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date Tue Jun 22 08:54:26 2004 +0000 (2004-06-22)
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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 (Xenlinux). 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/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-2.4.26
55 Xen / linux-2.4.26 using cmdline IP configuration
56 Xen / linux-2.4.26 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/xeno-1.3, 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 xc_dom_create.py 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 xc_dom_create.py -Dip=, -Dmem=72
182 [multiple variables may also be set with a single '-D' flag by
183 separating them with ':'. Also, it's possible to use DNS hostnames
184 rather than IP addresses.]
186 When invoked with the '-n' option xc_dom_create.py will do a dry run
187 and just print out what resources and configuration the domain will
188 have e.g.:
190 [root@xendemo]# xc_dom_create.py -D ip=commando-1.xeno, -Dmem=100
191 Parsing config file 'defaults'
193 VM image : "/boot/xenlinux.gz"
194 VM ramdisk : "/boot/initrd.gz"
195 VM memory (MB) : "100"
196 VM IP address(es) : ""
197 VM block device(s) : "phy:cdrom,hdd,r"
198 VM cmdline : "ip= root=/dev/ram0 rw init=/linuxrc 4 LOCALIP="
200 xc_dom_create.py will print the local TCP port to which you should
201 connect to perform console I/O. A suitable console client is provided
202 by the Python module xenctl.console_client: running this module from
203 the command line with <host> and <port> parameters will start a
204 terminal session. This module is also installed as /usr/bin/xencons,
205 from a copy in tools/misc/xencons. An alternative to manually running
206 a terminal client is to specify '-c' to xc_dom_create.py, or add
207 'auto_console=True' to the defaults file. This will cause
208 xc_dom_create.py to automatically become the console terminal after
209 starting the domain.
211 The 169.254.x.x network is special in that it is the 'link local'
212 subnet, and is isolated from the external network and hence can only
213 be used for communication between virtual machines. By convention, we
214 usually give each domain a link local address. The startup scripts on
215 the CD have been modified to accept a LINKLOCAL= parameter on the
216 kernel command line and initialise an IP alias accordingly (see
217 /etc/sysinit/network-scripts/ifcfg-eth0).
219 Linux only allows one IP address to be specified on the kernel command
220 line, so if you specify multiple IP addresses you'll need to configure
221 the new Linux VM with the other addresses manually (using ifconfig)
222 having logged in.
224 If you inspect the 'defaults' config script you'll see that the new
225 domain was started with a '4' on the kernel command line to tell
226 'init' to go to runlevel 4 rather than the default of 3 used by
227 domain0. This is done simply to suppress a bunch of harmless error
228 messages that would otherwise occur when the new (unprivileged) domain
229 tried to access physical hardware resources to try setting the
230 hwclock, system font, run gpm etc.
232 After it's booted, you should be able to ssh into your new domain from
233 domain0 using the link local 19.254.x.x address you assigned. If you
234 assigned a further IP address you should be able to ssh in using that
235 address too. If you ran the xen_enable_nat script, a bunch of port
236 redirects have been installed to enable you to ssh in to other domains
237 remotely even if you didn't assign an externally routeable address.
238 To access the new virtual machine remotely, use:
240 ssh -p2201 root@IP.address.Of.Domain0 # use 2202 for domain 2 etc.
242 You can manipulate running domains using the xc_dom_control.py tool.
243 Invoking it without arguments prints some usage information.
245 To see what domains are running, run 'xc_dom_control.py list'. Using the
246 tool you can change scheduling parameters, pause a domain, send it a
247 shutdown request, or blow it away with the 'destroy' command. You can
248 even suspend it to disk (but you probably won't have enough memory to
249 do the latter if you're running off the demo CD).
251 To find usage information for xc_dom_control.py, run the script with
252 no arguments.
255 Troubleshooting Problems
256 ========================
258 If you have problems booting Xen, there are a number of boot parameters
259 that may be able to help diagnose problems:
261 ignorebiostables Disable parsing of BIOS-supplied tables. This may
262 help with some chipsets that aren't fully supported
263 by Xen. If you specify this option then ACPI tables are
264 also ignored, and SMP support is disabled.
266 noreboot Don't reboot the machine automatically on errors.
267 This is useful to catch debug output if you aren't
268 catching console messages via the serial line.
270 nosmp Disable SMP support.
271 This option is implied by 'ignorebiostables'.
273 noacpi Disable ACPI tables, which confuse Xen on some chipsets.
