7: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
8: (i686-class or higher), which supports running multiple guest
9: operating systems on a single physical machine. Xen is a Type 1 or
10: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
11: memory and console, a dom0 operating system which mediates access to
12: other hardware (e.g., disks, network, USB), and one or more domU
13: operating systems which operate in an unprivileged virtualized
14: environment. IO requests from the domU systems are forwarded by the
15: hypervisor (Xen) to the dom0 to be fulfilled.
17: Xen supports two styles of guests. The original is Para-Virtualized
18: (PV) which means that the guest OS does not attempt to access hardware
19: directly, but instead makes hypercalls to the hypervisor. This is
20: analogous to a user-space program making system calls. (The dom0
21: operating system uses PV calls for some functions, such as updating
22: memory mapping page tables, but has direct hardware access for disk
23: and network.) PV guests must be specifically coded for Xen.
25: The more recent style is HVM, which means that the guest does not have
26: code for Xen and need not be aware that it is running under Xen.
27: Attempts to access hardware registers are trapped and emulated. This
28: style is less efficient but can run unmodified guests.
30: Generally any amd64 machine will work with Xen and PV guests. In
31: theory i386 computers without amd64 support can be used for Xen <=
32: 4.2, but we have no recent reports of this working (this is a hint).
33: For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT
34: (amd64) is needed; "cpuctl identify 0" will show this. TODO: Clean up
35: and check the above features.
37: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
38: The dom0 can start one or more domUs. (Booting is explained in detail
39: in the dom0 section.)
41: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
42: and that Xen kernels and tools are available in pkgsrc. This HOWTO
43: attempts to address both the case of running a NetBSD dom0 on hardware
44: and running domUs under it (NetBSD and other), and also running NetBSD
45: as a domU in a VPS.
47: Some versions of Xen support "PCI passthrough", which means that
48: specific PCI devices can be made available to a specific domU instead
49: of the dom0. This can be useful to let a domU run X11, or access some
50: network interface or other peripheral.
52: NetBSD used to support Xen2; this has been removed.
57: Installing NetBSD/Xen is not extremely difficult, but it is more
58: complex than a normal installation of NetBSD.
59: In general, this HOWTO is occasionally overly restrictive about how
60: things must be done, guiding the reader to stay on the established
61: path when there are no known good reasons to stray.
63: This HOWTO presumes a basic familiarity with the Xen system
64: architecture. This HOWTO presumes familiarity with installing NetBSD
65: on i386/amd64 hardware and installing software from pkgsrc.
66: See also the [Xen website](http://www.xenproject.org/).
68: Versions of Xen and NetBSD
71: Most of the installation concepts and instructions are independent
72: of Xen version and NetBSD version. This section gives advice on
73: which version to choose. Versions not in pkgsrc and older unsupported
74: versions of NetBSD are intentionally ignored.
79: In NetBSD, xen is provided in pkgsrc, via matching pairs of packages
80: xenkernel and xentools. We will refer only to the kernel versions,
81: but note that both packages must be installed together and must have
82: matching versions.
84: xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3. These no longer
85: receive security patches and should not be used. Xen 3.1 supports PCI
86: passthrough. Xen 3.1 supports non-PAE on i386.
88: xenkernel41 provides Xen 4.1. This is no longer maintained by Xen,
89: but as of 2014-12 receives backported security patches. It is a
90: reasonable although trailing-edge choice.
92: xenkernel42 provides Xen 4.2. This is maintained by Xen, but old as
93: of 2014-12.
95: xenkernel45 provides Xen 4.5. This is new to pkgsrc as of 2015-01 and
96: not yet recommended for other than experimental/testing use.
98: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
100: Ideally newer versions of Xen will be added to pkgsrc.
102: Note that NetBSD support is called XEN3. It works with Xen 3 and Xen
103: 4 because the hypercall interface has been stable.
105: Xen command program
108: Early Xen used a program called xm to manipulate the system from the
109: dom0. Starting in 4.1, a replacement program with similar behavior
110: called xl is provided, but it does not work well in 4.1. In 4.2, both
111: xm and xl work fine. 4.4 is the last version that has xm. You must
112: choose one or the other, because it affects which daemons you run.
117: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
118: reasonable choices, with more or less the same considerations for
119: non-Xen use. Therefore, netbsd-6 is recommended as the stable version
120: of the most recent release for production use. For those wanting to
121: learn Xen or without production stability concerns, netbsd-7 is likely
122: most appropriate.
