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author iap10@tetris.cl.cam.ac.uk
date Sat May 15 14:03:38 2004 +0000 (2004-05-15)
parents 8ca409420fb5
children 26483a083da1
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10 XenDemoCD 1.3
11 University of Cambridge Computer Laboratory
12 24 Jan 2004
14 http://www.cl.cam.ac.uk/netos/xen
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 and Linux-2.4 OS port (XenoLinux). It runs entirely off the CD,
23 without requiring hard disk installation. This is achieved using a RAM
24 disk to store mutable file system data while using the CD for
25 everything else. The CD can also be used for installing Xen/XenoLinux
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 The Xen VMM is currently fairly h/w specific, but porting new device
33 drivers is relatively straightforward thanks to Xen's Linux driver
34 compatibility layer. The current snapshot supports the following
35 hardware:
37 CPU: Pentium Pro/II/III/IV/Xeon, Athlon (i.e. P6 or newer) SMP supported
38 IDE: Intel PIIX chipset, others will be PIO only (slow)
39 SCSI: Adaptec / Dell PERC Raid (aacraid), fusion MPT, megaraid, Adaptec aic7xxx
40 Net: Recommended: Intel e1000, Broadcom BCM57xx (tg3), 3c905 (3c59x)
41 Working, but require extra copies : pcnet32, Intel e100, tulip
43 Because of the demo CD's use of RAM disks, make sure you have plenty
44 of RAM (256MB+).
46 To try out the Demo, boot from CD (you may need to change your BIOS
47 configuration to do this), then select one of the four boot options
48 from the Grub menu:
50 Xen / linux-2.4.24
51 Xen / linux-2.4.24 using cmdline IP configuration
52 Xen / linux-2.4.24 in "safe mode"
53 linux-2.4.22
55 The last option is a plain linux kernel that runs on the bare machine,
56 and is included simply to help diagnose driver compatibility
57 problems. The "safe mode" boot option might be useful if you're having
58 problems getting Xen to work with your hardware, as it disables various
59 features such as SMP, and enables some debugging.
61 If you are going for a command line IP config, hit "e" at
62 the grub menu, then edit the "ip=" parameters to reflect your setup
63 e.g. "ip=<ipaddr>::<gateway>:<netmask>::eth0:off". It shouldn't be
64 necessary to set either the nfs server or hostname
65 parameters. Alternatively, once XenoLinux has booted you can login and
66 setup networking with 'dhclient' or 'ifconfig' and 'route' in the
67 normal way.
69 To make things easier for yourself, it's worth trying to arrange for an
70 IP address which is the first in a sequential range of free IP
71 addresses. It's useful to give each VM instance its own public IP
72 address (though it is possible to do NAT or use private addresses),
73 and the configuration files on the CD allocate IP addresses
74 sequentially for subsequent domains unless told otherwise.
76 After selecting the kernel to boot, stand back and watch Xen boot,
77 closely followed by "domain 0" running the XenoLinux kernel. The boot
78 messages can also sent to the serial line by specifying the baud rate
79 on the Xen cmdline (e.g., 'com1=9600,8n1'); this can be very useful
80 for debugging should anything important scroll off the screen. Xen's
81 startup messages will look quite familiar as much of the hardware
82 initialisation (SMP boot, apic setup) and device drivers are derived
83 from Linux.
85 If everything is well, you should see the linux rc scripts start a
86 bunch of standard services including sshd. Login on the console or
87 via ssh::
88 username: user root
89 password: xendemo xendemo
91 Once logged in, it should look just like any regular linux box. All
92 the usual tools and commands should work as per usual. However,
93 because of the poor random access performance of CD drives, the
94 machine will feel very slugish, and you may run out of memory if you
95 make significant modifications to the ramfs filesystem -- for the full
96 experience, install a Xen and XenoLinux image on you hard drive :-)
98 You can configure networking, either with 'dhclient' or manually via
99 'ifconfig' and 'route', remembering to edit /etc/resolv.conf if you
100 want DNS to work.
102 You can start an X server with 'startx'. It defaults to a conservative
103 1024x768, but you can edit the script for higher resoloutions. The CD
104 contains a load of standard software. You should be able to start
105 Apache, PostgreSQL, Mozilla etc in the normal way, but because
106 everything is running off CD the performance will be very sluggish and
107 you may run out of memory for the 'tmpfs' file system. You may wish
108 to go ahead and install Xen/XenoLinux on your hard drive, either
109 dropping Xen and the XenoLinux kernel down onto a pre-existing Linux
110 distribution, or using the file systems from the CD (which are based
111 on RH9). See the installation instructions later in this document.