274 This option is implied by 'ignorebiostables'.
276 watchdog Enable NMI watchdog which can report certain failures.
278 noht Disable Hyperthreading.
280 ifname=ethXX Select which Ethernet interface to use.
282 ifname=dummy Don't use any network interface.
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,tty']
310 dom0_mem=xxx Set the initial amount of memory for domain0.
312 pdb=xxx Enable the pervasive debugger. See docs/pdb.txt
313 xxx defines how the gdb stub will communicate:
314 com1 use com1
315 com1H use com1 (with high bit set)
316 com2 use on com2
317 com2H use com2 (with high bit set)
319 It's probably a good idea to join the Xen developer's mailing list on
320 Sourceforge: http://lists.sourceforge.net/lists/listinfo/xen-devel
323 About The Xen Demo CD
324 =====================
326 The purpose of the Demo CD is to distribute a snapshot of Xen's
327 source, and simultaneously provide a convenient means for enabling
328 people to get experience playing with Xen without needing to install
329 it on their hard drive. If you decide to install Xen/Xenlinux you can
330 do so simply by following the installation instructions below -- which
331 essentially involves copying the contents of the CD on to a suitably
332 formated disk partition, and then installing or updating the Grub
333 bootloader.
335 This is a bootable CD that loads Xen, and then a Linux 2.4.22 OS image
336 ported to run on Xen. The CD contains a copy of a file system based on
337 the RedHat 9 distribution that is able to run directly off the CD
338 ("live ISO"), using a "tmpfs" RAM-based file system for root (/etc
339 /var etc). Changes you make to the tmpfs will obviously not be
340 persistent across reboots!
342 Because of the use of a RAM-based file system for root, you'll need
343 plenty of memory to run this CD -- something like 96MB per VM. This is
344 not a restriction of Xen : once you've installed Xen, Xenlinux and
345 the file system images on your hard drive you'll find you can boot VMs
346 in just a few MBs.
348 The CD contains a snapshot of the Xen and Xenlinux code base that we
349 believe to be pretty stable, but lacks some of the features that are
350 currently still work in progress e.g. OS suspend/resume to disk, and
351 various memory management enhancements to provide fast inter-OS
352 communication and sharing of memory pages between OSs. We'll release
353 newer snapshots as required, making use of a BitKeeper repository
354 hosted on http://xen.bkbits.net (follow instructions from the project
355 home page). We're obviously grateful to receive any bug fixes or
356 other code you can contribute. We suggest you join the
357 xen-devel@lists.sourceforge.net mailing list.
360 Installing from the CD
361 ======================
363 If you're installing Xen/Xenlinux onto an existing linux file system
364 distribution, just copy the Xen VMM (/boot/image.gz) and Xenlinux
365 kernels (/boot/xenlinux.gz), then modify the Grub config
366 (/boot/grub/menu.lst or /boot/grub/grub.conf) on the target system.
367 It should work on pretty much any distribution.
369 Xen is a "multiboot" standard boot image. Despite being a 'standard',
370 few boot loaders actually support it. The only two we know of are
371 Grub, and our modified version of linux kexec (for booting off a
372 XenoBoot CD -- PlanetLab have adopted the same boot CD approach).
374 If you need to install grub on your system, you can do so either by
375 building the Grub source tree
376 /usr/local/src/grub-0.93-iso9660-splashimage or by copying over all
377 the files in /boot/grub and then running /sbin/grub and following the
378 usual grub documentation. You'll then need to edit the Grub
379 config file.
381 A typical Grub menu option might look like:
383 title Xen / Xenlinux 2.4.22
384 kernel /boot/image.gz dom0_mem=131072 com1=115200,8n1 noht
385 module /boot/xenlinux.gz root=/dev/sda4 ro console=tty0
387 The first line specifies which Xen image to use, and what command line
388 arguments to pass to Xen. In this case we set the maximum amount of
389 memory to allocate to domain0, and enable serial I/O at 9600 baud.
390 We could also disable smp support (nosmp) or disable hyper-threading
391 support (noht). If you have multiple network interface you can use
392 ifname=ethXX to select which one to use. If your network card is
393 unsupported, use ifname=dummy
395 The second line specifies which xenlinux image to use, and the
396 standard linux command line arguments to pass to the kernel. In this
397 case, we're configuring the root partition and stating that it should
398 initially be mounted read-only (normal practice).
