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16.5. Booting virtual machines from a PXE server

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Virtual machines (VMs) that use Preboot Execution Environment (PXE) can boot and load their configuration from a network. This chapter describes how to use libvirt to boot VMs from a PXE server on a virtual or bridged network.

Avertissement

These procedures are provided only as an example. Ensure that you have sufficient backups before proceeding.

16.5.1. Setting up a PXE boot server on a virtual network

This procedure describes how to configure a libvirt virtual network to provide Preboot Execution Environment (PXE). This enables virtual machines on your host to be configured to boot from a boot image available on the virtual network.

Conditions préalables

  • A local PXE server (DHCP and TFTP), such as:

    • libvirt internal server
    • manually configured dhcpd and tftpd
    • dnsmasq
    • Cobbler server
  • PXE boot images, such as PXELINUX configured by Cobbler or manually.

Procédure

  1. Place the PXE boot images and configuration in /var/lib/tftpboot folder.

  2. Set folder permissions: 

    # chmod -R a+r /var/lib/tftpboot

  3. Set folder ownership: 

    # chown -R nobody: /var/lib/tftpboot

  4. Update SELinux context: 

    # chcon -R --reference /usr/sbin/dnsmasq /var/lib/tftpboot
# chcon -R --reference /usr/libexec/libvirt_leaseshelper /var/lib/tftpboot

  5. Shut down the virtual network: 

    # virsh net-destroy default

  6. Open the virtual network configuration file in your default editor: 

    # virsh net-edit default

  7. Edit the <ip> element to include the appropriate address, network mask, DHCP address range, and boot file, where BOOT_FILENAME is the name of the boot image file. 

    <ip address='192.168.122.1' netmask='255.255.255.0'>
   <tftp root='/var/lib/tftpboot' />
   <dhcp>
      <range start='192.168.122.2' end='192.168.122.254' />
      <bootp file='BOOT_FILENAME' />
   </dhcp>
</ip>

  8. Start the virtual network: 

    # virsh net-start default

Vérification

  • Verify that the default virtual network is active: 

    # virsh net-list
Name             State    Autostart   Persistent
---------------------------------------------------
default          active   no          no

Ressources supplémentaires

16.5.2. Booting virtual machines using PXE and a virtual network

To boot virtual machines (VMs) from a Preboot Execution Environment (PXE) server available on a virtual network, you must enable PXE booting.

Conditions préalables

Procédure

  • Create a new VM with PXE booting enabled. For example, to install from a PXE, available on the default virtual network, into a new 10 GB qcow2 image file: 

    # virt-install --pxe --network network=default --memory 2048 --vcpus 2 --disk size=10

    • Alternatively, you can manually edit the XML configuration file of an existing VM:

      1. Ensure the <os> element has a <boot dev='network'/> element inside: 

        <os>
   <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
   <boot dev='network'/>
   <boot dev='hd'/>
</os>

      2. Ensure the guest network is configured to use your virtual network: 

        <interface type='network'>
   <mac address='52:54:00:66:79:14'/>
   <source network='default'/>
   <target dev='vnet0'/>
   <alias name='net0'/>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>

Vérification

  • Start the VM using the virsh start command. If PXE is configured correctly, the VM boots from a boot image available on the PXE server.

16.5.3. Booting virtual machines using PXE and a bridged network

To boot virtual machines (VMs) from a Preboot Execution Environment (PXE) server available on a bridged network, you must enable PXE booting.

Conditions préalables

  • Network bridging is enabled.
  • A PXE boot server is available on the bridged network.

Procédure

  • Create a new VM with PXE booting enabled. For example, to install from a PXE, available on the breth0 bridged network, into a new 10 GB qcow2 image file: 

    # virt-install --pxe --network bridge=breth0 --memory 2048 --vcpus 2 --disk size=10

    • Alternatively, you can manually edit the XML configuration file of an existing VM:

      1. Ensure the <os> element has a <boot dev='network'/> element inside: 

        <os>
   <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
   <boot dev='network'/>
   <boot dev='hd'/>
</os>

      2. Ensure the VM is configured to use your bridged network: 

        <interface type='bridge'>
   <mac address='52:54:00:5a:ad:cb'/>
   <source bridge='breth0'/>
   <target dev='vnet0'/>
   <alias name='net0'/>
   <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>

Vérification

  • Start the VM using the virsh start command. If PXE is configured correctly, the VM boots from a boot image available on the PXE server.

Ressources supplémentaires

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