113 If your video card requires 'agpgart' then it unfortunately won't yet
114 work with Xen, and you'll only be able to configure a VGA X
115 server. We're working on a fix for this for the next release.
117 If you want to browse the Xen / XenoLinux source, it's all located
118 under /usr/local/src/xeno-1.2, complete with BitKeeper
119 repository. We've also included source code and configuration
120 information for the various benchmarks we used in the SOSP paper.
123 Starting other domains
124 ======================
126 Xen's privileged control interfaces can be accessed using a C library
127 (libxc.so) or an easier-to-use Python wrapper module (Xc). Example
128 script templates are provided in tools/examples/.
130 Abyway, the first thing to do is to set up a window in which you will
131 receive console output from other domains. Console output will arrive
132 as UDP packets destined for The DemoCD's startup scripts
133 automatically bring up as an alias called eth0:xen (see
134 /etc/sysconfig/network-scripts/ifcfg-eth0 )
136 If you're not intending to configure the new domain with an IP address
137 on your LAN, then you'll probably want to use NAT. The
138 'xen_nat_enable' installs a few useful iptables rules into domain0 to
139 enable NAT. [ NB: The intention is that in future Xen will do NAT
140 itsel (actually RSIP), but this is part of a larger work package that
141 isn't ready to release.]
143 Xen has a management interface that can be manipulated from domain0 to
144 create new domains, control their CPU, network and memory resource
145 allocations, allocate IP addresses, grant access to disk partitions,
146 and suspend/resume domains to files, etc. The management interface is
147 implemented as a set of library functions (implemented in C) for which
148 there are Python language bindings.
150 We have developed a simple set of example python tools for
151 manipulating the interface, with the intention that more sophisticated
152 high-level management tools will be developed in due course. Within
153 the source repository the tools live in tools/examples/ but are
154 installed in /usr/local/bin/ on the CD.
156 Starting a new domain is achieved using xc_dom_create.py which
157 allocates resources to a new domain, populates it with a kernel image
158 (and optionally a ramdisk) and then starts it.
160 It parses a configuration file written in the Python language, the
161 default location of which is "/etc/xc/defaults", but this may be
162 overridden with the "-f" option. For the Demo CD, the defaults file
163 will cause domains to be created with ram-based root file systems, and
164 mount their /usr partition from the CD, just like domain0. (If you are
165 writing your own config file, the "example" script may be a better
166 starting point)
168 Variables can be initialised and passed into configuration files. Some
169 of these may be compulsory, others optional.
171 The 'defaults' file on the CD requires the 'ip' variable to be set to
172 tell Xen what IP address(es) should be routed to this domain. Xen
173 will route packets to the domain if they bear one of these addresses
174 as a destination address, and will also ensure that packets sent from
175 the domain contain one of the addresses as a source address (to
176 prevent spoofing). If multiple IP addresses are to be assigned to a
177 domain they can be listed in a comma separated list (with no
178 whitespace).
180 The 'mem' variable can be used to change the default memory allocation
181 of 64MB. For example to start a domain with two IP addresses and
182 72MB:
184 xc_dom_create.py -Dip=, -Dmem=72
186 [multiple variables may also be set with a single '-D' flag by
187 separating them with ':'. Also, it's possible to use DNS hostnames
188 rather than IP addresses.]
190 When invoked with the '-n' option xc_dom_create.py will do a dry run
191 and just print out what resources and configuration the domain will
192 have e.g.:
194 [root@xendemo]# xc_dom_create.py -D ip=commando-1.xeno, -Dmem=100
195 Parsing config file 'defaults'
197 VM image : "/boot/xenolinux.gz"
198 VM ramdisk : "/boot/initrd.gz"
199 VM memory (MB) : "100"
200 VM IP address(es) : ""
201 VM block device(s) : "phy:cdrom,hdd,r"
202 VM cmdline : "ip= root=/dev/ram0 rw init=/linuxrc 4 LOCALIP="
204 xc_dom_create.py will print the local TCP port to which you should
205 connect to perform console I/O. A suitable console client is provided
206 by the Python module xenctl.console_client: running this module from
207 the command line with <host> and <port> parameters will start a
208 terminal session. This module is also installed as /usr/bin/xencons,
209 from a copy in tools/misc/xencons. An alternative to manually running
210 a terminal client is to specify '-c' to xc_dom_create.py, or add
211 'auto_console=True' to the defaults file. This will cause
212 xc_dom_create.py to automatically become the console terminal after
213 starting the domain.
