Explore information related to kvm pxe boot

Boot a guest using PXE - Do it now

This article covers how to boot a guest using PXE. PXE booting is supported for Guest Operating Systems that are listed in the VMware Guest Operating System Compatibility list and whose operating system vendor supports PXE booting of the operating system.

The virtual machine must meet the following requirements:

1. Have a virtual disk without operating system software and with enough free disk space to store the intended system software.

2. Have a network adapter connected to the network where the PXE server resides.

A virtual machine is not complete until you install the guest operating system and VMware Tools. Installing a guest operating system in your virtual machine is essentially the same as installing it in a physical computer.

To use PXE with Virtual Machines:

You can start a virtual machine from a network device and remotely install a guest operating system using a Preboot Execution Environment (PXE). 

You do not need the operating system installation media. When you turn on the virtual machine, the virtual machine detects the PXE server.

To Install a Guest Operating System from Media:

You can install a guest operating system from a CD-ROM or from an ISO image. Installing from an ISO image is typically faster and more convenient than a CD-ROM installation. 

To Upload ISO Image Installation Media for a Guest Operating System:

You can upload an ISO image file to a datastore from your local computer. You can do this when a virtual machine, host, or cluster does not have access to a datastore or to a shared datastore that has the guest operating system installation media that you require.

How to Use a private libvirt network ?

1. Boot a guest virtual machine using libvirt with PXE booting enabled. You can use the virt-install command to create/install a new virtual machine using PXE:

virt-install --pxe --network network=default --prompt

2. Alternatively, ensure that the guest network is configured to use your private libvirt network, and that the XML guest configuration file has a <boot dev='network'/> element inside the <os> element, as shown in the following example:


   <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>

   <boot dev='network'/>

   <boot dev='hd'/>


3. Also ensure that the guest virtual machine is connected to the private 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'/>


Read More

PXE Boot or DHCP Failure on Guest - Fix it now

This article covers how to fix PXE Boot (or DHCP) Failure on Guest.

Nature of this error:

A guest virtual machine starts successfully, but is then either unable to acquire an IP address from DHCP or boot using the PXE protocol, or both. There are two common causes of this error: having a long forward delay time set for the bridge, and when the iptables package and kernel do not support checksum mangling rules.


Long forward delay time on bridge.

This is the most common cause of this error. If the guest network interface is connecting to a bridge device that has STP (Spanning Tree Protocol) enabled, as well as a long forward delay set, the bridge will not forward network packets from the guest virtual machine onto the bridge until at least that number of forward delay seconds have elapsed since the guest connected to the bridge. This delay allows the bridge time to watch traffic from the interface and determine the MAC addresses behind it, and prevent forwarding loops in the network topology. If the forward delay is longer than the timeout of the guest's PXE or DHCP client, then the client's operation will fail, and the guest will either fail to boot (in the case of PXE) or fail to acquire an IP address (in the case of DHCP).


If this is the case, change the forward delay on the bridge to 0, or disable STP on the bridge.

This solution applies only if the bridge is not used to connect multiple networks, but just to connect multiple endpoints to a single network (the most common use case for bridges used by libvirt).

If the guest has interfaces connecting to a libvirt-managed virtual network, edit the definition for the network, and restart it. 

For example, edit the default network with the following command:

# virsh net-edit default

Add the following attributes to the <bridge> element:

<name_of_bridge='virbr0' delay='0' stp='on'/>


If this problem is still not resolved, the issue may be due to a conflict between firewalld and the default libvirt network.

To fix this, stop firewalld with the service firewalld stop command, then restart libvirt with the service libvirtd restart command.

Read More