\documentclass[11pt,twoside,final,openright]{report} \usepackage{a4,graphicx,html,parskip,setspace,times,xspace} \setstretch{1.15} \def\Xend{{Xend}\xspace} \def\xend{{xend}\xspace} \latexhtml{\newcommand{\path}[1]{{\small {\tt #1}}}}{\newcommand{\path}[1]{{\tt #1}}} \begin{document} % TITLE PAGE \pagestyle{empty} \begin{center} \vspace*{\fill} \includegraphics{figs/xenlogo.eps} \vfill \vfill \vfill \begin{tabular}{l} {\Huge \bf Users' manual} \\[4mm] {\huge Xen v2.0 for x86} \\[80mm] {\Large Xen is Copyright (c) 2002-2004, The Xen Team} \\[3mm] {\Large University of Cambridge, UK} \\[20mm] \end{tabular} \end{center} {\bf DISCLAIMER: This documentation is currently under active development and as such there may be mistakes and omissions --- watch out for these and please report any you find to the developer's mailing list. Contributions of material, suggestions and corrections are welcome. } \vfill \cleardoublepage % TABLE OF CONTENTS \pagestyle{plain} \pagenumbering{roman} { \parskip 0pt plus 1pt \tableofcontents } \cleardoublepage % PREPARE FOR MAIN TEXT \pagenumbering{arabic} \raggedbottom \widowpenalty=10000 \clubpenalty=10000 \parindent=0pt \parskip=5pt \renewcommand{\topfraction}{.8} \renewcommand{\bottomfraction}{.8} \renewcommand{\textfraction}{.2} \renewcommand{\floatpagefraction}{.8} \setstretch{1.1} \part{Introduction and Tutorial} \chapter{Introduction} Xen is a {\em paravirtualising} virtual machine monitor (VMM), or `hypervisor', for the x86 processor architecture. Xen can securely execute multiple virtual machines on a single physical system with close-to-native performance. The virtual machine technology facilitates enterprise-grade functionality, including: \begin{itemize} \item Virtual machines with performance close to native hardware. \item Live migration of running virtual machines between physical hosts. \item Excellent hardware support (supports most Linux device drivers). \item Sandboxed, restartable device drivers. \end{itemize} Paravirtualisation permits very high performance virtualisation, even on architectures like x86 that are traditionally very hard to virtualise. The drawback of this approach is that it requires operating systems to be {\em ported} to run on Xen. Porting an OS to run on Xen is similar to supporting a new hardware platform, however the process is simplified because the paravirtual machine architecture is very similar to the underlying native hardware. Even though operating system kernels must explicitly support Xen, a key feature is that user space applications and libraries {\em do not} require modification. Xen support is available for increasingly many operating systems: right now, Linux 2.4, Linux 2.6 and NetBSD are available for Xen 2.0. A FreeBSD port is undergoing testing and will be incorporated into the release soon. Other OS ports, including Plan 9, are in progress. We hope that that arch-xen patches will be incorporated into the mainstream releases of these operating systems in due course (as has already happened for NetBSD). Possible usage scenarios for Xen include: \begin{description} \item [Kernel development.] Test and debug kernel modifications in a sandboxed virtual machine --- no need for a separate test machine. \item [Multiple OS configurations.] Run multiple operating systems simultaneously, for instance for compatibility or QA purposes. \item [Server consolidation.] Move multiple servers onto a single physical host with performance and fault isolation provided at virtual machine boundaries. \item [Cluster computing.] Management at VM granularity provides more flexibility than separately managing each physical host, but better control and isolation than single-system image solutions, particularly by using live migration for load balancing. \item [Hardware support for custom OSes.] Allow development of new OSes while benefiting from the wide-ranging hardware support of existing OSes such as Linux. \end{description} \section{Structure of a Xen-Based System} A Xen system has multiple layers, the lowest and most privileged of which is Xen itself. Xen in turn may host multiple {\em guest} operating systems, each of which is executed within a secure virtual machine (in Xen terminology, a {\em domain}). Domains are scheduled by Xen to make effective use of the available physical CPUs. Each guest OS manages its own applications, which includes responsibility for scheduling each application within the time allotted to the VM by Xen. The first domain, {\em domain 0}, is created automatically when the system boots and has special management privileges. Domain 0 builds other domains and manages their virtual devices. It also performs administrative tasks such as suspending, resuming and migrating other virtual machines. Within domain 0, a process called \emph{xend} runs to manage the system. \Xend is responsible for managing virtual machines and providing access to their consoles. Commands are issued to \xend over an HTTP interface, either from a command-line tool or from a web browser. \section{Hardware Support} Xen currently runs only on the x86 architecture, requiring a `P6' or newer processor (e.g. Pentium Pro, Celeron, Pentium II, Pentium III, Pentium IV, Xeon, AMD Athlon, AMD Duron). Multiprocessor machines are supported, and we also have basic support for HyperThreading (SMT), although this remains a topic for ongoing research. A port specifically for x86/64 is in progress, although Xen already runs on such systems in 32-bit legacy mode. In addition a port to the IA64 architecture is approaching completion. We hope to add other architectures such as PPC and ARM in due course. Xen can currently use up to 4GB of memory. It is possible for x86 machines to address up to 64GB of physical memory but there are no current plans to support these systems: The x86/64 port is the planned route to supporting larger memory sizes. Xen offloads most of the hardware support issues to the guest OS running in Domain~0. Xen itself contains only the code required to detect and start secondary processors, set up interrupt routing, and perform PCI bus enumeration. Device drivers run within a privileged guest OS rather than within Xen itself. This approach provides compatibility with the majority of device hardware supported by Linux. The default XenLinux build contains support for relatively modern server-class network and disk hardware, but you can add support for other hardware by configuring your XenLinux kernel in the normal way. \section{History} Xen was originally developed by the Systems Research Group at the University of Cambridge Computer Laboratory as part of the XenoServers project, funded by the UK-EPSRC. XenoServers aim to provide a `public infrastructure for global distributed computing', and Xen plays a key part in that, allowing us to efficiently partition a single machine to enable multiple independent clients to run their operating systems and applications in an environment providing protection, resource isolation and accounting. The project web page contains further information along with pointers to papers and technical reports: \path{http://www.cl.cam.ac.uk/xeno} Xen has since grown into a fully-fledged project in its own right, enabling us to investigate interesting research issues regarding the best techniques for virtualising resources such as the CPU, memory, disk and network. The project has been bolstered by support from Intel Research Cambridge, and HP Labs, who are now working closely with us. Xen was first described in a paper presented at SOSP in 2003\footnote{\tt http://www.cl.cam.ac.uk/netos/papers/2003-xensosp.pdf}, and the first public release (1.0) was made that October. Since then, Xen has significantly matured and is now used in production scenarios on many sites. Xen 2.0 features greatly enhanced hardware support, configuration flexibility, usability and a larger complement of supported operating systems. This latest release takes Xen a step closer to becoming the definitive open source solution for virtualisation. \chapter{Installation} The Xen distribution includes three main components: Xen itself, ports of Linux 2.4 and 2.6 and NetBSD to run on Xen, and the user-space tools required to manage a Xen-based system. This chapter describes how to install the Xen 2.0 distribution from source. Alternatively, there may be pre-built packages available as part of your operating system distribution. \section{Prerequisites} \label{sec:prerequisites} The following is a full list of prerequisites. Items marked `$\dag$' are required by the \xend control tools, and hence required if you want to run more than one virtual machine; items marked `$*$' are only required if you wish to build from source. \begin{itemize} \item A working Linux distribution using the GRUB bootloader and running on a P6-class (or newer) CPU. \item [$\dag$] The \path{iproute2} package. \item [$\dag$] The Linux bridge-utils\footnote{Available from {\tt http://bridge.sourceforge.net}} (e.g., \path{/sbin/brctl}) \item [$\dag$] An installation of Twisted v1.3 or above\footnote{Available from {\tt http://www.twistedmatrix.com}}. There may be a binary package available for your distribution; alternatively it can be installed by running `{\sl make install-twisted}' in the root of the Xen source tree. \item [$*$] Build tools (gcc v3.2.x or v3.3.x, binutils, GNU make). \item [$*$] Development installation of libcurl (e.g., libcurl-devel) \item [$*$] Development installation of zlib (e.g., zlib-dev). \item [$*$] Development installation of Python v2.2 or later (e.g., python-dev). \item [$*$] \LaTeX and transfig are required to build the documentation. \end{itemize} Once you have satisfied the relevant prerequisites, you can now install either a binary or source distribution of Xen. \section{Installing from Binary Tarball} Pre-built tarballs are available for download from the Xen download page \begin{quote} {\tt http://xen.sf.net} \end{quote} Once you've downloaded the tarball, simply unpack and install: \begin{verbatim} # tar zxvf xen-2.0-install.tgz # cd xen-2.0-install # sh ./install.sh \end{verbatim} Once you've installed the binaries you need to configure your system as described in Section~\ref{s:configure}. \section{Installing from Source} This section describes how to obtain, build, and install Xen from source. \subsection{Obtaining the Source} The Xen source tree is available as either a compressed source tar ball or as a clone of our master BitKeeper repository. \begin{description} \item[Obtaining the Source Tarball]\mbox{} \\ Stable versions (and daily snapshots) of the Xen source tree are available as compressed tarballs from the Xen download page \begin{quote} {\tt http://xen.sf.net} \end{quote} \item[Using BitKeeper]\mbox{} \\ If you wish to install Xen from a clone of our latest BitKeeper repository then you will need to install the BitKeeper tools. Download instructions for BitKeeper can be obtained by filling out the form at: \begin{quote} {\tt http://www.bitmover.com/cgi-bin/download.cgi} \end{quote} The public master BK repository for the 2.0 release lives at: \begin{quote} {\tt bk://xen.bkbits.net/xen-2.0.bk} \end{quote} You can use BitKeeper to download it and keep it updated with the latest features and fixes. Change to the directory in which you want to put the source code, then run: \begin{verbatim} # bk clone bk://xen.bkbits.net/xen-2.0.bk \end{verbatim} Under your current directory, a new directory named \path{xen-2.0.bk} has been created, which contains all the source code for Xen, the OS ports, and the control tools. You can update your repository with the latest changes at any time by running: \begin{verbatim} # cd xen-2.0.bk # to change into the local repository # bk pull # to update the repository \end{verbatim} \end{description} %\section{The distribution} % %The Xen source code repository is structured as follows: % %\begin{description} %\item[\path{tools/}] Xen node controller daemon (Xend), command line tools, % control libraries %\item[\path{xen/}] The Xen VMM. %\item[\path{linux-*-xen-sparse/}] Xen support for Linux. %\item[\path{linux-*-patches/}] Experimental patches for Linux. %\item[\path{netbsd-*-xen-sparse/}] Xen support for NetBSD. %\item[\path{docs/}] Various documentation files for users and developers. %\item[\path{extras/}] Bonus extras. %\end{description} \subsection{Building from Source} The top-level Xen Makefile includes a target `world' that will do the following: \begin{itemize} \item Build Xen \item Build the control tools, including \xend \item Download (if necessary) and unpack the Linux 2.6 source code, and patch it for use with Xen \item Build a Linux kernel to use in domain 0 and a smaller unprivileged kernel, which can optionally be used for unprivileged virtual machines. \end{itemize} After the build has completed you should have a top-level directory called \path{dist/} in which all resulting targets will be placed; of particular interest are the two kernels XenLinux kernel images, one with a `-xen0' extension which contains hardware device drivers and drivers for Xen's virtual devices, and one with a `-xenU' extension that just contains the virtual ones. These are found in \path{dist/install/boot/} along with the image for Xen itself and the configuration files used during the build. The NetBSD port can be built using: \begin{quote} \begin{verbatim} # make netbsd20 \end{verbatim} \end{quote} NetBSD port is built using a snapshot of the netbsd-2-0 cvs branch. The snapshot is downloaded as part of the build process, if it is not yet present in the \path{NETBSD\_SRC\_PATH} search path. The build process also downloads a toolchain which includes all the tools necessary to build the NetBSD kernel under Linux. To customize further the set of kernels built you need to edit the top-level Makefile. Look for the line: \begin{quote} \begin{verbatim} KERNELS ?= mk.linux-2.6-xen0 mk.linux-2.6-xenU \end{verbatim} \end{quote} You can edit this line to include any set of operating system kernels which have configurations in the top-level \path{buildconfigs/} directory, for example \path{mk.linux-2.4-xenU} to build a Linux 2.4 kernel containing only virtual device drivers. %% Inspect the Makefile if you want to see what goes on during a build. %% Building Xen and the tools is straightforward, but XenLinux is more %% complicated. The makefile needs a `pristine' Linux kernel tree to which %% it will then add the Xen architecture files. You can tell the %% makefile the location of the appropriate Linux compressed tar file by %% setting the LINUX\_SRC environment variable, e.g. \\ %% \verb!# LINUX_SRC=/tmp/linux-2.6.11.tar.bz2 make world! \\ or by %% placing the tar file somewhere in the search path of {\tt %% LINUX\_SRC\_PATH} which defaults to `{\tt .:..}'. If the makefile %% can't find a suitable kernel tar file it attempts to download it from %% kernel.org (this won't work if you're behind a firewall). %% After untaring the pristine kernel tree, the makefile uses the {\tt %% mkbuildtree} script to add the Xen patches to the kernel. %% The procedure is similar to build the Linux 2.4 port: \\ %% \verb!# LINUX_SRC=/path/to/linux2.4/source make linux24! %% \framebox{\parbox{5in}{ %% {\bf Distro specific:} \\ %% {\it Gentoo} --- if not using udev (most installations, currently), you'll need %% to enable devfs and devfs mount at boot time in the xen0 config. %% }} \subsection{Custom XenLinux Builds} % If you have an SMP machine you may wish to give the {\tt '-j4'} % argument to make to get a parallel build. If you wish to build a customized XenLinux kernel (e.g. to support additional devices or enable distribution-required features), you can use the standard Linux configuration mechanisms, specifying that the architecture being built for is \path{xen}, e.g: \begin{quote} \begin{verbatim} # cd linux-2.6.11-xen0 # make ARCH=xen xconfig # cd .. # make \end{verbatim} \end{quote} You can also copy an existing Linux configuration (\path{.config}) into \path{linux-2.6.11-xen0} and execute: \begin{quote} \begin{verbatim} # make ARCH=xen oldconfig \end{verbatim} \end{quote} You may be prompted with some Xen-specific options; we advise accepting the defaults for these options. Note that the only difference between the two types of Linux kernel that are built is the configuration file used for each. The "U" suffixed (unprivileged) versions don't contain any of the physical hardware device drivers, leading to a 30\% reduction in size; hence you may prefer these for your non-privileged domains. The `0' suffixed privileged versions can be used to boot the system, as well as in driver domains and unprivileged domains. \subsection{Installing the Binaries} The files produced by the build process are stored under the \path{dist/install/} directory. To install them in their default locations, do: \begin{quote} \begin{verbatim} # make install \end{verbatim} \end{quote} Alternatively, users with special installation requirements may wish to install them manually by copying the files to their appropriate destinations. %% Files in \path{install/boot/} include: %% \begin{itemize} %% \item \path{install/boot/xen-2.0.gz} Link to the Xen 'kernel' %% \item \path{install/boot/vmlinuz-2.6-xen0} Link to domain 0 XenLinux kernel %% \item \path{install/boot/vmlinuz-2.6-xenU} Link to unprivileged XenLinux kernel %% \end{itemize} The \path{dist/install/boot} directory will also contain the config files used for building the XenLinux kernels, and also versions of Xen and XenLinux kernels that contain debug symbols (\path{xen-syms-2.0.6} and \path{vmlinux-syms-2.6.11.11-xen0}) which are essential for interpreting crash dumps. Retain these files as the developers may wish to see them if you post on the mailing list. \section{Configuration} \label{s:configure} Once you have built and installed the Xen distribution, it is simple to prepare the machine for booting and running Xen. \subsection{GRUB Configuration} An entry should be added to \path{grub.conf} (often found under \path{/boot/} or \path{/boot/grub/}) to allow Xen / XenLinux to boot. This file is sometimes called \path{menu.lst}, depending on your distribution. The entry should look something like the following: {\small \begin{verbatim} title Xen 2.0 / XenLinux 2.6 kernel /boot/xen-2.0.gz dom0_mem=131072 module /boot/vmlinuz-2.6-xen0 root=/dev/sda4 ro console=tty0 \end{verbatim} } The kernel line tells GRUB where to find Xen itself and what boot parameters should be passed to it (in this case, setting domain 0's memory allocation and the settings for the serial port). For more details on the various Xen boot parameters see Section~\ref{s:xboot}. The module line of the configuration describes the location of the XenLinux kernel that Xen should start and the parameters that should be passed to it (these are standard Linux parameters, identifying the root device and specifying it be initially mounted read only and instructing that console output be sent to the screen). Some distributions such as SuSE do not require the \path{ro} parameter. %% \framebox{\parbox{5in}{ %% {\bf Distro specific:} \\ %% {\it SuSE} --- Omit the {\tt ro} option from the XenLinux kernel %% command line, since the partition won't be remounted rw during boot. %% }} If you want to use an initrd, just add another \path{module} line to the configuration, as usual: {\small \begin{verbatim} module /boot/my_initrd.gz \end{verbatim} } As always when installing a new kernel, it is recommended that you do not delete existing menu options from \path{menu.lst} --- you may want to boot your old Linux kernel in future, particularly if you have problems. \subsection{Serial Console (optional)} %% kernel /boot/xen-2.0.gz dom0_mem=131072 com1=115200,8n1 %% module /boot/vmlinuz-2.6-xen0 root=/dev/sda4 ro In order to configure Xen serial console output, it is necessary to add an boot option to your GRUB config; e.g. replace the above kernel line with: \begin{quote} {\small \begin{verbatim} kernel /boot/xen.gz dom0_mem=131072 com1=115200,8n1 \end{verbatim}} \end{quote} This configures Xen to output on COM1 at 115,200 baud, 8 data bits, 1 stop bit and no parity. Modify these parameters for your set up. One can also configure XenLinux to share the serial console; to achieve this append ``\path{console=ttyS0}'' to your module line. If you wish to be able to log in over the XenLinux serial console it is necessary to add a line into \path{/etc/inittab}, just as per regular Linux. Simply add the line: \begin{quote} {\small {\tt c:2345:respawn:/sbin/mingetty ttyS0} } \end{quote} and you should be able to log in. Note that to successfully log in as root over the serial line will require adding \path{ttyS0} to \path{/etc/securetty} in most modern distributions. \subsection{TLS Libraries} Users of the XenLinux 2.6 kernel should disable Thread Local Storage (e.g.