view README.CD @ 775:9cdb7ea6e922

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1.0rc1 -> 1.0
date Mon Sep 29 14:08:44 2003 +0000 (2003-09-29)
parents 5201797ee24a
children 2025cb2d599a
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10 XenDemoCD 1.0
11 University of Cambridge Computer Laboratory
12 29 Sep 2003
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), 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-2.4.22
51 Xen / linux-2.4.22 using cmdline IP configuration
52 Xen / linux-2.4.22 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., 'ser_baud=9600'); 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 rather 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.
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, complete with BitKeeper repository. We've also
119 included source code and configuration information for the various
120 benchmarks we used in the SOSP paper.
123 Starting other domains
124 ======================
126 There's a web interface for starting and managing other domains (VMs),
127 but since we generally use the command line tools they're probably
128 rather better debugged at present. The key command is 'xenctl' which
129 lives in /usr/local/bin and uses /etc/xenctl.xml for its default
130 configuration. Run 'xenctl' without any arguments to get a help
131 message. Note that xenctl is a java front end to various underlying
132 internal tools written in C (xi_*). Running off CD, it seems to take
133 an age to start...
135 Abyway, the first thing to do is to set up a window in which you will
136 receive console output from other domains. Console output will arrive
137 as UDP packets destined for, so its necessary to setup an
138 alias on eth0. The easiest way to do this is to run:
140 xen_nat_enable
142 This also inserts a few NAT rules into "domain0", in case you'll be
143 starting other domains without their own IP addresses. Alternatively,
144 just do "ifconfig eth0:0 up". NB: The intention is that in
145 future Xen will do NAT itsel (actually RSIP), but this is part of a
146 larger work package that isn't stable enough to release.
148 Next, run a the xen UDP console displayer:
150 xen_read_console &
153 As mentioned above, xenctl uses /etc/xenctl.xml as its default
154 configuration. The directory contains two different configs depending
155 on whether you want to use NAT, or multiple sequential external IPs
156 (it's possible to override any of the parameters on the command line
157 if you want to set specific IPs, etc).
159 The default configuration file supports NAT. To change to use multiple IPs:
161 cp /etc/xenctl.xml-publicip /etc/xenctl.xml
163 A sequence of commands must be given to xenctl to start a new
164 domain. First a new domain must be created, which requires specifying
165 the initial memory allocation, the kernel image to use, and the kernel
166 command line. As well as the root file system details, you'll need to
167 set the IP address on the command line: since Xen currently doesn't
168 support a virtual console for domains >1, you won't be able to log to
169 your new domain unless you've got networking configured and an sshd
170 running! (using dhcp for new domains should work too).
172 After creating the domain, xenctl must be used to grant the domain
173 access to other resources such as physical or virtual disk partions.
174 Then, the domain must be started.
176 These commands can be entered manually, but for convenience, xenctl
177 will also read them from a script and infer which domain number you're
178 referring to (-nX). To use the sample script:
180 xenctl script -f/etc/xen-mynewdom [NB: no space after the -f]
182 You should see the domain booting on your xen_read_console window.
184 The xml defaults start another domain running off the CD, using a
185 separate RAM-based file system for mutable data in root (just like
186 domain 0).
188 The new domain is started with a '4' on the kernel command line to
189 tell 'init' to go to runlevel 4 rather than the default of 3. This is
190 done simply to suppress a bunch of harmless error messages that would
191 otherwise occur when the new (unprivileged) domain tried to access
192 physical hardware resources to try setting the hwclock, system font,
193 run gpm etc.
195 After it's booted, you should be able to ssh into your new domain. If
196 you went for a NATed address, from domain 0 you should be able to ssh
197 into '169.254.1.X' where X is the domain number. If you ran the
198 xen_enable_nat script, a bunch of port redirects have been installed
199 to enable you to ssh in to other domains remotely. To access the new
200 virtual machine remotely, use:
202 ssh -p2201 root@IP.address.Of.Domain0 # use 2202 for domain 2 etc.
204 If you configured the new domain with its own IP address, you should
205 be able to ssh into it directly.
208 "xenctl domain list" provides status information about running domains,
209 though is currently only allowed to be run by domain 0. It accesses
210 /proc/xeno/domains to read this information from Xen. You can also use
211 xenctl to 'stop' (pause) a domain, or 'kill' a domain. You can either
212 kill it nicely by sending a shutdown event and waiting for it to
213 terminate, or blow the sucker away with extreme prejudice.
