1: [[!meta title="Xen HowTo"]]
9: Xen is a hypervisor for x86 hardware, which supports running multiple guest
10: operating systems on a single physical machine. Xen is a Type 1 or
11: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
12: memory and console, a dom0 operating system which mediates access to
13: other hardware (e.g., disks, network, USB), and one or more domU
14: operating systems which operate in an unprivileged virtualized
15: environment. IO requests from the domU systems are forwarded by the
16: Xen hypervisor to the dom0 to be fulfilled.
18: Xen supports different styles of guest:
20: [[!table data="""
21: Style of guest |Supported by NetBSD
22: PV |Yes
23: HVM |Yes
24: PVHVM |No
25: PVH |No
28: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
29: hardware directly, but instead makes hypercalls to the hypervisor; PV
30: guests must be specifically coded for Xen. In HVM mode, no guest
31: modification is required; however, hardware support is required, such
32: as VT-x on Intel CPUs and SVM on AMD CPUs.
34: There are further features for IOMMU virtualization, Intel's VT-d and
35: AMD's AMD-Vi. TODO: Explain whether Xen on NetBSD makes use of these
36: features. TODO: Review by someone who really understands this.
38: Generally any machine that runs NetBSD/amd64 will work with Xen and PV
39: guests. In theory i386 computers (without x86_64/amd64 support) can
40: be used for Xen <= 4.2, but we have no recent reports of this working
41: (this is a hint). For HVM guests, hardware support is needed, but it
42: is common on recent machines.
44: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
45: The dom0 can start one or more domUs. (Booting is explained in detail
46: in the dom0 section.)
48: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
49: and that Xen kernels and tools are available in pkgsrc. This HOWTO
50: attempts to address both the case of running a NetBSD dom0 on hardware
51: and running domUs under it (NetBSD and other), and also running NetBSD
52: as a domU in a VPS.
54: Xen 3.1 in pkgsrc used to support "PCI passthrough", which means that
55: specific PCI devices can be made available to a specific domU instead
56: of the dom0. This can be useful to let a domU run X11, or access some
57: network interface or other peripheral.
59: NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD
60: 7. Xen 2 has been removed from pkgsrc.
65: Installing NetBSD/Xen is not extremely difficult, but it is more
66: complex than a normal installation of NetBSD.
67: In general, this HOWTO is occasionally overly restrictive about how
68: things must be done, guiding the reader to stay on the established
69: path when there are no known good reasons to stray.
71: This HOWTO presumes a basic familiarity with the Xen system
72: architecture, with installing NetBSD on i386/amd64 hardware, and with
73: installing software from pkgsrc. See also the [Xen
76: Versions of Xen and NetBSD
79: Most of the installation concepts and instructions are independent
80: of Xen version and NetBSD version. This section gives advice on
81: which version to choose. Versions not in pkgsrc and older unsupported
82: versions of NetBSD are intentionally ignored.
84: The term "amd64" is used to refer to both the NetBSD port and to the
85: hardware architecture on which it runs. (Such hardware is made by
86: both Intel and AMD, and in 2016 a normal PC has this CPU
89: Xen versions
92: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
93: xenkernel and xentools. We will refer only to the kernel versions,
94: but note that both packages must be installed together and must have
95: matching versions.
97: Versions available in pkgsrc:
99: [[!table data="""
100: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
101: 4.2 |xenkernel42 |32bit, 64bit |Yes
102: 4.5 |xenkernel45 |64bit |Yes
103: 4.6 |xenkernel46 |64bit |Partially
104: 4.8 |xenkernel48 |64bit |No
105: 4.11 |xenkernel411 |64bit |No
108: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
110: Note: Xen 4.2 was the last version to support 32bit CPUs.
112: Xen command program
115: Early Xen used a program called xm to manipulate the system from the
116: dom0. Starting in 4.1, a replacement program with similar behavior
117: called xl is provided, but it does not work well in 4.1. In 4.2, both
118: xm and xl work fine. 4.4 is the last version that has xm.
120: You must make a global choice to use xm or xl, because it affects not
121: only which command you use, but the command used by rc.d scripts
122: (specifically xendomains) and which daemons should be run. The
123: xentools packages provide xl for 4.2 and up.