124: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
125: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
126: need SMP; the lack of support is really a problem when using a dom0 as
127: a normal computer.)
132: Xen itself can run on i386 or amd64 machines. (Practically, almost
133: any computer where one would want to run Xen today supports amd64.)
135: Xen, the dom0 kernel, and each domU kernel can be either i386 or
136: amd64. When building a xenkernel package, one obtains i386 on an i386
137: host, and amd64 on an amd64 host. If the xen kernel is i386, then the
138: dom0 kernel and all domU kernels must be i386. With an amd64 xen
139: kernel, an amd64 dom0 kernel is known to work, and an i386 dom0 kernel
140: should in theory work. An amd64 xen/dom0 is known to support both
141: i386 and amd64 domUs.
143: Except for an odd case with Xen 3.1, i386 dom0 and domU kernels must
144: be PAE; these are built by default. (Note that emacs (at least) fails
145: if run on i386 with PAE when built without, and vice versa, presumably
146: due to bugs in the undump code.)
148: Because of the above, the standard approach is to use amd64 for the
151: Xen 4.2 is the last version to support i386 as a host. TODO: Clarify
152: if this is about the CPU having to be amd64, or about the dom0 kernel
153: having to be amd64.
158: Mostly, NetBSD as a dom0 or domU is quite stable.
159: However, there are some open PRs indicating problems.
161: - [PR 48125](http://gnats.netbsd.org/48125)
162: - [PR 47720](http://gnats.netbsd.org/47720)
164: Note also that there are issues with sparse vnd(4) instances, but
165: these are not about Xen.
170: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
171: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
172: dom0. Either the i386 or amd64 of NetBSD may be used as domUs.
174: Build problems
177: Ideally, all versions of Xen in pkgsrc would build on all versions of
178: NetBSD on both i386 and amd64. However, that isn't the case. Besides
179: aging code and aging compilers, qemu (included in xentools for HVM
180: support) is difficult to build. The following are known to work or FAIL:
182: xenkernel3 netbsd-5 amd64
183: xentools3 netbsd-5 amd64
184: xentools3=hvm netbsd-5 amd64 ????
185: xenkernel33 netbsd-5 amd64
186: xentools33 netbsd-5 amd64
187: xenkernel41 netbsd-5 amd64
188: xentools41 netbsd-5 amd64
189: xenkernel42 netbsd-5 amd64
190: xentools42 netbsd-5 amd64
192: xenkernel3 netbsd-6 i386 FAIL
193: xentools3 netbsd-6 i386
194: xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
195: xenkernel33 netbsd-6 i386
196: xentools33 netbsd-6 i386
197: xenkernel41 netbsd-6 i386
198: xentools41 netbsd-6 i386
199: xenkernel42 netbsd-6 i386
200: xentools42 netbsd-6 i386 *MIXED
202: (all 3 and 33 seem to FAIL)
203: xenkernel41 netbsd-7 i386
204: xentools41 netbsd-7 i386
205: xenkernel42 netbsd-7 i386
206: xentools42 netbsd-7 i386 ??FAIL
208: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
209: but it does not build for gdt.)
211: NetBSD as a dom0
214: NetBSD can be used as a dom0 and works very well. The following
215: sections address installation, updating NetBSD, and updating Xen.
216: Note that it doesn't make sense to talk about installing a dom0 OS
217: without also installing Xen itself. We first address installing
218: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
219: NetBSD install to a dom0 install by just changing the kernel and boot
222: For experimenting with Xen, a machine with as little as 1G of RAM and
223: 100G of disk can work. For running many domUs in productions, far
224: more will be needed.
226: Styles of dom0 operation
229: There are two basic ways to use Xen. The traditional method is for
230: the dom0 to do absolutely nothing other than providing support to some
231: number of domUs. Such a system was probably installed for the sole
232: purpose of hosting domUs, and sits in a server room on a UPS.
234: The other way is to put Xen under a normal-usage computer, so that the
235: dom0 is what the computer would have been without Xen, perhaps a
236: desktop or laptop. Then, one can run domUs at will. Purists will
237: deride this as less secure than the previous approach, and for a
238: computer whose purpose is to run domUs, they are right. But Xen and a
239: dom0 (without domUs) is not meaningfully less secure than the same
240: things running without Xen. One can boot Xen or boot regular NetBSD
241: alternately with little problems, simply refraining from starting the
242: Xen daemons when not running Xen.
