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407 lines
15 KiB
Plaintext
###########################################
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Xen HOWTO
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University of Cambridge Computer Laboratory
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http://www.cl.cam.ac.uk/netos/xen
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#############################
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Get Xen Source Code
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=============================
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The public master BK repository for the 1.2 release lives at:
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'bk://xen.bkbits.net/xeno-1.2.bk'
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The current unstable release (1.3) is available at:
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'bk://xen.bkbits.net/xeno-unstable.bk'
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To fetch a local copy, first download the BitKeeper tools at:
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http://www.bitmover.com/download with username 'bitkeeper' and
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password 'get bitkeeper'.
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Then install the tools and then run:
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# bk clone bk://xen.bkbits.net/xeno-1.2.bk
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Under your current directory, a new directory named 'xeno-1.2.bk' has
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been created, which contains all the necessary source codes for the
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Xen hypervisor and Linux guest OSes.
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To get newest changes to the repository, run
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# cd xeno-1.2.bk
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# bk pull
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Configuring Xen
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=============================
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Xen's build configuration is managed via a set of environment
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variables. These should be set before invoking make
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(e.g., 'export debug=y; make', 'debug=y make').
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The options that can be configured are as follows (all options default
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to 'n' or off):
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debug=y -- Enable debug assertions and console output.
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(Primarily useful for tracing bugs in Xen).
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debugger=y -- Enable the in-Xen pervasive debugger (PDB).
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This can be used to debug Xen, guest OSes, and
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applications. For more information see the
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XenDebugger-HOWTO.
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perfc=y -- Enable performance-counters for significant events
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within Xen. The counts can be reset or displayed
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on Xen's console via console control keys.
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trace=y -- Enable per-cpu trace buffers which log a range of
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events within Xen for collection by control
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software.
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Build Xen
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=============================
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Hint: To see how to build Xen and all the control tools, inspect the
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tools/misc/xen-clone script in the BK repository. This script can be
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used to clone the repository and perform a full build.
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To build Xen manually:
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# cd xeno-1.2.bk/xen
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# make clean
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# make
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This will (should) produce a file called 'xen' in the current
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directory. This is the ELF 32-bit LSB executable file of Xen. You
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can also find a gzip version, named 'xen.gz'.
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To install the built files on your server under /usr, type 'make
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install' at the root of the BK repository. You will need to be root to
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do this!
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Hint: There is also a 'make dist' rule which copies built files to an
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install directory just outside the BK repo; if this suits your setup,
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go for it.
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Build Linux as a Xen guest OS
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==============================
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This is a little more involved since the repository only contains a
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"sparse" tree -- this is essentially an 'overlay' on a standard linux
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kernel source tree. It contains only those files currently 'in play'
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which are either modified versions of files in the vanilla linux tree,
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or brand new files specific to the Xen port.
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So, first you need a vanilla linux-2.4.26 tree, which is located at:
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http://www.kernel.org/pub/linux/kernel/v2.4
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Then:
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# mv linux-2.4.26.tar.gz /xeno-1.2.bk
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# cd /xeno-1.2.bk
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# tar -zxvf linux-2.4.26.tar.gz
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You'll find a new directory 'linux-2.4.26' which contains all
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the vanilla Linux 2.4.26 kernel source codes.
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Hint: You should choose the vanilla linux kernel tree that has the
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same version as the "sparse" tree.
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Next, you need to 'overlay' this sparse tree on the full vanilla Linux
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kernel tree:
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# cd /xeno-1.2.bk/xenolinux-2.4.26-sparse
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# ./mkbuildtree ../linux-2.4.26
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Finally, rename the buildtree since it is now a 'xenolinux' buildtree.
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# cd /xeno-1.2.bk
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# mv linux-2.4.26 xenolinux-2.4.26
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Now that the buildtree is there, you can build the xenolinux kernel.
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The default configuration should work fine for most people (use 'make
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oldconfig') but you can customise using one of the other config tools
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if you want.
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# cd /xeno-1.2.bk/xenolinux-2.4.26
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# ARCH=xen make oldconfig { or menuconfig, or xconfig, or config }
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# ARCH=xen make dep
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# ARCH=xen make bzImage
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Assuming the build works, you'll end up with
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/xeno-1.2.bk/xenolinux-2.4.26/arch/xen/boot/xenolinux.gz. This is the
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gzip version of XenoLinux kernel image.
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Build the Domain Control Tools
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==============================
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Under '/xeno-1.2.bk/tools', there are three sub-directories:
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'balloon', 'xc' and 'misc', each containing
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a group of tools. You can enter any of the four sub-directories
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and type 'make' to compile the corresponding group of tools.
