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date Wed Oct 13 20:55:54 2004 +0000 (2004-10-13)
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10 XenDemoCD 2.0
11 University of Cambridge Computer Laboratory
12 28 Aug 2004
16 Welcome to the Xen Demo CD!
18 Executive Summary
19 =================
21 This CD is a standalone demo of the Xen Virtual Machine Monitor (VMM),
22 Linux-2.4 and Linux-2.6 OS port (Xenlinux). It runs entirely off the
23 CD, without requiring hard disk installation. This is achieved using a
24 RAM disk to store mutable file system data while using the CD for
25 everything else. The CD can also be used for installing Xen/Xenlinux
26 to disk, and includes a source code snapshot along with all of the
27 tools required to build it.
29 Booting the CD
30 ==============
32 It should be possible to get Xen working with any relatively modern
33 hardware supported by standard Linux. However, the version of XenLinux
34 built for the DemoCD is fairly h/w specific. If you need other
35 hardware, you'll have to configure and build your own xenlinux kernel.
36 Xen does require an 'i686'-class CPU or newer, so won't work on 486's
37 or plain Pentiums.
39 We have compiled in drivers for the following hardware:
41 CPU: Pentium Pro/II/III/IV/Xeon, Athlon (i.e. P6 or newer) SMP supported
42 IDE: Intel PIIX chipset, others will be PIO only (slow)
43 SCSI: Adaptec / Dell PERC Raid (aacraid), fusion MPT, megaraid, Adaptec aic7xxx
44 Net: Recommended: Intel e1000, Broadcom BCM57xx (tg3), 3c905 (3c59x)
45 Also supported: pcnet32, Intel e100, tulip
47 Because of the demo CD's use of RAM disks, make sure you have plenty
48 of RAM (256MB+).
50 To try out the Demo, boot from CD (you may need to change your BIOS
51 configuration to do this), then select one of the four boot options
52 from the Grub menu:
54 Xen / linux-2.4.27
55 Xen / linux-2.4.27 using cmdline IP configuration
56 Xen / linux-2.4.27 in "safe mode"
57 linux-2.4.22
59 The last option is a plain linux kernel that runs on the bare machine,
60 and is included simply to help diagnose driver compatibility
61 problems. The "safe mode" boot option might be useful if you're having
62 problems getting Xen to work with your hardware, as it disables various
63 features such as SMP, and enables some debugging.
65 If you are going for a command line IP config, hit "e" at
66 the grub menu, then edit the "ip=" parameters to reflect your setup
67 e.g. "ip=<ipaddr>::<gateway>:<netmask>::eth0:off". It shouldn't be
68 necessary to set either the nfs server or hostname
69 parameters. Alternatively, once Xenlinux has booted you can login and
70 setup networking with 'dhclient' or 'ifconfig' and 'route' in the
71 normal way.
73 To make things easier for yourself, it's worth trying to arrange for an
74 IP address which is the first in a sequential range of free IP
75 addresses. It's useful to give each VM instance its own public IP
76 address (though it is possible to do NAT or use private addresses),
77 and the configuration files on the CD allocate IP addresses
78 sequentially for subsequent domains unless told otherwise.
80 After selecting the kernel to boot, stand back and watch Xen boot,
81 closely followed by "domain 0" running the Xenlinux kernel. The boot
82 messages can also sent to the serial line by specifying the baud rate
83 on the Xen cmdline (e.g., 'com1=9600,8n1'); this can be very useful
84 for debugging should anything important scroll off the screen. Xen's
85 startup messages will look quite familiar as much of the hardware
86 initialisation (SMP boot, apic setup) and device drivers are derived
87 from Linux.
89 If everything is well, you should see the linux rc scripts start a
90 bunch of standard services including sshd. Login on the console or
91 via ssh::
92 username: user root
93 password: xendemo xendemo
95 Once logged in, it should look just like any regular linux box. All
96 the usual tools and commands should work as per usual. However,
97 because of the poor random access performance of CD drives, the
98 machine will feel very slugish, and you may run out of memory if you
99 make significant modifications to the ramfs filesystem -- for the full
100 experience, install a Xen and Xenlinux image on you hard drive :-)
102 You can configure networking, either with 'dhclient' or manually via
103 'ifconfig' and 'route', remembering to edit /etc/resolv.conf if you
104 want DNS to work.