\ by doing a \path{mv /lib/tls /lib/tls.disabled}) before attempting to run with a XenLinux kernel\footnote{If you boot without first disabling TLS, you will get a warning message during the boot process. In this case, simply perform the rename after the machine is up and then run \texttt{/sbin/ldconfig} to make it take effect.}. You can always reenable it by restoring the directory to its original location (i.e.\ \path{mv /lib/tls.disabled /lib/tls}). The reason for this is that the current TLS implementation uses segmentation in a way that is not permissible under Xen. If TLS is not disabled, an emulation mode is used within Xen which reduces performance substantially. We hope that this issue can be resolved by working with Linux distribution vendors to implement a minor backward-compatible change to the TLS library. \section{Booting Xen} It should now be possible to restart the system and use Xen. Reboot as usual but choose the new Xen option when the Grub screen appears. What follows should look much like a conventional Linux boot. The first portion of the output comes from Xen itself, supplying low level information about itself and the machine it is running on. The following portion of the output comes from XenLinux. You may see some errors during the XenLinux boot. These are not necessarily anything to worry about --- they may result from kernel configuration differences between your XenLinux kernel and the one you usually use. When the boot completes, you should be able to log into your system as usual. If you are unable to log in to your system running Xen, you should still be able to reboot with your normal Linux kernel. \chapter{Starting Additional Domains} The first step in creating a new domain is to prepare a root filesystem for it to boot off. Typically, this might be stored in a normal partition, an LVM or other volume manager partition, a disk file or on an NFS server. A simple way to do this is simply to boot from your standard OS install CD and install the distribution into another partition on your hard drive. To start the \xend control daemon, type \begin{quote} \verb!# xend start! \end{quote} If you wish the daemon to start automatically, see the instructions in Section~\ref{s:xend}. Once the daemon is running, you can use the \path{xm} tool to monitor and maintain the domains running on your system. This chapter provides only a brief tutorial: we provide full details of the \path{xm} tool in the next chapter. %\section{From the web interface} % %Boot the Xen machine and start Xensv (see Chapter~\ref{cha:xensv} for %more details) using the command: \\ %\verb_# xensv start_ \\ %This will also start Xend (see Chapter~\ref{cha:xend} for more information). % %The domain management interface will then be available at {\tt %http://your\_machine:8080/}. This provides a user friendly wizard for %starting domains and functions for managing running domains. % %\section{From the command line} \section{Creating a Domain Configuration File} Before you can start an additional domain, you must create a configuration file. We provide two example files which you can use as a starting point: \begin{itemize} \item \path{/etc/xen/xmexample1} is a simple template configuration file for describing a single VM. \item \path{/etc/xen/xmexample2} file is a template description that is intended to be reused for multiple virtual machines. Setting the value of the \path{vmid} variable on the \path{xm} command line fills in parts of this template. \end{itemize} Copy one of these files and edit it as appropriate. Typical values you may wish to edit include: \begin{quote} \begin{description} \item[kernel] Set this to the path of the kernel you compiled for use with Xen (e.g.\ \path{kernel = '/boot/vmlinuz-2.6-xenU'}) \item[memory] Set this to the size of the domain's memory in megabytes (e.g.\ \path{memory = 64}) \item[disk] Set the first entry in this list to calculate the offset of the domain's root partition, based on the domain ID. Set the second to the location of \path{/usr} if you are sharing it between domains (e.g.\ \path{disk = ['phy:your\_hard\_drive\%d,sda1,w' \% (base\_partition\_number + vmid), 'phy:your\_usr\_partition,sda6,r' ]} \item[dhcp] Uncomment the dhcp variable, so that the domain will receive its IP address from a DHCP server (e.g.\ \path{dhcp='dhcp'}) \end{description} \end{quote} You may also want to edit the {\bf vif} variable in order to choose the MAC address of the virtual ethernet interface yourself. For example: \begin{quote} \verb_vif = ['mac=00:06:AA:F6:BB:B3']_ \end{quote} If you do not set this variable, \xend will automatically generate a random MAC address from an unused range. \section{Booting the Domain} The \path{xm} tool provides a variety of commands for managing domains. Use the \path{create} command to start new domains. Assuming you've created a configuration file \path{myvmconf} based around \path{/etc/xen/xmexample2}, to start a domain with virtual machine ID~1 you should type: \begin{quote} \begin{verbatim} # xm create -c myvmconf vmid=1 \end{verbatim} \end{quote} The \path{-c} switch causes \path{xm} to turn into the domain's console after creation. The \path{vmid=1} sets the \path{vmid} variable used in the \path{myvmconf} file. You should see the console boot messages from the new domain appearing in the terminal in which you typed the command, culminating in a login prompt. \section{Example: ttylinux} Ttylinux is a very small Linux distribution, designed to require very few resources. We will use it as a concrete example of how to start a Xen domain. Most users will probably want to install a full-featured distribution once they have mastered the basics\footnote{ttylinux is maintained by Pascal Schmidt. You can download source packages from the distribution's home page: {\tt http://www.minimalinux.org/ttylinux/}}. \begin{enumerate} \item Download and extract the ttylinux disk image from the Files section of the project's SourceForge site (see \path{http://sf.net/projects/xen/}). \item Create a configuration file like the following: \begin{verbatim} kernel = "/boot/vmlinuz-2.6-xenU" memory = 64 name = "ttylinux" nics = 1 ip = "1.2.3.4" disk = ['file:/path/to/ttylinux/rootfs,sda1,w'] root = "/dev/sda1 ro" \end{verbatim} \item Now start the domain and connect to its console: \begin{verbatim} xm create configfile -c \end{verbatim} \item Login as root, password root. \end{enumerate} \section{Starting / Stopping Domains Automatically} It is possible to have certain domains start automatically at boot time and to have dom0 wait for all running domains to shutdown before it shuts down the system. To specify a domain is to start at boot-time, place its configuration file (or a link to it) under \path{/etc/xen/auto/}. A Sys-V style init script for RedHat and LSB-compliant systems is provided and will be automatically copied to \path{/etc/init.d/} during install. You can then enable it in the appropriate way for your distribution. For instance, on RedHat: \begin{quote} \verb_# chkconfig --add xendomains_ \end{quote} By default, this will start the boot-time domains in runlevels 3, 4 and 5. You can also use the \path{service} command to run this script manually, e.g: \begin{quote} \verb_# service xendomains start_ Starts all the domains with config files under /etc/xen/auto/. \end{quote} \begin{quote} \verb_# service xendomains stop_ Shuts down ALL running Xen domains. \end{quote} \chapter{Domain Management Tools} The previous chapter described a simple example of how to configure and start a domain. This chapter summarises the tools available to manage running domains. \section{Command-line Management} Command line management tasks are also performed using the \path{xm} tool. For online help for the commands available, type: \begin{quote} \verb_# xm help_ \end{quote} You can also type \path{xm help $<$command$>$} for more information on a given command. \subsection{Basic Management Commands} The most important \path{xm} commands are: \begin{quote} \verb_# xm list_: Lists all domains running.\\ \verb_# xm consoles_ : Gives information about the domain consoles.\\ \verb_# xm console_: Opens a console to a domain (e.g.