215 If you want to configure a new domain differently, type 'xenctl' to
216 get a list of arguments, e.g. at the 'xenctl domain new' command line
217 use the "-4" option to set a diffrent IPv4 address.
219 xenctl can be used to set the new kernel's command line, and hence
220 determine what it uses as a root file system, etc. Although the default
221 is to boot in the same manner that domain0 did (using the RAM-based
222 file system for root and the CD for /usr) it's possible to configure any
223 of the following possibilities, for example:
225 * initrd=/boot/initrd init=/linuxrc
226 boot using an initial ram disk, executing /linuxrc (as per this CD)
228 * root=/dev/hda3 ro
229 boot using a standard hard disk partition as root
231 * root=/dev/xvda1 ro
232 boot using a pre-configured 'virtual block device' that will be
233 attached to a virtual disk that previously has had a file system
234 installed on it.
236 * root=/dev/nfs nfsroot=/path/on/server ip=<blah_including server_IP>
237 Boot using an NFS mounted root file system. This could be from a
238 remote NFS server, or from an NFS server running in another
239 domain. The latter is rather a useful option.
242 A typical setup might be to allocate a standard disk partition for
243 each domain and populate it with files. To save space, having a shared
244 read-only usr partition might make sense.
246 Alternatively, you can use 'virtual disks', which are stored as files
247 within a custom file system. "xenctl partitions add" can be used to
248 'format' a partition with the file system, and then virtual disks can
249 be created with "xenctl vd create". Virtual disks can then be attached
250 to a running domain as a 'virtual block device' using "xenctl vbd
251 create". The virtual disk can optionally be partitioned (e.g. "fdisk
252 /dev/xvda") or have a file system created on it directly (e.g. "mkfs
253 -t ext3 /dev/xvda"). The virtual disk can then be accessed by a
254 virtual block device associated with another domain, and even used as
255 a boot device.
257 Both virtual disks and real partitions should only be shared between
258 domains in a read-only fashion otherwise the linux kernels will
259 obviously get very confused as the file system structure may change
260 underneath them (having the same partition mounted rw twice is a sure
261 fire way to cause irreparable damage)! If you want read-write
262 sharing, export the directory to other domains via NFS from domain0.
265 Troubleshooting Problems
266 ========================
268 If you have problems booting Xen, there are a number of boot parameters
269 that may be able to help diagnose problems:
271 ignorebiostables Disable parsing of BIOS-supplied tables. This may
272 help with some chipsets that aren't fully supported
273 by Xen. If you specify this option then ACPI tables are
274 also ignored, and SMP support is disabled.
276 nosmp Disable SMP support.
277 This option is implied by 'ignorebiostables'.
279 noacpi Disable ACPI tables, which confuse Xen on some chipsets.
280 This option is implied by 'ignorebiostables'.
282 watchdog Enable NMI watchdog which can report certain failures.
284 noht Disable Hyperthreading.
286 ifname=ethXX Select which Ethernet interface to use.
288 ifname=dummy Don't use any network interface.
290 ser_baud=xxx Enable serial I/O and set the baud rate.
292 dom0_mem=xxx Set the initial amount of memory for domain0.
295 It's probably a good idea to join the Xen developer's mailing list on
296 Sourceforge:
299 About The Xen Demo CD
300 =====================
302 The purpose of the Demo CD is to distribute a snapshot of Xen's
303 source, and simultaneously provide a convenient means for enabling
304 people to get experience playing with Xen without needing to install
305 it on their hard drive. If you decide to install Xen/XenoLinux you can
306 do so simply by following the installation instructions below -- which
307 essentially involves copying the contents of the CD on to a suitably
308 formated disk partition, and then installing or updating the Grub
309 bootloader.
311 This is a bootable CD that loads Xen, and then a Linux 2.4.22 OS image
312 ported to run on Xen. The CD contains a copy of a file system based on
313 the RedHat 9 distribution that is able to run directly off the CD
314 ("live ISO"), using a "tmpfs" RAM-based file system for root (/etc
315 /var etc). Changes you make to the tmpfs will obviously not be
316 persistent across reboots!
318 Because of the use of a RAM-based file system for root, you'll need
319 plenty of memory to run this CD -- something like 96MB per VM. This is
320 not a restriction of Xen : once you've installed Xen, XenoLinux and
321 the file system images on your hard drive you'll find you can boot VMs
322 in just a few MBs.