106 You can start an X server with 'startx'. It defaults to a conservative
107 1024x768, but you can edit the script for higher resoloutions. The CD
108 contains a load of standard software. You should be able to start
109 Apache, PostgreSQL, Mozilla etc in the normal way, but because
110 everything is running off CD the performance will be very sluggish and
111 you may run out of memory for the 'tmpfs' file system. You may wish
112 to go ahead and install Xen/Xenlinux on your hard drive, either
113 dropping Xen and the Xenlinux kernel down onto a pre-existing Linux
114 distribution, or using the file systems from the CD (which are based
115 on RH9). See the installation instructions later in this document.
117 If your video card requires 'agpgart' then it unfortunately won't yet
118 work with Xen, and you'll only be able to configure a VGA X
119 server. We're working on a fix for this for the next release.
121 If you want to browse the Xen / Xenlinux source, it's all located
122 under /usr/local/src/xen-2.0.bk, complete with BitKeeper
123 repository. We've also included source code and configuration
124 information for the various benchmarks we used in the SOSP paper.
127 Starting other domains
128 ======================
130 The first thing you need to do is to start the "xend" control daemon
131 with "xend start". You may wish to add an appropriate link to xend in
132 you /etc/rcX.d directory e.g. "ln -sf ../init.d/xend S97xend"
134 If you're not intending to configure the new domain with an IP address
135 on your LAN, then you'll probably want to use NAT. The
136 'xen_nat_enable' installs a few useful iptables rules into domain0 to
137 enable NAT. [NB: We plan to support RSIP in future]
139 Xen has a management interface that can be manipulated from domain0 to
140 create new domains, control their CPU, network and memory resource
141 allocations, allocate IP addresses, grant access to disk partitions,
142 and suspend/resume domains to files, etc. The management interface is
143 implemented as a set of library functions (implemented in C) for which
144 there are Python language bindings.
146 We have developed a simple set of example python tools for
147 manipulating the interface, with the intention that more sophisticated
148 high-level management tools will be developed in due course. Within
149 the source repository the tools live in tools/examples/ but are
150 installed in /usr/local/bin/ on the CD.
152 Starting a new domain is achieved using the command 'xm create' which
153 allocates resources to a new domain, populates it with a kernel image
154 (and optionally a ramdisk) and then starts it.
156 It parses a configuration file written in the Python language, the
157 default location of which is "/etc/xc/defaults", but this may be
158 overridden with the "-f" option. For the Demo CD, the defaults file
159 will cause domains to be created with ram-based root file systems, and
160 mount their /usr partition from the CD, just like domain0. (If you are
161 writing your own config file, the "example" script may be a better
162 starting point)
164 Variables can be initialised and passed into configuration files. Some
165 of these may be compulsory, others optional.
167 The 'defaults' file on the CD requires the 'ip' variable to be set to
168 tell Xen what IP address(es) should be routed to this domain. Xen
169 will route packets to the domain if they bear one of these addresses
170 as a destination address, and will also ensure that packets sent from
171 the domain contain one of the addresses as a source address (to
172 prevent spoofing). If multiple IP addresses are to be assigned to a
173 domain they can be listed in a comma separated list (with no
174 whitespace).
176 The 'mem' variable can be used to change the default memory allocation
177 of 64MB. For example to start a domain with two IP addresses and
178 72MB:
180 xm create ip=,
182 When invoked with the '-n' option 'xm create' will do a dry run
183 and just print out what resources and configuration the domain will
184 have e.g.:
186 [root@xendemo]# xm create -n ip=commando-1.xeno, mem=100
187 Parsing config file 'defaults'
189 VM image : "/boot/xenlinux.gz"
190 VM ramdisk : "/boot/initrd.gz"
191 VM memory (MB) : "100"
192 VM IP address(es) : ""
193 VM block device(s) : "phy:cdrom,hdd,r"
194 VM cmdline : "ip= root=/dev/ram0 rw init=/linuxrc 4 LOCALIP="
196 xm create will print the local TCP port to which you should
197 connect to perform console I/O. A suitable console client is provided
198 by the Python module xenctl.console_client: running this module from
199 the command line with <host> and <port> parameters will start a
200 terminal session. This module is also installed as /usr/bin/xencons,
201 from a copy in tools/misc/xencons. An alternative to manually running
202 a terminal client is to specify '-c' to xm create, or add
203 'auto_console=True' to the defaults file. This will cause
204 'xm create' to automatically become the console terminal after
205 starting the domain.