\ \verb_# xm console myVM_ \end{quote} \subsection{\tt xm list} The output of \path{xm list} is in rows of the following format: \begin{center} {\tt name domid memory cpu state cputime console} \end{center} \begin{quote} \begin{description} \item[name] The descriptive name of the virtual machine. \item[domid] The number of the domain ID this virtual machine is running in. \item[memory] Memory size in megabytes. \item[cpu] The CPU this domain is running on. \item[state] Domain state consists of 5 fields: \begin{description} \item[r] running \item[b] blocked \item[p] paused \item[s] shutdown \item[c] crashed \end{description} \item[cputime] How much CPU time (in seconds) the domain has used so far. \item[console] TCP port accepting connections to the domain's console. \end{description} \end{quote} The \path{xm list} command also supports a long output format when the \path{-l} switch is used. This outputs the fulls details of the running domains in \xend's SXP configuration format. For example, suppose the system is running the ttylinux domain as described earlier. The list command should produce output somewhat like the following: \begin{verbatim} # xm list Name Id Mem(MB) CPU State Time(s) Console Domain-0 0 251 0 r---- 172.2 ttylinux 5 63 0 -b--- 3.0 9605 \end{verbatim} Here we can see the details for the ttylinux domain, as well as for domain 0 (which, of course, is always running). Note that the console port for the ttylinux domain is 9605. This can be connected to by TCP using a terminal program (e.g. \path{telnet} or, better, \path{xencons}). The simplest way to connect is to use the \path{xm console} command, specifying the domain name or ID. To connect to the console of the ttylinux domain, we could use any of the following: \begin{verbatim} # xm console ttylinux # xm console 5 # xencons localhost 9605 \end{verbatim} \section{Domain Save and Restore} The administrator of a Xen system may suspend a virtual machine's current state into a disk file in domain 0, allowing it to be resumed at a later time. The ttylinux domain described earlier can be suspended to disk using the command: \begin{verbatim} # xm save ttylinux ttylinux.xen \end{verbatim} This will stop the domain named `ttylinux' and save its current state into a file called \path{ttylinux.xen}. To resume execution of this domain, use the \path{xm restore} command: \begin{verbatim} # xm restore ttylinux.xen \end{verbatim} This will restore the state of the domain and restart it. The domain will carry on as before and the console may be reconnected using the \path{xm console} command, as above. \section{Live Migration} Live migration is used to transfer a domain between physical hosts whilst that domain continues to perform its usual activities --- from the user's perspective, the migration should be imperceptible. To perform a live migration, both hosts must be running Xen / \xend and the destination host must have sufficient resources (e.g. memory capacity) to accommodate the domain after the move. Furthermore we currently require both source and destination machines to be on the same L2 subnet. Currently, there is no support for providing automatic remote access to filesystems stored on local disk when a domain is migrated. Administrators should choose an appropriate storage solution (i.e. SAN, NAS, etc.) to ensure that domain filesystems are also available on their destination node. GNBD is a good method for exporting a volume from one machine to another. iSCSI can do a similar job, but is more complex to set up. When a domain migrates, it's MAC and IP address move with it, thus it is only possible to migrate VMs within the same layer-2 network and IP subnet. If the destination node is on a different subnet, the administrator would need to manually configure a suitable etherip or IP tunnel in the domain 0 of the remote node. A domain may be migrated using the \path{xm migrate} command. To live migrate a domain to another machine, we would use the command: \begin{verbatim} # xm migrate --live mydomain destination.ournetwork.com \end{verbatim} Without the \path{--live} flag, \xend simply stops the domain and copies the memory image over to the new node and restarts it. Since domains can have large allocations this can be quite time consuming, even on a Gigabit network. With the \path{--live} flag \xend attempts to keep the domain running while the migration is in progress, resulting in typical `downtimes' of just 60--300ms. For now it will be necessary to reconnect to the domain's console on the new machine using the \path{xm console} command. If a migrated domain has any open network connections then they will be preserved, so SSH connections do not have this limitation. \section{Managing Domain Memory} XenLinux domains have the ability to relinquish / reclaim machine memory at the request of the administrator or the user of the domain. \subsection{Setting memory footprints from dom0} The machine administrator can request that a domain alter its memory footprint using the \path{xm balloon} command. For instance, we can request that our example ttylinux domain reduce its memory footprint to 32 megabytes. \begin{verbatim} # xm balloon ttylinux 32 \end{verbatim} We can now see the result of this in the output of \path{xm list}: \begin{verbatim} # xm list Name Id Mem(MB) CPU State Time(s) Console Domain-0 0 251 0 r---- 172.2 ttylinux 5 31 0 -b--- 4.3 9605 \end{verbatim} The domain has responded to the request by returning memory to Xen. We can restore the domain to its original size using the command line: \begin{verbatim} # xm balloon ttylinux 64 \end{verbatim} \subsection{Setting memory footprints from within a domain} The virtual file \path{/proc/xen/memory\_target} allows the owner of a domain to adjust their own memory footprint. Reading the file (e.g. \path{cat /proc/xen/memory\_target}) prints out the current memory footprint of the domain. Writing the file (e.g. \path{echo new\_target > /proc/xen/memory\_target}) requests that the kernel adjust the domain's memory footprint to a new value. \subsection{Setting memory limits} Xen associates a memory size limit with each domain. By default, this is the amount of memory the domain is originally started with, preventing the domain from ever growing beyond this size. To permit a domain to grow beyond its original allocation or to prevent a domain you've shrunk from reclaiming the memory it relinquished, use the \path{xm maxmem} command. \chapter{Domain Filesystem Storage} It is possible to directly export any Linux block device in dom0 to another domain, or to export filesystems / devices to virtual machines using standard network protocols (e.g. NBD, iSCSI, NFS, etc). This chapter covers some of the possibilities. \section{Exporting Physical Devices as VBDs} \label{s:exporting-physical-devices-as-vbds} One of the simplest configurations is to directly export individual partitions from domain 0 to other domains. To achieve this use the \path{phy:} specifier in your domain configuration file. For example a line like \begin{quote} \verb_disk = ['phy:hda3,sda1,w']_ \end{quote} specifies that the partition \path{/dev/hda3} in domain 0 should be exported read-write to the new domain as \path{/dev/sda1}; one could equally well export it as \path{/dev/hda} or \path{/dev/sdb5} should one wish. In addition to local disks and partitions, it is possible to export any device that Linux considers to be ``a disk'' in the same manner. For example, if you have iSCSI disks or GNBD volumes imported into domain 0 you can export these to other domains using the \path{phy:} disk syntax. E.g.: \begin{quote} \verb_disk = ['phy:vg/lvm1,sda2,w']_ \end{quote} \begin{center} \framebox{\bf Warning: Block device sharing} \end{center} \begin{quote} Block devices should typically only be shared between domains in a read-only fashion otherwise the Linux kernel's file systems will get very confused as the file system structure may change underneath them (having the same ext3 partition mounted rw twice is a sure fire way to cause irreparable damage)! \Xend will attempt to prevent you from doing this by checking that the device is not mounted read-write in domain 0, and hasn't already been exported read-write to another domain. If you want read-write sharing, export the directory to other domains via NFS from domain0 (or use a cluster file system such as GFS or ocfs2). \end{quote} \section{Using File-backed VBDs} It is also possible to use a file in Domain 0 as the primary storage for a virtual machine. As well as being convenient, this also has the advantage that the virtual block device will be {\em sparse} --- space will only really be allocated as parts of the file are used. So if a virtual machine uses only half of its disk space then the file really takes up half of the size allocated. For example, to create a 2GB sparse file-backed virtual block device (actually only consumes 1KB of disk): \begin{quote} \verb_# dd if=/dev/zero of=vm1disk bs=1k seek=2048k count=1_ \end{quote} Make a file system in the disk file: \begin{quote} \verb_# mkfs -t ext3 vm1disk_ \end{quote} (when the tool asks for confirmation, answer `y') Populate the file system e.g. by copying from the current root: \begin{quote} \begin{verbatim} # mount -o loop vm1disk /mnt # cp -ax /{root,dev,var,etc,usr,bin,sbin,lib} /mnt # mkdir /mnt/{proc,sys,home,tmp} \end{verbatim} \end{quote} Tailor the file system by editing \path{/etc/fstab}, \path{/etc/hostname}, etc (don't forget to edit the files in the mounted file system, instead of your domain 0 filesystem, e.g. you would edit \path{/mnt/etc/fstab} instead of \path{/etc/fstab} ). For this example put \path{/dev/sda1} to root in fstab. Now unmount (this is important!): \begin{quote} \verb_# umount /mnt_ \end{quote} In the configuration file set: \begin{quote} \verb_disk = ['file:/full/path/to/vm1disk,sda1,w']_ \end{quote} As the virtual machine writes to its `disk', the sparse file will be filled in and consume more space up to the original 2GB. {\bf Note that file-backed VBDs may not be appropriate for backing I/O-intensive domains.