324 The CD contains a snapshot of the Xen and XenoLinux code base that we
325 believe to be pretty stable, but lacks some of the features that are
326 currently still work in progress e.g. OS suspend/resume to disk, and
327 various memory management enhancements to provide fast inter-OS
328 communication and sharing of memory pages between OSs. We'll release
329 newer snapshots as required, making use of a BitKeeper repository
330 hosted on (follow instructions from the project
331 home page). We're obviously grateful to receive any bug fixes or
332 other code you can contribute. We suggest you join the
333 mailing list.
336 Installing from the CD
337 ======================
339 If you're installing Xen/XenoLinux onto an existing linux file system
340 distribution, just copy the Xen VMM (/boot/image.gz) and XenoLinux
341 kernels (/boot/xenolinux.gz), then modify the Grub config
342 (/boot/grub/menu.lst or /boot/grub/grub.conf) on the target system.
343 It should work on pretty much any distribution.
345 Xen is a "multiboot" standard boot image. Despite being a 'standard',
346 few boot loaders actually support it. The only two we know of are
347 Grub, and our modified version of linux kexec (for booting off a
348 XenoBoot CD -- PlanetLab have adopted the same boot CD approach).
350 If you need to install grub on your system, you can do so either by
351 building the Grub source tree
352 /usr/local/src/grub-0.93-iso9660-splashimage or by copying over all
353 the files in /boot/grub and then running /sbin/grub and following the
354 usual grub documentation. You'll then need to edit the Grub
355 config file.
357 A typical Grub menu option might look like:
359 title Xen / XenoLinux 2.4.22
360 kernel /boot/image.gz dom0_mem=131072 ser_baud=115200 noht
361 module /boot/xenolinux.gz root=/dev/sda4 ro console=tty0
363 The first line specifies which Xen image to use, and what command line
364 arguments to pass to Xen. In this case we set the maximum amount of
365 memory to allocate to domain0, and enable serial I/O at 9600 baud.
366 We could also disable smp support (nosmp) or disable hyper-threading
367 support (noht). If you have multiple network interface you can use
368 ifname=ethXX to select which one to use. If your network card is
369 unsupported, use ifname=dummy
371 The second line specifies which xenolinux image to use, and the
372 standard linux command line arguments to pass to the kernel. In this
373 case, we're configuring the root partition and stating that it should
374 be mounted read-only (normal practice).
376 If we were booting with an initial ram disk (initrd), then this would
377 require a second "module" line.
380 Installing the file systems from the CD
381 =======================================
383 If you haven't an existing Linux installation onto which you can just
384 drop down the Xen and XenoLinux images, then the file systems on the
385 CD provide a quick way of doing an install.
387 Choose one or two partitions, depending on whether you want a separate
388 /usr or not. Make file systems on it/them e.g.:
389 mkfs -t ext3 /dev/hda3
390 [or mkfs -t ext2 /dev/hda3 && tune2fs -j /dev/hda3 if using an old
391 version of mkfs]
393 Next, mount the file system(s) e.g.:
394 mkdir /mnt/root && mount /dev/hda3 /mnt/root
395 [mkdir /mnt/usr && mount /dev/hda4 /mnt/usr]
397 To install the root file system, simply untar /usr/XenDemoCD/root.tar.gz:
398 cd /mnt/root && tar -zxpf /usr/XenDemoCD/root.tar.gz
400 You'll need to edit /mnt/root/etc/fstab to reflect your file system
401 configuration. Changing the password file (etc/shadow) is probably a
402 good idea too.
404 To install the usr file system, copy the file system from CD on /usr,
405 though leaving out the "XenDemoCD" and "boot" directories:
406 cd /usr && cp -a X11R6 etc java libexec root src bin dict kerberos local sbin tmp doc include lib man share /mnt/usr
408 If you intend to boot off these file systems (i.e. use them for
409 domain 0), then you probably want to copy the /usr/boot directory on
410 the cd over the top of the current symlink to /boot on your root
411 filesystem (after deleting the current symlink) i.e.:
412 cd /mnt/root ; rm boot ; cp -a /usr/boot .
414 The XenDemoCD directory is only useful if you want to build your own
415 version of the XenDemoCD (see below).
