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author kaf24@scramble.cl.cam.ac.uk
date Thu Mar 18 15:57:28 2004 +0000 (2004-03-18)
parents 0c707d7680c9
children 5f1ec88d7c3a
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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 xend.console_client: running this module from the
207 command line with <host> and <port> parameters will start a terminal
208 session. An alternative is to specify '-c' to xc_dom_create.py, or add
209 'auto_console=True' to the defaults file. This will cause
210 xc_dom_create.py to automatically become teh console terminal after
211 starting the domain.
213 The 169.254.x.x network is special in that it is the 'link local'
214 subnet, and is isolated from the external network and hence can only
215 be used for communication between virtual machines. By convention, we
216 usually give each domain a link local address. The startup scripts on
217 the CD have been modified to accept a LINKLOCAL= parameter on the
218 kernel command line and initialise an IP alias accordingly (see
219 /etc/sysinit/network-scripts/ifcfg-eth0).
221 Linux only allows one IP address to be specified on the kernel command
222 line, so if you specify multiple IP addresses you'll need to configure
223 the new Linux VM with the other addresses manually (using ifconfig)
224 having logged in.
226 If you inspect the 'defaults' config script you'll see that the new
227 domain was started with a '4' on the kernel command line to tell
228 'init' to go to runlevel 4 rather than the default of 3 used by
229 domain0. This is done simply to suppress a bunch of harmless error
230 messages that would otherwise occur when the new (unprivileged) domain
231 tried to access physical hardware resources to try setting the
232 hwclock, system font, run gpm etc.
234 After it's booted, you should be able to ssh into your new domain from
235 domain0 using the link local 19.254.x.x address you assigned. If you
236 assigned a further IP address you should be able to ssh in using that
237 address too. If you ran the xen_enable_nat script, a bunch of port
238 redirects have been installed to enable you to ssh in to other domains
239 remotely even if you didn't assign an externally routeable address.
240 To access the new virtual machine remotely, use:
242 ssh -p2201 root@IP.address.Of.Domain0 # use 2202 for domain 2 etc.
244 You can manipulate running domains using the xc_dom_control.py tool.
245 Invoking it without arguments prints some usage information.
247 To see what domains are running, run 'xc_dom_control.py list'. Using the
248 tool you can change scheduling parameters, pause a domain, send it a
249 shutdown request, or blow it away with the 'destroy' command. You can
250 even suspend it to disk (but you probably won't have enough memory to
251 do the latter if you're running off the demo CD).
253 To find usage information for xc_dom_control.py, run the script with
254 no arguments.
257 Troubleshooting Problems
258 ========================
260 If you have problems booting Xen, there are a number of boot parameters
261 that may be able to help diagnose problems:
263 ignorebiostables Disable parsing of BIOS-supplied tables. This may
264 help with some chipsets that aren't fully supported
265 by Xen. If you specify this option then ACPI tables are
266 also ignored, and SMP support is disabled.
268 noreboot Don't reboot the machine automatically on errors.
269 This is useful to catch debug output if you aren't
270 catching console messages via the serial line.
272 nosmp Disable SMP support.
273 This option is implied by 'ignorebiostables'.
275 noacpi Disable ACPI tables, which confuse Xen on some chipsets.
276 This option is implied by 'ignorebiostables'.
278 watchdog Enable NMI watchdog which can report certain failures.
280 noht Disable Hyperthreading.
282 ifname=ethXX Select which Ethernet interface to use.
284 ifname=dummy Don't use any network interface.
286 com1=<baud>,DPS[,<io_base>,<irq>]
287 com2=<baud>,DPS[,<io_base>,<irq>]
288 Xen supports up to two 16550-compatible serial ports.
289 For example: 'com1=9600,8n1,0x408,5' maps COM1 to a
290 9600-baud port, 8 data bits, no parity, 1 stop bit,
291 I/O port base 0x408, IRQ 5.
292 If the I/O base and IRQ are standard (com1:0x3f8,4;
293 com2:0x2f8,3) then they need not be specified.
295 console=<specifier list>
296 Specify the destination for Xen console I/O.
297 This is a comma-separated list of, for example:
298 vga: use VGA console and allow keyboard input
299 com1: use serial port com1
300 com2H: use serial port com2. Transmitted chars will
301 have the MSB set. Received chars must have
302 MSB set.
303 com2L: use serial port com2. Transmitted chars will
304 have the MSB cleared. Received chars must
305 have MSB cleared.