} File-backed VBDs are known to experience substantial slowdowns under heavy I/O workloads, due to the I/O handling by the loopback block device used to support file-backed VBDs in dom0. Better I/O performance can be achieved by using either LVM-backed VBDs (Section~\ref{s:using-lvm-backed-vbds}) or physical devices as VBDs (Section~\ref{s:exporting-physical-devices-as-vbds}). Linux supports a maximum of eight file-backed VBDs across all domains by default. This limit can be statically increased by using the {\em max\_loop} module parameter if CONFIG\_BLK\_DEV\_LOOP is compiled as a module in the dom0 kernel, or by using the {\em max\_loop=n} boot option if CONFIG\_BLK\_DEV\_LOOP is compiled directly into the dom0 kernel. \section{Using LVM-backed VBDs} \label{s:using-lvm-backed-vbds} A particularly appealing solution is to use LVM volumes as backing for domain file-systems since this allows dynamic growing/shrinking of volumes as well as snapshot and other features. To initialise a partition to support LVM volumes: \begin{quote} \begin{verbatim} # pvcreate /dev/sda10 \end{verbatim} \end{quote} Create a volume group named `vg' on the physical partition: \begin{quote} \begin{verbatim} # vgcreate vg /dev/sda10 \end{verbatim} \end{quote} Create a logical volume of size 4GB named `myvmdisk1': \begin{quote} \begin{verbatim} # lvcreate -L4096M -n myvmdisk1 vg \end{verbatim} \end{quote} You should now see that you have a \path{/dev/vg/myvmdisk1} Make a filesystem, mount it and populate it, e.g.: \begin{quote} \begin{verbatim} # mkfs -t ext3 /dev/vg/myvmdisk1 # mount /dev/vg/myvmdisk1 /mnt # cp -ax / /mnt # umount /mnt \end{verbatim} \end{quote} Now configure your VM with the following disk configuration: \begin{quote} \begin{verbatim} disk = [ 'phy:vg/myvmdisk1,sda1,w' ] \end{verbatim} \end{quote} LVM enables you to grow the size of logical volumes, but you'll need to resize the corresponding file system to make use of the new space. Some file systems (e.g. ext3) now support on-line resize. See the LVM manuals for more details. You can also use LVM for creating copy-on-write clones of LVM volumes (known as writable persistent snapshots in LVM terminology). This facility is new in Linux 2.6.8, so isn't as stable as one might hope. In particular, using lots of CoW LVM disks consumes a lot of dom0 memory, and error conditions such as running out of disk space are not handled well. Hopefully this will improve in future. To create two copy-on-write clone of the above file system you would use the following commands: \begin{quote} \begin{verbatim} # lvcreate -s -L1024M -n myclonedisk1 /dev/vg/myvmdisk1 # lvcreate -s -L1024M -n myclonedisk2 /dev/vg/myvmdisk1 \end{verbatim} \end{quote} Each of these can grow to have 1GB of differences from the master volume. You can grow the amount of space for storing the differences using the lvextend command, e.g.: \begin{quote} \begin{verbatim} # lvextend +100M /dev/vg/myclonedisk1 \end{verbatim} \end{quote} Don't let the `differences volume' ever fill up otherwise LVM gets rather confused. It may be possible to automate the growing process by using \path{dmsetup wait} to spot the volume getting full and then issue an \path{lvextend}. In principle, it is possible to continue writing to the volume that has been cloned (the changes will not be visible to the clones), but we wouldn't recommend this: have the cloned volume as a `pristine' file system install that isn't mounted directly by any of the virtual machines. \section{Using NFS Root} First, populate a root filesystem in a directory on the server machine. This can be on a distinct physical machine, or simply run within a virtual machine on the same node. Now configure the NFS server to export this filesystem over the network by adding a line to \path{/etc/exports}, for instance: \begin{quote} \begin{small} \begin{verbatim} /export/vm1root 1.2.3.4/24 (rw,sync,no_root_squash) \end{verbatim} \end{small} \end{quote} Finally, configure the domain to use NFS root. In addition to the normal variables, you should make sure to set the following values in the domain's configuration file: \begin{quote} \begin{small} \begin{verbatim} root = '/dev/nfs' nfs_server = '2.3.4.5' # substitute IP address of server nfs_root = '/path/to/root' # path to root FS on the server \end{verbatim} \end{small} \end{quote} The domain will need network access at boot time, so either statically configure an IP address (Using the config variables \path{ip}, \path{netmask}, \path{gateway}, \path{hostname}) or enable DHCP ( \path{dhcp='dhcp'}). Note that the Linux NFS root implementation is known to have stability problems under high load (this is not a Xen-specific problem), so this configuration may not be appropriate for critical servers. \part{User Reference Documentation} \chapter{Control Software} The Xen control software includes the \xend node control daemon (which must be running), the xm command line tools, and the prototype xensv web interface. \section{\Xend (node control daemon)} \label{s:xend} The Xen Daemon (\Xend) performs system management functions related to virtual machines. It forms a central point of control for a machine and can be controlled using an HTTP-based protocol. \Xend must be running in order to start and manage virtual machines. \Xend must be run as root because it needs access to privileged system management functions. A small set of commands may be issued on the \xend command line: \begin{tabular}{ll} \verb!# xend start! & start \xend, if not already running \\ \verb!# xend stop! & stop \xend if already running \\ \verb!# xend restart! & restart \xend if running, otherwise start it \\ % \verb!# xend trace_start! & start \xend, with very detailed debug logging \\ \verb!# xend status! & indicates \xend status by its return code \end{tabular} A SysV init script called {\tt xend} is provided to start \xend at boot time. {\tt make install} installs this script in {\path{/etc/init.d}. To enable it, you have to make symbolic links in the appropriate runlevel directories or use the {\tt chkconfig} tool, where available. Once \xend is running, more sophisticated administration can be done using the xm tool (see Section~\ref{s:xm}) and the experimental Xensv web interface (see Section~\ref{s:xensv}). As \xend runs, events will be logged to \path{/var/log/xend.log} and, if the migration assistant daemon (\path{xfrd}) has been started, \path{/var/log/xfrd.log}. These may be of use for troubleshooting problems. \section{Xm (command line interface)} \label{s:xm} The xm tool is the primary tool for managing Xen from the console. The general format of an xm command line is: \begin{verbatim} # xm command [switches] [arguments] [variables] \end{verbatim} The available {\em switches} and {\em arguments} are dependent on the {\em command} chosen. The {\em variables} may be set using declarations of the form {\tt variable=value} and command line declarations override any of the values in the configuration file being used, including the standard variables described above and any custom variables (for instance, the \path{xmdefconfig} file uses a {\tt vmid} variable). The available commands are as follows: \begin{description} \item[balloon] Request a domain to adjust its memory footprint. \item[create] Create a new domain. \item[destroy] Kill a domain immediately. \item[list] List running domains. \item[shutdown] Ask a domain to shutdown. \item[dmesg] Fetch the Xen (not Linux!) boot output. \item[consoles] Lists the available consoles. \item[console] Connect to the console for a domain. \item[help] Get help on xm commands. \item[save] Suspend a domain to disk. \item[restore] Restore a domain from disk. \item[pause] Pause a domain's execution. \item[unpause] Unpause a domain. \item[pincpu] Pin a domain to a CPU. \item[bvt] Set BVT scheduler parameters for a domain. \item[bvt\_ctxallow] Set the BVT context switching allowance for the system. \item[atropos] Set the atropos parameters for a domain. \item[rrobin] Set the round robin time slice for the system. \item[info] Get information about the Xen host. \item[call] Call a \xend HTTP API function directly. \end{description} For a detailed overview of switches, arguments and variables to each command try \begin{quote} \begin{verbatim} # xm help command \end{verbatim} \end{quote} \section{Xensv (web control interface)} \label{s:xensv} Xensv is the experimental web control interface for managing a Xen machine. It can be used to perform some (but not yet all) of the management tasks that can be done using the xm tool. It can be started using: \begin{quote} \verb_# xensv start_ \end{quote} and stopped using: \begin{quote} \verb_# xensv stop_ \end{quote} By default, Xensv will serve out the web interface on port 8080. This can be changed by editing \path{/usr/lib/python2.3/site-packages/xen/sv/params.py}. Once Xensv is running, the web interface can be used to create and manage running domains. \chapter{Domain Configuration} \label{cha:config} The following contains the syntax of the domain configuration files and description of how to further specify networking, driver domain and general scheduling behaviour. \section{Configuration Files} \label{s:cfiles} Xen configuration files contain the following standard variables. Unless otherwise stated, configuration items should be enclosed in quotes: see \path{/etc/xen/xmexample1} and \path{/etc/xen/xmexample2} for concrete examples of the syntax. \begin{description} \item[kernel] Path to the kernel image \item[ramdisk] Path to a ramdisk image (optional). % \item[builder] The name of the domain build function (e.g. {\tt'linux'} or {\tt'netbsd'}. \item[memory] Memory size in megabytes. \item[cpu] CPU to run this domain on, or {\tt -1} for auto-allocation. \item[console] Port to export the domain console on (default 9600 + domain ID). \item[nics] Number of virtual network interfaces. \item[vif] List of MAC addresses (random addresses are assigned if not given) and bridges to use for the domain's network interfaces, e.g. \begin{verbatim} vif = [ 'mac=aa:00:00:00:00:11, bridge=xen-br0', 'bridge=xen-br1' ] \end{verbatim} to assign a MAC address and bridge to the first interface and assign a different bridge to the second interface, leaving \xend to choose the MAC address. \item[disk] List of block devices to export to the domain, e.g. \\ \verb_disk = [ 'phy:hda1,sda1,r' ]_ \\ exports physical device \path{/dev/hda1} to the domain as \path{/dev/sda1} with read-only access. Exporting a disk read-write which is currently mounted is dangerous -- if you are \emph{certain} you wish to do this, you can specify \path{w!