207 The 169.254.x.x network is special in that it is the 'link local'
208 subnet, and is isolated from the external network and hence can only
209 be used for communication between virtual machines. By convention, we
210 usually give each domain a link local address. The startup scripts on
211 the CD have been modified to accept a LINKLOCAL= parameter on the
212 kernel command line and initialise an IP alias accordingly (see
213 /etc/sysinit/network-scripts/ifcfg-eth0).
215 Linux only allows one IP address to be specified on the kernel command
216 line, so if you specify multiple IP addresses you'll need to configure
217 the new Linux VM with the other addresses manually (using ifconfig)
218 having logged in.
220 If you inspect the 'defaults' config script you'll see that the new
221 domain was started with a '4' on the kernel command line to tell
222 'init' to go to runlevel 4 rather than the default of 3 used by
223 domain0. This is done simply to suppress a bunch of harmless error
224 messages that would otherwise occur when the new (unprivileged) domain
225 tried to access physical hardware resources to try setting the
226 hwclock, system font, run gpm etc.
228 After it's booted, you should be able to ssh into your new domain from
229 domain0 using the link local 19.254.x.x address you assigned. If you
230 assigned a further IP address you should be able to ssh in using that
231 address too. If you ran the xen_enable_nat script, a bunch of port
232 redirects have been installed to enable you to ssh in to other domains
233 remotely even if you didn't assign an externally routeable address.
234 To access the new virtual machine remotely, use:
236 ssh -p2201 root@IP.address.Of.Domain0 # use 2202 for domain 2 etc.
238 You can manipulate running domains using the xm tool.
239 Invoking it without arguments prints some usage information.
241 To see what domains are running, run 'xm list'. Using the
242 tool you can change scheduling parameters, pause a domain, send it a
243 shutdown request, or blow it away with the 'destroy' command. You can
244 even suspend it to disk (but you probably won't have enough memory to
245 do the latter if you're running off the demo CD).
247 To find usage information for xm, run the script with no arguments or
248 with the 'help' argument. To get help on a particular xm command, use
249 'xm cmdname help'.
252 Troubleshooting Problems
253 ========================
255 If you have problems booting Xen, there are a number of boot parameters
256 that may be able to help diagnose problems:
258 ignorebiostables Disable parsing of BIOS-supplied tables. This may
259 help with some chipsets that aren't fully supported
260 by Xen. If you specify this option then ACPI tables are
261 also ignored, and SMP support is disabled.
263 noreboot Don't reboot the machine automatically on errors.
264 This is useful to catch debug output if you aren't
265 catching console messages via the serial line.
267 nosmp Disable SMP support.
268 This option is implied by 'ignorebiostables'.
270 noacpi Disable ACPI tables, which confuse Xen on some chipsets.
271 This option is implied by 'ignorebiostables'.
273 watchdog Enable NMI watchdog which can report certain failures.
275 noht Disable Hyperthreading.
277 badpage=<page number>[,<page number>]*
278 Specify a list of pages not to be allocated for use
279 because they contain bad bytes. For example, if your
280 memory tester says that byte 0x12345678 is bad, you would
281 place 'badpage=0x12345' on Xen's command line (i.e., the
282 last three digits of the byte address are not included!).
284 com1=<baud>,DPS[,<io_base>,<irq>]
285 com2=<baud>,DPS[,<io_base>,<irq>]
286 Xen supports up to two 16550-compatible serial ports.
287 For example: 'com1=9600,8n1,0x408,5' maps COM1 to a
288 9600-baud port, 8 data bits, no parity, 1 stop bit,
289 I/O port base 0x408, IRQ 5.
290 If the I/O base and IRQ are standard (com1:0x3f8,4;
291 com2:0x2f8,3) then they need not be specified.
293 console=<specifier list>
294 Specify the destination for Xen console I/O.
295 This is a comma-separated list of, for example:
296 vga: use VGA console and allow keyboard input
297 com1: use serial port com1
298 com2H: use serial port com2. Transmitted chars will
299 have the MSB set. Received chars must have
300 MSB set.
301 com2L: use serial port com2. Transmitted chars will
302 have the MSB cleared. Received chars must
303 have MSB cleared.
304 The latter two examples allow a single port to be
305 shared by two subsystems (eg. console and
306 debugger). Sharing is controlled by MSB of each
307 transmitted/received character.
