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16.6. Booting virtual machines from a PXE server

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

警告

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

16.6.1. Setting up a PXE boot server on a virtual network
复制链接

You can 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.

Prerequisites

  • 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.

Procedure

  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 example-pxelinux is the name of the boot image file. 

    <ip address='192.0.2.1' netmask='255.255.255.0'>
   <tftp root='/var/lib/tftpboot'/>
   <dhcp>
      <range start='192.0.2.2' end='192.0.2.254' />
      <bootp file='example-pxelinux'/>
   </dhcp>
</ip>

  8. Start the virtual network: 

    # virsh net-start default

Verification

  • Verify that the default virtual network is active: 

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

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

Prerequisites

Procedure

  • 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. To do so, ensure the guest network is configured to use your virtual network and that the network is configured to be the primary boot device: 

      <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'/>
   <boot order='1'/>
</interface>

Verification

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

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

Prerequisites

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

Procedure

  • 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. To do so, ensure that the VM is configured with a bridged network and that the network is configured to be the primary boot device: 

      <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'/>
   <boot order='1'/>
</interface>

Verification

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