418 Debugging
419 =========
421 Xen has a set of debugging features that can be useful to try and
422 figure out what's going on. Hit 'h' on the serial line (if you
423 specified a baud rate on the Xen command line) or ScrollLock-h on the
424 keyboard to get a list of supported commands.
426 If you have a crash you'll likely get a crash dump containing an EIP
427 (PC) which, along with an 'objdump -d image', can be useful in
428 figuring out what's happened. Debug a XenoLinux image just as you
429 would any other Linux kernel.
431 We supply a handy debug terminal program which you can find in
432 /usr/local/src/xen-1.0/xeno.bk/tools/misc/miniterm/
433 This should be built and executed on another machine that is connected
434 via a null modem cable. Documentation is included.
435 Alternatively, telnet can be used in 'char mode' if the Xen machine is
436 connected to a serial-port server.
439 Installing Xen / XenoLinux on a RedHat distribution
440 ===================================================
442 When using Xen / Xenolinux on a standard Linux distribution there are
443 a couple of things to watch out for:
445 The first Linux VM that is started when Xen boots start (Domain 0) is
446 given direct access to the graphics card, so it may use it as a
447 console. Other domains don't have ttyN consoles, so attempts to run a
448 'mingetty' against them will fail, generating periodic warning
449 messages from 'init' about services respawning too fast. They should
450 work for domain0 just fine.
452 In future, we may make the current 'xencons' accept input as well as
453 output, so that a getty can be run against it. In the meantime, other
454 domains don't have a console suitable for logging in on, so you'll
455 have to run sshd and ssh in to them.
457 To prevent the warning messages you'll need to remove them from
458 /etc/inittab for domains>0. Due to a bug in the RH9 /etc/rc.sysinit
459 script #'ing the lines out of /etc/inittab won't work as it ignores
460 the '#' and tries to access them anyway.
462 Also, because domains>0 don't have any privileged access at all,
463 certain commands in the default boot sequence will fail e.g. attempts
464 to update the hwclock, change the console font, update the keytable
465 map, start apmd (power management), or gpm (mouse cursor). Either
466 ignore the errors, or remove them from the startup scripts. Deleting
467 the following links are a good start: S24pcmcia S09isdn S17keytable
468 S26apmd S85gpm
470 If you want to use a single root file system that works cleanly for
471 domain0 and domains>0, one trick is to use different 'init' run
472 levels. For example, on the Xen Demo CD we use run level 3 for domain
473 0, and run level 4 for domains>0. This enables different startup
474 scripts to be run in depending on the run level number passed on the
475 kernel command line. The xenctl.xml config file on the CD passes '4'
476 on the kernel command line to domains that it starts.
478 Xenolinux kernels can be built to use runtime loadable modules just
479 like normal linux kernels. Modules should be installed under
480 /lib/modules in the normal way.
482 If there's some kernel feature that hasn't been built into our default
483 kernel, there's a pretty good change that if its a non-hardware
484 related option you'll just be able to enable it and rebuild. If its
485 not on the xconfig menu, hack the arch/xeno/ to put the menu
486 back in.
488 If you're going to use the link local 169.254.1.x addresses to
489 communicate between VMs, there are a couple of other issues to watch
490 out for. RH9 appears to have a bug where by default it configures the
491 loopback interface with a 169.254 address, which stops it working
492 properly on eth0 for communicating with other domains.
494 This utterly daft RH9 behaviour can be stopped by appending
495 "NOZEROCONF=yes" to /etc/sysconfig/networking-scripts/ifcfg-lo
497 If you're going to use NFS root files systems mounted either from an
498 external server or from domain0 there are a couple of other gotchas.
499 The default /etc/sysconfig/iptables rules block NFS, so part way
500 through the boot sequence things will suddenly go dead.
502 If you're planning on having a separate NFS /usr partition, the RH9
503 boot scripts don't make life easy, as they attempt to mount NFS file
504 systems way to late in the boot process. The easiest way I found to do
505 this was to have a '/linuxrc' script run ahead of /sbin/init that
506 mounts /usr:
507 #!/bin/bash
508 /sbin/ipconfig lo
509 /sbin/portmap
510 /bin/mount /usr
511 exec /sbin/init "$@" <>/dev/console 2>&1
513 The one slight complication with the above is that /sbib/portmap is
514 dynamically linked against /usr/lib/ Since this is in
515 /usr, it won't work. I solved this by copying the file (and link)
516 below the /usr mount point, and just let the file be 'covered' when
517 the mount happens.