308 [NB. Default for this option is 'com1,vga']
310 conswitch=<switch-char><auto-switch-char>
311 Specify how to switch serial-console input between
312 Xen and DOM0. The required sequence is CTRL-<switch_char>
313 pressed three times. Specifying '`' disables switching.
314 The <auto-switch-char> specifies whether Xen should
315 auto-switch input to DOM0 when it boots -- if it is 'x'
316 then auto-switching is disabled. Any other value, or
317 omitting the character, enables auto-switching.
318 [NB. Default for this option is 'a']
320 nmi=<nmi-error-behaviour>
321 Specify what to do with an NMI parity or I/O error.
322 'nmi=fatal': Xen prints a diagnostic and then hangs.
323 'nmi=dom0': Inform DOM0 of the NMI.
324 'nmi=ignore': Ignore the NMI.
325 [NB. Default is 'dom0' ('fatal' for debug builds).]
327 dom0_mem=xxx Set the initial amount of memory for domain0.
329 pdb=xxx Enable the pervasive debugger. See docs/pdb.txt
330 xxx defines how the gdb stub will communicate:
331 com1 use com1
332 com1H use com1 (with high bit set)
333 com2 use on com2
334 com2H use com2 (with high bit set)
336 It's probably a good idea to join the Xen developer's mailing list on
337 Sourceforge:
340 About The Xen Demo CD
341 =====================
343 The purpose of the Demo CD is to distribute a snapshot of Xen's
344 source, and simultaneously provide a convenient means for enabling
345 people to get experience playing with Xen without needing to install
346 it on their hard drive. If you decide to install Xen/Xenlinux you can
347 do so simply by following the installation instructions below -- which
348 essentially involves copying the contents of the CD on to a suitably
349 formated disk partition, and then installing or updating the Grub
350 bootloader.
352 This is a bootable CD that loads Xen, and then a Linux 2.4.27 OS image
353 ported to run on Xen. The CD contains a copy of a file system based on
354 the RedHat 9 distribution that is able to run directly off the CD
355 ("live ISO"), using a "tmpfs" RAM-based file system for root (/etc
356 /var etc). Changes you make to the tmpfs will obviously not be
357 persistent across reboots!
359 Because of the use of a RAM-based file system for root, you'll need
360 plenty of memory to run this CD -- something like 96MB per VM. This is
361 not a restriction of Xen : once you've installed Xen, Xenlinux and
362 the file system images on your hard drive you'll find you can boot VMs
363 in just a few MBs.
365 The CD contains a snapshot of the Xen and Xenlinux code base that we
366 believe to be pretty stable, but lacks some of the features that are
367 currently still work in progress e.g. OS suspend/resume to disk, and
368 various memory management enhancements to provide fast inter-OS
369 communication and sharing of memory pages between OSs. We'll release
370 newer snapshots as required, making use of a BitKeeper repository
371 hosted on (follow instructions from the project
372 home page). We're obviously grateful to receive any bug fixes or
373 other code you can contribute. We suggest you join the
374 mailing list.
377 Installing from the CD
378 ======================
380 If you're installing Xen/Xenlinux onto an existing linux file system
381 distribution, just copy the Xen VMM (/boot/image.gz) and Xenlinux
382 kernels (/boot/xenlinux.gz), then modify the Grub config
383 (/boot/grub/menu.lst or /boot/grub/grub.conf) on the target system.
384 It should work on pretty much any distribution.
386 Xen is a "multiboot" standard boot image. Despite being a 'standard',
387 few boot loaders actually support it. The only two we know of are
388 Grub, and our modified version of linux kexec (for booting off a
389 XenoBoot CD -- PlanetLab have adopted the same boot CD approach).
391 If you need to install grub on your system, you can do so either by
392 building the Grub source tree
393 /usr/local/src/grub-0.93-iso9660-splashimage or by copying over all
394 the files in /boot/grub and then running /sbin/grub and following the
395 usual grub documentation. You'll then need to edit the Grub
396 config file.
398 A typical Grub menu option might look like:
400 title Xen 2.0 / Xenlinux 2.4.27
401 kernel /boot/xen.gz dom0_mem=131072 com1=115200 noht watchdog
402 module /boot/vmlinuz-2.4.27-xen0 root=/dev/sda4 ro
404 The first line specifies which Xen image to use, and what command line
405 arguments to pass to Xen. In this case we set the maximum amount of
406 memory to allocate to domain0, and enable serial I/O on COM1 at 115200
407 baud. We could also disable smp support (nosmp) or disable
408 hyper-threading support (noht).