} as the mode. \item[dhcp] Set to {\tt 'dhcp'} if you want to use DHCP to configure networking. \item[netmask] Manually configured IP netmask. \item[gateway] Manually configured IP gateway. \item[hostname] Set the hostname for the virtual machine. \item[root] Specify the root device parameter on the kernel command line. \item[nfs\_server] IP address for the NFS server (if any). \item[nfs\_root] Path of the root filesystem on the NFS server (if any). \item[extra] Extra string to append to the kernel command line (if any) \item[restart] Three possible options: \begin{description} \item[always] Always restart the domain, no matter what its exit code is. \item[never] Never restart the domain. \item[onreboot] Restart the domain iff it requests reboot. \end{description} \end{description} For additional flexibility, it is also possible to include Python scripting commands in configuration files. An example of this is the \path{xmexample2} file, which uses Python code to handle the \path{vmid} variable. %\part{Advanced Topics} \section{Network Configuration} For many users, the default installation should work `out of the box'. More complicated network setups, for instance with multiple ethernet interfaces and/or existing bridging setups will require some special configuration. The purpose of this section is to describe the mechanisms provided by \xend to allow a flexible configuration for Xen's virtual networking. \subsection{Xen virtual network topology} Each domain network interface is connected to a virtual network interface in dom0 by a point to point link (effectively a `virtual crossover cable'). These devices are named {\tt vif$<$domid$>$.$<$vifid$>$} (e.g. {\tt vif1.0} for the first interface in domain 1, {\tt vif3.1} for the second interface in domain 3). Traffic on these virtual interfaces is handled in domain 0 using standard Linux mechanisms for bridging, routing, rate limiting, etc. Xend calls on two shell scripts to perform initial configuration of the network and configuration of new virtual interfaces. By default, these scripts configure a single bridge for all the virtual interfaces. Arbitrary routing / bridging configurations can be configured by customising the scripts, as described in the following section. \subsection{Xen networking scripts} Xen's virtual networking is configured by two shell scripts (by default \path{network} and \path{vif-bridge}). These are called automatically by \xend when certain events occur, with arguments to the scripts providing further contextual information. These scripts are found by default in \path{/etc/xen/scripts}. The names and locations of the scripts can be configured in \path{/etc/xen/xend-config.sxp}. \begin{description} \item[network:] This script is called whenever \xend is started or stopped to respectively initialise or tear down the Xen virtual network. In the default configuration initialisation creates the bridge `xen-br0' and moves eth0 onto that bridge, modifying the routing accordingly. When \xend exits, it deletes the Xen bridge and removes eth0, restoring the normal IP and routing configuration. %% In configurations where the bridge already exists, this script could %% be replaced with a link to \path{/bin/true} (for instance). \item[vif-bridge:] This script is called for every domain virtual interface and can configure firewalling rules and add the vif to the appropriate bridge. By default, this adds and removes VIFs on the default Xen bridge. \end{description} For more complex network setups (e.g. where routing is required or integrate with existing bridges) these scripts may be replaced with customised variants for your site's preferred configuration. %% There are two possible types of privileges: IO privileges and %% administration privileges. \section{Driver Domain Configuration} I/O privileges can be assigned to allow a domain to directly access PCI devices itself. This is used to support driver domains. Setting backend privileges is currently only supported in SXP format config files. To allow a domain to function as a backend for others, somewhere within the {\tt vm} element of its configuration file must be a {\tt backend} element of the form {\tt (backend ({\em type}))} where {\tt \em type} may be either {\tt netif} or {\tt blkif}, according to the type of virtual device this domain will service. %% After this domain has been built, \xend will connect all new and %% existing {\em virtual} devices (of the appropriate type) to that %% backend. Note that a block backend cannot currently import virtual block devices from other domains, and a network backend cannot import virtual network devices from other domains. Thus (particularly in the case of block backends, which cannot import a virtual block device as their root filesystem), you may need to boot a backend domain from a ramdisk or a network device. Access to PCI devices may be configured on a per-device basis. Xen will assign the minimal set of hardware privileges to a domain that are required to control its devices. This can be configured in either format of configuration file: \begin{itemize} \item SXP Format: Include device elements of the form: \\ \centerline{ {\tt (device (pci (bus {\em x}) (dev {\em y}) (func {\em z})))}} \\ inside the top-level {\tt vm} element. Each one specifies the address of a device this domain is allowed to access --- the numbers {\em x},{\em y} and {\em z} may be in either decimal or hexadecimal format. \item Flat Format: Include a list of PCI device addresses of the format: \\ \centerline{{\tt pci = ['x,y,z', ...]}} \\ where each element in the list is a string specifying the components of the PCI device address, separated by commas. The components ({\tt \em x}, {\tt \em y} and {\tt \em z}) of the list may be formatted as either decimal or hexadecimal. \end{itemize} %% \section{Administration Domains} %% Administration privileges allow a domain to use the `dom0 %% operations' (so called because they are usually available only to %% domain 0). A privileged domain can build other domains, set scheduling %% parameters, etc. % Support for other administrative domains is not yet available... perhaps % we should plumb it in some time \section{Scheduler Configuration} \label{s:sched} Xen offers a boot time choice between multiple schedulers. To select a scheduler, pass the boot parameter {\em sched=sched\_name} to Xen, substituting the appropriate scheduler name. Details of the schedulers and their parameters are included below; future versions of the tools will provide a higher-level interface to these tools. It is expected that system administrators configure their system to use the scheduler most appropriate to their needs. Currently, the BVT scheduler is the recommended choice. \subsection{Borrowed Virtual Time} {\tt sched=bvt} (the default) \\ BVT provides proportional fair shares of the CPU time. It has been observed to penalise domains that block frequently (e.g. I/O intensive domains), but this can be compensated for by using warping. \subsubsection{Global Parameters} \begin{description} \item[ctx\_allow] the context switch allowance is similar to the `quantum' in traditional schedulers. It is the minimum time that a scheduled domain will be allowed to run before being pre-empted. \end{description} \subsubsection{Per-domain parameters} \begin{description} \item[mcuadv] the MCU (Minimum Charging Unit) advance determines the proportional share of the CPU that a domain receives. It is set inversely proportionally to a domain's sharing weight. \item[warp] the amount of `virtual time' the domain is allowed to warp backwards \item[warpl] the warp limit is the maximum time a domain can run warped for \item[warpu] the unwarp requirement is the minimum time a domain must run unwarped for before it can warp again \end{description} \subsection{Atropos} {\tt sched=atropos} \\ Atropos is a soft real time scheduler. It provides guarantees about absolute shares of the CPU, with a facility for sharing slack CPU time on a best-effort basis. It can provide timeliness guarantees for latency-sensitive domains. Every domain has an associated period and slice. The domain should receive `slice' nanoseconds every `period' nanoseconds. This allows the administrator to configure both the absolute share of the CPU a domain receives and the frequency with which it is scheduled. %% When %% domains unblock, their period is reduced to the value of the latency %% hint (the slice is scaled accordingly so that they still get the same %% proportion of the CPU). For each subsequent period, the slice and %% period times are doubled until they reach their original values. Note: don't overcommit the CPU when using Atropos (i.e. don't reserve more CPU than is available --- the utilisation should be kept to slightly less than 100\% in order to ensure predictable behaviour). \subsubsection{Per-domain parameters} \begin{description} \item[period] The regular time interval during which a domain is guaranteed to receive its allocation of CPU time. \item[slice] The length of time per period that a domain is guaranteed to run for (in the absence of voluntary yielding of the CPU). \item[latency] The latency hint is used to control how soon after waking up a domain it should be scheduled. \item[xtratime] This is a boolean flag that specifies whether a domain should be allowed a share of the system slack time. \end{description} \subsection{Round Robin} {\tt sched=rrobin} \\ The round robin scheduler is included as a simple demonstration of Xen's internal scheduler API. It is not intended for production use. \subsubsection{Global Parameters} \begin{description} \item[rr\_slice] The maximum time each domain runs before the next scheduling decision is made. \end{description} \chapter{Build, Boot and Debug options} This chapter describes the build- and boot-time options which may be used to tailor your Xen system. \section{Xen Build Options} Xen provides a number of build-time options which should be set as environment variables or passed on make's command-line. \begin{description} \item[verbose=y] Enable debugging messages when Xen detects an unexpected condition. Also enables console output from all domains. \item[debug=y] Enable debug assertions. Implies {\bf verbose=y}. (Primarily useful for tracing bugs in Xen). \item[debugger=y] Enable the in-Xen debugger. This can be used to debug Xen, guest OSes, and applications. \item[perfc=y] Enable performance counters for significant events within Xen. The counts can be reset or displayed on Xen's console via console control keys. \item[trace=y] Enable per-cpu trace buffers which log a range of events within Xen for collection by control software. \end{description} \section{Xen Boot Options} \label{s:xboot} These options