244: Note that NetBSD as dom0 does not support multiple CPUs. This will
245: limit the performance of the Xen/dom0 workstation approach. In theory
246: the only issue is that the "backend drivers" are not yet MPSAFE:
249: Installation of NetBSD
253: [install NetBSD/amd64](/guide/inst/)
254: just as you would if you were not using Xen.
255: However, the partitioning approach is very important.
257: If you want to use RAIDframe for the dom0, there are no special issues
258: for Xen. Typically one provides RAID storage for the dom0, and the
259: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
260: over a RAID1 header to find /boot from a filesystem within a RAID
261: partition; this is no different when booting Xen.
263: There are 4 styles of providing backing storage for the virtual disks
264: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
266: With raw partitions, one has a disklabel (or gpt) partition sized for
267: each virtual disk to be used by the domU. (If you are able to predict
268: how domU usage will evolve, please add an explanation to the HOWTO.
269: Seriously, needs tend to change over time.)
271: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
272: for domU disks. This is almost as efficient as raw disk partitions
273: and more flexible. Hence raw disk partitions should typically not
274: be used.
276: One can use files in the dom0 filesystem, typically created by dd'ing
277: /dev/zero to create a specific size. This is somewhat less efficient,
278: but very convenient, as one can cp the files for backup, or move them
279: between dom0 hosts.
281: Finally, in theory one can place the files backing the domU disks in a
282: SAN. (This is an invitation for someone who has done this to add a
283: HOWTO page.)
285: Installation of Xen
288: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
289: pkgsrc (or another matching pair).
290: See [the pkgsrc
291: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
293: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
294: recent versions have HVM support integrated in the main xentools
295: package. It is entirely reasonable to run only PV guests.
297: Next you need to install the selected Xen kernel itself, which is
298: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
299: For debugging, one may copy xen-debug.gz; this is conceptually similar
300: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
301: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
302: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
303: of a NetBSD build. If using i386, use
304: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
305: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
306: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
307: typically are) left compressed.
309: In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
310: kernel, so ensure that /kern is in fstab. TODO: Say this is default,
311: or file a PR and give a reference.
313: Because you already installed NetBSD, you have a working boot setup
314: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
315: beginning of your root filesystem, /boot present, and likely
316: /boot.cfg. (If not, fix before continuing!)
318: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
319: example. The basic line is
321: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
323: which specifies that the dom0 should have 256M, leaving the rest to be
324: allocated for domUs. To use a serial console, use
326: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
328: which will use the first serial port for Xen (which counts starting
329: from 1), forcing speed/parity, and also for NetBSD (which counts
330: starting at 0). In an attempt to add performance, one can also add
332: dom0_max_vcpus=1 dom0_vcpus_pin
334: to force only one vcpu to be provided (since NetBSD dom0 can't use
335: more) and to pin that vcpu to a physical cpu. TODO: benchmark this.
337: Xen has [many boot
339: and other tham dom0 memory and max_vcpus, they are generally not
342: As with non-Xen systems, you should have a line to boot /netbsd (a
343: kernel that works without Xen) and fallback versions of the non-Xen
344: kernel, Xen, and the dom0 kernel.
346: Now, reboot so that you are running a DOM0 kernel under Xen, rather
347: than GENERIC without Xen.
349: Using grub (historic)
352: Before NetBSD's native bootloader could support Xen, the use of
353: grub was recommended. If necessary, see the
354: [old grub information](/ports/xen/howto-grub/).
356: The [HowTo on Installing into
358: explains how to set up booting a dom0 with Xen using grub with
359: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
362: Configuring Xen
365: Xen logs will be in /var/log/xen.
367: Now, you have a system that will boot Xen and the dom0 kernel, but not
368: do anything else special. Make sure that you have rebooted into Xen.
369: There will be no domUs, and none can be started because you still have
370: to configure the dom0 tools. The daemons which should be run vary
371: with Xen version and with whether one is using xm or xl. Note that
372: xend is for supporting "xm", and should only be used if you plan on
373: using "xm". Do NOT enable xend if you plan on using "xl" as it will
374: cause problems. Running xl without xencommons=YES (and starting it)
375: will result in a hang (so don't do that; follow the HOWTO!).
377: The installation of NetBSD should already have created devices for xen
378: (xencons, xenevt), but if they are not present, create them:
380: cd /dev && sh MAKEDEV xen
382: TODO: Give 3.1 advice (or remove it from pkgsrc).
384: For 3.3 (and thus xm), add to rc.conf (but note that you should have
385: installed 4.1 or 4.2):
390: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
395: (If you are using xentools41 from before 2014-12-26, change
396: rc.d/xendomains to use xm rather than xl.)
