V Xen Virtualization in red Hat enterprise linuX 5

V Xen Virtualization in red Hat enterprise linuX 5
Xen Virtualization
in Red Hat
Enterprise Linux 5
By Jose de la Rosa
Puneet Dhawan
Related Categories:
Red Hat Enterprise Linux
The open source Xen virtualization hypervisor included
in the Red Hat ® Enterprise Linux ® 5 OS provides key
components to help build dynamic, scalable virtualized
environments. This article describes the basic features
of Xen virtualization in Red Hat Enterprise Linux 5 and
how organizations can deploy it on ninth-generation
Dell™ PowerEdge™ servers.
irtualization enables enterprises to consolidate
allows operating systems to run inside a VM without modi-
multiple servers without sacrificing application
fication, but may require overhead that can reduce
isolation, scale their infrastructure as their needs
grow, and increase availability through dynamic provisioning
Paravirtualization—the approach used by Xen—modifies
and relocation of critical systems. Combining the open
guest operating systems to run in a virtualized environ-
source Xen hypervisor in Red Hat Enterprise Linux 5 with
ment. The VMs interface with the Xen hypervisor using
ninth-generation Dell PowerEdge servers and Dell storage
hypercalls, rather than the system calls used by full virtu-
enables enterprises to create a dynamic data center that can
alization. As shown in Figure 1, the real device drivers run
in a special VM, or domain, called Domain 0 (Dom0).
scale easily to meet enterprise requirements.
Rather than abstracting standard devices for the VMs,
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Xen architecture
Dom0 exposes a set of class devices, such as networks
The virtualization layer, often called the hypervisor or vir-
and storage blocks, to the VMs. I/O data transfers to and
tual machine (VM) monitor, abstracts underlying physical
from each VM through Xen use the XenBus memory-mapped
hardware to present a uniform set of hardware resources—
communication channel. The VMs use paravirtualized
such as processors, memory, networks, and storage
device drivers and a paravirtualized kernel to interoperate
blocks—to VMs. VMs running on a single system share
with Dom0 and the Xen hypervisor.
available physical resources, with the hypervisor multiplex-
Paravirtualization requires modifying guest operating
ing key resources and maintaining isolation among differ-
systems, which is not possible for all popular OS distribu-
ent VMs. Figure 1 shows the architecture of the Xen
tions. However, Xen can take advantage of Intel ®
Virtualization Technology (Intel VT) and AMD Virtualization™
How the hypervisor abstracts the underlying physical
(AMD-V™) technology to run unmodified operating systems
resources defines key characteristics of the virtualization
as well. The virtualization capabilities of Red Hat Enterprise
architecture. Two popular approaches are full virtualization
Linux 5 coupled with ninth-generation Dell PowerEdge serv-
and paravirtualization. Full virtualization presents emu-
ers can create a flexible, powerful virtualized environment
lated resources to VMs that mimic a standard PC architec-
that accommodates both modified and unmodified guest
ture and standard peripheral devices. Using this approach
operating systems.
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
Combining the open source Xen hypervisor
in Red Hat Enterprise Linux 5 with ninthgeneration Dell PowerEdge servers and Dell
storage enables enterprises to create a dynamic
data center that can scale easily to meet
enterprise requirements.”
space is unique and cannot be shared
between VMs. The disk space made available to VMs can be either an image file or a
disk partition.
• Network interfaces: Virtual network interface cards are configured with a persistent
virtual Media Access Control (MAC)
address. When a new VM is created, this
address is selected at random from a
reserved pool of over 16 million addresses,
When Red Hat Enterprise Linux 5 is installed
Manager can schedule virtual processors
making it unlikely that any two VMs will
with virtualization capabilities, the integrated
according to the physical processor
be assigned the same one. Administrators
Xen hypervisor takes control of the system
workload to help optimize available
for complex sites with a large number of
hardware and launches the installed Red Hat
VMs can allocate MAC addresses manu-
Enterprise Linux 5 distribution as Dom0. In
• Memory: Each VM is assigned a part of
ally to help ensure that they remain
addition to serving as the main driver domain
the host system’s physical memory.
unique on the network. Red Hat virtualiza-
for VMs, Dom0 also runs a set of control and
Administrators should typically assign the
tion supports 10/100/1,000 Mbps Ethernet
management services that administrators can
same amount of memory to a VM as they
and 10 Gigabit Ethernet, Fibre Channel,
access through command-line interface (CLI)
would for the same configuration in a non-
and InfiniBand networks.
tools such as xm and virsh or graphical user
virtualized environment. Administrators can
interface (GUI) tools such as Virtual Machine
define the initial and maximum memory
Each VM also has a virtual text console that
Manager (virt-manager).
size when creating VMs, then increase or
connects to the host system. Administrators
decrease the memory allocation at runtime
can redirect guest logins and console output to
without exceeding the specified maximum.
the text console, or configure VMs to use a
The minimum amount of memory recom-
virtual GUI console that corresponds to the
mended for a VM is 256 MB.
physical host’s standard video console. This
Virtualization support and requirements
in Red Hat Enterprise Linux 5
Before creating a virtualized environment with the
Xen technology in Red Hat Enterprise Linux 5,
• Disk space: Each VM is assigned a part of
GUI employs standard graphic adapter features
administrators should be sure they understand
the host system’s disk space. This disk
such as boot messaging, graphical booting,
the support and system requirements for elements such as virtual resources, host servers
and operating systems, processors, storage,
packages, and the Security-Enhanced Linux
Device manager
and control
Red Hat
Enterprise Linux 5
Red Hat
Enterprise Linux 5
Red Hat
Enterprise Linux 5
Windows XP
(fully virtualized)
(SELinux) security policy.
Virtual resources
Red Hat virtualization with Xen technology can
host multiple guest operating systems, each of
which runs in its own domain. Each VM handles
its own applications and can only access the
resources assigned to it. Assigned resources
Port (AGP)
and Power
Interface (ACPI)
Back end
device drivers
device drivers
device drivers
Intel VT
or AMD-V
include the following:
• Processors: Administrators can configure
Safe hardware
Virtual memory
unit (MMU)
Xen hypervisor
a VM with multiple virtual processors, but
the total number of virtual processors
Dell PowerEdge server (SMP, MMU, physical memory, Ethernet, SCSI/IDE)
assigned to a VM must be less than or
equal to the total number of logical processors in the host system. Virtual Machine
Figure 1. Xen hypervisor architecture
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
and multiple virtual terminals, and can launch
the X Window System.
VMs can be identified in any of three
Note: Red Hat virtualization only fully sup-
the BIOS. Administrators can verify that the
ports matching host/guest architectures—that
feature is enabled by running the command
is, environments in which both the host and
grep hvm /sys/hypervisor/properties/
guest OS are either 32-bit or 64-bit operating
capabilities, which should return output
systems. Running a 32-bit guest OS on a 64-bit
similar to the following:
• Domain name: Text string that corresponds
host OS is supported only with paravirtualiza-
to a VM configuration file, used to launch,
tion, and running a 64-bit guest OS on a 32-bit
identify, and control VMs
host OS is not supported.
xen-3.0-x86_32p hvm-3.0-x86_
32 hvm-3.0-x86_32p
• Domain ID: Unique, nonpersistent number
assigned to an active domain, used to iden-
tify and control VMs
Red Hat virtualization requires that the host sys-
trators should look for a setting related to virtual-
• Universally unique identifier: Identifier con-
tem’s processors support Physical Address
ization in the system’s BIOS setup utility, enable
trolled from the VM configuration file that
Extension (PAE) and have either Intel VT or AMD-V
that setting, save, and reboot the system.
helps ensure that VMs are uniquely identi-
enabled. Administrators can determine whether
fied by systems management tools
a system’s processors support PAE using the
command grep pae /proc/cpuinfo. If this
For VM storage, Red Hat virtualization supports
Host servers and operating systems
command returns output similar to the follow-
direct access storage devices as well as network
The following Dell PowerEdge servers and
ing, including the pae entry, then the system
attached storage (NAS) and storage area net-
workstations are certified by Red Hat to run in
supports PAE:
works (SANs) based on Internet SCSI (iSCSI),
If the command returns no output, adminis-
Fibre Channel, and standard network protocols
virtualized environments with Red Hat
Enterprise Linux 5 as the host OS:
flags : fpu vme de pse tsc
• Servers: Dell PowerEdge server model num-
such as Network File System (NFS) and Cluster
msr pae mce cx8 apic mtrr
Logical Volume Manager (CLVM). Administrators
pge mca cmov pat clflush
can manage VM storage in multiple ways. A
bers 700, 750, 800, 830, 840, 850, 860, 1650,
dts acpi mmx fxsr sse sse2
physical block device (hard disk partition or ISO
2600, 2650, 4600, 6600, 6650, 1750, 1800,
ss tm pbe nx up est tm2
image) on the host system can be exported to
a guest domain as a virtual block device.
1850, 1855, 2800, 2850, 6800, 6850, 1900,
1950, 1955, 2900, 2950, 2970, 6950, SC440,
If the command returns no output, then the
system does not support PAE.
SC1420, SC1425, SC1430, and SC1435
• Workstations: Dell Precision workstation
Xen uses a generic Hardware VM (HVM) layer
To run a virtualized environment, the kernel-xen
model numbers 380n, 390n, 470n, 490n,
to support both Intel and AMD™ processors.
kernel must be installed and running on the
670n, and 690n
Administrators can determine whether a sys-
host system. Administrators can determine
tem’s processors support Intel VT or AMD-V
which kernel is running using the command
Red Hat Enterprise Linux 3, Red Hat
using the command egrep -e 'vmx|svm'
uname -r; if this command does not return a
Enterprise Linux 4, and Red Hat Enterprise
/proc/cpuinfo. If this command returns output
kernel with the word “xen” in it, then kernel-xen
Linux 5 can run as fully virtualized guest operat-
similar to the following, including the vmx entry,
is not running. If it is not running, administrators
ing systems, but only Red Hat Enterprise Linux
then the system supports Intel VT or AMD-V:
can determine whether it is installed using the
command rpm -qa | grep kernel-xen. If
4 Update 5 and Red Hat Enterprise Linux 5 can
run as paravirtualized guest operating systems.
flags : fpu tsc msr pae mce
this command returns no output, they must
Other Linux distributions, as well as Microsoft
cx8 apic mtrr mca cmov pat
install the kernel from the installation media
Windows® operating systems, can run as fully
clflush dts acpi mmx fxsr
with the command rpm -ivh kernel-xen.
virtualized guest operating systems, but are not
sse sse2 ss ht tm pbe
supported by Red Hat.
constant_tsc pni monitor
xen the default boot kernel, which they can do
vmx est tm2 xtpr
by changing the default parameter in /boot/
As a host OS, Red Hat Enterprise Linux 5 sup-
grub/grub.conf to the correct number (typically
ports up to four VMs. Red Hat Enterprise Linux 5
Advanced Platform (for four-socket servers)
allows an unlimited number of VMs, enabling
administrators to create as many VMs as the
underlying physical hardware can support.
Next, administrators should make kernel-
If the command returns no output, then the
system does not support Intel VT or AMD-V.
0). They should also verify that the xen, xen-libs,
bridge-utils, gnome-python2-gnomekeyring,
For systems that support Intel VT or AMD-V,
libvirt, libvirt-python, python-virtinst, virt-
administrators must also enable that feature in
manager, and vnc Red Hat Package Manager
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
(RPM™) files are installed, or install them from
If administrators want to create VM image
6. Specify how to assign the VM disk space—a
files in other directories, they must add those
partition on the host system or an image
Because of the interdependencies between
directories to the SELinux policy. For example,
file—and how much space to allocate, then
these RPM packages, administrators should
they could use the following command to create
click the Forward button (see Figure 3). If
typically update them using the yum (Yellowdog
an image in the directory /newdir:
allocating the entire virtual disk now, be
the installation media if necessary.
sure to verify that the host system has
Updater, Modified) package installer. They
must first define the yum repository in
semanage fcontext --add
/etc/yum.conf, then use the command yum
-t xen_image_t '/
install rpm_name to install the necessary
enough disk space to accommodate the
specified amount.
7. Allocate the amount of memory and number
of virtual processors, then click the Forward
packages. For example:
They could then give this directory the
yum install xen
appropriate context using the command
yum install virt-manager
restorecon -v /newdir.
button (see Figure 4).
8. Review the specified parameters and click
the Finish button to begin the VM creation. The OS installation process is the
yum install vnc
Virtual machine creation
in Red Hat Enterprise Linux 5
same as a non-virtual OS installation. If
administrators should reboot the system.
Administrators can take advantage of two primary
shown in Figure 3), then the system
Finally, they should verify that the xend and
tools when creating VMs: the Virtual Machine
xendomains daemons are running using the
Manager GUI tool and the virt-install CLI tool.
After installing the necessary packages,
allocating the entire virtual disk now (as
commands service xend status and
daemon provides virtualization services, while
Creating a virtual machine
with Virtual Machine Manager
the xendomains daemon allows VMs to start
Virtual Machine Manager is a GUI tool provided
and stop automatically when the host system
in Red Hat Enterprise Linux 5 that administrators
boots or shuts down. Both daemons must be
can use to create, pause, resume, stop, and
running to create VMs. If they are not running,
monitor VMs. For example, administrators can
administrators should start them using the com-
use it to create a paravirtualized 32-bit Red Hat
mands service xend start and service
Enterprise Linux 5 guest OS on a 32-bit Red Hat
xendomains start.
Enterprise Linux 5 host OS by performing the
service xendomains status. The xend
following steps:
SELinux security policy
The targeted SELinux security policy for Xen
1. Run Virtual Machine Manager using the com-
requires that disk images have the xen_image_t
mand virt-manager and connect to the
context. If a VM file image is not in that context,
local Xen host. At this point, the only domain
the host system is denied access to that image.
By default, only two directories are in the
Figure 2. “Locating installation media” step
when creating a virtual machine in Red Hat
Enterprise Linux 5 Virtual Machine Manager
running is Dom0.
2. To create a new VM, select File > New
xen_image_t context, as shown by the output
Machine, then click the Forward button.
of the command semanage fcontext -l |
3. Provide a name for the VM—for example,
vm_rhel5_i386—then click the Forward
grep xen_image_t:
all files
4. Select “Paravirtualized” as the virtualization
method, then click the Forward button.
5. Provide the location of the extracted
installation media files for the guest OS
all files
and, if desired, the location of a kickstart
file with the system parameters already
defined, then click the Forward button
(see Figure 2).
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
Figure 3. “Assigning storage space” step
when creating a virtual machine in Red Hat
Enterprise Linux 5 Virtual Machine Manager
Figure 5. Red Hat Enterprise Linux 5 Virtual Machine Manager after creating a virtual machine
Figure 4. “Allocate memory and CPU” step
when creating a virtual machine in Red Hat
Enterprise Linux 5 Virtual Machine Manager
typically takes several minutes to create
the disk space before it begins installation. When the OS installation process
ends, the virtual window closes and the
VM is ready to start.
9. To start the VM, enter the command xm
create vm_name. Virtual Machine Manager
should now show both Dom0 and the VM
running (see Figure 5). To open a Virtual
Network Computing (VNC) display window
for this VM, select the VM and click the Open
button (see Figure 6).
Creating a virtual machine with virt-install
Administrators can also use the virt-install CLI
tool to create a paravirtualized VM. Specifying
parameters in this way enables administrators
to automate VM creation using shell scripts. The
syntax is as follows:
Figure 6. Virtual machine booting in Red Hat Enterprise Linux 5
virt-install --name=vm_name
For example, administrators could create
--ram=memory --vcpus=no_of_
allocate to the VM, vm_image_file is the
vcpus --file=vm_image_file
file to use as the disk image, vm_disk_size
is the amount of VM disk space to allocate to
--vnc --paravirt
the VM (in gigabytes), --vnc sets the VM to
use VNC for graphics support, --paravirt
i386 --ram=1000 --vcpus=2
denotes that the VM should be paravirtual-
In this command, vm_name is the name of
ized, and OS_source_location is the loca-
vm_rhel5_i386 --file-
the VM, memory is the amount of memory to
tion of the extracted installation media files
size=10 --vnc --paravirt
allocate to the VM (in megabytes), no_of_
for the guest OS. This command also launches
vcpus is the number of virtual processors to
a VNC display window.
the VM from the preceding section as follows:
virt-install --name=vm_rhel5_
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
# Automatically generated xen config file
name = "vm_rhel5_i386"
memory = "1000"
disk = [ 'tap:aio:/var/lib/xen/images/vm_rhel5_i386,xvda,w', ]
vif = [ 'mac=00:16:3e:0c:77:c5, bridge=xenbr0', ]
vfb = ["type=vnc,vncunused=1"]
uuid = "9847a069-51e4-8173-9d1b-2d033cf63d5b"
= 'restart'
= 'restart'
Specifies the name of the virtual guest.
Specifies the amount of memory in megabytes.
Lists the block and physical devices to export to the domain. In this case, it lists
the virtual guest image file, the device name and the access permissions (write).
Lists the randomly-assigned MAC addresses and bridges.
Specifies the virtual frame buffer. In this case, we use VNC.
Used to uniquely identify the virtual guest.
bootloader Specifies to use the Xen bootloader.
Specifies the numbers of virtual CPUs.
Specifies what action to take when the guest reboots.
Specifies what action to take when the guest crashes.
Figure 7. /etc/xen/vm_rhel5_i386 configuration file
Red Hat Enterprise Linux 5 Xen
configuration and log files
xend daemon and qemu-dm process, for exam-
hot-plug events, including events when a
ple, write to multiple log files:
device or network script does not come
The Red Hat Enterprise Linux 5 Xen configuration
files are located in the /etc/xen directory. Each
• xend-debug.log: Contains logs of event
• qemu-dm.pid.log: Created by the qemu-dm
VM has a corresponding configuration file in
errors from xend and the virtualization sub-
process for each fully virtualized guest
/etc/xen, which is created automatically when
systems (such as the frame buffer and
(where pid is the process identifier)
the VMs are created and has the same name
Python scripts)
as its corresponding VM. Figure 7 shows the
• xend.log: Contains data collected by the
/etc/xen/vm_rhel5_i386 configuration file for the
xend daemon, including system events,
Virtual machine management
VM created in the “Virtual machine creation in
administrator actions, and VM operations
Administrators can use the xm and virsh
Red Hat Enterprise Linux 5” section in this article.
such as create, shutdown, and destroy;
command-line interface tools to create,
For more information on available configuration
this log is typically the first place adminis-
manage, and troubleshoot VMs (see Figure 8).
items, see the xmdomain.cfg man page.
trators should look when troubleshooting
event- or performance-related problems
arguments; for more information, see the xm
The Red Hat Enterprise Linux 5 Xen log files
are located in the /var/log/xen directory. The
• xen-hotplug.log: Contains data from
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
and virsh man pages.
Dynamic, scalable virtualized environments
Starting and
stopping VMs
Red Hat Enterprise Linux 5 incorporates Xen
xm create
Creates a domain based on a configuration file
virtualization technology to help create a robust,
xm destroy
Terminates a domain
xm pause
Pauses execution of a domain
Combined with ninth-generation Dell PowerEdge
xm reboot
Reboots a domain
servers, Red Hat virtualization can provide
xm shutdown
Shuts down a domain
xm save
Saves a domain state to restore later
xm restore
Restores a domain from a saved state
xm uptime
Displays uptime for a domain
xm top
Monitors a host and its domains in real time
xm list
Displays domain information
xm info
Displays host information
xm vcpu-list
Lists domain virtual processors
xm network-list
Lists domain virtual network interfaces
Puneet has a bachelor’s degree in Electrical
virsh nodeinfo
Displays node information
Engineering from Punjab Engineering College
virsh vcpuinfo
Displays domain virtual processor information
xm console
Attaches to a domain console
xm dump-core
Displays a core dump for a specific domain
xm dmesg
Reads and/or clears the xend daemon’s message buffer
xm log
Displays the xend log
virsh dominfo
Displays domain information
xm mem-max
Sets the maximum amount of memory for a domain
xm mem-set
Sets the current memory usage for a domain
xm vcpu-set
Sets the number of active processors for a domain
virsh dumpxml
Displays domain information in XML
virsh dump
Saves a core dump for a specific domain to a file
xm rename
Renames a domain
xm sysrq
Sends a system request to a domain
xm block-attach
Creates a new virtual block device
xm block-detach
Destroys a domain’s virtual block device
xm block-list
Lists virtual block devices for a domain
xm network-attach
Creates a new network device
xm network-detach
Destroys a network device
secure, easy-to-manage virtualization platform
that can scale flexibly to meet enterprise needs.
high-performance virtualized environments for
enterprises of all sizes.
Jose De la Rosa is a member of the Dell Linux
Engineering Group. He has a bachelor’s degree
in Electrical Engineering and a master’s degree
in Computer Engineering from the University of
Texas at El Paso.
Puneet Dhawan is a systems engineer in the
Dell Virtualization Solutions Engineering Group.
(PEC) and a master’s degree in Computer
Engineering from Texas A&M University.
Figure 8. Commands for the xm and virsh tools for creating, managing, and troubleshooting
virtual machines
Reprinted from Dell Power Solutions, November 2007. Copyright © 2007 Dell Inc. All rights reserved.
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