306 The latter two examples allow a single port to be
307 shared by two subsystems (eg. console and
308 debugger). Sharing is controlled by MSB of each
309 transmitted/received character.
310 [NB. Default for this option is 'com1,tty']
312 dom0_mem=xxx Set the initial amount of memory for domain0.
314 pdb=xxx Enable the pervasive debugger. See docs/pdb.txt
315 xxx defines how the gdb stub will communicate:
316 com1 use com1
317 com1H use com1 (with high bit set)
318 com2 use on com2
319 com2H use com2 (with high bit set)
321 It's probably a good idea to join the Xen developer's mailing list on
322 Sourceforge: http://lists.sourceforge.net/lists/listinfo/xen-devel
325 About The Xen Demo CD
326 =====================
328 The purpose of the Demo CD is to distribute a snapshot of Xen's
329 source, and simultaneously provide a convenient means for enabling
330 people to get experience playing with Xen without needing to install
331 it on their hard drive. If you decide to install Xen/XenoLinux you can
332 do so simply by following the installation instructions below -- which
333 essentially involves copying the contents of the CD on to a suitably
334 formated disk partition, and then installing or updating the Grub
335 bootloader.
337 This is a bootable CD that loads Xen, and then a Linux 2.4.22 OS image
338 ported to run on Xen. The CD contains a copy of a file system based on
339 the RedHat 9 distribution that is able to run directly off the CD
340 ("live ISO"), using a "tmpfs" RAM-based file system for root (/etc
341 /var etc). Changes you make to the tmpfs will obviously not be
342 persistent across reboots!
344 Because of the use of a RAM-based file system for root, you'll need
345 plenty of memory to run this CD -- something like 96MB per VM. This is
346 not a restriction of Xen : once you've installed Xen, XenoLinux and
347 the file system images on your hard drive you'll find you can boot VMs
348 in just a few MBs.
350 The CD contains a snapshot of the Xen and XenoLinux code base that we
351 believe to be pretty stable, but lacks some of the features that are
352 currently still work in progress e.g. OS suspend/resume to disk, and
353 various memory management enhancements to provide fast inter-OS
354 communication and sharing of memory pages between OSs. We'll release
355 newer snapshots as required, making use of a BitKeeper repository
356 hosted on http://xen.bkbits.net (follow instructions from the project
357 home page). We're obviously grateful to receive any bug fixes or
358 other code you can contribute. We suggest you join the
359 xen-devel@lists.sourceforge.net mailing list.
362 Installing from the CD
363 ======================
365 If you're installing Xen/XenoLinux onto an existing linux file system
366 distribution, just copy the Xen VMM (/boot/image.gz) and XenoLinux
367 kernels (/boot/xenolinux.gz), then modify the Grub config
368 (/boot/grub/menu.lst or /boot/grub/grub.conf) on the target system.
369 It should work on pretty much any distribution.
371 Xen is a "multiboot" standard boot image. Despite being a 'standard',
372 few boot loaders actually support it. The only two we know of are
373 Grub, and our modified version of linux kexec (for booting off a
374 XenoBoot CD -- PlanetLab have adopted the same boot CD approach).
376 If you need to install grub on your system, you can do so either by
377 building the Grub source tree
378 /usr/local/src/grub-0.93-iso9660-splashimage or by copying over all
379 the files in /boot/grub and then running /sbin/grub and following the
380 usual grub documentation. You'll then need to edit the Grub
381 config file.
383 A typical Grub menu option might look like:
385 title Xen / XenoLinux 2.4.22
386 kernel /boot/image.gz dom0_mem=131072 com1=115200,8n1 noht
387 module /boot/xenolinux.gz root=/dev/sda4 ro console=tty0
389 The first line specifies which Xen image to use, and what command line
390 arguments to pass to Xen. In this case we set the maximum amount of
391 memory to allocate to domain0, and enable serial I/O at 9600 baud.
392 We could also disable smp support (nosmp) or disable hyper-threading
393 support (noht). If you have multiple network interface you can use
394 ifname=ethXX to select which one to use. If your network card is
395 unsupported, use ifname=dummy
397 The second line specifies which xenolinux image to use, and the
398 standard linux command line arguments to pass to the kernel. In this
399 case, we're configuring the root partition and stating that it should
400 initially be mounted read-only (normal practice).