398: For 4.2 with xm, add to rc.conf
403: For 4.2 with xl, add to rc.conf:
406: TODO: explain if there is a xend replacement
408: For 4.5 (and thus with xl), add to rc.conf:
411: TODO: explain if there is a xend replacement
413: TODO: Recommend for/against xen-watchdog.
415: After you have configured the daemons and either started them (in the
416: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
417: available resources, and running domains. An example with xm follows:
419: # xm dmesg
420: [xen's boot info]
421: # xm info
422: [available memory, etc.]
423: # xm list
424: Name Id Mem(MB) CPU State Time(s) Console
425: Domain-0 0 64 0 r---- 58.1
427: With xl, the commands are the same, and the output may be slightly
428: different. TODO: add example output for xl before the xm example,
429: after confirming on 4.2 and resolving the TODO about rc.conf.
431: ### Issues with xencommons
433: xencommons starts xenstored, which stores data on behalf of dom0 and
434: domUs. It does not currently work to stop and start xenstored.
435: Certainly all domUs should be shutdown first, following the sort order
436: of the rc.d scripts. However, the dom0 sets up state with xenstored,
437: and is not notified when xenstored exits, leading to not recreating
438: the state when the new xenstored starts. Until there's a mechanism to
439: make this work, one should not expect to be able to restart xenstored
440: (and thus xencommons). There is currently no reason to expect that
441: this will get fixed any time soon.
443: anita (for testing NetBSD)
446: With the setup so far (assuming 4.2/xl), one should be able to run
447: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
448: root, because anita must create a domU):
450: anita --vmm=xl test file:///usr/obj/i386/
452: Alternatively, one can use --vmm=xm to use xm-based domU creation
453: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
455: Xen-specific NetBSD issues
458: There are (at least) two additional things different about NetBSD as a
459: dom0 kernel compared to hardware.
461: One is that modules are not usable in DOM0 kernels, so one must
462: compile in what's needed. It's not really that modules cannot work,
463: but that modules must be built for XEN3_DOM0 because some of the
464: defines change and the normal module builds don't do this. Basically,
465: enabling Xen changes the kernel ABI, and the module build system
466: doesn't cope with this.
468: The other difference is that XEN3_DOM0 does not have exactly the same
469: options as GENERIC. While it is debatable whether or not this is a
470: bug, users should be aware of this and can simply add missing config
471: items if desired.
473: Updating NetBSD in a dom0
476: This is just like updating NetBSD on bare hardware, assuming the new
477: version supports the version of Xen you are running. Generally, one
478: replaces the kernel and reboots, and then overlays userland binaries
479: and adjusts /etc.
481: Note that one must update both the non-Xen kernel typically used for
482: rescue purposes and the DOM0 kernel used with Xen.
484: Converting from grub to /boot
487: These instructions were [TODO: will be] used to convert a system from
488: grub to /boot. The system was originally installed in February of
489: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
490: over time. Before these commands, it was running NetBSD 6 i386, Xen
491: 4.1 and grub, much like the message linked earlier in the grub
494: # Install mbr bootblocks on both disks.
495: fdisk -i /dev/rwd0d
496: fdisk -i /dev/rwd1d
497: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
498: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
499: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
500: # Install secondary boot loader
501: cp -p /usr/mdec/boot /
502: # Create boog.cfg following earlier guidance:
503: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
504: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
506: menu=GENERIC single-user:boot -s
507: menu=GENERIC.ok:boot netbsd.ok
508: menu=GENERIC.ok single-user:boot netbsd.ok -s
509: menu=Drop to boot prompt:prompt
513: TODO: actually do this and fix it if necessary.
515: Updating Xen versions
518: Updating Xen is conceptually not difficult, but can run into all the
519: issues found when installing Xen. Assuming migration from 4.1 to 4.2,
520: remove the xenkernel41 and xentools41 packages and install the
521: xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz to /.
523: Ensure that the contents of /etc/rc.d/xen* are correct. Enable the
524: correct set of daemons. Ensure that the domU config files are valid
525: for the new version.
527: Hardware known to work
530: Arguably, this section is misplaced, and there should be a page of
531: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
532: assumption that NetBSD/xen runs fine on any modern hardware that
533: NetBSD/amd64 runs well on. Until then, we give motherboard/CPU/RAM
534: triples to aid those choosing a motherboard. Note that Xen systems
535: usually do not run X, so a listing here does not imply that X works at
538: Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
539: Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
540: ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
542: Older hardware:
544: Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
546: Running Xen under qemu
549: The astute reader will note that this section is somewhat twisted.
550: However, it can be useful to run Xen under qemu either because the
551: version of NetBSD as a dom0 does not run on the hardware in use, or to
552: generate automated test cases involving Xen.
554: In 2015-01, the following combination was reported to mostly work:
556: host OS: NetBSD/amd64 6.1.4
557: qemu: 2.2.0 from pkgsrc
558: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
559: dom0 kernel: NetBSD/amd64 6.1.5
560: Xen tools: xentools42-4.2.5 from pkgsrc
562: See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0
565: Unprivileged domains (domU)
568: This section describes general concepts about domUs. It does not
569: address specific domU operating systems or how to install them. The
570: config files for domUs are typically in /usr/pkg/etc/xen, and are
571: typically named so that the file name, domU name and the domU's host
572: name match.
574: The domU is provided with cpu and memory by Xen, configured by the
575: dom0. The domU is provided with disk and network by the dom0,
576: mediated by Xen, and configured in the dom0.
578: Entropy in domUs can be an issue; physical disks and network are on
579: the dom0. NetBSD's /dev/random system works, but is often challenged.
581: Config files
584: There is no good order to present config files and the concepts
585: surrounding what is being configured. We first show an example config
586: file, and then in the various sections give details.
588: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
589: for a large number of well-commented examples, mostly for running
592: The following is an example minimal domain configuration file
593: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
594: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
595: i386 domU). The domU serves as a network file server.
597: # -*- mode: python; -*-
599: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
600: memory = 1024
601: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
602: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
603: 'file:/n0/xen/foo-wd1,0x1,w' ]
605: The domain will have the same name as the file. The kernel has the
606: host/domU name in it, so that on the dom0 one can update the various
607: domUs independently. The vif line causes an interface to be provided,
608: with a specific mac address (do not reuse MAC addresses!), in bridge
609: mode. Two disks are provided, and they are both writable; the bits
610: are stored in files and Xen attaches them to a vnd(4) device in the
611: dom0 on domain creation. The system treates xbd0 as the boot device
612: without needing explicit configuration.
614: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
615: that "xm create" takes the name of a config file, while other commands
616: take the name of a domain. To create the domain, connect to the
617: console, create the domain while attaching the console, shutdown the
618: domain, and see if it has finished stopping, do (or xl with Xen >=
621: xm create foo
622: xm console foo
623: xm create -c foo
624: xm shutdown foo
625: xm list
627: Typing ^] will exit the console session. Shutting down a domain is
628: equivalent to pushing the power button; a NetBSD domU will receive a
629: power-press event and do a clean shutdown. Shutting down the dom0
630: will trigger controlled shutdowns of all configured domUs.
632: domU kernels
635: On a physical computer, the BIOS reads sector 0, and a chain of boot
636: loaders finds and loads a kernel. Normally this comes from the root
637: filesystem. With Xen domUs, the process is totally different. The
638: normal path is for the domU kernel to be a file in the dom0's
639: filesystem. At the request of the dom0, Xen loads that kernel into a
640: new domU instance and starts execution. While domU kernels can be
641: anyplace, reasonable places to store domU kernels on the dom0 are in /
642: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
643: config files), or in /u0/xen (where the vdisks are).
645: Note that loading the domU kernel from the dom0 implies that boot
646: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
647: See the VPS section near the end for discussion of alternate ways to
648: obtain domU kernels.
650: CPU and memory
653: A domain is provided with some number of vcpus, less than the number
654: of cpus seen by the hypervisor. (For a dom0, this is controlled by
655: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
656: from the config file by the "vcpus = N" directive.
658: A domain is provided with memory; this is controlled in the config
659: file by "memory = N" (in megabytes). In the straightforward case, the
660: sum of the the memory allocated to the dom0 and all domUs must be less
661: than the available memory.
663: Xen also provides a "balloon" driver, which can be used to let domains
664: use more memory temporarily. TODO: Explain better, and explain how
665: well it works with NetBSD.
667: Virtual disks
670: With the file/vnd style, typically one creates a directory,
671: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
672: domUs. Then, for each domU disk, one writes zeros to a file that then
673: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
674: for the first virtual disk for the domU called foo. Writing zeros to
675: the file serves two purposes. One is that preallocating the contents
676: improves performance. The other is that vnd on sparse files has
677: failed to work. TODO: give working/notworking NetBSD versions for
678: sparse vnd. Note that the use of file/vnd for Xen is not really
679: different than creating a file-backed virtual disk for some other
680: purpose, except that xentools handles the vnconfig commands. To
681: create an empty 4G virtual disk, simply do
683: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
685: Do not use qemu-img-xen, because this will create sparse file. There
686: have been recent (2015) reports of sparse vnd(4) devices causing
687: lockups, but there is apparently no PR.
689: With the lvm style, one creates logical devices. They are then used
690: similarly to vnds. TODO: Add an example with lvm.
692: In domU config files, the disks are defined as a sequence of 3-tuples.
693: The first element is "method:/path/to/disk". Common methods are
694: "file:" for file-backed vnd. and "phy:" for something that is already
695: a (TODO: character or block) device.
697: The second element is an artifact of how virtual disks are passed to
698: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
699: are given a device name to associate with the disk, and values like
700: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
701: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
702: second argument. The name given is converted to a major/minor by
703: calling stat(2) on the name in /dev and this is passed to the domU.
704: In the general case, the dom0 and domU can be different operating
705: systems, and it is an unwarranted assumption that they have consistent
706: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
707: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
708: for the second works fine and avoids this issue. For a GNU/Linux
709: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
712: The third element is "w" for writable disks, and "r" for read-only
715: Virtual Networking
718: Xen provides virtual ethernets, each of which connects the dom0 and a
719: domU. For each virtual network, there is an interface "xvifN.M" in
720: the dom0, and in domU index N, a matching interface xennetM (NetBSD
721: name). The interfaces behave as if there is an Ethernet with two
722: adaptors connected. From this primitive, one can construct various
723: configurations. We focus on two common and useful cases for which
724: there are existing scripts: bridging and NAT.
726: With bridging (in the example above), the domU perceives itself to be
727: on the same network as the dom0. For server virtualization, this is
728: usually best. Bridging is accomplished by creating a bridge(4) device
729: and adding the dom0's physical interface and the various xvifN.0
730: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
731: config file. The bridge must be set up already in the dom0; an
732: example /etc/ifconfig.bridge0 is:
736: !brconfig bridge0 add wm0
738: With NAT, the domU perceives itself to be behind a NAT running on the
739: dom0. This is often appropriate when running Xen on a workstation.
740: TODO: NAT appears to be configured by "vif = [ '' ]".
742: The MAC address specified is the one used for the interface in the new
743: domain. The interface in dom0 will use this address XOR'd with
744: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
746: Sizing domains
749: Modern x86 hardware has vast amounts of resources. However, many
750: virtual servers can function just fine on far less. A system with
751: 256M of RAM and a 4G disk can be a reasonable choice. Note that it is
752: far easier to adjust virtual resources than physical ones. For
753: memory, it's just a config file edit and a reboot. For disk, one can
754: create a new file and vnconfig it (or lvm), and then dump/restore,
755: just like updating physical disks, but without having to be there and
756: without those pesky connectors.
758: Starting domains automatically
761: To start domains foo at bar at boot and shut them down cleanly on dom0
762: shutdown, in rc.conf add:
764: xendomains="foo bar"
766: Note that earlier versions of the xentools41 xendomains rc.d scripth
767: usd xl, when one should use xm with 4.1.
769: Creating specific unprivileged domains (domU)
772: Creating domUs is almost entirely independent of operating system. We
773: have already presented the basics of config files. Note that you must
774: have already completed the dom0 setup so that "xl list" (or "xm list")
777: Creating an unprivileged NetBSD domain (domU)
780: See the earlier config file, and adjust memory. Decide on how much
781: storage you will provide, and prepare it (file or lvm).
783: While the kernel will be obtained from the dom0 filesystem, the same
784: file should be present in the domU as /netbsd so that tools like
785: savecore(8) can work. (This is helpful but not necessary.)
787: The kernel must be specifically for Xen and for use as a domU. The
788: i386 and amd64 provide the following kernels:
790: i386 XEN3_DOMU
791: i386 XEN3PAE_DOMU
792: amd64 XEN3_DOMU
794: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
795: use the PAE version of the i386 kernel.
797: This will boot NetBSD, but this is not that useful if the disk is
798: empty. One approach is to unpack sets onto the disk outside of xen
799: (by mounting it, just as you would prepare a physical disk for a
800: system you can't run the installer on).
802: A second approach is to run an INSTALL kernel, which has a miniroot
803: and can load sets from the network. To do this, copy the INSTALL
804: kernel to / and change the kernel line in the config file to:
806: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
808: Then, start the domain as "xl create -c configname".
810: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
811: line should be used in the config file.