519 In some installations, where a shared read-only /usr is being used, it
520 may be desirable to move other large directories over into the
521 read-only /usr. For example, on the XenDemoCD we replace /bin /lib and
522 /sbin with links into /usr/root/bin /usr/root/lib and /usr/root/sbin
523 respectively. This creates other problems for running the /linuxrc
524 script, requiring bash, portmap, mount, ifconfig, and a handful of
525 other shared libraries to be copied below the mount point. I guess I
526 should have written a little statically linked C program...
530 Description of how the XenDemoCD boots
531 ======================================
533 1. Grub is used to load Xen, a XenoLinux kernel, and an initrd (initial
534 ram disk). [The source of the version of Grub used is in /usr/local/src]
536 2. the init=/linuxrc command line causes linux to execute /linuxrc in
537 the initrd.
539 3. the /linuxrc file attempts to mount the CD by trying the likely
540 locations : /dev/hd[abcd].
542 4. it then creates a 'tmpfs' file system and untars the
543 'XenDemoCD/root.tar.gz' file into the tmpfs. This contains hopefully
544 all the files that need to be mutable (this would be so much easier
545 if Linux supported 'stacked' or union file systems...)
547 5. Next, /linuxrc uses the pivot_root call to change the root file
548 system to the tmpfs, with the CD mounted as /usr.
550 6. It then invokes /sbin/init in the tmpfs and the boot proceeds
551 normally.
554 Building your own version of the XenDemoCD
555 ==========================================
557 The 'live ISO' version of RedHat is based heavily on Peter Anvin's
558 SuperRescue CD version 2.1.2 and J. McDaniel's Plan-B:
563 Since Xen uses a "multiboot" image format, it was necessary to change
564 the bootloader from isolinux to Grub0.93 with Leonid Lisovskiy's
565 <> grub.0.93-iso9660.patch
567 The Xen Demo CD contains all of the build scripts that were used to
568 create it, so it is possible to 'unpack' the current iso, modifiy it,
569 then build a new iso. The procedure for doing so is as follows:
571 First, mount either the CD, or the iso image of the CD:
573 mount /dev/cdrom /mnt/cdrom
574 or:
575 mount -o loop xendemo-1.0.iso /mnt/cdrom
577 cd to the directory you want to 'unpack' the iso into then run the
578 unpack script:
580 cd /local/xendemocd
581 /mnt/cdrom/XenDemoCD/
583 The result is a 'build' directory containing the file system tree
584 under the 'root' directory. e.g. /local/xendemocd/build/root
586 To add or remove rpms, its possible to use 'rpm' with the --root
587 option to set the path. For more complex changes, it easiest to boot a
588 machine using using the tree via NFS root. Before doing this, you'll
589 need to edit fstab to comment out the seperate mount of /usr.
591 One thing to watch out for: as part of the CD build process, the
592 contents of the 'rootpatch' tree gets copied over the existing 'root'
593 tree replacing various files. The intention of the rootpatch tree is
594 to contain the files that have been modified from the original RH
595 distribution (e.g. various /etc files). This was done to make it
596 easier to upgrade to newer RH versions in the future. The downside of
597 this is that if you edit an existing file in the root tree you should
598 check that you don't also need to propagate the change to the
599 rootpatch tree to avoid it being overwritten.
601 Once you've made the changes and want to build a new iso, here's the
602 procedure:
604 cd /local/xendemocd/build
605 echo '<put_your_name_here>' > Builder
606 ./ put_your_version_id_here >../buildlog 2>&1
608 This process can take 30 mins even on a fast machine, but you should
609 eventually end up with an iso image in the build directory.
611 Notes:
613 root - the root of the file system heirarchy as presented to the
614 running system
616 rootpatch - contains files that have been modified from the standard
617 RH, and copied over the root tree as part of the build
618 procedure.
620 irtree - the file system tree that will go into the initrd (initial
621 ram disk)
623 work - a working directory used in the build process
625 usr - this should really be in 'work' as its created as part of the
626 build process. It contains the 'immutable' files that will
627 be served from the CD rather than the tmpfs containing the
628 contents of root.tar.gz. Some files that are normally in /etc
629 or /var that are large and actually unlikely to need changing
630 have been moved into /usr/root and replaced with links.
633 Ian Pratt
634 9 Sep 2003