export all VMs listed in '/etc/kvm_box/machines_enabled_export' to the current directory" 
    echo "  start-vm <VM name>     start the given VM" 
    echo "  stop-vm <VM name>      acpi-shutdown the given VM" 
    echo "  poweroff-vm <VM name>  poweroff the given VM" 
    echo "  export-vm <VM name>    export the given VM to the current directory" 
    exit 3
esac

exit 0

restore 'exported' kvm-machines¶

tar xvf mach-name_202x-01-01.tar.gz 

• copy the image-files to /var/lib/libvirt/images/

set ownership

chown qemu:qemu /var/lib/libvirt/images/*

define the machine by

virsh define mach-name.xml