400 If we were booting with an initial ram disk (initrd), then this would
401 require a second "module" line.
403 Installing the Xen tools and source
404 ===================================
406 The tools and source live in the /usr/local/src/xen-1.2 directory on
407 the CD (and may also be downloaded from the project downloads
408 page). You'll need to copy them to some mutable storage before using
409 them.
411 If you have the BitKeeper BK tools installed you can check the
412 repository is up to date by cd'ing into the xeno-1.2.bk directory and
413 typing 'bk pull' (assuming you have an Internet connection).
415 You can rebuild Xen and the tools by typing 'make'. You can install
416 them to the standard directories with 'make install', or into the
417 ../install subtree with 'make dist'.
419 If you're using the virtual disk control tools (xc_vd_tool) you'll
420 need the SQLite library and python binding pysqlite. There's a tar
421 ball containing the necessary binaries on the project downloads page.
424 Modifying xc_mycreatelinuxdom1.py
425 =================================
427 xc_mycreatelinuxdom1.py.py can be used to set the new kernel's command line,
428 and hence determine what it uses as a root file system, etc. Although
429 the default is to boot in the same manner that domain0 did (using the
430 RAM-based file system for root and the CD for /usr) it's possible to
431 configure any of the following possibilities, for example:
433 * initrd=/boot/initrd init=/linuxrc
434 boot using an initial ram disk, executing /linuxrc (as per this CD)
436 * root=/dev/hda3 ro
437 boot using a standard hard disk partition as root
438 !!! remember to grant access in createlinuxdom.py.
440 * root=/dev/xvda1 ro
441 boot using a pre-configured 'virtual block device' that will be
442 attached to a virtual disk that previously has had a file system
443 installed on it.
445 * root=/dev/nfs nfsroot=/path/on/server ip=<blah_including server_IP>
446 Boot using an NFS mounted root file system. This could be from a
447 remote NFS server, or from an NFS server running in another
448 domain. The latter is rather a useful option.
450 A typical setup might be to allocate a standard disk partition for
451 each domain and populate it with files. To save space, having a shared
452 read-only usr partition might make sense.
454 Block devices should only be shared between domains in a read-only
455 fashion otherwise the linux kernels will obviously get very confused
456 as the file system structure may change underneath them (having the
457 same partition mounted rw twice is a sure fire way to cause
458 irreparable damage)! If you want read-write sharing, export the
459 directory to other domains via NFS from domain0.
464 Installing the file systems from the CD
465 =======================================
467 If you haven't got an existing Linux installation onto which you can
468 just drop down the Xen and Xenlinux images, then the file systems on
469 the CD provide a quick way of doing an install. However, you're
470 probably better off in the long run doing a proper Redhat, Fedora,
471 Debian etc install rather than just doing the hack described below:
473 Choose one or two partitions, depending on whether you want a separate
474 /usr or not. Make file systems on it/them e.g.:
475 mkfs -t ext3 /dev/hda3
476 [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
477 version of mkfs]
479 Next, mount the file system(s) e.g.:
480 mkdir /mnt/root && mount /dev/hda3 /mnt/root
481 [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
483 To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
484 cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
486 You'll need to edit /mnt/root/etc/fstab to reflect your file system
487 configuration. Changing the password file (etc/shadow) is probably a
488 good idea too.
490 To install the usr file system, copy the file system from CD on /usr,
491 though leaving out the "XenDemoCD" and "boot" directories:
492 cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr
494 If you intend to boot off these file systems (i.e. use them for
495 domain 0), then you probably want to copy the /usr/boot directory on
496 the cd over the top of the current symlink to /boot on your root
497 filesystem (after deleting the current symlink) i.e.:
498 cd /mnt/root ; rm boot ; cp -a /usr/boot .
500 The XenDemoCD directory is only useful if you want to build your own
501 version of the XenDemoCD (see below).
504 Debugging
505 =========
507 Xen has a set of debugging features that can be useful to try and
508 figure out what's going on. Hit 'h' on the serial line (if you
509 specified a baud rate on the Xen command line) or ScrollLock-h on the
510 keyboard to get a list of supported commands.
512 If you have a crash you'll likely get a crash dump containing an EIP
513 (PC) which, along with an 'objdump -d image', can be useful in
514 figuring out what's happened. Debug a Xenlinux image just as you
515 would any other Linux kernel.