215 The 169.254.x.x network is special in that it is the 'link local'
216 subnet, and is isolated from the external network and hence can only
217 be used for communication between virtual machines. By convention, we
218 usually give each domain a link local address. The startup scripts on
219 the CD have been modified to accept a LINKLOCAL= parameter on the
220 kernel command line and initialise an IP alias accordingly (see
221 /etc/sysinit/network-scripts/ifcfg-eth0).
223 Linux only allows one IP address to be specified on the kernel command
224 line, so if you specify multiple IP addresses you'll need to configure
225 the new Linux VM with the other addresses manually (using ifconfig)
226 having logged in.
228 If you inspect the 'defaults' config script you'll see that the new
229 domain was started with a '4' on the kernel command line to tell
230 'init' to go to runlevel 4 rather than the default of 3 used by
231 domain0. This is done simply to suppress a bunch of harmless error
232 messages that would otherwise occur when the new (unprivileged) domain
233 tried to access physical hardware resources to try setting the
234 hwclock, system font, run gpm etc.
236 After it's booted, you should be able to ssh into your new domain from
237 domain0 using the link local 19.254.x.x address you assigned. If you
238 assigned a further IP address you should be able to ssh in using that
239 address too. If you ran the xen_enable_nat script, a bunch of port
240 redirects have been installed to enable you to ssh in to other domains
241 remotely even if you didn't assign an externally routeable address.
242 To access the new virtual machine remotely, use:
244 ssh -p2201 root@IP.address.Of.Domain0 # use 2202 for domain 2 etc.
246 You can manipulate running domains using the xc_dom_control.py tool.
247 Invoking it without arguments prints some usage information.
249 To see what domains are running, run 'xc_dom_control.py list'. Using the
250 tool you can change scheduling parameters, pause a domain, send it a
251 shutdown request, or blow it away with the 'destroy' command. You can
252 even suspend it to disk (but you probably won't have enough memory to
253 do the latter if you're running off the demo CD).
255 To find usage information for xc_dom_control.py, run the script with
256 no arguments.
259 Troubleshooting Problems
260 ========================
262 If you have problems booting Xen, there are a number of boot parameters
263 that may be able to help diagnose problems:
265 ignorebiostables Disable parsing of BIOS-supplied tables. This may
266 help with some chipsets that aren't fully supported
267 by Xen. If you specify this option then ACPI tables are
268 also ignored, and SMP support is disabled.
270 noreboot Don't reboot the machine automatically on errors.
271 This is useful to catch debug output if you aren't
272 catching console messages via the serial line.
274 nosmp Disable SMP support.
275 This option is implied by 'ignorebiostables'.
277 noacpi Disable ACPI tables, which confuse Xen on some chipsets.
278 This option is implied by 'ignorebiostables'.
280 watchdog Enable NMI watchdog which can report certain failures.
282 noht Disable Hyperthreading.
284 ifname=ethXX Select which Ethernet interface to use.
286 ifname=dummy Don't use any network interface.
288 com1=<baud>,DPS[,<io_base>,<irq>]
289 com2=<baud>,DPS[,<io_base>,<irq>]
290 Xen supports up to two 16550-compatible serial ports.
291 For example: 'com1=9600,8n1,0x408,5' maps COM1 to a
292 9600-baud port, 8 data bits, no parity, 1 stop bit,
293 I/O port base 0x408, IRQ 5.
294 If the I/O base and IRQ are standard (com1:0x3f8,4;
295 com2:0x2f8,3) then they need not be specified.
297 console=<specifier list>
298 Specify the destination for Xen console I/O.
299 This is a comma-separated list of, for example:
300 vga: use VGA console and allow keyboard input
301 com1: use serial port com1
302 com2H: use serial port com2. Transmitted chars will
303 have the MSB set. Received chars must have
304 MSB set.
305 com2L: use serial port com2. Transmitted chars will
306 have the MSB cleared. Received chars must
307 have MSB cleared.