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Or you can type 'make' under '/xeno-1.2.bk/tools' to compile
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all the tools.
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In order to compile the control-interface library in 'xc' you must
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have zlib and development headers installed. Also you will need at
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least Python v2.2.
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'make install' in the tools directory will place executables and
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libraries in /usr/bin and /usr/lib. You will need to be root to do this!
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As noted earlier, 'make dist' installs files to a local 'install'
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directory just outside the BK repository. These files will then need
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to be installed manually onto the server.
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The Example Scripts
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===================
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The scripts in tools/examples/ are generally useful for
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administering a Xen-based system. You can install them by running
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'make install' in that directory.
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The python scripts (*.py) are the main tools for controlling
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Xen domains.
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'defaults' and 'democd' are example configuration files for starting
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new domains.
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'xendomains' is a Sys-V style init script for starting and stopping
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Xen domains when the system boots / shuts down.
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These will be discussed below in more detail.
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Installation
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==============================
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First:
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# cp /xen-1.2.bk/xen/xen.gz /boot/xen.gz
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# cp /xen-1.2.bk/xenolinux-2.4.26/arch/xen/boot/xenolinux.gz /boot/xenolinux.gz
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Second, you must have 'GNU Grub' installed. Then you need to edit
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the Grub configuration file '/boot/grub/menu.lst'.
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A typical Grub menu option might look like:
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title Xen 1.2 / XenoLinux 2.4.26
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kernel /boot/xen.gz dom0_mem=131072 com1=115200,8n1 noht
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module /boot/xenolinux.gz root=/dev/sda4 ro console=tty0
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The first line specifies which Xen image to use, and what command line
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arguments to pass to Xen. In this case we set the maximum amount of
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memory to allocate to domain0, and enable serial I/O at 115200 baud.
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We could also disable smp support (nosmp) or disable hyper-threading
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support (noht). If you have multiple network interface you can use
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ifname=ethXX to select which one to use. If your network card is
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unsupported, use ifname=dummy
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The second line specifies which XenoLinux image to use, and the
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standard linux command line arguments to pass to the kernel. In this
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case, we're configuring the root partition and stating that it should
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(initially) be mounted read-only (normal practice).
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The following is a list of command line arguments to pass to Xen:
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ignorebiostables Disable parsing of BIOS-supplied tables. This may
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help with some chipsets that aren't fully supported
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by Xen. If you specify this option then ACPI tables are
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also ignored, and SMP support is disabled.
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noreboot Don't reboot the machine automatically on errors.
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This is useful to catch debug output if you aren't
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catching console messages via the serial line.
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nosmp Disable SMP support.
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This option is implied by 'ignorebiostables'.
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noacpi Disable ACPI tables, which confuse Xen on some chipsets.
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This option is implied by 'ignorebiostables'.
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watchdog Enable NMI watchdog which can report certain failures.
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noht Disable Hyperthreading.
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ifname=ethXX Select which Ethernet interface to use.
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ifname=dummy Don't use any network interface.
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com1=<baud>,DPS[,<io_base>,<irq>]
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com2=<baud>,DPS[,<io_base>,<irq>]
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Xen supports up to two 16550-compatible serial ports.
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For example: 'com1=9600,8n1,0x408,5' maps COM1 to a
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9600-baud port, 8 data bits, no parity, 1 stop bit,
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I/O port base 0x408, IRQ 5.
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If the I/O base and IRQ are standard (com1:0x3f8,4;
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com2:0x2f8,3) then they need not be specified.
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console=<specifier list>
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Specify the destination for Xen console I/O.
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This is a comma-separated list of, for example:
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vga: use VGA console and allow keyboard input
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com1: use serial port com1
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com2H: use serial port com2. Transmitted chars will
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have the MSB set. Received chars must have
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MSB set.
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com2L: use serial port com2. Transmitted chars will
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have the MSB cleared. Received chars must
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have MSB cleared.
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The latter two examples allow a single port to be
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shared by two subsystems (eg. console and
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debugger). Sharing is controlled by MSB of each
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transmitted/received character.
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[NB. Default for this option is 'com1,vga']
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conswitch=<switch-char><auto-switch-char>
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Specify how to switch serial-console input between
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Xen and DOM0. The required sequence is CTRL-<switch_char>
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pressed three times. Specifying '`' disables switching.
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The <auto-switch-char> specifies whether Xen should
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auto-switch input to DOM0 when it boots -- if it is 'x'
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then auto-switching is disabled. Any other value, or
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omitting the character, enables auto-switching.