410 The second line specifies which xenlinux image to use, and the
411 standard linux command line arguments to pass to the kernel. In this
412 case, we're configuring the root partition and stating that it should
413 initially be mounted read-only (normal practice).
415 If we were booting with an initial ram disk (initrd), then this would
416 require a second "module" line.
418 Installing the Xen tools and source
419 ===================================
421 The tools and source live in the /usr/local/src/xen-2.0.bk directory on
422 the CD (and may also be downloaded from the project downloads
423 page). You'll need to copy them to some mutable storage before using
424 them.
426 If you have the BitKeeper BK tools installed you can check the
427 repository is up to date by cd'ing into the xeno-2.0.bk directory and
428 typing 'bk pull' (assuming you have an Internet connection).
430 You can rebuild Xen, the tools and XenLinux by typing 'make
431 world'. You can install them to the standard directories with 'make
432 install', or into the ./install subtree with 'make dist'.
435 Modifying
436 =================================
438 can be used to set the new kernel's command line,
439 and hence determine what it uses as a root file system, etc. Although
440 the default is to boot in the same manner that domain0 did (using the
441 RAM-based file system for root and the CD for /usr) it's possible to
442 configure any of the following possibilities, for example:
444 * initrd=/boot/initrd init=/linuxrc
445 boot using an initial ram disk, executing /linuxrc (as per this CD)
447 * root=/dev/hda3 ro
448 boot using a standard hard disk partition as root
449 !!! remember to grant access in
451 * root=/dev/xvda1 ro
452 boot using a pre-configured 'virtual block device' that will be
453 attached to a virtual disk that previously has had a file system
454 installed on it.
456 * root=/dev/nfs nfsroot=/path/on/server ip=<blah_including server_IP>
457 Boot using an NFS mounted root file system. This could be from a
458 remote NFS server, or from an NFS server running in another
459 domain. The latter is rather a useful option.
461 A typical setup might be to allocate a standard disk partition for
462 each domain and populate it with files. To save space, having a shared
463 read-only usr partition might make sense.
465 Block devices should only be shared between domains in a read-only
466 fashion otherwise the linux kernels will obviously get very confused
467 as the file system structure may change underneath them (having the
468 same partition mounted rw twice is a sure fire way to cause
469 irreparable damage)! If you want read-write sharing, export the
470 directory to other domains via NFS from domain0.
475 Installing the file systems from the CD
476 =======================================
478 If you haven't got an existing Linux installation onto which you can
479 just drop down the Xen and Xenlinux images, then the file systems on
480 the CD provide a quick way of doing an install. However, you would be
481 better off in the long run doing a proper install of your preferred
482 distro and installing Xen onto that, rather than just doing the hack
483 described below:
485 Choose one or two partitions, depending on whether you want a separate
486 /usr or not. Make file systems on it/them e.g.:
487 mkfs -t ext3 /dev/hda3
488 [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
489 version of mkfs]
491 Next, mount the file system(s) e.g.:
492 mkdir /mnt/root && mount /dev/hda3 /mnt/root
493 [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
495 To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
496 cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
498 You'll need to edit /mnt/root/etc/fstab to reflect your file system
499 configuration. Changing the password file (etc/shadow) is probably a
500 good idea too.
502 To install the usr file system, copy the file system from CD on /usr,
503 though leaving out the "XenDemoCD" and "boot" directories:
504 cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr
506 If you intend to boot off these file systems (i.e. use them for
507 domain 0), then you probably want to copy the /usr/boot directory on
508 the cd over the top of the current symlink to /boot on your root
509 filesystem (after deleting the current symlink) i.e.:
510 cd /mnt/root ; rm boot ; cp -a /usr/boot .
512 The XenDemoCD directory is only useful if you want to build your own
513 version of the XenDemoCD (see below).
516 Debugging
517 =========
519 Xen has a set of debugging features that can be useful to try and
520 figure out what's going on. Hit 'h' on the serial line (if you
521 specified a baud rate on the Xen command line) or ScrollLock-h on the
522 keyboard to get a list of supported commands.
524 If you have a crash you'll likely get a crash dump containing an EIP
525 (PC) which, along with an 'objdump -d image', can be useful in
526 figuring out what's happened. Debug a Xenlinux image just as you
527 would any other Linux kernel.