813: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
815: After booting the domain, the option to install via CDROM may be
816: selected. The CDROM device should be changed to `xbd1d`.
818: Once done installing, "halt -p" the new domain (don't reboot or halt,
819: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
820: config file), switch the config file back to the XEN3_DOMU kernel,
821: and start the new domain again. Now it should be able to use "root on
822: xbd0a" and you should have a, functional NetBSD domU.
824: TODO: check if this is still accurate.
825: When the new domain is booting you'll see some warnings about *wscons*
826: and the pseudo-terminals. These can be fixed by editing the files
827: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
828: `/etc/ttys`, except *console*, like this:
830: console "/usr/libexec/getty Pc" vt100 on secure
831: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
832: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
833: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
834: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
836: Finally, all screens must be commented out from `/etc/wscons.conf`.
838: It is also desirable to add
842: in rc.conf. This way, the domain will be properly shut down if
843: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
845: It is not strictly necessary to have a kernel (as /netbsd) in the domU
846: filesystem. However, various programs (e.g. netstat) will use that
847: kernel to look up symbols to read from kernel virtual memory. If
848: /netbsd is not the running kernel, those lookups will fail. (This is
849: not really a Xen-specific issue, but because the domU kernel is
850: obtained from the dom0, it is far more likely to be out of sync or
851: missing with Xen.)
853: Creating an unprivileged Linux domain (domU)
856: Creating unprivileged Linux domains isn't much different from
857: unprivileged NetBSD domains, but there are some details to know.
859: First, the second parameter passed to the disk declaration (the '0x1' in
860: the example below)
862: disk = [ 'phy:/dev/wd0e,0x1,w' ]
864: does matter to Linux. It wants a Linux device number here (e.g. 0x300
865: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
866: So, hda1 which has major 3 and minor 1 on a Linux system will have
867: device number 0x301. Alternatively, devices names can be used (hda,
868: hdb, ...) as xentools has a table to map these names to devices
869: numbers. To export a partition to a Linux guest we can use:
871: disk = [ 'phy:/dev/wd0e,0x300,w' ]
872: root = "/dev/hda1 ro"
874: and it will appear as /dev/hda on the Linux system, and be used as root
877: To install the Linux system on the partition to be exported to the
878: guest domain, the following method can be used: install
879: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
880: that will be the root partition of your Linux domain, and mount it.
881: Then copy the files from a working Linux system, make adjustments in
882: `/etc` (fstab, network config). It should also be possible to extract
883: binary packages such as .rpm or .deb directly to the mounted partition
884: using the appropriate tool, possibly running under NetBSD's Linux
885: emulation. Once the filesystem has been populated, umount it. If
886: desirable, the filesystem can be converted to ext3 using tune2fs -j.
887: It should now be possible to boot the Linux guest domain, using one of
888: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
890: To get the linux console right, you need to add:
892: extra = "xencons=tty1"
894: to your configuration since not all linux distributions auto-attach a
895: tty to the xen console.
897: Creating an unprivileged Solaris domain (domU)
900: See possibly outdated
901: [Solaris domU instructions](/ports/xen/howto-solaris/).
904: PCI passthrough: Using PCI devices in guest domains
907: The dom0 can give other domains access to selected PCI
908: devices. This can allow, for example, a non-privileged domain to have
909: access to a physical network interface or disk controller. However,
910: keep in mind that giving a domain access to a PCI device most likely
911: will give the domain read/write access to the whole physical memory,
912: as PCs don't have an IOMMU to restrict memory access to DMA-capable
913: device. Also, it's not possible to export ISA devices to non-dom0
914: domains, which means that the primary VGA adapter can't be exported.
915: A guest domain trying to access the VGA registers will panic.
917: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
918: not been ported to later versions at this time.
920: For a PCI device to be exported to a domU, is has to be attached to
921: the "pciback" driver in dom0. Devices passed to the dom0 via the
922: pciback.hide boot parameter will attach to "pciback" instead of the
923: usual driver. The list of devices is specified as "(bus:dev.func)",
924: where bus and dev are 2-digit hexadecimal numbers, and func a
925: single-digit number:
929: pciback devices should show up in the dom0's boot messages, and the
930: devices should be listed in the `/kern/xen/pci` directory.
932: PCI devices to be exported to a domU are listed in the "pci" array of
933: the domU's config file, with the format "0000:bus:dev.func".