402 If we were booting with an initial ram disk (initrd), then this would
403 require a second "module" line.
405 Installing the Xen tools and source
406 ===================================
408 The tools and source live in the /usr/local/src/xen-1.2 directory on
409 the CD (and may also be downloaded from the project downloads
410 page). You'll need to copy them to some mutable storage before using
411 them.
413 If you have the BitKeeper BK tools installed you can check the
414 repository is up to date by cd'ing into the xeno-1.2.bk directory and
415 typing 'bk pull' (assuming you have an Internet connection).
417 You can rebuild Xen and the tools by typing 'make'. You can install
418 them to the standard directories with 'make install', or into the
419 ../install subtree with 'make dist'.
421 If you're using the virtual disk control tools (xc_vd_tool) you'll
422 need the SQLite library and python binding pysqlite. There's a tar
423 ball containing the necessary binaries on the project downloads page.
426 Modifying xc_mycreatelinuxdom1.py
427 =================================
429 xc_mycreatelinuxdom1.py.py can be used to set the new kernel's command line,
430 and hence determine what it uses as a root file system, etc. Although
431 the default is to boot in the same manner that domain0 did (using the
432 RAM-based file system for root and the CD for /usr) it's possible to
433 configure any of the following possibilities, for example:
435 * initrd=/boot/initrd init=/linuxrc
436 boot using an initial ram disk, executing /linuxrc (as per this CD)
438 * root=/dev/hda3 ro
439 boot using a standard hard disk partition as root
440 !!! remember to grant access in createlinuxdom.py.
442 * root=/dev/xvda1 ro
443 boot using a pre-configured 'virtual block device' that will be
444 attached to a virtual disk that previously has had a file system
445 installed on it.
447 * root=/dev/nfs nfsroot=/path/on/server ip=<blah_including server_IP>
448 Boot using an NFS mounted root file system. This could be from a
449 remote NFS server, or from an NFS server running in another
450 domain. The latter is rather a useful option.
452 A typical setup might be to allocate a standard disk partition for
453 each domain and populate it with files. To save space, having a shared
454 read-only usr partition might make sense.
456 Block devices should only be shared between domains in a read-only
457 fashion otherwise the linux kernels will obviously get very confused
458 as the file system structure may change underneath them (having the
459 same partition mounted rw twice is a sure fire way to cause
460 irreparable damage)! If you want read-write sharing, export the
461 directory to other domains via NFS from domain0.
466 Installing the file systems from the CD
467 =======================================
469 If you haven't got an existing Linux installation onto which you can
470 just drop down the Xen and XenoLinux images, then the file systems on
471 the CD provide a quick way of doing an install. However, you're
472 probably better off in the long run doing a proper Redhat, Fedora,
473 Debian etc install rather than just doing the hack described below:
475 Choose one or two partitions, depending on whether you want a separate
476 /usr or not. Make file systems on it/them e.g.:
477 mkfs -t ext3 /dev/hda3
478 [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
479 version of mkfs]
481 Next, mount the file system(s) e.g.:
482 mkdir /mnt/root && mount /dev/hda3 /mnt/root
483 [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
485 To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
486 cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
488 You'll need to edit /mnt/root/etc/fstab to reflect your file system
489 configuration. Changing the password file (etc/shadow) is probably a
490 good idea too.
492 To install the usr file system, copy the file system from CD on /usr,
493 though leaving out the "XenDemoCD" and "boot" directories:
494 cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr
496 If you intend to boot off these file systems (i.e. use them for
497 domain 0), then you probably want to copy the /usr/boot directory on
498 the cd over the top of the current symlink to /boot on your root
499 filesystem (after deleting the current symlink) i.e.:
500 cd /mnt/root ; rm boot ; cp -a /usr/boot .
502 The XenDemoCD directory is only useful if you want to build your own
503 version of the XenDemoCD (see below).
506 Debugging
507 =========
509 Xen has a set of debugging features that can be useful to try and
510 figure out what's going on. Hit 'h' on the serial line (if you
511 specified a baud rate on the Xen command line) or ScrollLock-h on the
512 keyboard to get a list of supported commands.