308 The latter two examples allow a single port to be
309 shared by two subsystems (eg. console and
310 debugger). Sharing is controlled by MSB of each
311 transmitted/received character.
312 [NB. Default for this option is 'com1,tty']
314 dom0_mem=xxx Set the initial amount of memory for domain0.
316 pdb=xxx Enable the pervasive debugger. See docs/pdb.txt
317 xxx defines how the gdb stub will communicate:
318 com1 use com1
319 com1H use com1 (with high bit set)
320 com2 use on com2
321 com2H use com2 (with high bit set)
323 It's probably a good idea to join the Xen developer's mailing list on
324 Sourceforge: http://lists.sourceforge.net/lists/listinfo/xen-devel
327 About The Xen Demo CD
328 =====================
330 The purpose of the Demo CD is to distribute a snapshot of Xen's
331 source, and simultaneously provide a convenient means for enabling
332 people to get experience playing with Xen without needing to install
333 it on their hard drive. If you decide to install Xen/XenoLinux you can
334 do so simply by following the installation instructions below -- which
335 essentially involves copying the contents of the CD on to a suitably
336 formated disk partition, and then installing or updating the Grub
337 bootloader.
339 This is a bootable CD that loads Xen, and then a Linux 2.4.22 OS image
340 ported to run on Xen. The CD contains a copy of a file system based on
341 the RedHat 9 distribution that is able to run directly off the CD
342 ("live ISO"), using a "tmpfs" RAM-based file system for root (/etc
343 /var etc). Changes you make to the tmpfs will obviously not be
344 persistent across reboots!
346 Because of the use of a RAM-based file system for root, you'll need
347 plenty of memory to run this CD -- something like 96MB per VM. This is
348 not a restriction of Xen : once you've installed Xen, XenoLinux and
349 the file system images on your hard drive you'll find you can boot VMs
350 in just a few MBs.
352 The CD contains a snapshot of the Xen and XenoLinux code base that we
353 believe to be pretty stable, but lacks some of the features that are
354 currently still work in progress e.g. OS suspend/resume to disk, and
355 various memory management enhancements to provide fast inter-OS
356 communication and sharing of memory pages between OSs. We'll release
357 newer snapshots as required, making use of a BitKeeper repository
358 hosted on http://xen.bkbits.net (follow instructions from the project
359 home page). We're obviously grateful to receive any bug fixes or
360 other code you can contribute. We suggest you join the
361 xen-devel@lists.sourceforge.net mailing list.
364 Installing from the CD
365 ======================
367 If you're installing Xen/XenoLinux onto an existing linux file system
368 distribution, just copy the Xen VMM (/boot/image.gz) and XenoLinux
369 kernels (/boot/xenolinux.gz), then modify the Grub config
370 (/boot/grub/menu.lst or /boot/grub/grub.conf) on the target system.
371 It should work on pretty much any distribution.
373 Xen is a "multiboot" standard boot image. Despite being a 'standard',
374 few boot loaders actually support it. The only two we know of are
375 Grub, and our modified version of linux kexec (for booting off a
376 XenoBoot CD -- PlanetLab have adopted the same boot CD approach).
378 If you need to install grub on your system, you can do so either by
379 building the Grub source tree
380 /usr/local/src/grub-0.93-iso9660-splashimage or by copying over all
381 the files in /boot/grub and then running /sbin/grub and following the
382 usual grub documentation. You'll then need to edit the Grub
383 config file.
385 A typical Grub menu option might look like:
387 title Xen / XenoLinux 2.4.22
388 kernel /boot/image.gz dom0_mem=131072 com1=115200,8n1 noht
389 module /boot/xenolinux.gz root=/dev/sda4 ro console=tty0
391 The first line specifies which Xen image to use, and what command line
392 arguments to pass to Xen. In this case we set the maximum amount of
393 memory to allocate to domain0, and enable serial I/O at 9600 baud.
394 We could also disable smp support (nosmp) or disable hyper-threading
395 support (noht). If you have multiple network interface you can use
396 ifname=ethXX to select which one to use. If your network card is
397 unsupported, use ifname=dummy
399 The second line specifies which xenolinux image to use, and the
400 standard linux command line arguments to pass to the kernel. In this
401 case, we're configuring the root partition and stating that it should
402 initially be mounted read-only (normal practice).
404 If we were booting with an initial ram disk (initrd), then this would
405 require a second "module" line.