are used to configure Xen's behaviour at runtime. They should be appended to Xen's command line, either manually or by editing \path{grub.conf}. \begin{description} \item [ignorebiostables ] Disable parsing of BIOS-supplied tables. This may help with some chipsets that aren't fully supported by Xen. If you specify this option then ACPI tables are also ignored, and SMP support is disabled. \item [noreboot ] Don't reboot the machine automatically on errors. This is useful to catch debug output if you aren't catching console messages via the serial line. \item [nosmp ] Disable SMP support. This option is implied by `ignorebiostables'. \item [noacpi ] Disable ACPI tables, which confuse Xen on some chipsets. This option is implied by `ignorebiostables'. \item [watchdog ] Enable NMI watchdog which can report certain failures. \item [noht ] Disable Hyperthreading. \item [badpage=$<$page number$>$,$<$page number$>$, \ldots ] Specify a list of pages not to be allocated for use because they contain bad bytes. For example, if your memory tester says that byte 0x12345678 is bad, you would place `badpage=0x12345' on Xen's command line. \item [com1=$<$baud$>$,DPS,$<$io\_base$>$,$<$irq$>$ com2=$<$baud$>$,DPS,$<$io\_base$>$,$<$irq$>$ ] \mbox{}\\ Xen supports up to two 16550-compatible serial ports. For example: `com1=9600, 8n1, 0x408, 5' maps COM1 to a 9600-baud port, 8 data bits, no parity, 1 stop bit, I/O port base 0x408, IRQ 5. If the I/O base and IRQ are standard (com1:0x3f8,4; com2:0x2f8,3) then they need not be specified. \item [console=$<$specifier list$>$ ] Specify the destination for Xen console I/O. This is a comma-separated list of, for example: \begin{description} \item[vga] use VGA console and allow keyboard input \item[com1] use serial port com1 \item[com2H] use serial port com2. Transmitted chars will have the MSB set. Received chars must have MSB set. \item[com2L] use serial port com2. Transmitted chars will have the MSB cleared. Received chars must have MSB cleared. \end{description} The latter two examples allow a single port to be shared by two subsystems (e.g. console and debugger). Sharing is controlled by MSB of each transmitted/received character. [NB. Default for this option is `com1,vga'] \item [conswitch=$<$switch-char$><$auto-switch-char$>$ ] Specify how to switch serial-console input between Xen and DOM0. The required sequence is CTRL-$<$switch-char$>$ pressed three times. Specifying the backtick character disables switching. The $<$auto-switch-char$>$ specifies whether Xen should auto-switch input to DOM0 when it boots --- if it is `x' then auto-switching is disabled. Any other value, or omitting the character, enables auto-switching. [NB. default switch-char is `a'] \item [nmi=xxx ] Specify what to do with an NMI parity or I/O error. \\ `nmi=fatal': Xen prints a diagnostic and then hangs. \\ `nmi=dom0': Inform DOM0 of the NMI. \\ `nmi=ignore': Ignore the NMI. \item [dom0\_mem=xxx ] Set the amount of memory (in kB) to be allocated to domain0. \item [tbuf\_size=xxx ] Set the size of the per-cpu trace buffers, in pages (default 1). Note that the trace buffers are only enabled in debug builds. Most users can ignore this feature completely. \item [sched=xxx ] Select the CPU scheduler Xen should use. The current possibilities are `bvt' (default), `atropos' and `rrobin'. For more information see Section~\ref{s:sched}. \item [physdev\_dom0\_hide=(xx:xx.x)(yy:yy.y)\ldots ] Hide selected PCI devices from domain 0 (for instance, to stop it taking ownership of them so that they can be driven by another domain). Device IDs should be given in hex format. Bridge devices do not need to be hidden --- they are hidden implicitly, since guest OSes do not need to configure them. \end{description} \section{XenLinux Boot Options} In addition to the standard Linux kernel boot options, we support: \begin{description} \item[xencons=xxx ] Specify the device node to which the Xen virtual console driver is attached. The following options are supported: \begin{center} \begin{tabular}{l} `xencons=off': disable virtual console \\ `xencons=tty': attach console to /dev/tty1 (tty0 at boot-time) \\ `xencons=ttyS': attach console to /dev/ttyS0 \end{tabular} \end{center} The default is ttyS for dom0 and tty for all other domains. \end{description} \section{Debugging} \label{s:keys} Xen has a set of debugging features that can be useful to try and figure out what's going on. Hit 'h' on the serial line (if you specified a baud rate on the Xen command line) or ScrollLock-h on the keyboard to get a list of supported commands. If you have a crash you'll likely get a crash dump containing an EIP (PC) which, along with an \path{objdump -d image}, can be useful in figuring out what's happened. Debug a Xenlinux image just as you would any other Linux kernel. %% We supply a handy debug terminal program which you can find in %% \path{/usr/local/src/xen-2.0.bk/tools/misc/miniterm/} %% This should be built and executed on another machine that is connected %% via a null modem cable. Documentation is included. %% Alternatively, if the Xen machine is connected to a serial-port server %% then we supply a dumb TCP terminal client, {\tt xencons}. \chapter{Further Support} If you have questions that are not answered by this manual, the sources of information listed below may be of interest to you. Note that bug reports, suggestions and contributions related to the software (or the documentation) should be sent to the Xen developers' mailing list (address below). \section{Other Documentation} For developers interested in porting operating systems to Xen, the {\em Xen Interface Manual} is distributed in the \path{docs/} directory of the Xen source distribution. %Various HOWTOs are available in \path{docs/HOWTOS} but this content is %being integrated into this manual. \section{Online References} The official Xen web site is found at: \begin{quote} {\tt http://www.cl.cam.ac.uk/netos/xen/} \end{quote} This contains links to the latest versions of all on-line documentation (including the lateset version of the FAQ). \section{Mailing Lists} There are currently four official Xen mailing lists: \begin{description} \item[xen-devel@lists.xensource.com] Used for development discussions and bug reports. Subscribe at: \\ {\small {\tt http://lists.xensource.com/xen-devel}} \item[xen-users@lists.xensource.com] Used for installation and usage discussions and requests for help. Subscribe at: \\ {\small {\tt http://lists.xensource.com/xen-users}} \item[xen-announce@lists.xensource.com] Used for announcements only. Subscribe at: \\ {\small {\tt http://lists.xensource.com/xen-announce}} \item[xen-changelog@lists.xensource.com] Changelog feed from the unstable and 2.0 trees - developer oriented. Subscribe at: \\ {\small {\tt http://lists.xensource.com/xen-changelog}} \end{description} \appendix \chapter{Installing Xen / XenLinux on Debian} The Debian project provides a tool called \path{debootstrap} which allows a base Debian system to be installed into a filesystem without requiring the host system to have any Debian-specific software (such as \path{apt}. Here's some info how to install Debian 3.1 (Sarge) for an unprivileged Xen domain: \begin{enumerate} \item Set up Xen 2.0 and test that it's working, as described earlier in this manual. \item Create disk images for root-fs and swap (alternatively, you might create dedicated partitions, LVM logical volumes, etc. if that suits your setup). \begin{small}\begin{verbatim} dd if=/dev/zero of=/path/diskimage bs=1024k count=size_in_mbytes dd if=/dev/zero of=/path/swapimage bs=1024k count=size_in_mbytes \end{verbatim}\end{small} If you're going to use this filesystem / disk image only as a `template' for other vm disk images, something like 300 MB should be enough.. (of course it depends what kind of packages you are planning to install to the template) \item Create the filesystem and initialise the swap image \begin{small}\begin{verbatim} mkfs.ext3 /path/diskimage mkswap /path/swapimage \end{verbatim}\end{small} \item Mount the disk image for installation \begin{small}\begin{verbatim} mount -o loop /path/diskimage /mnt/disk \end{verbatim}\end{small} \item Install \path{debootstrap} Make sure you have debootstrap installed on the host. If you are running Debian sarge (3.1 / testing) or unstable you can install it by running \path{apt-get install debootstrap}. Otherwise, it can be downloaded from the Debian project website. \item Install Debian base to the disk image: \begin{small}\begin{verbatim} debootstrap --arch i386 sarge /mnt/disk \ http://ftp..debian.org/debian \end{verbatim}\end{small} You can use any other Debian http/ftp mirror you want. \item When debootstrap completes successfully, modify settings: \begin{small}\begin{verbatim} chroot /mnt/disk /bin/bash \end{verbatim}\end{small} Edit the following files using vi or nano and make needed changes: \begin{small}\begin{verbatim} /etc/hostname /etc/hosts /etc/resolv.conf /etc/network/interfaces /etc/networks \end{verbatim}\end{small} Set up access to the services, edit: \begin{small}\begin{verbatim} /etc/hosts.deny /etc/hosts.allow /etc/inetd.conf \end{verbatim}\end{small} Add Debian mirror to: \begin{small}\begin{verbatim} /etc/apt/sources.list \end{verbatim}\end{small} Create fstab like this: \begin{small}\begin{verbatim} /dev/sda1 / ext3 errors=remount-ro 0 1 /dev/sda2 none swap sw 0 0 proc /proc proc defaults 0 0 \end{verbatim}\end{small} Logout \item Unmount the disk image \begin{small}\begin{verbatim} umount /mnt/disk \end{verbatim}\end{small} \item Create Xen 2.0 configuration file for the new domain. You can use the example-configurations coming with Xen as a template. Make sure you have the following set up: \begin{small}\begin{verbatim} disk = [ 'file:/path/diskimage,sda1,w', 'file:/path/swapimage,sda2,w' ] root = "/dev/sda1 ro" \end{verbatim}\end{small} \item Start the new domain \begin{small}\begin{verbatim} xm create -f domain_config_file \end{verbatim}\end{small} Check that the new domain is running: \begin{small}\begin{verbatim} xm list \end{verbatim}\end{small} \item