Installation guide

Chapter 1. Introduction
2
KSM
Kernel SamePage Merging (KSM) is used by the KVM hypervisor to allow KVM guests to share
identical memory pages. These shared pages are usually common libraries or other identical, high-use
data. KSM allows for greater guest density of identical or similar guest operating systems by avoiding
memory duplication.
For more information on KSM, refer to Chapter 21, KSM.
1.3. libvirt and the libvirt tools
Libvirt is a hypervisor-independent virtualization API that is able to interact with the virtualization
capabilities of a range of operating systems.
libvirt provides a common, generic and stable layer to securely manage virtualized guests on a host.
libvirt provides a common interface for managing local systems and networked hosts. libvirt provides
all APIs required to provision, create, modify, monitor, control, migrate and stop virtualized guests
if the hypervisor supports these operations. Although multiple hosts may be accessed with libvirt
simultaneously, the APIs are limited to single node operations.
libvirt is designed as a building block for higher level management tools and applications. libvirt
focuses on managing single hosts, with the exception of migration capabilities. libvirt provides APIs to
enumerate, monitor and use the resources available on the managed node, including CPUs, memory,
storage, networking and Non-Uniform Memory Access (NUMA) partitions. The management tools can
be located on separate physical machines from the host using secure protocols.
Red Hat Enterprise Linux 6 supports libvirt and included libvirt-based tools as its default method for
virtualization management.
libvirt is free software available under the GNU Lesser General Public License. The libvirt project aims
to provide a long term stable C API. The libvirt Open Source project currently supports Xen, QEmu,
KVM, LXC, OpenVZ, VirtualBox, OpenNebula, and VMware ESX. The Red Hat Enterprise Linux 6
libvirt package supports Xen on Red Hat Enterprise Linux 5 and KVM on Red Hat Enterprise Linux 5
and Red Hat Enterprise Linux 6.
virsh
The virsh command-line tool is built on the libvirt management API and operates as an
alternative to the graphical virt-manager application. The virsh command can be used in read-
only mode by unprivileged users or, with root access, full administration functionality. The virsh
command is ideal for scripting virtualization administration.
The virsh command is included in the libvirt-client package.
virt-manager
virt-manager is a graphical desktop tool for managing virtualized guests. virt-manager can be
used to perform virtualization administration, virtualized guest creation, migration and configuration
tasks. virt-manager allows access to graphical guest consoles. virt-manager can view
virtualized guests, host statistics, device information and performance graphs. virt-manager can
manage the local hypervisor and remote hypervisors using the same interface and methods.
1.4. Virtualized hardware devices
Virtualization on Red Hat Linux 6 presents three distinct types of system devices to virtualized guests.
The three types include: