view docs/src/user.tex @ 9694:1d42739fee3b

Fix user manual regarding trace buffers.
1. debug building is not needed for tracing buffer...
2. ...but trace buffer default size is 0

Signed-off-by: Atsushi SAKAI <>
date Fri Apr 21 09:09:29 2006 +0100 (2006-04-21)
parents 14659382edd3
children 6d476981e3a5
line source
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3 \setstretch{1.15}
5 \renewcommand{\ttdefault}{pcr}
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10 \latexhtml{\renewcommand{\path}[1]{{\small {\tt #1}}}}{\renewcommand{\path}[1]{{\tt #1}}}
13 \begin{document}
16 \pagestyle{empty}
17 \begin{center}
18 \vspace*{\fill}
19 \includegraphics{figs/xenlogo.eps}
20 \vfill
21 \vfill
22 \vfill
23 \begin{tabular}{l}
24 {\Huge \bf Users' Manual} \\[4mm]
25 {\huge Xen v3.0} \\[80mm]
26 \end{tabular}
27 \end{center}
29 {\bf DISCLAIMER: This documentation is always under active development
30 and as such there may be mistakes and omissions --- watch out for
31 these and please report any you find to the developers' mailing list,
32 The latest version is always available
33 on-line. Contributions of material, suggestions and corrections are
34 welcome.}
36 \vfill
37 \clearpage
41 \pagestyle{empty}
43 \vspace*{\fill}
45 Xen is Copyright \copyright 2002-2005, University of Cambridge, UK, XenSource
46 Inc., IBM Corp., Hewlett-Packard Co., Intel Corp., AMD Inc., and others. All
47 rights reserved.
49 Xen is an open-source project. Most portions of Xen are licensed for copying
50 under the terms of the GNU General Public License, version 2. Other portions
51 are licensed under the terms of the GNU Lesser General Public License, the
52 Zope Public License 2.0, or under ``BSD-style'' licenses. Please refer to the
53 COPYING file for details.
55 Xen includes software by Christopher Clark. This software is covered by the
56 following licence:
58 \begin{quote}
59 Copyright (c) 2002, Christopher Clark. All rights reserved.
61 Redistribution and use in source and binary forms, with or without
62 modification, are permitted provided that the following conditions are met:
64 \begin{itemize}
65 \item Redistributions of source code must retain the above copyright notice,
66 this list of conditions and the following disclaimer.
68 \item Redistributions in binary form must reproduce the above copyright
69 notice, this list of conditions and the following disclaimer in the
70 documentation and/or other materials provided with the distribution.
72 \item Neither the name of the original author; nor the names of any
73 contributors may be used to endorse or promote products derived from this
74 software without specific prior written permission.
75 \end{itemize}
87 \end{quote}
89 \cleardoublepage
93 \pagestyle{plain}
94 \pagenumbering{roman}
95 { \parskip 0pt plus 1pt
96 \tableofcontents }
97 \cleardoublepage
101 \pagenumbering{arabic}
102 \raggedbottom
103 \widowpenalty=10000
104 \clubpenalty=10000
105 \parindent=0pt
106 \parskip=5pt
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111 \setstretch{1.1}
114 %% Chapter Introduction moved to introduction.tex
115 \chapter{Introduction}
118 Xen is an open-source \emph{para-virtualizing} virtual machine monitor
119 (VMM), or ``hypervisor'', for the x86 processor architecture. Xen can
120 securely execute multiple virtual machines on a single physical system
121 with close-to-native performance. Xen facilitates enterprise-grade
122 functionality, including:
124 \begin{itemize}
125 \item Virtual machines with performance close to native hardware.
126 \item Live migration of running virtual machines between physical hosts.
127 \item Up to 32 virtual CPUs per guest virtual machine, with VCPU hotplug.
128 \item x86/32, x86/32 with PAE, and x86/64 platform support.
129 \item Intel Virtualization Technology (VT-x) for unmodified guest operating systems (including Microsoft Windows).
130 \item Excellent hardware support (supports almost all Linux device
131 drivers).
132 \end{itemize}
135 \section{Usage Scenarios}
137 Usage scenarios for Xen include:
139 \begin{description}
140 \item [Server Consolidation.] Move multiple servers onto a single
141 physical host with performance and fault isolation provided at the
142 virtual machine boundaries.
143 \item [Hardware Independence.] Allow legacy applications and operating
144 systems to exploit new hardware.
145 \item [Multiple OS configurations.] Run multiple operating systems
146 simultaneously, for development or testing purposes.
147 \item [Kernel Development.] Test and debug kernel modifications in a
148 sand-boxed virtual machine --- no need for a separate test machine.
149 \item [Cluster Computing.] Management at VM granularity provides more
150 flexibility than separately managing each physical host, but better
151 control and isolation than single-system image solutions,
152 particularly by using live migration for load balancing.
153 \item [Hardware support for custom OSes.] Allow development of new
154 OSes while benefiting from the wide-ranging hardware support of
155 existing OSes such as Linux.
156 \end{description}
159 \section{Operating System Support}
161 Para-virtualization permits very high performance virtualization, even
162 on architectures like x86 that are traditionally very hard to
163 virtualize.
165 This approach requires operating systems to be \emph{ported} to run on
166 Xen. Porting an OS to run on Xen is similar to supporting a new
167 hardware platform, however the process is simplified because the
168 para-virtual machine architecture is very similar to the underlying
169 native hardware. Even though operating system kernels must explicitly
170 support Xen, a key feature is that user space applications and
171 libraries \emph{do not} require modification.
173 With hardware CPU virtualization as provided by Intel VT and AMD
174 SVM technology, the ability to run an unmodified guest OS kernel
175 is available. No porting of the OS is required, although some
176 additional driver support is necessary within Xen itself. Unlike
177 traditional full virtualization hypervisors, which suffer a tremendous
178 performance overhead, the combination of Xen and VT or Xen and
179 Pacifica technology complement one another to offer superb performance
180 for para-virtualized guest operating systems and full support for
181 unmodified guests running natively on the processor. Full support for
182 VT and Pacifica chipsets will appear in early 2006.
184 Paravirtualized Xen support is available for increasingly many
185 operating systems: currently, mature Linux support is available and
186 included in the standard distribution. Other OS ports---including
187 NetBSD, FreeBSD and Solaris x86 v10---are nearing completion.
190 \section{Hardware Support}
192 Xen currently runs on the x86 architecture, requiring a ``P6'' or
193 newer processor (e.g.\ Pentium Pro, Celeron, Pentium~II, Pentium~III,
194 Pentium~IV, Xeon, AMD~Athlon, AMD~Duron). Multiprocessor machines are
195 supported, and there is support for HyperThreading (SMT). In
196 addition, ports to IA64 and Power architectures are in progress.
198 The default 32-bit Xen supports up to 4GB of memory. However Xen 3.0
199 adds support for Intel's Physical Addressing Extensions (PAE), which
200 enable x86/32 machines to address up to 64 GB of physical memory. Xen
201 3.0 also supports x86/64 platforms such as Intel EM64T and AMD Opteron
202 which can currently address up to 1TB of physical memory.
204 Xen offloads most of the hardware support issues to the guest OS
205 running in the \emph{Domain~0} management virtual machine. Xen itself
206 contains only the code required to detect and start secondary
207 processors, set up interrupt routing, and perform PCI bus
208 enumeration. Device drivers run within a privileged guest OS rather
209 than within Xen itself. This approach provides compatibility with the
210 majority of device hardware supported by Linux. The default XenLinux
211 build contains support for most server-class network and disk
212 hardware, but you can add support for other hardware by configuring
213 your XenLinux kernel in the normal way.
216 \section{Structure of a Xen-Based System}
218 A Xen system has multiple layers, the lowest and most privileged of
219 which is Xen itself.
221 Xen may host multiple \emph{guest} operating systems, each of which is
222 executed within a secure virtual machine. In Xen terminology, a
223 \emph{domain}. Domains are scheduled by Xen to make effective use of the
224 available physical CPUs. Each guest OS manages its own applications.
225 This management includes the responsibility of scheduling each
226 application within the time allotted to the VM by Xen.
228 The first domain, \emph{domain~0}, is created automatically when the
229 system boots and has special management privileges. Domain~0 builds
230 other domains and manages their virtual devices. It also performs
231 administrative tasks such as suspending, resuming and migrating other
232 virtual machines.
234 Within domain~0, a process called \emph{xend} runs to manage the system.
235 \Xend\ is responsible for managing virtual machines and providing access
236 to their consoles. Commands are issued to \xend\ over an HTTP interface,
237 via a command-line tool.
240 \section{History}
242 Xen was originally developed by the Systems Research Group at the
243 University of Cambridge Computer Laboratory as part of the XenoServers
244 project, funded by the UK-EPSRC\@.
246 XenoServers aim to provide a ``public infrastructure for global
247 distributed computing''. Xen plays a key part in that, allowing one to
248 efficiently partition a single machine to enable multiple independent
249 clients to run their operating systems and applications in an
250 environment. This environment provides protection, resource isolation
251 and accounting. The project web page contains further information along
252 with pointers to papers and technical reports:
253 \path{}
255 Xen has grown into a fully-fledged project in its own right, enabling us
256 to investigate interesting research issues regarding the best techniques
257 for virtualizing resources such as the CPU, memory, disk and network.
258 Project contributors now include XenSource, Intel, IBM, HP, AMD, Novell,
259 RedHat.
261 Xen was first described in a paper presented at SOSP in
262 2003\footnote{\tt
263}, and the first
264 public release (1.0) was made that October. Since then, Xen has
265 significantly matured and is now used in production scenarios on many
266 sites.
268 \section{What's New}
270 Xen 3.0.0 offers:
272 \begin{itemize}
273 \item Support for up to 32-way SMP guest operating systems
274 \item Intel (Physical Addressing Extensions) PAE to support 32-bit
275 servers with more than 4GB physical memory
276 \item x86/64 support (Intel EM64T, AMD Opteron)
277 \item Intel VT-x support to enable the running of unmodified guest
278 operating systems (Windows XP/2003, Legacy Linux)
279 \item Enhanced control tools
280 \item Improved ACPI support
281 \item AGP/DRM graphics
282 \end{itemize}
285 Xen 3.0 features greatly enhanced hardware support, configuration
286 flexibility, usability and a larger complement of supported operating
287 systems. This latest release takes Xen a step closer to being the
288 definitive open source solution for virtualization.
292 \part{Installation}
294 %% Chapter Basic Installation
295 \chapter{Basic Installation}
297 The Xen distribution includes three main components: Xen itself, ports
298 of Linux and NetBSD to run on Xen, and the userspace tools required to
299 manage a Xen-based system. This chapter describes how to install the
300 Xen~3.0 distribution from source. Alternatively, there may be pre-built
301 packages available as part of your operating system distribution.
304 \section{Prerequisites}
305 \label{sec:prerequisites}
307 The following is a full list of prerequisites. Items marked `$\dag$' are
308 required by the \xend\ control tools, and hence required if you want to
309 run more than one virtual machine; items marked `$*$' are only required
310 if you wish to build from source.
311 \begin{itemize}
312 \item A working Linux distribution using the GRUB bootloader and running
313 on a P6-class or newer CPU\@.
314 \item [$\dag$] The \path{iproute2} package.
315 \item [$\dag$] The Linux bridge-utils\footnote{Available from {\tt
316}} (e.g., \path{/sbin/brctl})
317 \item [$\dag$] The Linux hotplug system\footnote{Available from {\tt
318}} (e.g.,
319 \path{/sbin/hotplug} and related scripts). On newer distributions,
320 this is included alongside the Linux udev system\footnote{See {\tt
322 \item [$*$] Build tools (gcc v3.2.x or v3.3.x, binutils, GNU make).
323 \item [$*$] Development installation of zlib (e.g.,\ zlib-dev).
324 \item [$*$] Development installation of Python v2.2 or later (e.g.,\
325 python-dev).
326 \item [$*$] \LaTeX\ and transfig are required to build the
327 documentation.
328 \end{itemize}
330 Once you have satisfied these prerequisites, you can now install either
331 a binary or source distribution of Xen.
333 \section{Installing from Binary Tarball}
335 Pre-built tarballs are available for download from the XenSource downloads
336 page:
337 \begin{quote} {\tt}
338 \end{quote}
340 Once you've downloaded the tarball, simply unpack and install:
341 \begin{verbatim}
342 # tar zxvf xen-3.0-install.tgz
343 # cd xen-3.0-install
344 # sh ./
345 \end{verbatim}
347 Once you've installed the binaries you need to configure your system as
348 described in Section~\ref{s:configure}.
350 \section{Installing from RPMs}
351 Pre-built RPMs are available for download from the XenSource downloads
352 page:
353 \begin{quote} {\tt}
354 \end{quote}
356 Once you've downloaded the RPMs, you typically install them via the
357 RPM commands:
359 \verb|# rpm -iv rpmname|
361 See the instructions and the Release Notes for each RPM set referenced at:
362 \begin{quote}
363 {\tt}.
364 \end{quote}
366 \section{Installing from Source}
368 This section describes how to obtain, build and install Xen from source.
370 \subsection{Obtaining the Source}
372 The Xen source tree is available as either a compressed source tarball
373 or as a clone of our master Mercurial repository.
375 \begin{description}
376 \item[Obtaining the Source Tarball]\mbox{} \\
377 Stable versions and daily snapshots of the Xen source tree are
378 available from the Xen download page:
379 \begin{quote} {\tt \tt}
380 \end{quote}
381 \item[Obtaining the source via Mercurial]\mbox{} \\
382 The source tree may also be obtained via the public Mercurial
383 repository at:
384 \begin{quote}{\tt}
385 \end{quote} See the instructions and the Getting Started Guide
386 referenced at:
387 \begin{quote}
388 {\tt}
389 \end{quote}
390 \end{description}
392 % \section{The distribution}
393 %
394 % The Xen source code repository is structured as follows:
395 %
396 % \begin{description}
397 % \item[\path{tools/}] Xen node controller daemon (Xend), command line
398 % tools, control libraries
399 % \item[\path{xen/}] The Xen VMM.
400 % \item[\path{buildconfigs/}] Build configuration files
401 % \item[\path{linux-*-xen-sparse/}] Xen support for Linux.
402 % \item[\path{patches/}] Experimental patches for Linux.
403 % \item[\path{docs/}] Various documentation files for users and
404 % developers.
405 % \item[\path{extras/}] Bonus extras.
406 % \end{description}
408 \subsection{Building from Source}
410 The top-level Xen Makefile includes a target ``world'' that will do the
411 following:
413 \begin{itemize}
414 \item Build Xen.
415 \item Build the control tools, including \xend.
416 \item Download (if necessary) and unpack the Linux 2.6 source code, and
417 patch it for use with Xen.
418 \item Build a Linux kernel to use in domain~0 and a smaller unprivileged
419 kernel, which can be used for unprivileged virtual machines.
420 \end{itemize}
422 After the build has completed you should have a top-level directory
423 called \path{dist/} in which all resulting targets will be placed. Of
424 particular interest are the two XenLinux kernel images, one with a
425 ``-xen0'' extension which contains hardware device drivers and drivers
426 for Xen's virtual devices, and one with a ``-xenU'' extension that
427 just contains the virtual ones. These are found in
428 \path{dist/install/boot/} along with the image for Xen itself and the
429 configuration files used during the build.
431 %The NetBSD port can be built using:
432 %\begin{quote}
433 %\begin{verbatim}
434 %# make netbsd20
435 %\end{verbatim}\end{quote}
436 %NetBSD port is built using a snapshot of the netbsd-2-0 cvs branch.
437 %The snapshot is downloaded as part of the build process if it is not
438 %yet present in the \path{NETBSD\_SRC\_PATH} search path. The build
439 %process also downloads a toolchain which includes all of the tools
440 %necessary to build the NetBSD kernel under Linux.
442 To customize the set of kernels built you need to edit the top-level
443 Makefile. Look for the line:
444 \begin{quote}
445 \begin{verbatim}
446 KERNELS ?= linux-2.6-xen0 linux-2.6-xenU
447 \end{verbatim}
448 \end{quote}
450 You can edit this line to include any set of operating system kernels
451 which have configurations in the top-level \path{buildconfigs/}
452 directory.
454 %% Inspect the Makefile if you want to see what goes on during a
455 %% build. Building Xen and the tools is straightforward, but XenLinux
456 %% is more complicated. The makefile needs a `pristine' Linux kernel
457 %% tree to which it will then add the Xen architecture files. You can
458 %% tell the makefile the location of the appropriate Linux compressed
459 %% tar file by
460 %% setting the LINUX\_SRC environment variable, e.g. \\
461 %% \verb!# LINUX_SRC=/tmp/linux-2.6.11.tar.bz2 make world! \\ or by
462 %% placing the tar file somewhere in the search path of {\tt
463 %% LINUX\_SRC\_PATH} which defaults to `{\tt .:..}'. If the
464 %% makefile can't find a suitable kernel tar file it attempts to
465 %% download it from (this won't work if you're behind a
466 %% firewall).
468 %% After untaring the pristine kernel tree, the makefile uses the {\tt
469 %% mkbuildtree} script to add the Xen patches to the kernel.
471 %% \framebox{\parbox{5in}{
472 %% {\bf Distro specific:} \\
473 %% {\it Gentoo} --- if not using udev (most installations,
474 %% currently), you'll need to enable devfs and devfs mount at boot
475 %% time in the xen0 config. }}
477 \subsection{Custom Kernels}
479 % If you have an SMP machine you may wish to give the {\tt '-j4'}
480 % argument to make to get a parallel build.
482 If you wish to build a customized XenLinux kernel (e.g.\ to support
483 additional devices or enable distribution-required features), you can
484 use the standard Linux configuration mechanisms, specifying that the
485 architecture being built for is \path{xen}, e.g:
486 \begin{quote}
487 \begin{verbatim}
488 # cd linux-2.6.12-xen0
489 # make ARCH=xen xconfig
490 # cd ..
491 # make
492 \end{verbatim}
493 \end{quote}
495 You can also copy an existing Linux configuration (\path{.config}) into
496 e.g.\ \path{linux-2.6.12-xen0} and execute:
497 \begin{quote}
498 \begin{verbatim}
499 # make ARCH=xen oldconfig
500 \end{verbatim}
501 \end{quote}
503 You may be prompted with some Xen-specific options. We advise accepting
504 the defaults for these options.
506 Note that the only difference between the two types of Linux kernels
507 that are built is the configuration file used for each. The ``U''
508 suffixed (unprivileged) versions don't contain any of the physical
509 hardware device drivers, leading to a 30\% reduction in size; hence you
510 may prefer these for your non-privileged domains. The ``0'' suffixed
511 privileged versions can be used to boot the system, as well as in driver
512 domains and unprivileged domains.
514 \subsection{Installing Generated Binaries}
516 The files produced by the build process are stored under the
517 \path{dist/install/} directory. To install them in their default
518 locations, do:
519 \begin{quote}
520 \begin{verbatim}
521 # make install
522 \end{verbatim}
523 \end{quote}
525 Alternatively, users with special installation requirements may wish to
526 install them manually by copying the files to their appropriate
527 destinations.
529 %% Files in \path{install/boot/} include:
530 %% \begin{itemize}
531 %% \item \path{install/boot/xen-3.0.gz} Link to the Xen 'kernel'
532 %% \item \path{install/boot/vmlinuz-2.6-xen0} Link to domain 0
533 %% XenLinux kernel
534 %% \item \path{install/boot/vmlinuz-2.6-xenU} Link to unprivileged
535 %% XenLinux kernel
536 %% \end{itemize}
538 The \path{dist/install/boot} directory will also contain the config
539 files used for building the XenLinux kernels, and also versions of Xen
540 and XenLinux kernels that contain debug symbols such as
541 (\path{xen-syms-3.0.0} and \path{vmlinux-syms-}) which are
542 essential for interpreting crash dumps. Retain these files as the
543 developers may wish to see them if you post on the mailing list.
546 \section{Configuration}
547 \label{s:configure}
549 Once you have built and installed the Xen distribution, it is simple to
550 prepare the machine for booting and running Xen.
552 \subsection{GRUB Configuration}
554 An entry should be added to \path{grub.conf} (often found under
555 \path{/boot/} or \path{/boot/grub/}) to allow Xen / XenLinux to boot.
556 This file is sometimes called \path{menu.lst}, depending on your
557 distribution. The entry should look something like the following:
559 %% KMSelf Thu Dec 1 19:06:13 PST 2005 262144 is useful for RHEL/RH and
560 %% related Dom0s.
561 {\small
562 \begin{verbatim}
563 title Xen 3.0 / XenLinux 2.6
564 kernel /boot/xen-3.0.gz dom0_mem=262144
565 module /boot/vmlinuz-2.6-xen0 root=/dev/sda4 ro console=tty0
566 \end{verbatim}
567 }
569 The kernel line tells GRUB where to find Xen itself and what boot
570 parameters should be passed to it (in this case, setting the domain~0
571 memory allocation in kilobytes and the settings for the serial port).
572 For more details on the various Xen boot parameters see
573 Section~\ref{s:xboot}.
575 The module line of the configuration describes the location of the
576 XenLinux kernel that Xen should start and the parameters that should be
577 passed to it. These are standard Linux parameters, identifying the root
578 device and specifying it be initially mounted read only and instructing
579 that console output be sent to the screen. Some distributions such as
580 SuSE do not require the \path{ro} parameter.
582 %% \framebox{\parbox{5in}{
583 %% {\bf Distro specific:} \\
584 %% {\it SuSE} --- Omit the {\tt ro} option from the XenLinux
585 %% kernel command line, since the partition won't be remounted rw
586 %% during boot. }}
588 To use an initrd, add another \path{module} line to the configuration,
589 like: {\small
590 \begin{verbatim}
591 module /boot/my_initrd.gz
592 \end{verbatim}
593 }
595 %% KMSelf Thu Dec 1 19:05:30 PST 2005 Other configs as an appendix?
597 When installing a new kernel, it is recommended that you do not delete
598 existing menu options from \path{menu.lst}, as you may wish to boot your
599 old Linux kernel in future, particularly if you have problems.
601 \subsection{Serial Console (optional)}
603 Serial console access allows you to manage, monitor, and interact with
604 your system over a serial console. This can allow access from another
605 nearby system via a null-modem (``LapLink'') cable or remotely via a serial
606 concentrator.
608 You system's BIOS, bootloader (GRUB), Xen, Linux, and login access must
609 each be individually configured for serial console access. It is
610 \emph{not} strictly necessary to have each component fully functional,
611 but it can be quite useful.
613 For general information on serial console configuration under Linux,
614 refer to the ``Remote Serial Console HOWTO'' at The Linux Documentation
615 Project: \url{}
617 \subsubsection{Serial Console BIOS configuration}
619 Enabling system serial console output neither enables nor disables
620 serial capabilities in GRUB, Xen, or Linux, but may make remote
621 management of your system more convenient by displaying POST and other
622 boot messages over serial port and allowing remote BIOS configuration.
624 Refer to your hardware vendor's documentation for capabilities and
625 procedures to enable BIOS serial redirection.
628 \subsubsection{Serial Console GRUB configuration}
630 Enabling GRUB serial console output neither enables nor disables Xen or
631 Linux serial capabilities, but may made remote management of your system
632 more convenient by displaying GRUB prompts, menus, and actions over
633 serial port and allowing remote GRUB management.
635 Adding the following two lines to your GRUB configuration file,
636 typically either \path{/boot/grub/menu.lst} or \path{/boot/grub/grub.conf}
637 depending on your distro, will enable GRUB serial output.
639 \begin{quote}
640 {\small \begin{verbatim}
641 serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
642 terminal --timeout=10 serial console
643 \end{verbatim}}
644 \end{quote}
646 Note that when both the serial port and the local monitor and keyboard
647 are enabled, the text ``\emph{Press any key to continue}'' will appear
648 at both. Pressing a key on one device will cause GRUB to display to
649 that device. The other device will see no output. If no key is
650 pressed before the timeout period expires, the system will boot to the
651 default GRUB boot entry.
653 Please refer to the GRUB documentation for further information.
656 \subsubsection{Serial Console Xen configuration}
658 Enabling Xen serial console output neither enables nor disables Linux
659 kernel output or logging in to Linux over serial port. It does however
660 allow you to monitor and log the Xen boot process via serial console and
661 can be very useful in debugging.
663 %% kernel /boot/xen-2.0.gz dom0_mem=131072 console=com1,vga com1=115200,8n1
664 %% module /boot/vmlinuz-2.6-xen0 root=/dev/sda4 ro
666 In order to configure Xen serial console output, it is necessary to
667 add a boot option to your GRUB config; e.g.\ replace the previous
668 example kernel line with:
669 \begin{quote} {\small \begin{verbatim}
670 kernel /boot/xen.gz dom0_mem=131072 com1=115200,8n1
671 \end{verbatim}}
672 \end{quote}
674 This configures Xen to output on COM1 at 115,200 baud, 8 data bits, no
675 parity and 1 stop bit. Modify these parameters for your environment.
676 See Section~\ref{s:xboot} for an explanation of all boot parameters.
678 One can also configure XenLinux to share the serial console; to achieve
679 this append ``\path{console=ttyS0}'' to your module line.
682 \subsubsection{Serial Console Linux configuration}
684 Enabling Linux serial console output at boot neither enables nor
685 disables logging in to Linux over serial port. It does however allow
686 you to monitor and log the Linux boot process via serial console and can be
687 very useful in debugging.
689 To enable Linux output at boot time, add the parameter
690 \path{console=ttyS0} (or ttyS1, ttyS2, etc.) to your kernel GRUB line.
691 Under Xen, this might be:
692 \begin{quote}
693 {\footnotesize \begin{verbatim}
694 module /vmlinuz-2.6-xen0 ro root=/dev/VolGroup00/LogVol00 \
695 console=ttyS0, 115200
696 \end{verbatim}}
697 \end{quote}
698 to enable output over ttyS0 at 115200 baud.
702 \subsubsection{Serial Console Login configuration}
704 Logging in to Linux via serial console, under Xen or otherwise, requires
705 specifying a login prompt be started on the serial port. To permit root
706 logins over serial console, the serial port must be added to
707 \path{/etc/securetty}.
709 \newpage
710 To automatically start a login prompt over the serial port,
711 add the line: \begin{quote} {\small {\tt c:2345:respawn:/sbin/mingetty
712 ttyS0}} \end{quote} to \path{/etc/inittab}. Run \path{init q} to force
713 a reload of your inttab and start getty.
715 To enable root logins, add \path{ttyS0} to \path{/etc/securetty} if not
716 already present.
718 Your distribution may use an alternate getty; options include getty,
719 mgetty and agetty. Consult your distribution's documentation
720 for further information.
723 \subsection{TLS Libraries}
725 Users of the XenLinux 2.6 kernel should disable Thread Local Storage
726 (TLS) (e.g.\ by doing a \path{mv /lib/tls /lib/tls.disabled}) before
727 attempting to boot a XenLinux kernel\footnote{If you boot without first
728 disabling TLS, you will get a warning message during the boot process.
729 In this case, simply perform the rename after the machine is up and
730 then run \path{/sbin/ldconfig} to make it take effect.}. You can
731 always reenable TLS by restoring the directory to its original location
732 (i.e.\ \path{mv /lib/tls.disabled /lib/tls}).
734 The reason for this is that the current TLS implementation uses
735 segmentation in a way that is not permissible under Xen. If TLS is not
736 disabled, an emulation mode is used within Xen which reduces performance
737 substantially. To ensure full performance you should install a
738 `Xen-friendly' (nosegneg) version of the library.
741 \section{Booting Xen}
743 It should now be possible to restart the system and use Xen. Reboot and
744 choose the new Xen option when the Grub screen appears.
746 What follows should look much like a conventional Linux boot. The first
747 portion of the output comes from Xen itself, supplying low level
748 information about itself and the underlying hardware. The last portion
749 of the output comes from XenLinux.
751 You may see some error messages during the XenLinux boot. These are not
752 necessarily anything to worry about---they may result from kernel
753 configuration differences between your XenLinux kernel and the one you
754 usually use.
756 When the boot completes, you should be able to log into your system as
757 usual. If you are unable to log in, you should still be able to reboot
758 with your normal Linux kernel by selecting it at the GRUB prompt.
761 % Booting Xen
762 \chapter{Booting a Xen System}
764 Booting the system into Xen will bring you up into the privileged
765 management domain, Domain0. At that point you are ready to create
766 guest domains and ``boot'' them using the \texttt{xm create} command.
768 \section{Booting Domain0}
770 After installation and configuration is complete, reboot the system
771 and and choose the new Xen option when the Grub screen appears.
773 What follows should look much like a conventional Linux boot. The
774 first portion of the output comes from Xen itself, supplying low level
775 information about itself and the underlying hardware. The last
776 portion of the output comes from XenLinux.
778 %% KMSelf Wed Nov 30 18:09:37 PST 2005: We should specify what these are.
780 When the boot completes, you should be able to log into your system as
781 usual. If you are unable to log in, you should still be able to
782 reboot with your normal Linux kernel by selecting it at the GRUB prompt.
784 The first step in creating a new domain is to prepare a root
785 filesystem for it to boot. Typically, this might be stored in a normal
786 partition, an LVM or other volume manager partition, a disk file or on
787 an NFS server. A simple way to do this is simply to boot from your
788 standard OS install CD and install the distribution into another
789 partition on your hard drive.
791 To start the \xend\ control daemon, type
792 \begin{quote}
793 \verb!# xend start!
794 \end{quote}
796 If you wish the daemon to start automatically, see the instructions in
797 Section~\ref{s:xend}. Once the daemon is running, you can use the
798 \path{xm} tool to monitor and maintain the domains running on your
799 system. This chapter provides only a brief tutorial. We provide full
800 details of the \path{xm} tool in the next chapter.
802 % \section{From the web interface}
803 %
804 % Boot the Xen machine and start Xensv (see Chapter~\ref{cha:xensv}
805 % for more details) using the command: \\
806 % \verb_# xensv start_ \\
807 % This will also start Xend (see Chapter~\ref{cha:xend} for more
808 % information).
809 %
810 % The domain management interface will then be available at {\tt
811 % http://your\_machine:8080/}. This provides a user friendly wizard
812 % for starting domains and functions for managing running domains.
813 %
814 % \section{From the command line}
815 \section{Booting Guest Domains}
817 \subsection{Creating a Domain Configuration File}
819 Before you can start an additional domain, you must create a
820 configuration file. We provide two example files which you can use as
821 a starting point:
822 \begin{itemize}
823 \item \path{/etc/xen/xmexample1} is a simple template configuration
824 file for describing a single VM\@.
825 \item \path{/etc/xen/xmexample2} file is a template description that
826 is intended to be reused for multiple virtual machines. Setting the
827 value of the \path{vmid} variable on the \path{xm} command line
828 fills in parts of this template.
829 \end{itemize}
831 There are also a number of other examples which you may find useful.
832 Copy one of these files and edit it as appropriate. Typical values
833 you may wish to edit include:
835 \begin{quote}
836 \begin{description}
837 \item[kernel] Set this to the path of the kernel you compiled for use
838 with Xen (e.g.\ \path{kernel = ``/boot/vmlinuz-2.6-xenU''})
839 \item[memory] Set this to the size of the domain's memory in megabytes
840 (e.g.\ \path{memory = 64})
841 \item[disk] Set the first entry in this list to calculate the offset
842 of the domain's root partition, based on the domain ID\@. Set the
843 second to the location of \path{/usr} if you are sharing it between
844 domains (e.g.\ \path{disk = ['phy:your\_hard\_drive\%d,sda1,w' \%
845 (base\_partition\_number + vmid),
846 'phy:your\_usr\_partition,sda6,r' ]}
847 \item[dhcp] Uncomment the dhcp variable, so that the domain will
848 receive its IP address from a DHCP server (e.g.\ \path{dhcp=``dhcp''})
849 \end{description}
850 \end{quote}
852 You may also want to edit the {\bf vif} variable in order to choose
853 the MAC address of the virtual ethernet interface yourself. For
854 example:
856 \begin{quote}
857 \verb_vif = ['mac=00:16:3E:F6:BB:B3']_
858 \end{quote}
859 If you do not set this variable, \xend\ will automatically generate a
860 random MAC address from the range 00:16:3E:xx:xx:xx, assigned by IEEE to
861 XenSource as an OUI (organizationally unique identifier). XenSource
862 Inc. gives permission for anyone to use addresses randomly allocated
863 from this range for use by their Xen domains.
865 For a list of IEEE OUI assignments, see
866 \url{}
869 \subsection{Booting the Guest Domain}
871 The \path{xm} tool provides a variety of commands for managing
872 domains. Use the \path{create} command to start new domains. Assuming
873 you've created a configuration file \path{myvmconf} based around
874 \path{/etc/xen/xmexample2}, to start a domain with virtual machine
875 ID~1 you should type:
877 \begin{quote}
878 \begin{verbatim}
879 # xm create -c myvmconf vmid=1
880 \end{verbatim}
881 \end{quote}
883 The \path{-c} switch causes \path{xm} to turn into the domain's
884 console after creation. The \path{vmid=1} sets the \path{vmid}
885 variable used in the \path{myvmconf} file.
887 You should see the console boot messages from the new domain appearing
888 in the terminal in which you typed the command, culminating in a login
889 prompt.
892 \section{Starting / Stopping Domains Automatically}
894 It is possible to have certain domains start automatically at boot
895 time and to have dom0 wait for all running domains to shutdown before
896 it shuts down the system.
898 To specify a domain is to start at boot-time, place its configuration
899 file (or a link to it) under \path{/etc/xen/auto/}.
901 A Sys-V style init script for Red Hat and LSB-compliant systems is
902 provided and will be automatically copied to \path{/etc/init.d/}
903 during install. You can then enable it in the appropriate way for
904 your distribution.
906 For instance, on Red Hat:
908 \begin{quote}
909 \verb_# chkconfig --add xendomains_
910 \end{quote}
912 By default, this will start the boot-time domains in runlevels 3, 4
913 and 5.
915 You can also use the \path{service} command to run this script
916 manually, e.g:
918 \begin{quote}
919 \verb_# service xendomains start_
921 Starts all the domains with config files under /etc/xen/auto/.
922 \end{quote}
924 \begin{quote}
925 \verb_# service xendomains stop_
927 Shuts down all running Xen domains.
928 \end{quote}
932 \part{Configuration and Management}
934 %% Chapter Domain Management Tools and Daemons
935 \chapter{Domain Management Tools}
937 This chapter summarizes the management software and tools available.
940 \section{\Xend\ }
941 \label{s:xend}
944 The \Xend\ node control daemon performs system management functions
945 related to virtual machines. It forms a central point of control of
946 virtualized resources, and must be running in order to start and manage
947 virtual machines. \Xend\ must be run as root because it needs access to
948 privileged system management functions.
950 An initialization script named \texttt{/etc/init.d/xend} is provided to
951 start \Xend\ at boot time. Use the tool appropriate (i.e. chkconfig) for
952 your Linux distribution to specify the runlevels at which this script
953 should be executed, or manually create symbolic links in the correct
954 runlevel directories.
956 \Xend\ can be started on the command line as well, and supports the
957 following set of parameters:
959 \begin{tabular}{ll}
960 \verb!# xend start! & start \xend, if not already running \\
961 \verb!# xend stop! & stop \xend\ if already running \\
962 \verb!# xend restart! & restart \xend\ if running, otherwise start it \\
963 % \verb!# xend trace_start! & start \xend, with very detailed debug logging \\
964 \verb!# xend status! & indicates \xend\ status by its return code
965 \end{tabular}
967 A SysV init script called {\tt xend} is provided to start \xend\ at
968 boot time. {\tt make install} installs this script in
969 \path{/etc/init.d}. To enable it, you have to make symbolic links in
970 the appropriate runlevel directories or use the {\tt chkconfig} tool,
971 where available. Once \xend\ is running, administration can be done
972 using the \texttt{xm} tool.
974 \subsection{Logging}
976 As \xend\ runs, events will be logged to \path{/var/log/xend.log} and
977 (less frequently) to \path{/var/log/xend-debug.log}. These, along with
978 the standard syslog files, are useful when troubleshooting problems.
980 \subsection{Configuring \Xend\ }
982 \Xend\ is written in Python. At startup, it reads its configuration
983 information from the file \path{/etc/xen/xend-config.sxp}. The Xen
984 installation places an example \texttt{xend-config.sxp} file in the
985 \texttt{/etc/xen} subdirectory which should work for most installations.
987 See the example configuration file \texttt{xend-debug.sxp} and the
988 section 5 man page \texttt{xend-config.sxp} for a full list of
989 parameters and more detailed information. Some of the most important
990 parameters are discussed below.
992 An HTTP interface and a Unix domain socket API are available to
993 communicate with \Xend. This allows remote users to pass commands to the
994 daemon. By default, \Xend does not start an HTTP server. It does start a
995 Unix domain socket management server, as the low level utility
996 \texttt{xm} requires it. For support of cross-machine migration, \Xend\
997 can start a relocation server. This support is not enabled by default
998 for security reasons.
1000 Note: the example \texttt{xend} configuration file modifies the defaults and
1001 starts up \Xend\ as an HTTP server as well as a relocation server.
1003 From the file:
1005 \begin{verbatim}
1006 #(xend-http-server no)
1007 (xend-http-server yes)
1008 #(xend-unix-server yes)
1009 #(xend-relocation-server no)
1010 (xend-relocation-server yes)
1011 \end{verbatim}
1013 Comment or uncomment lines in that file to disable or enable features
1014 that you require.
1016 Connections from remote hosts are disabled by default:
1018 \begin{verbatim}
1019 # Address xend should listen on for HTTP connections, if xend-http-server is
1020 # set.
1021 # Specifying 'localhost' prevents remote connections.
1022 # Specifying the empty string '' (the default) allows all connections.
1023 #(xend-address '')
1024 (xend-address localhost)
1025 \end{verbatim}
1027 It is recommended that if migration support is not needed, the
1028 \texttt{xend-relocation-server} parameter value be changed to
1029 ``\texttt{no}'' or commented out.
1031 \section{Xm}
1032 \label{s:xm}
1034 The xm tool is the primary tool for managing Xen from the console. The
1035 general format of an xm command line is:
1037 \begin{verbatim}
1038 # xm command [switches] [arguments] [variables]
1039 \end{verbatim}
1041 The available \emph{switches} and \emph{arguments} are dependent on the
1042 \emph{command} chosen. The \emph{variables} may be set using
1043 declarations of the form {\tt variable=value} and command line
1044 declarations override any of the values in the configuration file being
1045 used, including the standard variables described above and any custom
1046 variables (for instance, the \path{xmdefconfig} file uses a {\tt vmid}
1047 variable).
1049 For online help for the commands available, type:
1051 \begin{quote}
1052 \begin{verbatim}
1053 # xm help
1054 \end{verbatim}
1055 \end{quote}
1057 This will list the most commonly used commands. The full list can be obtained
1058 using \verb_xm help --long_. You can also type \path{xm help $<$command$>$}
1059 for more information on a given command.
1061 \subsection{Basic Management Commands}
1063 One useful command is \verb_# xm list_ which lists all domains running in rows
1064 of the following format:
1065 \begin{center} {\tt name domid memory vcpus state cputime}
1066 \end{center}
1068 The meaning of each field is as follows:
1069 \begin{quote}
1070 \begin{description}
1071 \item[name] The descriptive name of the virtual machine.
1072 \item[domid] The number of the domain ID this virtual machine is
1073 running in.
1074 \item[memory] Memory size in megabytes.
1075 \item[vcpus] The number of virtual CPUs this domain has.
1076 \item[state] Domain state consists of 5 fields:
1077 \begin{description}
1078 \item[r] running
1079 \item[b] blocked
1080 \item[p] paused
1081 \item[s] shutdown
1082 \item[c] crashed
1083 \end{description}
1084 \item[cputime] How much CPU time (in seconds) the domain has used so
1085 far.
1086 \end{description}
1087 \end{quote}
1089 The \path{xm list} command also supports a long output format when the
1090 \path{-l} switch is used. This outputs the full details of the
1091 running domains in \xend's SXP configuration format.
1094 You can get access to the console of a particular domain using
1095 the \verb_# xm console_ command (e.g.\ \verb_# xm console myVM_).
1099 %% Chapter Domain Configuration
1100 \chapter{Domain Configuration}
1101 \label{cha:config}
1103 The following contains the syntax of the domain configuration files
1104 and description of how to further specify networking, driver domain
1105 and general scheduling behavior.
1108 \section{Configuration Files}
1109 \label{s:cfiles}
1111 Xen configuration files contain the following standard variables.
1112 Unless otherwise stated, configuration items should be enclosed in
1113 quotes: see the configuration scripts in \path{/etc/xen/}
1114 for concrete examples.
1116 \begin{description}
1117 \item[kernel] Path to the kernel image.
1118 \item[ramdisk] Path to a ramdisk image (optional).
1119 % \item[builder] The name of the domain build function (e.g.
1120 % {\tt'linux'} or {\tt'netbsd'}.
1121 \item[memory] Memory size in megabytes.
1122 \item[vcpus] The number of virtual CPUs.
1123 \item[console] Port to export the domain console on (default 9600 +
1124 domain ID).
1125 \item[vif] Network interface configuration. This may simply contain
1126 an empty string for each desired interface, or may override various
1127 settings, e.g.\
1128 \begin{verbatim}
1129 vif = [ 'mac=00:16:3E:00:00:11, bridge=xen-br0',
1130 'bridge=xen-br1' ]
1131 \end{verbatim}
1132 to assign a MAC address and bridge to the first interface and assign
1133 a different bridge to the second interface, leaving \xend\ to choose
1134 the MAC address. The settings that may be overridden in this way are
1135 type, mac, bridge, ip, script, backend, and vifname.
1136 \item[disk] List of block devices to export to the domain e.g.
1137 \verb_disk = [ 'phy:hda1,sda1,r' ]_
1138 exports physical device \path{/dev/hda1} to the domain as
1139 \path{/dev/sda1} with read-only access. Exporting a disk read-write
1140 which is currently mounted is dangerous -- if you are \emph{certain}
1141 you wish to do this, you can specify \path{w!} as the mode.
1142 \item[dhcp] Set to {\tt `dhcp'} if you want to use DHCP to configure
1143 networking.
1144 \item[netmask] Manually configured IP netmask.
1145 \item[gateway] Manually configured IP gateway.
1146 \item[hostname] Set the hostname for the virtual machine.
1147 \item[root] Specify the root device parameter on the kernel command
1148 line.
1149 \item[nfs\_server] IP address for the NFS server (if any).
1150 \item[nfs\_root] Path of the root filesystem on the NFS server (if
1151 any).
1152 \item[extra] Extra string to append to the kernel command line (if
1153 any)
1154 \end{description}
1156 Additional fields are documented in the example configuration files
1157 (e.g. to configure virtual TPM functionality).
1159 For additional flexibility, it is also possible to include Python
1160 scripting commands in configuration files. An example of this is the
1161 \path{xmexample2} file, which uses Python code to handle the
1162 \path{vmid} variable.
1165 %\part{Advanced Topics}
1168 \section{Network Configuration}
1170 For many users, the default installation should work ``out of the
1171 box''. More complicated network setups, for instance with multiple
1172 Ethernet interfaces and/or existing bridging setups will require some
1173 special configuration.
1175 The purpose of this section is to describe the mechanisms provided by
1176 \xend\ to allow a flexible configuration for Xen's virtual networking.
1178 \subsection{Xen virtual network topology}
1180 Each domain network interface is connected to a virtual network
1181 interface in dom0 by a point to point link (effectively a ``virtual
1182 crossover cable''). These devices are named {\tt
1183 vif$<$domid$>$.$<$vifid$>$} (e.g.\ {\tt vif1.0} for the first
1184 interface in domain~1, {\tt vif3.1} for the second interface in
1185 domain~3).
1187 Traffic on these virtual interfaces is handled in domain~0 using
1188 standard Linux mechanisms for bridging, routing, rate limiting, etc.
1189 Xend calls on two shell scripts to perform initial configuration of
1190 the network and configuration of new virtual interfaces. By default,
1191 these scripts configure a single bridge for all the virtual
1192 interfaces. Arbitrary routing / bridging configurations can be
1193 configured by customizing the scripts, as described in the following
1194 section.
1196 \subsection{Xen networking scripts}
1198 Xen's virtual networking is configured by two shell scripts (by
1199 default \path{network-bridge} and \path{vif-bridge}). These are called
1200 automatically by \xend\ when certain events occur, with arguments to
1201 the scripts providing further contextual information. These scripts
1202 are found by default in \path{/etc/xen/scripts}. The names and
1203 locations of the scripts can be configured in
1204 \path{/etc/xen/xend-config.sxp}.
1206 \begin{description}
1207 \item[network-bridge:] This script is called whenever \xend\ is started or
1208 stopped to respectively initialize or tear down the Xen virtual
1209 network. In the default configuration initialization creates the
1210 bridge `xen-br0' and moves eth0 onto that bridge, modifying the
1211 routing accordingly. When \xend\ exits, it deletes the Xen bridge
1212 and removes eth0, restoring the normal IP and routing configuration.
1214 %% In configurations where the bridge already exists, this script
1215 %% could be replaced with a link to \path{/bin/true} (for instance).
1217 \item[vif-bridge:] This script is called for every domain virtual
1218 interface and can configure firewalling rules and add the vif to the
1219 appropriate bridge. By default, this adds and removes VIFs on the
1220 default Xen bridge.
1221 \end{description}
1223 Other example scripts are available (\path{network-route} and
1224 \path{vif-route}, \path{network-nat} and \path{vif-nat}).
1225 For more complex network setups (e.g.\ where routing is required or
1226 integrate with existing bridges) these scripts may be replaced with
1227 customized variants for your site's preferred configuration.
1229 \section{Driver Domain Configuration}
1230 \label{s:ddconf}
1232 \subsection{PCI}
1233 \label{ss:pcidd}
1235 Individual PCI devices can be assigned to a given domain (a PCI driver domain)
1236 to allow that domain direct access to the PCI hardware.
1238 While PCI Driver Domains can increase the stability and security of a system
1239 by addressing a number of security concerns, there are some security issues
1240 that remain that you can read about in Section~\ref{s:ddsecurity}.
1242 \subsubsection{Compile-Time Setup}
1243 To use this functionality, ensure
1244 that the PCI Backend is compiled in to a privileged domain (e.g. domain 0)
1245 and that the domains which will be assigned PCI devices have the PCI Frontend
1246 compiled in. In XenLinux, the PCI Backend is available under the Xen
1247 configuration section while the PCI Frontend is under the
1248 architecture-specific "Bus Options" section. You may compile both the backend
1249 and the frontend into the same kernel; they will not affect each other.
1251 \subsubsection{PCI Backend Configuration - Binding at Boot}
1252 The PCI devices you wish to assign to unprivileged domains must be "hidden"
1253 from your backend domain (usually domain 0) so that it does not load a driver
1254 for them. Use the \path{pciback.hide} kernel parameter which is specified on
1255 the kernel command-line and is configurable through GRUB (see
1256 Section~\ref{s:configure}). Note that devices are not really hidden from the
1257 backend domain. The PCI Backend appears to the Linux kernel as a regular PCI
1258 device driver. The PCI Backend ensures that no other device driver loads
1259 for the devices by binding itself as the device driver for those devices.
1260 PCI devices are identified by hexadecimal slot/funciton numbers (on Linux,
1261 use \path{lspci} to determine slot/funciton numbers of your devices) and
1262 can be specified with or without the PCI domain: \\
1263 \centerline{ {\tt ({\em bus}:{\em slot}.{\em func})} example {\tt (02:1d.3)}} \\
1264 \centerline{ {\tt ({\em domain}:{\em bus}:{\em slot}.{\em func})} example {\tt (0000:02:1d.3)}} \\
1266 An example kernel command-line which hides two PCI devices might be: \\
1267 \centerline{ {\tt root=/dev/sda4 ro console=tty0 pciback.hide=(02:01.f)(0000:04:1d.0) } } \\
1269 \subsubsection{PCI Backend Configuration - Late Binding}
1270 PCI devices can also be bound to the PCI Backend after boot through the manual
1271 binding/unbinding facilities provided by the Linux kernel in sysfs (allowing
1272 for a Xen user to give PCI devices to driver domains that were not specified
1273 on the kernel command-line). There are several attributes with the PCI
1274 Backend's sysfs directory (\path{/sys/bus/pci/drivers/pciback}) that can be
1275 used to bind/unbind devices:
1277 \begin{description}
1278 \item[slots] lists all of the PCI slots that the PCI Backend will try to seize
1279 (or "hide" from Domain 0). A PCI slot must appear in this list before it can
1280 be bound to the PCI Backend through the \path{bind} attribute.
1281 \item[new\_slot] write the name of a slot here (in 0000:00:00.0 format) to
1282 have the PCI Backend seize the device in this slot.
1283 \item[remove\_slot] write the name of a slot here (same format as
1284 \path{new\_slot}) to have the PCI Backend no longer try to seize devices in
1285 this slot. Note that this does not unbind the driver from a device it has
1286 already seized.
1287 \item[bind] write the name of a slot here (in 0000:00:00.0 format) to have
1288 the Linux kernel attempt to bind the device in that slot to the PCI Backend
1289 driver.
1290 \item[unbind] write the name of a skit here (same format as \path{bind}) to have
1291 the Linux kernel unbind the device from the PCI Backend. DO NOT unbind a
1292 device while it is currently given to a PCI driver domain!
1293 \end{description}
1295 Some examples:
1297 Bind a device to the PCI Backend which is not bound to any other driver.
1298 \begin{verbatim}
1299 # # Add a new slot to the PCI Backend's list
1300 # echo -n 0000:01:04.d > /sys/bus/pci/drivers/pciback/new_slot
1301 # # Now that the backend is watching for the slot, bind to it
1302 # echo -n 0000:01:04.d > /sys/bus/pci/drivers/pciback/bind
1303 \end{verbatim}
1305 Unbind a device from its driver and bind to the PCI Backend.
1306 \begin{verbatim}
1307 # # Unbind a PCI network card from its network driver
1308 # echo -n 0000:05:02.0 > /sys/bus/pci/drivers/3c905/unbind
1309 # # And now bind it to the PCI Backend
1310 # echo -n 0000:05:02.0 > /sys/bus/pci/drivers/pciback/new_slot
1311 # echo -n 0000:05:02.0 > /sys/bus/pci/drivers/pciback/bind
1312 \end{verbatim}
1314 Note that the "-n" option in the example is important as it causes echo to not
1315 output a new-line.
1317 \subsubsection{PCI Frontend Configuration}
1318 To configure a domU to receive a PCI device:
1320 \begin{description}
1321 \item[Command-line:]
1322 Use the {\em pci} command-line flag. For multiple devices, use the option
1323 multiple times. \\
1324 \centerline{ {\tt xm create netcard-dd pci=01:00.0 pci=02:03.0 }} \\
1326 \item[Flat Format configuration file:]
1327 Specify all of your PCI devices in a python list named {\em pci}. \\
1328 \centerline{ {\tt pci=['01:00.0','02:03.0'] }} \\
1330 \item[SXP Format configuration file:]
1331 Use a single PCI device section for all of your devices (specify the numbers
1332 in hexadecimal with the preceding '0x'). Note that {\em domain} here refers
1333 to the PCI domain, not a virtual machine within Xen.
1334 {\small
1335 \begin{verbatim}
1336 (device (pci
1337 (dev (domain 0x0)(bus 0x3)(slot 0x1a)(func 0x1)
1338 (dev (domain 0x0)(bus 0x1)(slot 0x5)(func 0x0)
1340 \end{verbatim}
1342 \end{description}
1344 %% There are two possible types of privileges: IO privileges and
1345 %% administration privileges.
1350 % Chapter Storage and FileSytem Management
1351 \chapter{Storage and File System Management}
1353 Storage can be made available to virtual machines in a number of
1354 different ways. This chapter covers some possible configurations.
1356 The most straightforward method is to export a physical block device (a
1357 hard drive or partition) from dom0 directly to the guest domain as a
1358 virtual block device (VBD).
1360 Storage may also be exported from a filesystem image or a partitioned
1361 filesystem image as a \emph{file-backed VBD}.
1363 Finally, standard network storage protocols such as NBD, iSCSI, NFS,
1364 etc., can be used to provide storage to virtual machines.
1367 \section{Exporting Physical Devices as VBDs}
1368 \label{s:exporting-physical-devices-as-vbds}
1370 One of the simplest configurations is to directly export individual
1371 partitions from domain~0 to other domains. To achieve this use the
1372 \path{phy:} specifier in your domain configuration file. For example a
1373 line like
1374 \begin{quote}
1375 \verb_disk = ['phy:hda3,sda1,w']_
1376 \end{quote}
1377 specifies that the partition \path{/dev/hda3} in domain~0 should be
1378 exported read-write to the new domain as \path{/dev/sda1}; one could
1379 equally well export it as \path{/dev/hda} or \path{/dev/sdb5} should
1380 one wish.
1382 In addition to local disks and partitions, it is possible to export
1383 any device that Linux considers to be ``a disk'' in the same manner.
1384 For example, if you have iSCSI disks or GNBD volumes imported into
1385 domain~0 you can export these to other domains using the \path{phy:}
1386 disk syntax. E.g.:
1387 \begin{quote}
1388 \verb_disk = ['phy:vg/lvm1,sda2,w']_
1389 \end{quote}
1391 \begin{center}
1392 \framebox{\bf Warning: Block device sharing}
1393 \end{center}
1394 \begin{quote}
1395 Block devices should typically only be shared between domains in a
1396 read-only fashion otherwise the Linux kernel's file systems will get
1397 very confused as the file system structure may change underneath
1398 them (having the same ext3 partition mounted \path{rw} twice is a
1399 sure fire way to cause irreparable damage)! \Xend\ will attempt to
1400 prevent you from doing this by checking that the device is not
1401 mounted read-write in domain~0, and hasn't already been exported
1402 read-write to another domain. If you want read-write sharing,
1403 export the directory to other domains via NFS from domain~0 (or use
1404 a cluster file system such as GFS or ocfs2).
1405 \end{quote}
1408 \section{Using File-backed VBDs}
1410 It is also possible to use a file in Domain~0 as the primary storage
1411 for a virtual machine. As well as being convenient, this also has the
1412 advantage that the virtual block device will be \emph{sparse} ---
1413 space will only really be allocated as parts of the file are used. So
1414 if a virtual machine uses only half of its disk space then the file
1415 really takes up half of the size allocated.
1417 For example, to create a 2GB sparse file-backed virtual block device
1418 (actually only consumes 1KB of disk):
1419 \begin{quote}
1420 \verb_# dd if=/dev/zero of=vm1disk bs=1k seek=2048k count=1_
1421 \end{quote}
1423 Make a file system in the disk file:
1424 \begin{quote}
1425 \verb_# mkfs -t ext3 vm1disk_
1426 \end{quote}
1428 (when the tool asks for confirmation, answer `y')
1430 Populate the file system e.g.\ by copying from the current root:
1431 \begin{quote}
1432 \begin{verbatim}
1433 # mount -o loop vm1disk /mnt
1434 # cp -ax /{root,dev,var,etc,usr,bin,sbin,lib} /mnt
1435 # mkdir /mnt/{proc,sys,home,tmp}
1436 \end{verbatim}
1437 \end{quote}
1439 Tailor the file system by editing \path{/etc/fstab},
1440 \path{/etc/hostname}, etc.\ Don't forget to edit the files in the
1441 mounted file system, instead of your domain~0 filesystem, e.g.\ you
1442 would edit \path{/mnt/etc/fstab} instead of \path{/etc/fstab}. For
1443 this example put \path{/dev/sda1} to root in fstab.
1445 Now unmount (this is important!):
1446 \begin{quote}
1447 \verb_# umount /mnt_
1448 \end{quote}
1450 In the configuration file set:
1451 \begin{quote}
1452 \verb_disk = ['file:/full/path/to/vm1disk,sda1,w']_
1453 \end{quote}
1455 As the virtual machine writes to its `disk', the sparse file will be
1456 filled in and consume more space up to the original 2GB.
1458 {\bf Note that file-backed VBDs may not be appropriate for backing
1459 I/O-intensive domains.} File-backed VBDs are known to experience
1460 substantial slowdowns under heavy I/O workloads, due to the I/O
1461 handling by the loopback block device used to support file-backed VBDs
1462 in dom0. Better I/O performance can be achieved by using either
1463 LVM-backed VBDs (Section~\ref{s:using-lvm-backed-vbds}) or physical
1464 devices as VBDs (Section~\ref{s:exporting-physical-devices-as-vbds}).
1466 Linux supports a maximum of eight file-backed VBDs across all domains
1467 by default. This limit can be statically increased by using the
1468 \emph{max\_loop} module parameter if CONFIG\_BLK\_DEV\_LOOP is
1469 compiled as a module in the dom0 kernel, or by using the
1470 \emph{max\_loop=n} boot option if CONFIG\_BLK\_DEV\_LOOP is compiled
1471 directly into the dom0 kernel.
1474 \section{Using LVM-backed VBDs}
1475 \label{s:using-lvm-backed-vbds}
1477 A particularly appealing solution is to use LVM volumes as backing for
1478 domain file-systems since this allows dynamic growing/shrinking of
1479 volumes as well as snapshot and other features.
1481 To initialize a partition to support LVM volumes:
1482 \begin{quote}
1483 \begin{verbatim}
1484 # pvcreate /dev/sda10
1485 \end{verbatim}
1486 \end{quote}
1488 Create a volume group named `vg' on the physical partition:
1489 \begin{quote}
1490 \begin{verbatim}
1491 # vgcreate vg /dev/sda10
1492 \end{verbatim}
1493 \end{quote}
1495 Create a logical volume of size 4GB named `myvmdisk1':
1496 \begin{quote}
1497 \begin{verbatim}
1498 # lvcreate -L4096M -n myvmdisk1 vg
1499 \end{verbatim}
1500 \end{quote}
1502 You should now see that you have a \path{/dev/vg/myvmdisk1} Make a
1503 filesystem, mount it and populate it, e.g.:
1504 \begin{quote}
1505 \begin{verbatim}
1506 # mkfs -t ext3 /dev/vg/myvmdisk1
1507 # mount /dev/vg/myvmdisk1 /mnt
1508 # cp -ax / /mnt
1509 # umount /mnt
1510 \end{verbatim}
1511 \end{quote}
1513 Now configure your VM with the following disk configuration:
1514 \begin{quote}
1515 \begin{verbatim}
1516 disk = [ 'phy:vg/myvmdisk1,sda1,w' ]
1517 \end{verbatim}
1518 \end{quote}
1520 LVM enables you to grow the size of logical volumes, but you'll need
1521 to resize the corresponding file system to make use of the new space.
1522 Some file systems (e.g.\ ext3) now support online resize. See the LVM
1523 manuals for more details.
1525 You can also use LVM for creating copy-on-write (CoW) clones of LVM
1526 volumes (known as writable persistent snapshots in LVM terminology).
1527 This facility is new in Linux 2.6.8, so isn't as stable as one might
1528 hope. In particular, using lots of CoW LVM disks consumes a lot of
1529 dom0 memory, and error conditions such as running out of disk space
1530 are not handled well. Hopefully this will improve in future.
1532 To create two copy-on-write clones of the above file system you would
1533 use the following commands:
1535 \begin{quote}
1536 \begin{verbatim}
1537 # lvcreate -s -L1024M -n myclonedisk1 /dev/vg/myvmdisk1
1538 # lvcreate -s -L1024M -n myclonedisk2 /dev/vg/myvmdisk1
1539 \end{verbatim}
1540 \end{quote}
1542 Each of these can grow to have 1GB of differences from the master
1543 volume. You can grow the amount of space for storing the differences
1544 using the lvextend command, e.g.:
1545 \begin{quote}
1546 \begin{verbatim}
1547 # lvextend +100M /dev/vg/myclonedisk1
1548 \end{verbatim}
1549 \end{quote}
1551 Don't let the `differences volume' ever fill up otherwise LVM gets
1552 rather confused. It may be possible to automate the growing process by
1553 using \path{dmsetup wait} to spot the volume getting full and then
1554 issue an \path{lvextend}.
1556 In principle, it is possible to continue writing to the volume that
1557 has been cloned (the changes will not be visible to the clones), but
1558 we wouldn't recommend this: have the cloned volume as a `pristine'
1559 file system install that isn't mounted directly by any of the virtual
1560 machines.
1563 \section{Using NFS Root}
1565 First, populate a root filesystem in a directory on the server
1566 machine. This can be on a distinct physical machine, or simply run
1567 within a virtual machine on the same node.
1569 Now configure the NFS server to export this filesystem over the
1570 network by adding a line to \path{/etc/exports}, for instance:
1572 \begin{quote}
1573 \begin{small}
1574 \begin{verbatim}
1575 /export/vm1root (rw,sync,no_root_squash)
1576 \end{verbatim}
1577 \end{small}
1578 \end{quote}
1580 Finally, configure the domain to use NFS root. In addition to the
1581 normal variables, you should make sure to set the following values in
1582 the domain's configuration file:
1584 \begin{quote}
1585 \begin{small}
1586 \begin{verbatim}
1587 root = '/dev/nfs'
1588 nfs_server = '' # substitute IP address of server
1589 nfs_root = '/path/to/root' # path to root FS on the server
1590 \end{verbatim}
1591 \end{small}
1592 \end{quote}
1594 The domain will need network access at boot time, so either statically
1595 configure an IP address using the config variables \path{ip},
1596 \path{netmask}, \path{gateway}, \path{hostname}; or enable DHCP
1597 (\path{dhcp='dhcp'}).
1599 Note that the Linux NFS root implementation is known to have stability
1600 problems under high load (this is not a Xen-specific problem), so this
1601 configuration may not be appropriate for critical servers.
1604 \chapter{CPU Management}
1606 %% KMS Something sage about CPU / processor management.
1608 Xen allows a domain's virtual CPU(s) to be associated with one or more
1609 host CPUs. This can be used to allocate real resources among one or
1610 more guests, or to make optimal use of processor resources when
1611 utilizing dual-core, hyperthreading, or other advanced CPU technologies.
1613 Xen enumerates physical CPUs in a `depth first' fashion. For a system
1614 with both hyperthreading and multiple cores, this would be all the
1615 hyperthreads on a given core, then all the cores on a given socket,
1616 and then all sockets. I.e. if you had a two socket, dual core,
1617 hyperthreaded Xeon the CPU order would be:
1620 \begin{center}
1621 \begin{tabular}{l|l|l|l|l|l|l|r}
1622 \multicolumn{4}{c|}{socket0} & \multicolumn{4}{c}{socket1} \\ \hline
1623 \multicolumn{2}{c|}{core0} & \multicolumn{2}{c|}{core1} &
1624 \multicolumn{2}{c|}{core0} & \multicolumn{2}{c}{core1} \\ \hline
1625 ht0 & ht1 & ht0 & ht1 & ht0 & ht1 & ht0 & ht1 \\
1626 \#0 & \#1 & \#2 & \#3 & \#4 & \#5 & \#6 & \#7 \\
1627 \end{tabular}
1628 \end{center}
1631 Having multiple vcpus belonging to the same domain mapped to the same
1632 physical CPU is very likely to lead to poor performance. It's better to
1633 use `vcpus-set' to hot-unplug one of the vcpus and ensure the others are
1634 pinned on different CPUs.
1636 If you are running IO intensive tasks, its typically better to dedicate
1637 either a hyperthread or whole core to running domain 0, and hence pin
1638 other domains so that they can't use CPU 0. If your workload is mostly
1639 compute intensive, you may want to pin vcpus such that all physical CPU
1640 threads are available for guest domains.
1642 \chapter{Migrating Domains}
1644 \section{Domain Save and Restore}
1646 The administrator of a Xen system may suspend a virtual machine's
1647 current state into a disk file in domain~0, allowing it to be resumed at
1648 a later time.
1650 For example you can suspend a domain called ``VM1'' to disk using the
1651 command:
1652 \begin{verbatim}
1653 # xm save VM1 VM1.chk
1654 \end{verbatim}
1656 This will stop the domain named ``VM1'' and save its current state
1657 into a file called \path{VM1.chk}.
1659 To resume execution of this domain, use the \path{xm restore} command:
1660 \begin{verbatim}
1661 # xm restore VM1.chk
1662 \end{verbatim}
1664 This will restore the state of the domain and resume its execution.
1665 The domain will carry on as before and the console may be reconnected
1666 using the \path{xm console} command, as described earlier.
1668 \section{Migration and Live Migration}
1670 Migration is used to transfer a domain between physical hosts. There
1671 are two varieties: regular and live migration. The former moves a
1672 virtual machine from one host to another by pausing it, copying its
1673 memory contents, and then resuming it on the destination. The latter
1674 performs the same logical functionality but without needing to pause
1675 the domain for the duration. In general when performing live migration
1676 the domain continues its usual activities and---from the user's
1677 perspective---the migration should be imperceptible.
1679 To perform a live migration, both hosts must be running Xen / \xend\ and
1680 the destination host must have sufficient resources (e.g.\ memory
1681 capacity) to accommodate the domain after the move. Furthermore we
1682 currently require both source and destination machines to be on the same
1683 L2 subnet.
1685 Currently, there is no support for providing automatic remote access
1686 to filesystems stored on local disk when a domain is migrated.
1687 Administrators should choose an appropriate storage solution (i.e.\
1688 SAN, NAS, etc.) to ensure that domain filesystems are also available
1689 on their destination node. GNBD is a good method for exporting a
1690 volume from one machine to another. iSCSI can do a similar job, but is
1691 more complex to set up.
1693 When a domain migrates, it's MAC and IP address move with it, thus it is
1694 only possible to migrate VMs within the same layer-2 network and IP
1695 subnet. If the destination node is on a different subnet, the
1696 administrator would need to manually configure a suitable etherip or IP
1697 tunnel in the domain~0 of the remote node.
1699 A domain may be migrated using the \path{xm migrate} command. To live
1700 migrate a domain to another machine, we would use the command:
1702 \begin{verbatim}
1703 # xm migrate --live mydomain
1704 \end{verbatim}
1706 Without the \path{--live} flag, \xend\ simply stops the domain and
1707 copies the memory image over to the new node and restarts it. Since
1708 domains can have large allocations this can be quite time consuming,
1709 even on a Gigabit network. With the \path{--live} flag \xend\ attempts
1710 to keep the domain running while the migration is in progress, resulting
1711 in typical down times of just 60--300ms.
1713 For now it will be necessary to reconnect to the domain's console on the
1714 new machine using the \path{xm console} command. If a migrated domain
1715 has any open network connections then they will be preserved, so SSH
1716 connections do not have this limitation.
1719 %% Chapter Securing Xen
1720 \chapter{Securing Xen}
1722 This chapter describes how to secure a Xen system. It describes a number
1723 of scenarios and provides a corresponding set of best practices. It
1724 begins with a section devoted to understanding the security implications
1725 of a Xen system.
1728 \section{Xen Security Considerations}
1730 When deploying a Xen system, one must be sure to secure the management
1731 domain (Domain-0) as much as possible. If the management domain is
1732 compromised, all other domains are also vulnerable. The following are a
1733 set of best practices for Domain-0:
1735 \begin{enumerate}
1736 \item \textbf{Run the smallest number of necessary services.} The less
1737 things that are present in a management partition, the better.
1738 Remember, a service running as root in the management domain has full
1739 access to all other domains on the system.
1740 \item \textbf{Use a firewall to restrict the traffic to the management
1741 domain.} A firewall with default-reject rules will help prevent
1742 attacks on the management domain.
1743 \item \textbf{Do not allow users to access Domain-0.} The Linux kernel
1744 has been known to have local-user root exploits. If you allow normal
1745 users to access Domain-0 (even as unprivileged users) you run the risk
1746 of a kernel exploit making all of your domains vulnerable.
1747 \end{enumerate}
1749 \section{Driver Domain Security Considerations}
1750 \label{s:ddsecurity}
1752 Driver domains address a range of security problems that exist regarding
1753 the use of device drivers and hardware. On many operating systems in common
1754 use today, device drivers run within the kernel with the same privileges as
1755 the kernel. Few or no mechanisms exist to protect the integrity of the kernel
1756 from a misbehaving (read "buggy") or malicious device driver. Driver
1757 domains exist to aid in isolating a device driver within its own virtual
1758 machine where it cannot affect the stability and integrity of other
1759 domains. If a driver crashes, the driver domain can be restarted rather than
1760 have the entire machine crash (and restart) with it. Drivers written by
1761 unknown or untrusted third-parties can be confined to an isolated space.
1762 Driver domains thus address a number of security and stability issues with
1763 device drivers.
1765 However, due to limitations in current hardware, a number of security
1766 concerns remain that need to be considered when setting up driver domains (it
1767 should be noted that the following list is not intended to be exhaustive).
1769 \begin{enumerate}
1770 \item \textbf{Without an IOMMU, a hardware device can DMA to memory regions
1771 outside of its controlling domain.} Architectures which do not have an
1772 IOMMU (e.g. most x86-based platforms) to restrict DMA usage by hardware
1773 are vulnerable. A hardware device which can perform arbitrary memory reads
1774 and writes can read/write outside of the memory of its controlling domain.
1775 A malicious or misbehaving domain could use a hardware device it controls
1776 to send data overwriting memory in another domain or to read arbitrary
1777 regions of memory in another domain.
1778 \item \textbf{Shared buses are vulnerable to sniffing.} Devices that share
1779 a data bus can sniff (and possible spoof) each others' data. Device A that
1780 is assigned to Domain A could eavesdrop on data being transmitted by
1781 Domain B to Device B and then relay that data back to Domain A.
1782 \item \textbf{Devices which share interrupt lines can either prevent the
1783 reception of that interrupt by the driver domain or can trigger the
1784 interrupt service routine of that guest needlessly.} A devices which shares
1785 a level-triggered interrupt (e.g. PCI devices) with another device can
1786 raise an interrupt and never clear it. This effectively blocks other devices
1787 which share that interrupt line from notifying their controlling driver
1788 domains that they need to be serviced. A device which shares an
1789 any type of interrupt line can trigger its interrupt continually which
1790 forces execution time to be spent (in multiple guests) in the interrupt
1791 service routine (potentially denying time to other processes within that
1792 guest). System architectures which allow each device to have its own
1793 interrupt line (e.g. PCI's Message Signaled Interrupts) are less
1794 vulnerable to this denial-of-service problem.
1795 \item \textbf{Devices may share the use of I/O memory address space.} Xen can
1796 only restrict access to a device's physical I/O resources at a certain
1797 granularity. For interrupt lines and I/O port address space, that
1798 granularity is very fine (per interrupt line and per I/O port). However,
1799 Xen can only restrict access to I/O memory address space on a page size
1800 basis. If more than one device shares use of a page in I/O memory address
1801 space, the domains to which those devices are assigned will be able to
1802 access the I/O memory address space of each other's devices.
1803 \end{enumerate}
1806 \section{Security Scenarios}
1809 \subsection{The Isolated Management Network}
1811 In this scenario, each node has two network cards in the cluster. One
1812 network card is connected to the outside world and one network card is a
1813 physically isolated management network specifically for Xen instances to
1814 use.
1816 As long as all of the management partitions are trusted equally, this is
1817 the most secure scenario. No additional configuration is needed other
1818 than forcing Xend to bind to the management interface for relocation.
1821 \subsection{A Subnet Behind a Firewall}
1823 In this scenario, each node has only one network card but the entire
1824 cluster sits behind a firewall. This firewall should do at least the
1825 following:
1827 \begin{enumerate}
1828 \item Prevent IP spoofing from outside of the subnet.
1829 \item Prevent access to the relocation port of any of the nodes in the
1830 cluster except from within the cluster.
1831 \end{enumerate}
1833 The following iptables rules can be used on each node to prevent
1834 migrations to that node from outside the subnet assuming the main
1835 firewall does not do this for you:
1837 \begin{verbatim}
1838 # this command disables all access to the Xen relocation
1839 # port:
1840 iptables -A INPUT -p tcp --destination-port 8002 -j REJECT
1842 # this command enables Xen relocations only from the specific
1843 # subnet:
1844 iptables -I INPUT -p tcp -{}-source \
1845 --destination-port 8002 -j ACCEPT
1846 \end{verbatim}
1848 \subsection{Nodes on an Untrusted Subnet}
1850 Migration on an untrusted subnet is not safe in current versions of Xen.
1851 It may be possible to perform migrations through a secure tunnel via an
1852 VPN or SSH. The only safe option in the absence of a secure tunnel is to
1853 disable migration completely. The easiest way to do this is with
1854 iptables:
1856 \begin{verbatim}
1857 # this command disables all access to the Xen relocation port
1858 iptables -A INPUT -p tcp -{}-destination-port 8002 -j REJECT
1859 \end{verbatim}
1861 \part{Reference}
1863 %% Chapter Build and Boot Options
1864 \chapter{Build and Boot Options}
1866 This chapter describes the build- and boot-time options which may be
1867 used to tailor your Xen system.
1869 \section{Top-level Configuration Options}
1871 Top-level configuration is achieved by editing one of two
1872 files: \path{} and \path{Makefile}.
1874 The former allows the overall build target architecture to be
1875 specified. You will typically not need to modify this unless
1876 you are cross-compiling or if you wish to build a PAE-enabled
1877 Xen system. Additional configuration options are documented
1878 in the \path{} file.
1880 The top-level \path{Makefile} is chiefly used to customize the set of
1881 kernels built. Look for the line:
1882 \begin{quote}
1883 \begin{verbatim}
1884 KERNELS ?= linux-2.6-xen0 linux-2.6-xenU
1885 \end{verbatim}
1886 \end{quote}
1888 Allowable options here are any kernels which have a corresponding
1889 build configuration file in the \path{buildconfigs/} directory.
1893 \section{Xen Build Options}
1895 Xen provides a number of build-time options which should be set as
1896 environment variables or passed on make's command-line.
1898 \begin{description}
1899 \item[verbose=y] Enable debugging messages when Xen detects an
1900 unexpected condition. Also enables console output from all domains.
1901 \item[debug=y] Enable debug assertions. Implies {\bf verbose=y}.
1902 (Primarily useful for tracing bugs in Xen).
1903 \item[debugger=y] Enable the in-Xen debugger. This can be used to
1904 debug Xen, guest OSes, and applications.
1905 \item[perfc=y] Enable performance counters for significant events
1906 within Xen. The counts can be reset or displayed on Xen's console
1907 via console control keys.
1908 \end{description}
1911 \section{Xen Boot Options}
1912 \label{s:xboot}
1914 These options are used to configure Xen's behaviour at runtime. They
1915 should be appended to Xen's command line, either manually or by
1916 editing \path{grub.conf}.
1918 \begin{description}
1919 \item [ noreboot ] Don't reboot the machine automatically on errors.
1920 This is useful to catch debug output if you aren't catching console
1921 messages via the serial line.
1922 \item [ nosmp ] Disable SMP support. This option is implied by
1923 `ignorebiostables'.
1924 \item [ watchdog ] Enable NMI watchdog which can report certain
1925 failures.
1926 \item [ noirqbalance ] Disable software IRQ balancing and affinity.
1927 This can be used on systems such as Dell 1850/2850 that have
1928 workarounds in hardware for IRQ-routing issues.
1929 \item [ badpage=$<$page number$>$,$<$page number$>$, \ldots ] Specify
1930 a list of pages not to be allocated for use because they contain bad
1931 bytes. For example, if your memory tester says that byte 0x12345678
1932 is bad, you would place `badpage=0x12345' on Xen's command line.
1933 \item [ com1=$<$baud$>$,DPS,$<$io\_base$>$,$<$irq$>$
1934 com2=$<$baud$>$,DPS,$<$io\_base$>$,$<$irq$>$ ] \mbox{}\\
1935 Xen supports up to two 16550-compatible serial ports. For example:
1936 `com1=9600, 8n1, 0x408, 5' maps COM1 to a 9600-baud port, 8 data
1937 bits, no parity, 1 stop bit, I/O port base 0x408, IRQ 5. If some
1938 configuration options are standard (e.g., I/O base and IRQ), then
1939 only a prefix of the full configuration string need be specified. If
1940 the baud rate is pre-configured (e.g., by the bootloader) then you
1941 can specify `auto' in place of a numeric baud rate.
1942 \item [ console=$<$specifier list$>$ ] Specify the destination for Xen
1943 console I/O. This is a comma-separated list of, for example:
1944 \begin{description}
1945 \item[ vga ] Use VGA console and allow keyboard input.
1946 \item[ com1 ] Use serial port com1.
1947 \item[ com2H ] Use serial port com2. Transmitted chars will have the
1948 MSB set. Received chars must have MSB set.
1949 \item[ com2L] Use serial port com2. Transmitted chars will have the
1950 MSB cleared. Received chars must have MSB cleared.
1951 \end{description}
1952 The latter two examples allow a single port to be shared by two
1953 subsystems (e.g.\ console and debugger). Sharing is controlled by
1954 MSB of each transmitted/received character. [NB. Default for this
1955 option is `com1,vga']
1956 \item [ sync\_console ] Force synchronous console output. This is
1957 useful if you system fails unexpectedly before it has sent all
1958 available output to the console. In most cases Xen will
1959 automatically enter synchronous mode when an exceptional event
1960 occurs, but this option provides a manual fallback.
1961 \item [ conswitch=$<$switch-char$><$auto-switch-char$>$ ] Specify how
1962 to switch serial-console input between Xen and DOM0. The required
1963 sequence is CTRL-$<$switch-char$>$ pressed three times. Specifying
1964 the backtick character disables switching. The
1965 $<$auto-switch-char$>$ specifies whether Xen should auto-switch
1966 input to DOM0 when it boots --- if it is `x' then auto-switching is
1967 disabled. Any other value, or omitting the character, enables
1968 auto-switching. [NB. Default switch-char is `a'.]
1969 \item [ nmi=xxx ]
1970 Specify what to do with an NMI parity or I/O error. \\
1971 `nmi=fatal': Xen prints a diagnostic and then hangs. \\
1972 `nmi=dom0': Inform DOM0 of the NMI. \\
1973 `nmi=ignore': Ignore the NMI.
1974 \item [ mem=xxx ] Set the physical RAM address limit. Any RAM
1975 appearing beyond this physical address in the memory map will be
1976 ignored. This parameter may be specified with a B, K, M or G suffix,
1977 representing bytes, kilobytes, megabytes and gigabytes respectively.
1978 The default unit, if no suffix is specified, is kilobytes.
1979 \item [ dom0\_mem=xxx ] Set the amount of memory to be allocated to
1980 domain0. In Xen 3.x the parameter may be specified with a B, K, M or
1981 G suffix, representing bytes, kilobytes, megabytes and gigabytes
1982 respectively; if no suffix is specified, the parameter defaults to
1983 kilobytes. In previous versions of Xen, suffixes were not supported
1984 and the value is always interpreted as kilobytes.
1985 \item [ tbuf\_size=xxx ] Set the size of the per-cpu trace buffers, in
1986 pages (default 0).
1987 \item [ sched=xxx ] Select the CPU scheduler Xen should use. The
1988 current possibilities are `sedf' (default) and `bvt'.
1989 \item [ apic\_verbosity=debug,verbose ] Print more detailed
1990 information about local APIC and IOAPIC configuration.
1991 \item [ lapic ] Force use of local APIC even when left disabled by
1992 uniprocessor BIOS.
1993 \item [ nolapic ] Ignore local APIC in a uniprocessor system, even if
1994 enabled by the BIOS.
1995 \item [ apic=bigsmp,default,es7000,summit ] Specify NUMA platform.
1996 This can usually be probed automatically.
1997 \end{description}
1999 In addition, the following options may be specified on the Xen command
2000 line. Since domain 0 shares responsibility for booting the platform,
2001 Xen will automatically propagate these options to its command line.
2002 These options are taken from Linux's command-line syntax with
2003 unchanged semantics.
2005 \begin{description}
2006 \item [ acpi=off,force,strict,ht,noirq,\ldots ] Modify how Xen (and
2007 domain 0) parses the BIOS ACPI tables.
2008 \item [ acpi\_skip\_timer\_override ] Instruct Xen (and domain~0) to
2009 ignore timer-interrupt override instructions specified by the BIOS
2010 ACPI tables.
2011 \item [ noapic ] Instruct Xen (and domain~0) to ignore any IOAPICs
2012 that are present in the system, and instead continue to use the
2013 legacy PIC.
2014 \end{description}
2017 \section{XenLinux Boot Options}
2019 In addition to the standard Linux kernel boot options, we support:
2020 \begin{description}
2021 \item[ xencons=xxx ] Specify the device node to which the Xen virtual
2022 console driver is attached. The following options are supported:
2023 \begin{center}
2024 \begin{tabular}{l}
2025 `xencons=off': disable virtual console \\
2026 `xencons=tty': attach console to /dev/tty1 (tty0 at boot-time) \\
2027 `xencons=ttyS': attach console to /dev/ttyS0
2028 \end{tabular}
2029 \end{center}
2030 The default is ttyS for dom0 and tty for all other domains.
2031 \end{description}
2034 %% Chapter Further Support
2035 \chapter{Further Support}
2037 If you have questions that are not answered by this manual, the
2038 sources of information listed below may be of interest to you. Note
2039 that bug reports, suggestions and contributions related to the
2040 software (or the documentation) should be sent to the Xen developers'
2041 mailing list (address below).
2044 \section{Other Documentation}
2046 For developers interested in porting operating systems to Xen, the
2047 \emph{Xen Interface Manual} is distributed in the \path{docs/}
2048 directory of the Xen source distribution.
2051 \section{Online References}
2053 The official Xen web site can be found at:
2054 \begin{quote} {\tt}
2055 \end{quote}
2057 This contains links to the latest versions of all online
2058 documentation, including the latest version of the FAQ.
2060 Information regarding Xen is also available at the Xen Wiki at
2061 \begin{quote} {\tt}\end{quote}
2062 The Xen project uses Bugzilla as its bug tracking system. You'll find
2063 the Xen Bugzilla at
2066 \section{Mailing Lists}
2068 There are several mailing lists that are used to discuss Xen related
2069 topics. The most widely relevant are listed below. An official page of
2070 mailing lists and subscription information can be found at \begin{quote}
2071 {\tt} \end{quote}
2073 \begin{description}
2074 \item[] Used for development
2075 discussions and bug reports. Subscribe at: \\
2076 {\small {\tt}}
2077 \item[] Used for installation and usage
2078 discussions and requests for help. Subscribe at: \\
2079 {\small {\tt}}
2080 \item[] Used for announcements only.
2081 Subscribe at: \\
2082 {\small {\tt}}
2083 \item[] Changelog feed
2084 from the unstable and 2.0 trees - developer oriented. Subscribe at: \\
2085 {\small {\tt}}
2086 \end{description}
2090 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
2092 \appendix
2094 \chapter{Unmodified (VMX) guest domains in Xen with Intel\textregistered Virtualization Technology (VT)}
2096 Xen supports guest domains running unmodified Guest operating systems using Virtualization Technology (VT) available on recent Intel Processors. More information about the Intel Virtualization Technology implementing Virtual Machine Extensions (VMX) in the processor is available on the Intel website at \\
2097 {\small {\tt}}
2099 \section{Building Xen with VT support}
2101 The following packages need to be installed in order to build Xen with VT support. Some Linux distributions do not provide these packages by default.
2103 \begin{tabular}{lp{11.0cm}}
2104 {\bfseries Package} & {\bfseries Description} \\
2106 dev86 & The dev86 package provides an assembler and linker for real mode 80x86 instructions. You need to have this package installed in order to build the BIOS code which runs in (virtual) real mode.
2108 If the dev86 package is not available on the x86\_64 distribution, you can install the i386 version of it. The dev86 rpm package for various distributions can be found at {\scriptsize {\tt\&submit=Search}} \\
2110 LibVNCServer & The unmodified guest's VGA display, keyboard, and mouse can be virtualized by the vncserver library. You can get the sources of libvncserver from {\small {\tt}}. Build and install the sources on the build system to get the libvncserver library. There is a significant performance degradation in 0.8 version. The current sources in the CVS tree have fixed this degradation. So it is highly recommended to download the latest CVS sources and install them.\\
2112 SDL-devel, SDL & Simple DirectMedia Layer (SDL) is another way of virtualizing the unmodified guest console. It provides an X window for the guest console.
2114 If the SDL and SDL-devel packages are not installed by default on the build system, they can be obtained from {\scriptsize {\tt\&amp;submit=Search}}
2115 , {\scriptsize {\tt\&submit=Search}} \\
2117 \end{tabular}
2119 \section{Configuration file for unmodified VMX guests}
2121 The Xen installation includes a sample configuration file, {\small {\tt /etc/xen/xmexample.vmx}}. There are comments describing all the options. In addition to the common options that are the same as those for paravirtualized guest configurations, VMX guest configurations have the following settings:
2123 \begin{tabular}{lp{11.0cm}}
2125 {\bfseries Parameter} & {\bfseries Description} \\
2127 kernel & The VMX firmware loader, {\small {\tt /usr/lib/xen/boot/vmxloader}}\\
2129 builder & The domain build function. The VMX domain uses the vmx builder.\\
2131 acpi & Enable VMX guest ACPI, default=0 (disabled)\\
2133 apic & Enable VMX guest APIC, default=0 (disabled)\\
2135 pae & Enable VMX guest PAE, default=0 (disabled)\\
2137 vif & Optionally defines MAC address and/or bridge for the network interfaces. Random MACs are assigned if not given. {\small {\tt type=ioemu}} means ioemu is used to virtualize the VMX NIC. If no type is specified, vbd is used, as with paravirtualized guests.\\
2139 disk & Defines the disk devices you want the domain to have access to, and what you want them accessible as. If using a physical device as the VMX guest's disk, each disk entry is of the form
2141 {\small {\tt phy:UNAME,ioemu:DEV,MODE,}}
2143 where UNAME is the device, DEV is the device name the domain will see, and MODE is r for read-only, w for read-write. ioemu means the disk will use ioemu to virtualize the VMX disk. If not adding ioemu, it uses vbd like paravirtualized guests.
2145 If using disk image file, its form should be like
2147 {\small {\tt file:FILEPATH,ioemu:DEV,MODE}}
2149 If using more than one disk, there should be a comma between each disk entry. For example:
2151 {\scriptsize {\tt disk = ['file:/var/images/image1.img,ioemu:hda,w', 'file:/var/images/image2.img,ioemu:hdb,w']}}\\
2153 cdrom & Disk image for CD-ROM. The default is {\small {\tt /dev/cdrom}} for Domain0. Inside the VMX domain, the CD-ROM will available as device {\small {\tt /dev/hdc}}. The entry can also point to an ISO file.\\
2155 boot & Boot from floppy (a), hard disk (c) or CD-ROM (d). For example, to boot from CD-ROM, the entry should be:
2157 boot='d'\\
2159 device\_model & The device emulation tool for VMX guests. This parameter should not be changed.\\
2161 sdl & Enable SDL library for graphics, default = 0 (disabled)\\
2163 vnc & Enable VNC library for graphics, default = 1 (enabled)\\
2165 vncviewer & Enable spawning of the vncviewer (only valid when vnc=1), default = 1 (enabled)
2167 If vnc=1 and vncviewer=0, user can use vncviewer to manually connect VMX from remote. For example:
2169 {\small {\tt vncviewer domain0\_IP\_address:VMX\_domain\_id}} \\
2171 ne2000 & Enable ne2000, default = 0 (disabled; use pcnet)\\
2173 serial & Enable redirection of VMX serial output to pty device\\
2175 localtime & Set the real time clock to local time [default=0, that is, set to UTC].\\
2177 enable-audio & Enable audio support. This is under development.\\
2179 full-screen & Start in full screen. This is under development.\\
2181 nographic & Another way to redirect serial output. If enabled, no 'sdl' or 'vnc' can work. Not recommended.\\
2183 \end{tabular}
2186 \section{Creating virtual disks from scratch}
2187 \subsection{Using physical disks}
2188 If you are using a physical disk or physical disk partition, you need to install a Linux OS on the disk first. Then the boot loader should be installed in the correct place. For example {\small {\tt dev/sda}} for booting from the whole disk, or {\small {\tt /dev/sda1}} for booting from partition 1.
2190 \subsection{Using disk image files}
2191 You need to create a large empty disk image file first; then, you need to install a Linux OS onto it. There are two methods you can choose. One is directly installing it using a VMX guest while booting from the OS installation CD-ROM. The other is copying an installed OS into it. The boot loader will also need to be installed.
2193 \subsubsection*{To create the image file:}
2194 The image size should be big enough to accommodate the entire OS. This example assumes the size is 1G (which is probably too small for most OSes).
2196 {\small {\tt \# dd if=/dev/zero of=hd.img bs=1M count=1 seek=1023}}
2198 \subsubsection*{To directly install Linux OS into an image file using a VMX guest:}
2200 Install Xen and create VMX with the original image file with booting from CD-ROM. Then it is just like a normal Linux OS installation. The VMX configuration file should have these two entries before creating:
2202 {\small {\tt cdrom='/dev/cdrom'
2203 boot='d'}}
2205 If this method does not succeed, you can choose the following method of copying an installed Linux OS into an image file.
2207 \subsubsection*{To copy a installed OS into an image file:}
2208 Directly installing is an easier way to make partitions and install an OS in a disk image file. But if you want to create a specific OS in your disk image, then you will most likely want to use this method.
2210 \begin{enumerate}
2211 \item {\bfseries Install a normal Linux OS on the host machine}\\
2212 You can choose any way to install Linux, such as using yum to install Red Hat Linux or YAST to install Novell SuSE Linux. The rest of this example assumes the Linux OS is installed in {\small {\tt /var/guestos/}}.
2214 \item {\bfseries Make the partition table}\\
2215 The image file will be treated as hard disk, so you should make the partition table in the image file. For example:
2217 {\scriptsize {\tt \# losetup /dev/loop0 hd.img\\
2218 \# fdisk -b 512 -C 4096 -H 16 -S 32 /dev/loop0\\
2219 press 'n' to add new partition\\
2220 press 'p' to choose primary partition\\
2221 press '1' to set partition number\\
2222 press "Enter" keys to choose default value of "First Cylinder" parameter.\\
2223 press "Enter" keys to choose default value of "Last Cylinder" parameter.\\
2224 press 'w' to write partition table and exit\\
2225 \# losetup -d /dev/loop0}}
2227 \item {\bfseries Make the file system and install grub}\\
2228 {\scriptsize {\tt \# ln -s /dev/loop0 /dev/loop\\
2229 \# losetup /dev/loop0 hd.img\\
2230 \# losetup -o 16384 /dev/loop1 hd.img\\
2231 \# mkfs.ext3 /dev/loop1\\
2232 \# mount /dev/loop1 /mnt\\
2233 \# mkdir -p /mnt/boot/grub\\
2234 \# cp /boot/grub/stage* /boot/grub/e2fs\_stage1\_5 /mnt/boot/grub\\
2235 \# umount /mnt\\
2236 \# grub\\
2237 grub> device (hd0) /dev/loop\\
2238 grub> root (hd0,0)\\
2239 grub> setup (hd0)\\
2240 grub> quit\\
2241 \# rm /dev/loop\\
2242 \# losetup -d /dev/loop0\\
2243 \# losetup -d /dev/loop1}}
2245 The {\small {\tt losetup}} option {\small {\tt -o 16384}} skips the partition table in the image file. It is the number of sectors times 512. We need {\small {\tt /dev/loop}} because grub is expecting a disk device \emph{name}, where \emph{name} represents the entire disk and \emph{name1} represents the first partition.
2247 \item {\bfseries Copy the OS files to the image}\\
2248 If you have Xen installed, you can easily use {\small {\tt lomount}} instead of {\small {\tt losetup}} and {\small {\tt mount}} when coping files to some partitions. {\small {\tt lomount}} just needs the partition information.
2250 {\scriptsize {\tt \# lomount -t ext3 -diskimage hd.img -partition 1 /mnt/guest\\
2251 \# cp -ax /var/guestos/\{root,dev,var,etc,usr,bin,sbin,lib\} /mnt/guest\\
2252 \# mkdir /mnt/guest/\{proc,sys,home,tmp\}}}
2254 \item {\bfseries Edit the {\small {\tt /etc/fstab}} of the guest image}\\
2255 The fstab should look like this:
2257 {\scriptsize {\tt \# vim /mnt/guest/etc/fstab\\
2258 /dev/hda1 / ext3 defaults 1 1\\
2259 none /dev/pts devpts gid=5,mode=620 0 0\\
2260 none /dev/shm tmpfs defaults 0 0\\
2261 none /proc proc defaults 0 0\\
2262 none /sys sysfs efaults 0 0}}
2264 \item {\bfseries umount the image file}\\
2265 {\small {\tt \# umount /mnt/guest}}
2266 \end{enumerate}
2268 Now, the guest OS image {\small {\tt hd.img}} is ready. You can also reference {\small {\tt}} for quickstart images. But make sure to install the boot loader.
2270 \subsection{Install Windows into an Image File using a VMX guest}
2271 In order to install a Windows OS, you should keep {\small {\tt acpi=0}} in your VMX configuration file.
2273 \section{VMX Guests}
2274 \subsection{Editing the Xen VMX config file}
2275 Make a copy of the example VMX configuration file {\small {\tt /etc/xen/xmeaxmple.vmx}} and edit the line that reads
2277 {\small {\tt disk = [ 'file:/var/images/\emph{guest.img},ioemu:hda,w' ]}}
2279 replacing \emph{guest.img} with the name of the guest OS image file you just made.
2281 \subsection{Creating VMX guests}
2282 Simply follow the usual method of creating the guest, using the -f parameter and providing the filename of your VMX configuration file:\\
2284 {\small {\tt \# xend start\\
2285 \# xm create /etc/xen/vmxguest.vmx}}
2287 In the default configuration, VNC is on and SDL is off. Therefore VNC windows will open when VMX guests are created. If you want to use SDL to create VMX guests, set {\small {\tt sdl=1}} in your VMX configuration file. You can also turn off VNC by setting {\small {\tt vnc=0}}.
2289 \subsection{Use mouse in VNC window}
2290 The default PS/2 mouse will not work properly in VMX by a VNC window. Summagraphics mouse emulation does work in this environment. A Summagraphics mouse can be enabled by reconfiguring 2 services:
2292 {\small {\tt 1. General Purpose Mouse (GPM). The GPM daemon is configured in different ways in different Linux distributions. On a Redhat distribution, this is accomplished by changing the file `/etc/sysconfig/mouse' to have the following:\\
2293 MOUSETYPE="summa"\\
2295 DEVICE=/dev/ttyS0\\
2296 \\
2297 2. X11. For all Linux distributions, change the Mouse0 stanza in `/etc/X11/xorg.conf' to:\\
2298 Section "InputDevice"\\
2299 Identifier "Mouse0"\\
2300 Driver "summa"\\
2301 Option "Device" "/dev/ttyS0"\\
2302 Option "InputFashion" "Tablet"\\
2303 Option "Mode" "Absolute"\\
2304 Option "Name" "EasyPen"\\
2305 Option "Compatible" "True"\\
2306 Option "Protocol" "Auto"\\
2307 Option "SendCoreEvents" "on"\\
2308 Option "Vendor" "GENIUS"\\
2309 EndSection}}
2311 If the Summagraphics mouse isn't the default mouse, you can manually kill 'gpm' and restart it with the command "gpm -m /dev/ttyS0 -t summa". Note that Summagraphics mouse makes no sense in an SDL window and is therefore not available in this environment.
2313 \subsection{Destroy VMX guests}
2314 VMX guests can be destroyed in the same way as can paravirtualized guests. We recommend that you type the command
2316 {\small {\tt poweroff}}
2318 in the VMX guest's console first to prevent data loss. Then execute the command
2320 {\small {\tt xm destroy \emph{vmx\_guest\_id} }}
2322 at the Domain0 console.
2324 \subsection{VMX window (X or VNC) Hot Key}
2325 If you are running in the X environment after creating a VMX guest, an X window is created. There are several hot keys for control of the VMX guest that can be used in the window.
2327 {\bfseries Ctrl+Alt+2} switches from guest VGA window to the control window. Typing {\small {\tt help }} shows the control commands help. For example, 'q' is the command to destroy the VMX guest.\\
2328 {\bfseries Ctrl+Alt+1} switches back to VMX guest's VGA.\\
2329 {\bfseries Ctrl+Alt+3} switches to serial port output. It captures serial output from the VMX guest. It works only if the VMX guest was configured to use the serial port. \\
2331 \subsection{Save/Restore and Migration}
2332 VMX guests currently cannot be saved and restored, nor migrated. These features are currently under active development.
2334 \chapter{Vnets - Domain Virtual Networking}
2336 Xen optionally supports virtual networking for domains using {\em vnets}.
2337 These emulate private LANs that domains can use. Domains on the same
2338 vnet can be hosted on the same machine or on separate machines, and the
2339 vnets remain connected if domains are migrated. Ethernet traffic
2340 on a vnet is tunneled inside IP packets on the physical network. A vnet is a virtual
2341 network and addressing within it need have no relation to addressing on
2342 the underlying physical network. Separate vnets, or vnets and the physical network,
2343 can be connected using domains with more than one network interface and
2344 enabling IP forwarding or bridging in the usual way.
2346 Vnet support is included in \texttt{xm} and \xend:
2347 \begin{verbatim}
2348 # xm vnet-create <config>
2349 \end{verbatim}
2350 creates a vnet using the configuration in the file \verb|<config>|.
2351 When a vnet is created its configuration is stored by \xend and the vnet persists until it is
2352 deleted using
2353 \begin{verbatim}
2354 # xm vnet-delete <vnetid>
2355 \end{verbatim}
2356 The vnets \xend knows about are listed by
2357 \begin{verbatim}
2358 # xm vnet-list
2359 \end{verbatim}
2360 More vnet management commands are available using the
2361 \texttt{vn} tool included in the vnet distribution.
2363 The format of a vnet configuration file is
2364 \begin{verbatim}
2365 (vnet (id <vnetid>)
2366 (bridge <bridge>)
2367 (vnetif <vnet interface>)
2368 (security <level>))
2369 \end{verbatim}
2370 White space is not significant. The parameters are:
2371 \begin{itemize}
2372 \item \verb|<vnetid>|: vnet id, the 128-bit vnet identifier. This can be given
2373 as 8 4-digit hex numbers separated by colons, or in short form as a single 4-digit hex number.
2374 The short form is the same as the long form with the first 7 fields zero.
2375 Vnet ids must be non-zero and id 1 is reserved.
2377 \item \verb|<bridge>|: the name of a bridge interface to create for the vnet. Domains
2378 are connected to the vnet by connecting their virtual interfaces to the bridge.
2379 Bridge names are limited to 14 characters by the kernel.
2381 \item \verb|<vnetif>|: the name of the virtual interface onto the vnet (optional). The
2382 interface encapsulates and decapsulates vnet traffic for the network and is attached
2383 to the vnet bridge. Interface names are limited to 14 characters by the kernel.
2385 \item \verb|<level>|: security level for the vnet (optional). The level may be one of
2386 \begin{itemize}
2387 \item \verb|none|: no security (default). Vnet traffic is in clear on the network.
2388 \item \verb|auth|: authentication. Vnet traffic is authenticated using IPSEC
2389 ESP with hmac96.
2390 \item \verb|conf|: confidentiality. Vnet traffic is authenticated and encrypted
2391 using IPSEC ESP with hmac96 and AES-128.
2392 \end{itemize}
2393 Authentication and confidentiality are experimental and use hard-wired keys at present.
2394 \end{itemize}
2395 When a vnet is created its configuration is stored by \xend and the vnet persists until it is
2396 deleted using \texttt{xm vnet-delete <vnetid>}. The interfaces and bridges used by vnets
2397 are visible in the output of \texttt{ifconfig} and \texttt{brctl show}.
2399 \section{Example}
2400 If the file \path{vnet97.sxp} contains
2401 \begin{verbatim}
2402 (vnet (id 97) (bridge vnet97) (vnetif vnif97)
2403 (security none))
2404 \end{verbatim}
2405 Then \texttt{xm vnet-create vnet97.sxp} will define a vnet with id 97 and no security.
2406 The bridge for the vnet is called vnet97 and the virtual interface for it is vnif97.
2407 To add an interface on a domain to this vnet set its bridge to vnet97
2408 in its configuration. In Python:
2409 \begin{verbatim}
2410 vif="bridge=vnet97"
2411 \end{verbatim}
2412 In sxp:
2413 \begin{verbatim}
2414 (dev (vif (mac aa:00:00:01:02:03) (bridge vnet97)))
2415 \end{verbatim}
2416 Once the domain is started you should see its interface in the output of \texttt{brctl show}
2417 under the ports for \texttt{vnet97}.
2419 To get best performance it is a good idea to reduce the MTU of a domain's interface
2420 onto a vnet to 1400. For example using \texttt{ifconfig eth0 mtu 1400} or putting
2421 \texttt{MTU=1400} in \texttt{ifcfg-eth0}.
2422 You may also have to change or remove cached config files for eth0 under
2423 \texttt{/etc/sysconfig/networking}. Vnets work anyway, but performance can be reduced
2424 by IP fragmentation caused by the vnet encapsulation exceeding the hardware MTU.
2426 \section{Installing vnet support}
2427 Vnets are implemented using a kernel module, which needs to be loaded before
2428 they can be used. You can either do this manually before starting \xend, using the
2429 command \texttt{vn insmod}, or configure \xend to use the \path{network-vnet}
2430 script in the xend configuration file \texttt{/etc/xend/xend-config.sxp}:
2431 \begin{verbatim}
2432 (network-script network-vnet)
2433 \end{verbatim}
2434 This script insmods the module and calls the \path{network-bridge} script.
2436 The vnet code is not compiled and installed by default.
2437 To compile the code and install on the current system
2438 use \texttt{make install} in the root of the vnet source tree,
2439 \path{tools/vnet}. It is also possible to install to an installation
2440 directory using \texttt{make dist}. See the \path{Makefile} in
2441 the source for details.
2443 The vnet module creates vnet interfaces \texttt{vnif0002},
2444 \texttt{vnif0003} and \texttt{vnif0004} by default. You can test that
2445 vnets are working by configuring IP addresses on these interfaces
2446 and trying to ping them across the network. For example, using machines
2447 hostA and hostB:
2448 \begin{verbatim}
2449 hostA# ifconfig vnif0004 up
2450 hostB# ifconfig vnif0004 up
2451 hostB# ping
2452 \end{verbatim}
2454 The vnet implementation uses IP multicast to discover vnet interfaces, so
2455 all machines hosting vnets must be reachable by multicast. Network switches
2456 are often configured not to forward multicast packets, so this often
2457 means that all machines using a vnet must be on the same LAN segment,
2458 unless you configure vnet forwarding.
2460 You can test multicast coverage by pinging the vnet multicast address:
2461 \begin{verbatim}
2462 # ping -b
2463 \end{verbatim}
2464 You should see replies from all machines with the vnet module running.
2465 You can see if vnet packets are being sent or received by dumping traffic
2466 on the vnet UDP port:
2467 \begin{verbatim}
2468 # tcpdump udp port 1798
2469 \end{verbatim}
2471 If multicast is not being forwaded between machines you can configure
2472 multicast forwarding using vn. Suppose we have machines hostA on
2473 and hostB on and that multicast is not forwarded between them.
2474 We use vn to configure each machine to forward to the other:
2475 \begin{verbatim}
2476 hostA# vn peer-add hostB
2477 hostB# vn peer-add hostA
2478 \end{verbatim}
2479 Multicast forwarding needs to be used carefully - you must avoid creating forwarding
2480 loops. Typically only one machine on a subnet needs to be configured to forward,
2481 as it will forward multicasts received from other machines on the subnet.
2483 %% Chapter Glossary of Terms moved to glossary.tex
2484 \chapter{Glossary of Terms}
2486 \begin{description}
2488 \item[BVT] The BVT scheduler is used to give proportional fair shares
2489 of the CPU to domains.
2491 \item[Domain] A domain is the execution context that contains a
2492 running {\bf virtual machine}. The relationship between virtual
2493 machines and domains on Xen is similar to that between programs and
2494 processes in an operating system: a virtual machine is a persistent
2495 entity that resides on disk (somewhat like a program). When it is
2496 loaded for execution, it runs in a domain. Each domain has a {\bf
2497 domain ID}.
2499 \item[Domain 0] The first domain to be started on a Xen machine.
2500 Domain 0 is responsible for managing the system.
2502 \item[Domain ID] A unique identifier for a {\bf domain}, analogous to
2503 a process ID in an operating system.
2505 \item[Full virtualization] An approach to virtualization which
2506 requires no modifications to the hosted operating system, providing
2507 the illusion of a complete system of real hardware devices.
2509 \item[Hypervisor] An alternative term for {\bf VMM}, used because it
2510 means `beyond supervisor', since it is responsible for managing
2511 multiple `supervisor' kernels.
2513 \item[Live migration] A technique for moving a running virtual machine
2514 to another physical host, without stopping it or the services
2515 running on it.
2517 \item[Paravirtualization] An approach to virtualization which requires
2518 modifications to the operating system in order to run in a virtual
2519 machine. Xen uses paravirtualization but preserves binary
2520 compatibility for user space applications.
2522 \item[Shadow pagetables] A technique for hiding the layout of machine
2523 memory from a virtual machine's operating system. Used in some {\bf
2524 VMMs} to provide the illusion of contiguous physical memory, in
2525 Xen this is used during {\bf live migration}.
2527 \item[Virtual Block Device] Persistant storage available to a virtual
2528 machine, providing the abstraction of an actual block storage device.
2529 {\bf VBD}s may be actual block devices, filesystem images, or
2530 remote/network storage.
2532 \item[Virtual Machine] The environment in which a hosted operating
2533 system runs, providing the abstraction of a dedicated machine. A
2534 virtual machine may be identical to the underlying hardware (as in
2535 {\bf full virtualization}, or it may differ, as in {\bf
2536 paravirtualization}).
2538 \item[VMM] Virtual Machine Monitor - the software that allows multiple
2539 virtual machines to be multiplexed on a single physical machine.
2541 \item[Xen] Xen is a paravirtualizing virtual machine monitor,
2542 developed primarily by the Systems Research Group at the University
2543 of Cambridge Computer Laboratory.
2545 \item[XenLinux] A name for the port of the Linux kernel that
2546 runs on Xen.
2548 \end{description}
2551 \end{document}
2554 %% Other stuff without a home
2556 %% Instructions Re Python API
2558 %% Other Control Tasks using Python
2559 %% ================================
2561 %% A Python module 'Xc' is installed as part of the tools-install
2562 %% process. This can be imported, and an 'xc object' instantiated, to
2563 %% provide access to privileged command operations:
2565 %% # import Xc
2566 %% # xc =
2567 %% # dir(xc)
2568 %% # help(xc.domain_create)
2570 %% In this way you can see that the class 'xc' contains useful
2571 %% documentation for you to consult.
2573 %% A further package of useful routines (xenctl) is also installed:
2575 %% # import xenctl.utils
2576 %% # help(xenctl.utils)
2578 %% You can use these modules to write your own custom scripts or you
2579 %% can customise the scripts supplied in the Xen distribution.
2583 % Explain about AGP GART
2586 %% If you're not intending to configure the new domain with an IP
2587 %% address on your LAN, then you'll probably want to use NAT. The
2588 %% 'xen_nat_enable' installs a few useful iptables rules into domain0
2589 %% to enable NAT. [NB: We plan to support RSIP in future]
2593 %% Installing the file systems from the CD
2594 %% =======================================
2596 %% If you haven't got an existing Linux installation onto which you
2597 %% can just drop down the Xen and Xenlinux images, then the file
2598 %% systems on the CD provide a quick way of doing an install. However,
2599 %% you would be better off in the long run doing a proper install of
2600 %% your preferred distro and installing Xen onto that, rather than
2601 %% just doing the hack described below:
2603 %% Choose one or two partitions, depending on whether you want a
2604 %% separate /usr or not. Make file systems on it/them e.g.:
2605 %% mkfs -t ext3 /dev/hda3
2606 %% [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
2607 %% version of mkfs]
2609 %% Next, mount the file system(s) e.g.:
2610 %% mkdir /mnt/root && mount /dev/hda3 /mnt/root
2611 %% [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
2613 %% To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
2614 %% cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
2616 %% You'll need to edit /mnt/root/etc/fstab to reflect your file system
2617 %% configuration. Changing the password file (etc/shadow) is probably a
2618 %% good idea too.
2620 %% To install the usr file system, copy the file system from CD on
2621 %% /usr, though leaving out the "XenDemoCD" and "boot" directories:
2622 %% cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos
2623 %% local sbin tmp doc include lib man share /mnt/usr
2625 %% If you intend to boot off these file systems (i.e. use them for
2626 %% domain 0), then you probably want to copy the /usr/boot
2627 %% directory on the cd over the top of the current symlink to /boot
2628 %% on your root filesystem (after deleting the current symlink)
2629 %% i.e.:
2630 %% cd /mnt/root ; rm boot ; cp -a /usr/boot .