407 Installing the Xen tools and source
408 ===================================
410 The tools and source live in the /usr/local/src/xen-1.2 directory on
411 the CD (and may also be downloaded from the project downloads
412 page). You'll need to copy them to some mutable storage before using
413 them.
415 If you have the BitKeeper BK tools installed you can check the
416 repository is up to date by cd'ing into the xeno-1.2.bk directory and
417 typing 'bk pull' (assuming you have an Internet connection).
419 You can rebuild Xen and the tools by typing 'make'. You can install
420 them to the standard directories with 'make install', or into the
421 ../install subtree with 'make dist'.
423 If you're using the virtual disk control tools (xc_vd_tool) you'll
424 need the SQLite library and python binding pysqlite. There's a tar
425 ball containing the necessary binaries on the project downloads page.
428 Modifying xc_mycreatelinuxdom1.py
429 =================================
431 xc_mycreatelinuxdom1.py.py can be used to set the new kernel's command line,
432 and hence determine what it uses as a root file system, etc. Although
433 the default is to boot in the same manner that domain0 did (using the
434 RAM-based file system for root and the CD for /usr) it's possible to
435 configure any of the following possibilities, for example:
437 * initrd=/boot/initrd init=/linuxrc
438 boot using an initial ram disk, executing /linuxrc (as per this CD)
440 * root=/dev/hda3 ro
441 boot using a standard hard disk partition as root
442 !!! remember to grant access in createlinuxdom.py.
444 * root=/dev/xvda1 ro
445 boot using a pre-configured 'virtual block device' that will be
446 attached to a virtual disk that previously has had a file system
447 installed on it.
449 * root=/dev/nfs nfsroot=/path/on/server ip=<blah_including server_IP>
450 Boot using an NFS mounted root file system. This could be from a
451 remote NFS server, or from an NFS server running in another
452 domain. The latter is rather a useful option.
454 A typical setup might be to allocate a standard disk partition for
455 each domain and populate it with files. To save space, having a shared
456 read-only usr partition might make sense.
458 Block devices should only be shared between domains in a read-only
459 fashion otherwise the linux kernels will obviously get very confused
460 as the file system structure may change underneath them (having the
461 same partition mounted rw twice is a sure fire way to cause
462 irreparable damage)! If you want read-write sharing, export the
463 directory to other domains via NFS from domain0.
468 Installing the file systems from the CD
469 =======================================
471 If you haven't got an existing Linux installation onto which you can
472 just drop down the Xen and XenoLinux images, then the file systems on
473 the CD provide a quick way of doing an install. However, you're
474 probably better off in the long run doing a proper Redhat, Fedora,
475 Debian etc install rather than just doing the hack described below:
477 Choose one or two partitions, depending on whether you want a separate
478 /usr or not. Make file systems on it/them e.g.:
479 mkfs -t ext3 /dev/hda3
480 [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
481 version of mkfs]
483 Next, mount the file system(s) e.g.:
484 mkdir /mnt/root && mount /dev/hda3 /mnt/root
485 [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
487 To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
488 cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
490 You'll need to edit /mnt/root/etc/fstab to reflect your file system
491 configuration. Changing the password file (etc/shadow) is probably a
492 good idea too.
494 To install the usr file system, copy the file system from CD on /usr,
495 though leaving out the "XenDemoCD" and "boot" directories:
496 cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr
498 If you intend to boot off these file systems (i.e. use them for
499 domain 0), then you probably want to copy the /usr/boot directory on
500 the cd over the top of the current symlink to /boot on your root
501 filesystem (after deleting the current symlink) i.e.:
502 cd /mnt/root ; rm boot ; cp -a /usr/boot .
504 The XenDemoCD directory is only useful if you want to build your own
505 version of the XenDemoCD (see below).
508 Debugging
509 =========
511 Xen has a set of debugging features that can be useful to try and
512 figure out what's going on. Hit 'h' on the serial line (if you
513 specified a baud rate on the Xen command line) or ScrollLock-h on the
514 keyboard to get a list of supported commands.
516 If you have a crash you'll likely get a crash dump containing an EIP
517 (PC) which, along with an 'objdump -d image', can be useful in
518 figuring out what's happened. Debug a XenoLinux image just as you
519 would any other Linux kernel.
521 We supply a handy debug terminal program which you can find in
522 /usr/local/src/xen-1.0/xeno-1.0.bk/tools/misc/miniterm/
523 This should be built and executed on another machine that is connected
524 via a null modem cable. Documentation is included.