529 We supply a handy debug terminal program which you can find in
530 /usr/local/src/xen-2.0.bk/tools/misc/miniterm/
531 This should be built and executed on another machine that is connected
532 via a null modem cable. Documentation is included.
533 Alternatively, if the Xen machine is connected to a serial-port server
534 then we supply a dumb TCP terminal client:
535 'tools/xenctl/lib/ <server host> <server port>'
538 Installing Xen / Xenlinux on a RedHat distribution
539 ===================================================
541 When using Xen / Xenlinux on a standard Linux distribution there are
542 a couple of things to watch out for:
544 The first Linux VM that is started when Xen boots start (Domain 0) is
545 given direct access to the graphics card, so it may use it as a
546 console. Other domains don't have ttyN consoles, so attempts to run a
547 'mingetty' against them will fail, generating periodic warning
548 messages from 'init' about services respawning too fast. They should
549 work for domain0 just fine.
550 IMPORTANT: To prevent warning messages when running RH9 you'll need to
551 remove ttyN from /etc/inittab for domains>0. Due to a bug in the RH9
552 /etc/rc.sysinit script #'ing the lines out of /etc/inittab won't work
553 as it ignores the '#' and tries to access them anyway.
555 Every Xenlinux instance owns a bidirectional 'virtual console'.
556 The device node to which this console is attached can be configured
557 by specifying 'xencons=' on the OS command line:
558 'xencons=off' --> disable virtual console
559 'xencons=tty' --> attach console to /dev/tty1 (tty0 at boot-time)
560 'xencons=ttyS' --> attach console to /dev/ttyS0
561 The default is to attach to /dev/tty1, and also to create dummy
562 devices for /dev/tty2-63 to avoid warnings from many standard distro
563 startup scripts. The exception is domain 0, which by default attaches
564 to /dev/ttyS0.
566 Note that, because domains>0 don't have any privileged access at all,
567 certain commands in the default boot sequence will fail e.g. attempts
568 to update the hwclock, change the console font, update the keytable
569 map, start apmd (power management), or gpm (mouse cursor). Either
570 ignore the errors, or remove them from the startup scripts. Deleting
571 the following links are a good start: S24pcmcia S09isdn S17keytable
572 S26apmd S85gpm
574 If you want to use a single root file system that works cleanly for
575 domain0 and domains>0, one trick is to use different 'init' run
576 levels. For example, on the Xen Demo CD we use run level 3 for domain
577 0, and run level 4 for domains>0. This enables different startup
578 scripts to be run in depending on the run level number passed on the
579 kernel command line.
581 Xenlinux kernels can be built to use runtime loadable modules just
582 like normal linux kernels. Modules should be installed under
583 /lib/modules in the normal way.
585 If there's some kernel feature that hasn't been built into our default
586 kernel, there's a pretty good change that if its a non-hardware
587 related option you'll just be able to enable it and rebuild. If its
588 not on the xconfig menu, hack the arch/xen/ to put the menu
589 back in.
591 If you're going to use the link local 169.254.1.x addresses to
592 communicate between VMs, there are a couple of other issues to watch
593 out for. RH9 appears to have a bug where by default it configures the
594 loopback interface with a 169.254 address, which stops it working
595 properly on eth0 for communicating with other domains.
597 This utterly daft RH9 behaviour can be stopped by appending
598 "NOZEROCONF=yes" to /etc/sysconfig/networking-scripts/ifcfg-lo
600 If you're going to use NFS root files systems mounted either from an
601 external server or from domain0 there are a couple of other gotchas.
602 The default /etc/sysconfig/iptables rules block NFS, so part way
603 through the boot sequence things will suddenly go dead.
605 If you're planning on having a separate NFS /usr partition, the RH9
606 boot scripts don't make life easy, as they attempt to mount NFS file
607 systems way to late in the boot process. The easiest way I found to do
608 this was to have a '/linuxrc' script run ahead of /sbin/init that
609 mounts /usr:
610 #!/bin/bash
611 /sbin/ipconfig lo
612 /sbin/portmap
613 /bin/mount /usr
614 exec /sbin/init "$@" <>/dev/console 2>&1
616 The one slight complication with the above is that /sbib/portmap is
617 dynamically linked against /usr/lib/ Since this is in
618 /usr, it won't work. I solved this by copying the file (and link)
619 below the /usr mount point, and just let the file be 'covered' when
620 the mount happens.