514 If you have a crash you'll likely get a crash dump containing an EIP
515 (PC) which, along with an 'objdump -d image', can be useful in
516 figuring out what's happened. Debug a XenoLinux image just as you
517 would any other Linux kernel.
519 We supply a handy debug terminal program which you can find in
520 /usr/local/src/xen-1.0/xeno-1.0.bk/tools/misc/miniterm/
521 This should be built and executed on another machine that is connected
522 via a null modem cable. Documentation is included.
523 Alternatively, if the Xen machine is connected to a serial-port server
524 then we supply a dumb TCP terminal client:
525 'tools/xenctl/lib/console_client.py <server host> <server port>'
528 Installing Xen / XenoLinux on a RedHat distribution
529 ===================================================
531 When using Xen / Xenolinux on a standard Linux distribution there are
532 a couple of things to watch out for:
534 The first Linux VM that is started when Xen boots start (Domain 0) is
535 given direct access to the graphics card, so it may use it as a
536 console. Other domains don't have ttyN consoles, so attempts to run a
537 'mingetty' against them will fail, generating periodic warning
538 messages from 'init' about services respawning too fast. They should
539 work for domain0 just fine.
541 In future, we may make the current 'xencons' accept input as well as
542 output, so that a getty can be run against it. In the meantime, other
543 domains don't have a console suitable for logging in on, so you'll
544 have to run sshd and ssh in to them.
546 To prevent the warning messages you'll need to remove them from
547 /etc/inittab for domains>0. Due to a bug in the RH9 /etc/rc.sysinit
548 script #'ing the lines out of /etc/inittab won't work as it ignores
549 the '#' and tries to access them anyway.
551 Also, because domains>0 don't have any privileged access at all,
552 certain commands in the default boot sequence will fail e.g. attempts
553 to update the hwclock, change the console font, update the keytable
554 map, start apmd (power management), or gpm (mouse cursor). Either
555 ignore the errors, or remove them from the startup scripts. Deleting
556 the following links are a good start: S24pcmcia S09isdn S17keytable
557 S26apmd S85gpm
559 If you want to use a single root file system that works cleanly for
560 domain0 and domains>0, one trick is to use different 'init' run
561 levels. For example, on the Xen Demo CD we use run level 3 for domain
562 0, and run level 4 for domains>0. This enables different startup
563 scripts to be run in depending on the run level number passed on the
564 kernel command line.
566 Xenolinux kernels can be built to use runtime loadable modules just
567 like normal linux kernels. Modules should be installed under
568 /lib/modules in the normal way.
570 If there's some kernel feature that hasn't been built into our default
571 kernel, there's a pretty good change that if its a non-hardware
572 related option you'll just be able to enable it and rebuild. If its
573 not on the xconfig menu, hack the arch/xeno/config.in to put the menu
574 back in.
576 If you're going to use the link local 169.254.1.x addresses to
577 communicate between VMs, there are a couple of other issues to watch
578 out for. RH9 appears to have a bug where by default it configures the
579 loopback interface with a 169.254 address, which stops it working
580 properly on eth0 for communicating with other domains.
582 This utterly daft RH9 behaviour can be stopped by appending
583 "NOZEROCONF=yes" to /etc/sysconfig/networking-scripts/ifcfg-lo
585 If you're going to use NFS root files systems mounted either from an
586 external server or from domain0 there are a couple of other gotchas.
587 The default /etc/sysconfig/iptables rules block NFS, so part way
588 through the boot sequence things will suddenly go dead.
590 If you're planning on having a separate NFS /usr partition, the RH9
591 boot scripts don't make life easy, as they attempt to mount NFS file
592 systems way to late in the boot process. The easiest way I found to do
593 this was to have a '/linuxrc' script run ahead of /sbin/init that
594 mounts /usr:
595 #!/bin/bash
596 /sbin/ipconfig lo
597 /sbin/portmap
598 /bin/mount /usr
599 exec /sbin/init "$@" <>/dev/console 2>&1
601 The one slight complication with the above is that /sbib/portmap is
602 dynamically linked against /usr/lib/libwrap.so.0 Since this is in
603 /usr, it won't work. I solved this by copying the file (and link)
604 below the /usr mount point, and just let the file be 'covered' when
605 the mount happens.