125: In 4.2, you can choose to use xm by simply changing the ctl_command
126: variable and setting xend=YES in rc.conf.
128: With xl, virtual devices are configured in parallel, which can cause
129: problems if they are written assuming serial operation (e.g., updating
130: firewall rules without explicit locking). There is now locking for
131: the provided scripts, which works for normal casses (e.g, file-backed
132: xbd, where a vnd must be allocated). But, as of 201612, it has not
133: been adequately tested for a complex custom setup with a large number
134: of interfaces.
136: NetBSD versions
139: The netbsd-7, netbsd-8, and -current branches are all reasonable
140: choices, with more or less the same considerations for non-Xen use.
141: NetBSD 8 is recommended as the stable version of the most recent
142: release for production use.
144: For developing Xen, netbsd-current may be appropriate.
146: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
147: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
148: need SMP for dom0 functions; the lack of support is really a problem
149: when using a dom0 as a normal computer.)
151: Note: NetBSD support is called XEN3. However, it does support Xen 4,
152: because the hypercall interface has remained identical.
157: Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen
158: versions). (Practically, almost any computer where one would want to
159: run Xen today supports amd64.)
161: Xen, the dom0 system, and each domU system can be either i386 or
162: amd64. When building a xenkernel package, one obtains an i386 Xen
163: kernel on an i386 host, and an amd64 Xen kernel on an amd64 host. If
164: the Xen kernel is i386, then the dom0 kernel and all domU kernels must
165: be i386. With an amd64 Xen kernel, an amd64 dom0 kernel is known to
166: work, and an i386 dom0 kernel should in theory work. An amd64
167: Xen/dom0 is known to support both i386 and amd64 domUs.
169: i386 dom0 and domU kernels must be PAE (except for an i386 Xen 3.1
170: kernel, where one can use non-PAE for dom0 and all domUs); PAE kernels
171: are included in the NetBSD default build. (Note that emacs (at least)
172: fails if run on i386 with PAE when built without, and vice versa,
173: presumably due to bugs in the undump code.)
175: Because of the above, the standard approach is to use an amd64 Xen
176: kernel and NetBSD/amd64 for the dom0. For domUs, NetBSD/i386 (with
177: the PAE kernel) and NetBSD/amd64 are in widespread use, and there is
178: little to no Xen-specific reason to prefer one over the other.
180: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
181: (or obtain from pre-built packages) an amd64 Xen kernel and install
182: that on the system. (One must also use a PAE i386 kernel, but this is
183: also required with an i386 Xen kernel.). Almost no one in the
184: NetBSD/Xen community does this, and the standard, well-tested,
185: approach is to use an amd64 dom0.
187: A [posting on
189: explained that PV system call overhead was higher on amd64, and thus
190: there is some notion that i386 guests are faster. It goes on to
191: caution that the total situation is complex and not entirely
192: understood. On top of that caution, the post is about Linux, not
193: NetBSD. TODO: Include link to benchmarks, if someone posts them.
198: Therefore, this HOWTO recommends running xenkernel46, xl, the NetBSD 7
199: stable branch, and therefore to use an amd64 kernel as the dom0.
200: Either the i386PAE or amd64 version of NetBSD may be used as domUs.
202: A tentative replacement recommendation is xenkernel48, xl, and NetBSD
205: Because bugs are fixed quite often, and because of Xen security
206: advisories, it is good to stay up to date with NetBSD (tracking a
207: stable branch), with the Xen kernel (tracking a Xen version via
208: pkgsrc), and with the Xen tools. Specifically, NetBSD (-7 and
209: -current) got an important fix affecting dom0/domU timesharing in
210: November, 2015, and xentools46 got a fix to enable Ubuntu guests to
211: boot in December, 2016.
213: NetBSD as a dom0
216: NetBSD can be used as a dom0 and works very well. The following
217: sections address installation, updating NetBSD, and updating Xen.