622 In some installations, where a shared read-only /usr is being used, it
623 may be desirable to move other large directories over into the
624 read-only /usr. For example, on the XenDemoCD we replace /bin /lib and
625 /sbin with links into /usr/root/bin /usr/root/lib and /usr/root/sbin
626 respectively. This creates other problems for running the /linuxrc
627 script, requiring bash, portmap, mount, ifconfig, and a handful of
628 other shared libraries to be copied below the mount point. I guess I
629 should have written a little statically linked C program...
633 Description of how the XenDemoCD boots
634 ======================================
636 1. Grub is used to load Xen, a Xenlinux kernel, and an initrd (initial
637 ram disk). [The source of the version of Grub used is in /usr/local/src]
639 2. the init=/linuxrc command line causes linux to execute /linuxrc in
640 the initrd.
642 3. the /linuxrc file attempts to mount the CD by trying the likely
643 locations : /dev/hd[abcd].
645 4. it then creates a 'tmpfs' file system and untars the
646 'XenDemoCD/root.tar.gz' file into the tmpfs. This contains hopefully
647 all the files that need to be mutable (this would be so much easier
648 if Linux supported 'stacked' or union file systems...)
650 5. Next, /linuxrc uses the pivot_root call to change the root file
651 system to the tmpfs, with the CD mounted as /usr.
653 6. It then invokes /sbin/init in the tmpfs and the boot proceeds
654 normally.
657 Building your own version of the XenDemoCD
658 ==========================================
660 The 'live ISO' version of RedHat is based heavily on Peter Anvin's
661 SuperRescue CD version 2.1.2 and J. McDaniel's Plan-B:
666 Since Xen uses a "multiboot" image format, it was necessary to change
667 the bootloader from isolinux to Grub0.93 with Leonid Lisovskiy's
668 <> grub.0.93-iso9660.patch
670 The Xen Demo CD contains all of the build scripts that were used to
671 create it, so it is possible to 'unpack' the current iso, modifiy it,
672 then build a new iso. The procedure for doing so is as follows:
674 First, mount either the CD, or the iso image of the CD:
676 mount /dev/cdrom /mnt/cdrom
677 or:
678 mount -o loop xendemo-1.0.iso /mnt/cdrom
680 cd to the directory you want to 'unpack' the iso into then run the
681 unpack script:
683 cd /local/xendemocd
684 /mnt/cdrom/XenDemoCD/
686 The result is a 'build' directory containing the file system tree
687 under the 'root' directory. e.g. /local/xendemocd/build/root
689 To add or remove rpms, its possible to use 'rpm' with the --root
690 option to set the path. For more complex changes, it easiest to boot a
691 machine using using the tree via NFS root. Before doing this, you'll
692 need to edit fstab to comment out the seperate mount of /usr.
694 One thing to watch out for: as part of the CD build process, the
695 contents of the 'rootpatch' tree gets copied over the existing 'root'
696 tree replacing various files. The intention of the rootpatch tree is
697 to contain the files that have been modified from the original RH
698 distribution (e.g. various /etc files). This was done to make it
699 easier to upgrade to newer RH versions in the future. The downside of
700 this is that if you edit an existing file in the root tree you should
701 check that you don't also need to propagate the change to the
702 rootpatch tree to avoid it being overwritten.
704 Once you've made the changes and want to build a new iso, here's the
705 procedure:
707 cd /local/xendemocd/build
708 echo '<put_your_name_here>' > Builder
709 ./ put_your_version_id_here >../buildlog 2>&1
711 This process can take 30 mins even on a fast machine, but you should
712 eventually end up with an iso image in the build directory.
714 Notes:
716 root - the root of the file system heirarchy as presented to the
717 running system
719 rootpatch - contains files that have been modified from the standard
720 RH, and copied over the root tree as part of the build
721 procedure.
723 irtree - the file system tree that will go into the initrd (initial
724 ram disk)
726 work - a working directory used in the build process
728 usr - this should really be in 'work' as its created as part of the
729 build process. It contains the 'immutable' files that will
730 be served from the CD rather than the tmpfs containing the
731 contents of root.tar.gz. Some files that are normally in /etc
732 or /var that are large and actually unlikely to need changing
733 have been moved into /usr/root and replaced with links.
736 Ian Pratt
737 9 Sep 2003