Attach to the console of the new domain. You should see something like this when starting the new domain: \begin{small}\begin{verbatim} Started domain testdomain2, console on port 9626 \end{verbatim}\end{small} There you can see the ID of the console: 26. You can also list the consoles with \path{xm consoles} (ID is the last two digits of the port number.) Attach to the console: \begin{small}\begin{verbatim} xm console 26 \end{verbatim}\end{small} or by telnetting to the port 9626 of localhost (the xm console program works better). \item Log in and run base-config As a default there's no password for the root. Check that everything looks OK, and the system started without errors. Check that the swap is active, and the network settings are correct. Run \path{/usr/sbin/base-config} to set up the Debian settings. Set up the password for root using passwd. \item Done. You can exit the console by pressing \path{Ctrl + ]} \end{enumerate} If you need to create new domains, you can just copy the contents of the `template'-image to the new disk images, either by mounting the template and the new image, and using \path{cp -a} or \path{tar} or by simply copying the image file. Once this is done, modify the image-specific settings (hostname, network settings, etc). \chapter{Installing Xen / XenLinux on Redhat or Fedora Core} When using Xen / XenLinux on a standard Linux distribution there are a couple of things to watch out for: Note that, because domains>0 don't have any privileged access at all, certain commands in the default boot sequence will fail e.g. attempts to update the hwclock, change the console font, update the keytable map, start apmd (power management), or gpm (mouse cursor). Either ignore the errors (they should be harmless), or remove them from the startup scripts. Deleting the following links are a good start: {\path{S24pcmcia}}, {\path{S09isdn}}, {\path{S17keytable}}, {\path{S26apmd}}, {\path{S85gpm}}. If you want to use a single root file system that works cleanly for both domain 0 and unprivileged domains, a useful trick is to use different 'init' run levels. For example, use run level 3 for domain 0, and run level 4 for other domains. This enables different startup scripts to be run in depending on the run level number passed on the kernel command line. If using NFS root files systems mounted either from an external server or from domain0 there are a couple of other gotchas. The default {\path{/etc/sysconfig/iptables}} rules block NFS, so part way through the boot sequence things will suddenly go dead. If you're planning on having a separate NFS {\path{/usr}} partition, the RH9 boot scripts don't make life easy - they attempt to mount NFS file systems way to late in the boot process. The easiest way I found to do this was to have a {\path{/linuxrc}} script run ahead of {\path{/sbin/init}} that mounts {\path{/usr}}: \begin{quote} \begin{small}\begin{verbatim} #!/bin/bash /sbin/ipconfig lo 127.0.0.1 /sbin/portmap /bin/mount /usr exec /sbin/init "$@" <>/dev/console 2>&1 \end{verbatim}\end{small} \end{quote} %$ XXX SMH: font lock fix :-) The one slight complication with the above is that {\path{/sbin/portmap}} is dynamically linked against {\path{/usr/lib/libwrap.so.0}} Since this is in {\path{/usr}}, it won't work. This can be solved by copying the file (and link) below the /usr mount point, and just let the file be 'covered' when the mount happens. In some installations, where a shared read-only {\path{/usr}} is being used, it may be desirable to move other large directories over into the read-only {\path{/usr}}. For example, you might replace {\path{/bin}}, {\path{/lib}} and {\path{/sbin}} with links into {\path{/usr/root/bin}}, {\path{/usr/root/lib}} and {\path{/usr/root/sbin}} respectively. This creates other problems for running the {\path{/linuxrc}} script, requiring bash, portmap, mount, ifconfig, and a handful of other shared libraries to be copied below the mount point --- a simple statically-linked C program would solve this problem. \chapter{Glossary of Terms} \begin{description} \item[Atropos] One of the CPU schedulers provided by Xen. Atropos provides domains with absolute shares of the CPU, with timeliness guarantees and a mechanism for sharing out `slack time'. \item[BVT] The BVT scheduler is used to give proportional fair shares of the CPU to domains. \item[Exokernel] A minimal piece of privileged code, similar to a {\bf microkernel} but providing a more `hardware-like' interface to the tasks it manages. This is similar to a paravirtualising VMM like {\bf Xen} but was designed as a new operating system structure, rather than specifically to run multiple conventional OSs. \item[Domain] A domain is the execution context that contains a running {\bf virtual machine}. The relationship between virtual machines and domains on Xen is similar to that between programs and processes in an operating system: a virtual machine is a persistent entity that resides on disk (somewhat like a program). When it is loaded for execution, it runs in a domain. Each domain has a {\bf domain ID}. \item[Domain 0] The first domain to be started on a Xen machine. Domain 0 is responsible for managing the system. \item[Domain ID] A unique identifier for a {\bf domain}, analogous to a process ID in an operating system. \item[Full virtualisation] An approach to virtualisation which requires no modifications to the hosted operating system, providing the illusion of a complete system of real hardware devices. \item[Hypervisor] An alternative term for {\bf VMM}, used because it means `beyond supervisor', since it is responsible for managing multiple `supervisor' kernels. \item[Live migration] A technique for moving a running virtual machine to another physical host, without stopping it or the services running on it. \item[Microkernel] A small base of code running at the highest hardware privilege level. A microkernel is responsible for sharing CPU and memory (and sometimes other devices) between less privileged tasks running on the system. This is similar to a VMM, particularly a {\bf paravirtualising} VMM but typically addressing a different problem space and providing different kind of interface. \item[NetBSD/Xen] A port of NetBSD to the Xen architecture. \item[Paravirtualisation] An approach to virtualisation which requires modifications to the operating system in order to run in a virtual machine. Xen uses paravirtualisation but preserves binary compatibility for user space applications. \item[Shadow pagetables] A technique for hiding the layout of machine memory from a virtual machine's operating system. Used in some {\bf VMMs} to provide the illusion of contiguous physical memory, in Xen this is used during {\bf live migration}. \item[Virtual Machine] The environment in which a hosted operating system runs, providing the abstraction of a dedicated machine. A virtual machine may be identical to the underlying hardware (as in {\bf full virtualisation}, or it may differ, as in {\bf paravirtualisation}. \item[VMM] Virtual Machine Monitor - the software that allows multiple virtual machines to be multiplexed on a single physical machine. \item[Xen] Xen is a paravirtualising virtual machine monitor, developed primarily by the Systems Research Group at the University of Cambridge Computer Laboratory. \item[XenLinux] Official name for the port of the Linux kernel that runs on Xen. \end{description} \end{document} %% Other stuff without a home %% Instructions Re Python API %% Other Control Tasks using Python %% ================================ %% A Python module 'Xc' is installed as part of the tools-install %% process. This can be imported, and an 'xc object' instantiated, to %% provide access to privileged command operations: %% # import Xc %% # xc = Xc.new() %% # dir(xc) %% # help(xc.domain_create) %% In this way you can see that the class 'xc' contains useful %% documentation for you to consult. %% A further package of useful routines (xenctl) is also installed: %% # import xenctl.utils %% # help(xenctl.utils) %% You can use these modules to write your own custom scripts or you can %% customise the scripts supplied in the Xen distribution. % Explain about AGP GART %% If you're not intending to configure the new domain with an IP address %% on your LAN, then you'll probably want to use NAT. The %% 'xen_nat_enable' installs a few useful iptables rules into domain0 to %% enable NAT. [NB: We plan to support RSIP in future] %% Installing the file systems from the CD %% ======================================= %% If you haven't got an existing Linux installation onto which you can %% just drop down the Xen and Xenlinux images, then the file systems on %% the CD provide a quick way of doing an install. However, you would be %% better off in the long run doing a proper install of your preferred %% distro and installing Xen onto that, rather than just doing the hack %% described below: %% Choose one or two partitions, depending on whether you want a separate %% /usr or not. Make file systems on it/them e.g.: %% mkfs -t ext3 /dev/hda3 %% [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old %% version of mkfs] %% Next, mount the file system(s) e.g.: %% mkdir /mnt/root && mount /dev/hda3 /mnt/root %% [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr] %% To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz: %% cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz %% You'll need to edit /mnt/root/etc/fstab to reflect your file system %% configuration. Changing the password file (etc/shadow) is probably a %% good idea too. %% To install the usr file system, copy the file system from CD on /usr, %% though leaving out the "XenDemoCD" and "boot" directories: %% cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr %% If you intend to boot off these file systems (i.e. use them for %% domain 0), then you probably want to copy the /usr/boot directory on %% the cd over the top of the current symlink to /boot on your root %% filesystem (after deleting the current symlink) i.e.: %% cd /mnt/root ; rm boot ; cp -a /usr/boot .