218: Note that it doesn't make sense to talk about installing a dom0 OS
219: without also installing Xen itself. We first address installing
220: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
221: NetBSD install to a dom0 install by just changing the kernel and boot
224: For experimenting with Xen, a machine with as little as 1G of RAM and
225: 100G of disk can work. For running many domUs in productions, far
226: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
227: half-dozen domUs of 512M and 32G each. Basically, the RAM and disk
228: have to be bigger than the sum of the RAM/disk needs of the dom0 and
229: all the domUs.
231: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
232: 512M it worked reliably. This does not make sense, but if you see
233: "not ELF" after Xen boots, try increasing dom0 RAM.
235: Styles of dom0 operation
238: There are two basic ways to use Xen. The traditional method is for
239: the dom0 to do absolutely nothing other than providing support to some
240: number of domUs. Such a system was probably installed for the sole
241: purpose of hosting domUs, and sits in a server room on a UPS.
243: The other way is to put Xen under a normal-usage computer, so that the
244: dom0 is what the computer would have been without Xen, perhaps a
245: desktop or laptop. Then, one can run domUs at will. Purists will
246: deride this as less secure than the previous approach, and for a
247: computer whose purpose is to run domUs, they are right. But Xen and a
248: dom0 (without domUs) is not meaningfully less secure than the same
249: things running without Xen. One can boot Xen or boot regular NetBSD
250: alternately with little problems, simply refraining from starting the
251: Xen daemons when not running Xen.
253: Note that NetBSD as dom0 does not support multiple CPUs. This will
254: limit the performance of the Xen/dom0 workstation approach. In theory
255: the only issue is that the "backend drivers" are not yet MPSAFE:
258: Installation of NetBSD
262: [install NetBSD/amd64](/guide/inst/)
263: just as you would if you were not using Xen.
264: However, the partitioning approach is very important.
266: If you want to use RAIDframe for the dom0, there are no special issues
267: for Xen. Typically one provides RAID storage for the dom0, and the
268: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
269: over a RAID1 header to find /boot from a file system within a RAID
270: partition; this is no different when booting Xen.
272: There are 4 styles of providing backing storage for the virtual disks
273: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
275: With raw partitions, one has a disklabel (or gpt) partition sized for
276: each virtual disk to be used by the domU. (If you are able to predict
277: how domU usage will evolve, please add an explanation to the HOWTO.
278: Seriously, needs tend to change over time.)
280: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
281: for domU disks. This is almost as efficient as raw disk partitions
282: and more flexible. Hence raw disk partitions should typically not
283: be used.
285: One can use files in the dom0 file system, typically created by dd'ing
286: /dev/zero to create a specific size. This is somewhat less efficient,
287: but very convenient, as one can cp the files for backup, or move them
288: between dom0 hosts.
290: Finally, in theory one can place the files backing the domU disks in a
291: SAN. (This is an invitation for someone who has done this to add a
292: HOWTO page.)
294: Installation of Xen
297: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
298: pkgsrc (or another matching pair). See [the pkgsrc
299: documentation](https://www.NetBSD.org/docs/pkgsrc/) for help with
300: pkgsrc. Ensure that your packages are recent; the HOWTO does not
301: contemplate old builds.
304: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
305: recent versions have HVM support integrated in the main xentools
306: package. It is entirely reasonable to run only PV guests.
308: Next you need to install the selected Xen kernel itself, which is
309: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
310: For debugging, one may copy xen-debug.gz; this is conceptually similar
311: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
312: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
313: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
314: of a NetBSD build. If using i386, use
315: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
316: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
317: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
318: typically are) left compressed.
320: In a dom0, kernfs is mandatory for xend to communicate with the
321: kernel, so ensure that /kern is in fstab. (A standard NetBSD install
322: should already mount /kern.)
324: Because you already installed NetBSD, you have a working boot setup
325: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
326: beginning of your root file system, have /boot, and likely also
327: /boot.cfg. (If not, fix before continuing!)
329: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
330: example. The basic line is
332: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
334: which specifies that the dom0 should have 512M, leaving the rest to be
335: allocated for domUs. To use a serial console, use
337: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
339: which will use the first serial port for Xen (which counts starting
340: from 1, unlike NetBSD which counts starting from 0), forcing
341: speed/parity. Because the NetBSD command line lacks a
342: "console=pc" argument, it will use the default "xencons" console device,
343: which directs the console I/O through Xen to the same console device Xen
344: itself uses (in this case, the serial port).