525 Alternatively, if the Xen machine is connected to a serial-port server
526 then we supply a dumb TCP terminal client:
527 'tools/xenctl/lib/console_client.py <server host> <server port>'
530 Installing Xen / XenoLinux on a RedHat distribution
531 ===================================================
533 When using Xen / Xenolinux on a standard Linux distribution there are
534 a couple of things to watch out for:
536 The first Linux VM that is started when Xen boots start (Domain 0) is
537 given direct access to the graphics card, so it may use it as a
538 console. Other domains don't have ttyN consoles, so attempts to run a
539 'mingetty' against them will fail, generating periodic warning
540 messages from 'init' about services respawning too fast. They should
541 work for domain0 just fine.
542 IMPORTANT: To prevent warning messages when running RH9 you'll need to
543 remove ttyN from /etc/inittab for domains>0. Due to a bug in the RH9
544 /etc/rc.sysinit script #'ing the lines out of /etc/inittab won't work
545 as it ignores the '#' and tries to access them anyway.
547 Every Xenolinux instance owns a bidirectional 'virtual
548 console'. Boot-time output can be directed to this console by
549 specifying 'console=xencons0' as a boot parameter. It is also possible
550 to log in via the virtual console. To do this, you must run a mingetty
551 on the virtual console, which you can achieve as follows:
552 # mkdir -p /dev/xen
553 # mknod /dev/xen/cons c 4 123
554 # echo "c:2345:respawn:/sbin/mingetty --noclear xen/cons" >>/etc/inittab
555 If you wish to permit root logins via the virtual console then you must
556 also add 'xen/cons' to the list of trusted ttys in /etc/securetty.
558 Note that, because domains>0 don't have any privileged access at all,
559 certain commands in the default boot sequence will fail e.g. attempts
560 to update the hwclock, change the console font, update the keytable
561 map, start apmd (power management), or gpm (mouse cursor). Either
562 ignore the errors, or remove them from the startup scripts. Deleting
563 the following links are a good start: S24pcmcia S09isdn S17keytable
564 S26apmd S85gpm
566 If you want to use a single root file system that works cleanly for
567 domain0 and domains>0, one trick is to use different 'init' run
568 levels. For example, on the Xen Demo CD we use run level 3 for domain
569 0, and run level 4 for domains>0. This enables different startup
570 scripts to be run in depending on the run level number passed on the
571 kernel command line.
573 Xenolinux kernels can be built to use runtime loadable modules just
574 like normal linux kernels. Modules should be installed under
575 /lib/modules in the normal way.
577 If there's some kernel feature that hasn't been built into our default
578 kernel, there's a pretty good change that if its a non-hardware
579 related option you'll just be able to enable it and rebuild. If its
580 not on the xconfig menu, hack the arch/xen/config.in to put the menu
581 back in.
583 If you're going to use the link local 169.254.1.x addresses to
584 communicate between VMs, there are a couple of other issues to watch
585 out for. RH9 appears to have a bug where by default it configures the
586 loopback interface with a 169.254 address, which stops it working
587 properly on eth0 for communicating with other domains.
589 This utterly daft RH9 behaviour can be stopped by appending
590 "NOZEROCONF=yes" to /etc/sysconfig/networking-scripts/ifcfg-lo
592 If you're going to use NFS root files systems mounted either from an
593 external server or from domain0 there are a couple of other gotchas.
594 The default /etc/sysconfig/iptables rules block NFS, so part way
595 through the boot sequence things will suddenly go dead.
597 If you're planning on having a separate NFS /usr partition, the RH9
598 boot scripts don't make life easy, as they attempt to mount NFS file
599 systems way to late in the boot process. The easiest way I found to do
600 this was to have a '/linuxrc' script run ahead of /sbin/init that
601 mounts /usr:
602 #!/bin/bash
603 /sbin/ipconfig lo
604 /sbin/portmap
605 /bin/mount /usr
606 exec /sbin/init "$@" <>/dev/console 2>&1
608 The one slight complication with the above is that /sbib/portmap is
609 dynamically linked against /usr/lib/libwrap.so.0 Since this is in
610 /usr, it won't work. I solved this by copying the file (and link)
611 below the /usr mount point, and just let the file be 'covered' when
612 the mount happens.