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[NB. Default for this option is 'a']
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dom0_mem=xxx Set the maximum amount of memory for domain0.
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tbuf_size=xxx Set the size of the per-cpu trace buffers, in pages
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(default 1). Note that the trace buffers are only
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enabled in debug builds. Most users can ignore
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this feature completely.
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sched=xxx Select the CPU scheduler Xen should use. The current
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possibilities are 'bvt', 'atropos' and 'rrobin'. The
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default is 'bvt'. For more information see
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Sched-HOWTO.txt.
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Boot into Domain 0
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==============================
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Reboot your computer; After selecting the kernel to boot, stand back
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and watch Xen boot, closely followed by "domain 0" running the
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XenoLinux kernel. Depending on which root partition you have assigned
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to XenoLinux kernel in Grub configuration file, you can use the
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corresponding username / password to log in.
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Once logged in, it should look just like any regular linux box. All
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the usual tools and commands should work as per usual.
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Start New Domains
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==============================
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You must be 'root' to start new domains.
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Make sure you have successfully configured at least one
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physical network interface. Then:
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# xen_nat_enable
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The xc_dom_create.py program is useful for starting Xen domains.
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You can specify configuration files using the -f switch on the command
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line. The default configuration is in /etc/xc/defaults. You can
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create custom versions of this to suit your local configuration.
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You can override the settings in a configuration file using command
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line arguments to xc_dom_create.py. However, you may find it simplest
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to create a separate configuration file for each domain you start.
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xc_dom_create.py will print the local TCP port to which you should
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connect to perform console I/O. A suitable console client is provided
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by the Python module xenctl.console_client: running this module from
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the command line with <host> and <port> parameters will start a
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terminal session. This module is also installed as /usr/bin/xencons,
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from a copy in tools/misc/xencons. An alternative to manually running
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a terminal client is to specify '-c' to xc_dom_create.py, or add
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'auto_console=True' to the defaults file. This will cause
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xc_dom_create.py to automatically become the console terminal after
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starting the domain.
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Boot-time output will be directed to this console by default, because
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the console name is tty0. It is also possible to log in via the
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virtual console --- once again, your normal startup scripts will work
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as normal (e.g., by running mingetty on tty1-7). The device node to
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which the virtual console is attached can be configured by specifying
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'xencons=' on the OS command line:
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'xencons=off' --> disable virtual console
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'xencons=tty' --> attach console to /dev/tty1 (tty0 at boot-time)
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'xencons=ttyS' --> attach console to /dev/ttyS0
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Manage Running Domains
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==============================
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You can see a list of existing domains with:
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# xc_dom_control.py list
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In order to stop a domain, you use:
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# xc_dom_control.py stop <domain_id>
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To shutdown a domain cleanly use:
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# xc_dom_control.py shutdown <domain_id>
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To destroy a domain immediately:
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# xc_dom_control.py destroy <domain_id>
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There are other more advanced options, including pinning domains to
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specific CPUs and saving / resuming domains to / from disk files. To
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get more information, run the tool without any arguments:
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# xc_dom_control.py
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There is more information available in the Xen README files, the
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VBD-HOWTO and the contributed FAQ / HOWTO documents on the web.
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Other Control Tasks using Python
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================================
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A Python module 'Xc' is installed as part of the tools-install
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process. This can be imported, and an 'xc object' instantiated, to
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provide access to privileged command operations:
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# import Xc
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# xc = Xc.new()
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# dir(xc)
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# help(xc.domain_create)
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In this way you can see that the class 'xc' contains useful
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documentation for you to consult.
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A further package of useful routines (xenctl) is also installed:
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# import xenctl.utils
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# help(xenctl.utils)
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You can use these modules to write your own custom scripts or you can
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customise the scripts supplied in the Xen distribution.
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Automatically start / stop domains at boot / shutdown
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=====================================================
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A Sys-V style init script for RedHat systems is provided in
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tools/examples/xendomains. When you run 'make install' in that
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directory, it should be automatically copied to /etc/init.d/. You can
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then enable it using the chkconfig command, e.g.:
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# chkconfig --add xendomains
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By default, this will start the boot-time domains in runlevels 3, 4
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and 5. To specify a domain is to start at boot-time, place its
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configuration file (or a link to it) under /etc/xc/auto/.
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The script will also stop ALL domains when the system is shut down,
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even domains that it did not start originally.
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You can also use the "service" command (part of the RedHat standard
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distribution) to run this script manually, e.g:
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# service xendomains start
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Starts all the domains with config files under /etc/xc/auto/.
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# service xendomains stop
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Shuts down ALL running Xen domains.
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