517 We supply a handy debug terminal program which you can find in
518 /usr/local/src/xen-1.0/xeno-1.0.bk/tools/misc/miniterm/
519 This should be built and executed on another machine that is connected
520 via a null modem cable. Documentation is included.
521 Alternatively, if the Xen machine is connected to a serial-port server
522 then we supply a dumb TCP terminal client:
523 'tools/xenctl/lib/console_client.py <server host> <server port>'
526 Installing Xen / Xenlinux on a RedHat distribution
527 ===================================================
529 When using Xen / Xenlinux on a standard Linux distribution there are
530 a couple of things to watch out for:
532 The first Linux VM that is started when Xen boots start (Domain 0) is
533 given direct access to the graphics card, so it may use it as a
534 console. Other domains don't have ttyN consoles, so attempts to run a
535 'mingetty' against them will fail, generating periodic warning
536 messages from 'init' about services respawning too fast. They should
537 work for domain0 just fine.
538 IMPORTANT: To prevent warning messages when running RH9 you'll need to
539 remove ttyN from /etc/inittab for domains>0. Due to a bug in the RH9
540 /etc/rc.sysinit script #'ing the lines out of /etc/inittab won't work
541 as it ignores the '#' and tries to access them anyway.
543 Every Xenlinux instance owns a bidirectional 'virtual console'.
544 The device node to which this console is attached can be configured
545 by specifying 'xencons=' on the OS command line:
546 'xencons=off' --> disable virtual console
547 'xencons=tty' --> attach console to /dev/tty1 (tty0 at boot-time)
548 'xencons=ttyS' --> attach console to /dev/ttyS0
549 The default is to attach to /dev/tty1, and also to create dummy
550 devices for /dev/tty2-63 to avoid warnings from many standard distro
551 startup scripts. The exception is domain 0, which by default attaches
552 to /dev/ttyS0.
554 Note that, because domains>0 don't have any privileged access at all,
555 certain commands in the default boot sequence will fail e.g. attempts
556 to update the hwclock, change the console font, update the keytable
557 map, start apmd (power management), or gpm (mouse cursor). Either
558 ignore the errors, or remove them from the startup scripts. Deleting
559 the following links are a good start: S24pcmcia S09isdn S17keytable
560 S26apmd S85gpm
562 If you want to use a single root file system that works cleanly for
563 domain0 and domains>0, one trick is to use different 'init' run
564 levels. For example, on the Xen Demo CD we use run level 3 for domain
565 0, and run level 4 for domains>0. This enables different startup
566 scripts to be run in depending on the run level number passed on the
567 kernel command line.
569 Xenlinux kernels can be built to use runtime loadable modules just
570 like normal linux kernels. Modules should be installed under
571 /lib/modules in the normal way.
573 If there's some kernel feature that hasn't been built into our default
574 kernel, there's a pretty good change that if its a non-hardware
575 related option you'll just be able to enable it and rebuild. If its
576 not on the xconfig menu, hack the arch/xen/config.in to put the menu
577 back in.
579 If you're going to use the link local 169.254.1.x addresses to
580 communicate between VMs, there are a couple of other issues to watch
581 out for. RH9 appears to have a bug where by default it configures the
582 loopback interface with a 169.254 address, which stops it working
583 properly on eth0 for communicating with other domains.
585 This utterly daft RH9 behaviour can be stopped by appending
586 "NOZEROCONF=yes" to /etc/sysconfig/networking-scripts/ifcfg-lo
588 If you're going to use NFS root files systems mounted either from an
589 external server or from domain0 there are a couple of other gotchas.
590 The default /etc/sysconfig/iptables rules block NFS, so part way
591 through the boot sequence things will suddenly go dead.
593 If you're planning on having a separate NFS /usr partition, the RH9
594 boot scripts don't make life easy, as they attempt to mount NFS file
595 systems way to late in the boot process. The easiest way I found to do
596 this was to have a '/linuxrc' script run ahead of /sbin/init that
597 mounts /usr:
598 #!/bin/bash
599 /sbin/ipconfig lo
600 /sbin/portmap
601 /bin/mount /usr
602 exec /sbin/init "$@" <>/dev/console 2>&1
604 The one slight complication with the above is that /sbib/portmap is
605 dynamically linked against /usr/lib/libwrap.so.0 Since this is in
606 /usr, it won't work. I solved this by copying the file (and link)
607 below the /usr mount point, and just let the file be 'covered' when
608 the mount happens.