935: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
937: In the domU an "xpci" device will show up, to which one or more pci
938: busses will attach. Then the PCI drivers will attach to PCI busses as
939: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
940: or any PCI drivers built in by default; you have to build your own
941: kernel to use PCI devices in a domU. Here's a kernel config example;
942: note that only the "xpci" lines are unusual.
944: include "arch/i386/conf/XEN3_DOMU"
946: # Add support for PCI busses to the XEN3_DOMU kernel
947: xpci* at xenbus ?
948: pci* at xpci ?
950: # PCI USB controllers
951: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
953: # USB bus support
954: usb* at uhci?
956: # USB Hubs
957: uhub* at usb?
958: uhub* at uhub? port ? configuration ? interface ?
960: # USB Mass Storage
961: umass* at uhub? port ? configuration ? interface ?
962: wd* at umass?
963: # SCSI controllers
964: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
966: # SCSI bus support (for both ahc and umass)
967: scsibus* at scsi?
969: # SCSI devices
970: sd* at scsibus? target ? lun ? # SCSI disk drives
971: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
974: NetBSD as a domU in a VPS
977: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
978: hardware. This section explains how to deal with Xen in a domU as a
979: virtual private server where you do not control or have access to the
980: dom0. This is not intended to be an exhaustive list of VPS providers;
981: only a few are mentioned that specifically support NetBSD.
983: VPS operators provide varying degrees of access and mechanisms for
984: configuration. The big issue is usually how one controls which kernel
985: is booted, because the kernel is nominally in the dom0 filesystem (to
986: which VPS users do not normally have acesss). A second issue is how
987: to install NetBSD.
988: A VPS user may want to compile a kernel for security updates, to run
989: npf, run IPsec, or any other reason why someone would want to change
990: their kernel.
992: One approach is to have an adminstrative interface to upload a kernel,
993: or to select from a prepopulated list. Other approaches are pygrub
994: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
995: kernel from the domU filesystem. This is closer to a regular physical
996: computer, where someone who controls a machine can replace the kernel.
998: A second issue is multiple CPUs. With NetBSD 6, domUs support
999: multiple vcpus, and it is typical for VPS providers to enable multiple
1000: CPUs for NetBSD domUs.
1005: pygrub runs in the dom0 and looks into the domU filesystem. This
1006: implies that the domU must have a kernel in a filesystem in a format
1007: known to pygrub. As of 2014, pygrub seems to be of mostly historical
1013: pvgrub is a version of grub that uses PV operations instead of BIOS
1014: calls. It is booted from the dom0 as the domU kernel, and then reads
1015: /grub/menu.lst and loads a kernel from the domU filesystem.
1017: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
1018: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
1019: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
1020: page](http://www.panix.com/v-colo/grub.html), which describes only
1021: Linux but should be updated to cover NetBSD :-).
1023: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
1024: their own kernel. See then [prgmr.com NetBSD
1026: (which is in need of updating).
1028: It appears that [grub's FFS
1030: does not support all aspects of modern FFS, but there are also reports
1031: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1032: partition for the kernel with the intent that grub can understand it,
1033: which leads to /netbsd not being the actual kernel. One must remember
1034: to update the special boot partiion.
1039: See the [Amazon EC2 page](../amazon_ec2/).
1041: Using npf
1044: In standard kernels, npf is a module, and thus cannot be loaded in a
1045: DOMU kernel.
1047: TODO: Explain how to compile npf into a custom kernel, answering (but
1048: note that the problem was caused by not booting the right kernel)
1049: [this email to
1052: TODO items for improving NetBSD/xen
1055: * Make the NetBSD dom0 kernel work with SMP.
1056: * Test the Xen 4.5 packages adequately to be able to recommend them as
1057: the standard approach.
1058: * Get PCI passthrough working on Xen 4.5
1059: * Get pvgrub into pkgsrc, either via xentools or separately.
1060: * grub
1061: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1062: fragsize/blocksize (UFS2 support may be present; the point is to
1063: make it so that with any UFS1/UFS2 filesystem setup that works
1064: with NetBSD grub will also work).
1065: See [pkg/40258](http://gnats.netbsd.org/40258).
1066: * Push patches upstream.
1067: * Get UFS2 patches into pvgrub.
1068: * Add support for PV ops to a version of /boot, and make it usable as
1069: a kernel in Xen, similar to pvgrub.
1070: * Solve somehow the issue with modules for GENERIC not being loadable
1071: in a Xen dom0 or domU kernel.
1073: Random pointers
1076: TODO: This section contains links from elsewhere not yet integrated
1077: into the HOWTO.
1079: * http://www.lumbercartel.ca/library/xen/
1080: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
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