607 In some installations, where a shared read-only /usr is being used, it
608 may be desirable to move other large directories over into the
609 read-only /usr. For example, on the XenDemoCD we replace /bin /lib and
610 /sbin with links into /usr/root/bin /usr/root/lib and /usr/root/sbin
611 respectively. This creates other problems for running the /linuxrc
612 script, requiring bash, portmap, mount, ifconfig, and a handful of
613 other shared libraries to be copied below the mount point. I guess I
614 should have written a little statically linked C program...
618 Description of how the XenDemoCD boots
619 ======================================
621 1. Grub is used to load Xen, a XenoLinux kernel, and an initrd (initial
622 ram disk). [The source of the version of Grub used is in /usr/local/src]
624 2. the init=/linuxrc command line causes linux to execute /linuxrc in
625 the initrd.
627 3. the /linuxrc file attempts to mount the CD by trying the likely
628 locations : /dev/hd[abcd].
630 4. it then creates a 'tmpfs' file system and untars the
631 'XenDemoCD/root.tar.gz' file into the tmpfs. This contains hopefully
632 all the files that need to be mutable (this would be so much easier
633 if Linux supported 'stacked' or union file systems...)
635 5. Next, /linuxrc uses the pivot_root call to change the root file
636 system to the tmpfs, with the CD mounted as /usr.
638 6. It then invokes /sbin/init in the tmpfs and the boot proceeds
639 normally.
642 Building your own version of the XenDemoCD
643 ==========================================
645 The 'live ISO' version of RedHat is based heavily on Peter Anvin's
646 SuperRescue CD version 2.1.2 and J. McDaniel's Plan-B:
648 http://www.kernel.org/pub/dist/superrescue/v2/
649 http://projectplanb.org/
651 Since Xen uses a "multiboot" image format, it was necessary to change
652 the bootloader from isolinux to Grub0.93 with Leonid Lisovskiy's
653 <lly@pisem.net> grub.0.93-iso9660.patch
655 The Xen Demo CD contains all of the build scripts that were used to
656 create it, so it is possible to 'unpack' the current iso, modifiy it,
657 then build a new iso. The procedure for doing so is as follows:
659 First, mount either the CD, or the iso image of the CD:
661 mount /dev/cdrom /mnt/cdrom
662 or:
663 mount -o loop xendemo-1.0.iso /mnt/cdrom
665 cd to the directory you want to 'unpack' the iso into then run the
666 unpack script:
668 cd /local/xendemocd
669 /mnt/cdrom/XenDemoCD/unpack-iso.sh
671 The result is a 'build' directory containing the file system tree
672 under the 'root' directory. e.g. /local/xendemocd/build/root
674 To add or remove rpms, its possible to use 'rpm' with the --root
675 option to set the path. For more complex changes, it easiest to boot a
676 machine using using the tree via NFS root. Before doing this, you'll
677 need to edit fstab to comment out the seperate mount of /usr.
679 One thing to watch out for: as part of the CD build process, the
680 contents of the 'rootpatch' tree gets copied over the existing 'root'
681 tree replacing various files. The intention of the rootpatch tree is
682 to contain the files that have been modified from the original RH
683 distribution (e.g. various /etc files). This was done to make it
684 easier to upgrade to newer RH versions in the future. The downside of
685 this is that if you edit an existing file in the root tree you should
686 check that you don't also need to propagate the change to the
687 rootpatch tree to avoid it being overwritten.
689 Once you've made the changes and want to build a new iso, here's the
690 procedure:
692 cd /local/xendemocd/build
693 echo '<put_your_name_here>' > Builder
694 ./make.sh put_your_version_id_here >../buildlog 2>&1
696 This process can take 30 mins even on a fast machine, but you should
697 eventually end up with an iso image in the build directory.
699 Notes:
701 root - the root of the file system heirarchy as presented to the
702 running system
704 rootpatch - contains files that have been modified from the standard
705 RH, and copied over the root tree as part of the build
706 procedure.
708 irtree - the file system tree that will go into the initrd (initial
709 ram disk)
711 work - a working directory used in the build process
713 usr - this should really be in 'work' as its created as part of the
714 build process. It contains the 'immutable' files that will
715 be served from the CD rather than the tmpfs containing the
716 contents of root.tar.gz. Some files that are normally in /etc
717 or /var that are large and actually unlikely to need changing
718 have been moved into /usr/root and replaced with links.
721 Ian Pratt
722 9 Sep 2003