610 In some installations, where a shared read-only /usr is being used, it
611 may be desirable to move other large directories over into the
612 read-only /usr. For example, on the XenDemoCD we replace /bin /lib and
613 /sbin with links into /usr/root/bin /usr/root/lib and /usr/root/sbin
614 respectively. This creates other problems for running the /linuxrc
615 script, requiring bash, portmap, mount, ifconfig, and a handful of
616 other shared libraries to be copied below the mount point. I guess I
617 should have written a little statically linked C program...
621 Description of how the XenDemoCD boots
622 ======================================
624 1. Grub is used to load Xen, a Xenlinux kernel, and an initrd (initial
625 ram disk). [The source of the version of Grub used is in /usr/local/src]
627 2. the init=/linuxrc command line causes linux to execute /linuxrc in
628 the initrd.
630 3. the /linuxrc file attempts to mount the CD by trying the likely
631 locations : /dev/hd[abcd].
633 4. it then creates a 'tmpfs' file system and untars the
634 'XenDemoCD/root.tar.gz' file into the tmpfs. This contains hopefully
635 all the files that need to be mutable (this would be so much easier
636 if Linux supported 'stacked' or union file systems...)
638 5. Next, /linuxrc uses the pivot_root call to change the root file
639 system to the tmpfs, with the CD mounted as /usr.
641 6. It then invokes /sbin/init in the tmpfs and the boot proceeds
642 normally.
645 Building your own version of the XenDemoCD
646 ==========================================
648 The 'live ISO' version of RedHat is based heavily on Peter Anvin's
649 SuperRescue CD version 2.1.2 and J. McDaniel's Plan-B:
651 http://www.kernel.org/pub/dist/superrescue/v2/
652 http://projectplanb.org/
654 Since Xen uses a "multiboot" image format, it was necessary to change
655 the bootloader from isolinux to Grub0.93 with Leonid Lisovskiy's
656 <lly@pisem.net> grub.0.93-iso9660.patch
658 The Xen Demo CD contains all of the build scripts that were used to
659 create it, so it is possible to 'unpack' the current iso, modifiy it,
660 then build a new iso. The procedure for doing so is as follows:
662 First, mount either the CD, or the iso image of the CD:
664 mount /dev/cdrom /mnt/cdrom
665 or:
666 mount -o loop xendemo-1.0.iso /mnt/cdrom
668 cd to the directory you want to 'unpack' the iso into then run the
669 unpack script:
671 cd /local/xendemocd
672 /mnt/cdrom/XenDemoCD/unpack-iso.sh
674 The result is a 'build' directory containing the file system tree
675 under the 'root' directory. e.g. /local/xendemocd/build/root
677 To add or remove rpms, its possible to use 'rpm' with the --root
678 option to set the path. For more complex changes, it easiest to boot a
679 machine using using the tree via NFS root. Before doing this, you'll
680 need to edit fstab to comment out the seperate mount of /usr.
682 One thing to watch out for: as part of the CD build process, the
683 contents of the 'rootpatch' tree gets copied over the existing 'root'
684 tree replacing various files. The intention of the rootpatch tree is
685 to contain the files that have been modified from the original RH
686 distribution (e.g. various /etc files). This was done to make it
687 easier to upgrade to newer RH versions in the future. The downside of
688 this is that if you edit an existing file in the root tree you should
689 check that you don't also need to propagate the change to the
690 rootpatch tree to avoid it being overwritten.
692 Once you've made the changes and want to build a new iso, here's the
693 procedure:
695 cd /local/xendemocd/build
696 echo '<put_your_name_here>' > Builder
697 ./make.sh put_your_version_id_here >../buildlog 2>&1
699 This process can take 30 mins even on a fast machine, but you should
700 eventually end up with an iso image in the build directory.
702 Notes:
704 root - the root of the file system heirarchy as presented to the
705 running system
707 rootpatch - contains files that have been modified from the standard
708 RH, and copied over the root tree as part of the build
709 procedure.
711 irtree - the file system tree that will go into the initrd (initial
712 ram disk)
714 work - a working directory used in the build process
716 usr - this should really be in 'work' as its created as part of the
717 build process. It contains the 'immutable' files that will
718 be served from the CD rather than the tmpfs containing the
719 contents of root.tar.gz. Some files that are normally in /etc
720 or /var that are large and actually unlikely to need changing
721 have been moved into /usr/root and replaced with links.
724 Ian Pratt
725 9 Sep 2003