614 In some installations, where a shared read-only /usr is being used, it
615 may be desirable to move other large directories over into the
616 read-only /usr. For example, on the XenDemoCD we replace /bin /lib and
617 /sbin with links into /usr/root/bin /usr/root/lib and /usr/root/sbin
618 respectively. This creates other problems for running the /linuxrc
619 script, requiring bash, portmap, mount, ifconfig, and a handful of
620 other shared libraries to be copied below the mount point. I guess I
621 should have written a little statically linked C program...
625 Description of how the XenDemoCD boots
626 ======================================
628 1. Grub is used to load Xen, a XenoLinux kernel, and an initrd (initial
629 ram disk). [The source of the version of Grub used is in /usr/local/src]
631 2. the init=/linuxrc command line causes linux to execute /linuxrc in
632 the initrd.
634 3. the /linuxrc file attempts to mount the CD by trying the likely
635 locations : /dev/hd[abcd].
637 4. it then creates a 'tmpfs' file system and untars the
638 'XenDemoCD/root.tar.gz' file into the tmpfs. This contains hopefully
639 all the files that need to be mutable (this would be so much easier
640 if Linux supported 'stacked' or union file systems...)
642 5. Next, /linuxrc uses the pivot_root call to change the root file
643 system to the tmpfs, with the CD mounted as /usr.
645 6. It then invokes /sbin/init in the tmpfs and the boot proceeds
646 normally.
649 Building your own version of the XenDemoCD
650 ==========================================
652 The 'live ISO' version of RedHat is based heavily on Peter Anvin's
653 SuperRescue CD version 2.1.2 and J. McDaniel's Plan-B:
655 http://www.kernel.org/pub/dist/superrescue/v2/
656 http://projectplanb.org/
658 Since Xen uses a "multiboot" image format, it was necessary to change
659 the bootloader from isolinux to Grub0.93 with Leonid Lisovskiy's
660 <lly@pisem.net> grub.0.93-iso9660.patch
662 The Xen Demo CD contains all of the build scripts that were used to
663 create it, so it is possible to 'unpack' the current iso, modifiy it,
664 then build a new iso. The procedure for doing so is as follows:
666 First, mount either the CD, or the iso image of the CD:
668 mount /dev/cdrom /mnt/cdrom
669 or:
670 mount -o loop xendemo-1.0.iso /mnt/cdrom
672 cd to the directory you want to 'unpack' the iso into then run the
673 unpack script:
675 cd /local/xendemocd
676 /mnt/cdrom/XenDemoCD/unpack-iso.sh
678 The result is a 'build' directory containing the file system tree
679 under the 'root' directory. e.g. /local/xendemocd/build/root
681 To add or remove rpms, its possible to use 'rpm' with the --root
682 option to set the path. For more complex changes, it easiest to boot a
683 machine using using the tree via NFS root. Before doing this, you'll
684 need to edit fstab to comment out the seperate mount of /usr.
686 One thing to watch out for: as part of the CD build process, the
687 contents of the 'rootpatch' tree gets copied over the existing 'root'
688 tree replacing various files. The intention of the rootpatch tree is
689 to contain the files that have been modified from the original RH
690 distribution (e.g. various /etc files). This was done to make it
691 easier to upgrade to newer RH versions in the future. The downside of
692 this is that if you edit an existing file in the root tree you should
693 check that you don't also need to propagate the change to the
694 rootpatch tree to avoid it being overwritten.
696 Once you've made the changes and want to build a new iso, here's the
697 procedure:
699 cd /local/xendemocd/build
700 echo '<put_your_name_here>' > Builder
701 ./make.sh put_your_version_id_here >../buildlog 2>&1
703 This process can take 30 mins even on a fast machine, but you should
704 eventually end up with an iso image in the build directory.
706 Notes:
708 root - the root of the file system heirarchy as presented to the
709 running system
711 rootpatch - contains files that have been modified from the standard
712 RH, and copied over the root tree as part of the build
713 procedure.
715 irtree - the file system tree that will go into the initrd (initial
716 ram disk)
718 work - a working directory used in the build process
720 usr - this should really be in 'work' as its created as part of the
721 build process. It contains the 'immutable' files that will
722 be served from the CD rather than the tmpfs containing the
723 contents of root.tar.gz. Some files that are normally in /etc
724 or /var that are large and actually unlikely to need changing
725 have been moved into /usr/root and replaced with links.
728 Ian Pratt
729 9 Sep 2003