346: In an attempt to add performance, one can also add
348: dom0_max_vcpus=1 dom0_vcpus_pin
350: to force only one vcpu to be provided (since NetBSD dom0 can't use
351: more) and to pin that vcpu to a physical CPU. TODO: benchmark this.
353: Xen has [many boot
355: and other than dom0 memory and max_vcpus, they are generally not
358: As with non-Xen systems, you should have a line to boot /netbsd (a
359: kernel that works without Xen). Consider a line to boot /netbsd.ok (a
360: fallback version of the non-Xen kernel, updated manually when you are
361: sure /netbsd is ok). Consider also a line to boot fallback versions
362: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
363: to resolve Xen booting issues.
365: Probably you want a default=N line to choose Xen in the absence of
368: Now, reboot so that you are running a DOM0 kernel under Xen, rather
369: than GENERIC without Xen.
371: Using grub (historic)
374: Before NetBSD's native bootloader could support Xen, the use of
375: grub was recommended. If necessary, see the
376: [old grub information](/ports/xen/howto-grub).
378: The [HowTo on Installing into
380: explains how to set up booting a dom0 with Xen using grub with
381: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
382: boot. Now, just create a system with RAID-1, and alter /boot.cfg as
383: described above.)
385: Configuring Xen
388: Xen logs will be in /var/log/xen.
390: Now, you have a system that will boot Xen and the dom0 kernel, but not
391: do anything else special. Make sure that you have rebooted into Xen.
392: There will be no domUs, and none can be started because you still have
393: to configure the dom0 daemons.
395: The daemons which should be run vary with Xen version and with whether
396: one is using xm or xl. The Xen 3.1, 3.3 and 4.1 packages use xm. Xen
397: 4.2 and up packages use xl. To use xm with 4.2, edit xendomains to
398: use xm instead.
400: For 3.1 and 3.3, you should enable xend and xenbackendd:
405: For 4.1 and up, you should enable xencommons. Not enabling xencommons
406: will result in a hang; it is necessary to hit ^C on the console to let
407: the machine finish booting. If you are using xm (default in 4.1, or
408: if you changed xendomains in 4.2), you should also enable xend:
410: xend=YES # only if using xm, and only installed <= 4.2
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 xl follows:
419: # xl dmesg
420: [xen's boot info]
421: # xl info
422: [available memory, etc.]
423: # xl list
424: Name Id Mem(MB) CPU State Time(s) Console
425: Domain-0 0 64 0 r---- 58.1
427: ### Issues with xencommons
429: xencommons starts xenstored, which stores data on behalf of dom0 and
430: domUs. It does not currently work to stop and start xenstored.
431: Certainly all domUs should be shutdown first, following the sort order
432: of the rc.d scripts. However, the dom0 sets up state with xenstored,
433: and is not notified when xenstored exits, leading to not recreating
434: the state when the new xenstored starts. Until there's a mechanism to
435: make this work, one should not expect to be able to restart xenstored
436: (and thus xencommons). There is currently no reason to expect that
437: this will get fixed any time soon.
439: ### No-longer needed advice about devices
441: The installation of NetBSD should already have created devices for xen
442: (xencons, xenevt, xsd_kva), but if they are not present, create them:
444: cd /dev && sh MAKEDEV xen
446: anita (for testing NetBSD)
449: With the setup so far (assuming 4.2/xl), one should be able to run
450: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
451: root, because anita must create a domU):
453: anita --vmm=xl test file:///usr/obj/i386/
455: Alternatively, one can use --vmm=xm to use xm-based domU creation
456: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
458: Xen-specific NetBSD issues
461: There are (at least) two additional things different about NetBSD as a
462: dom0 kernel compared to hardware.
464: One is that the module ABI is different because some of the #defines
465: change, so one must build modules for Xen. As of netbsd-7, the build
466: system does this automatically. TODO: check this. (Before building
467: Xen modules was added, it was awkward to use modules to the point
468: where it was considered that it did not work.)
470: The other difference is that XEN3_DOM0 does not have exactly the same
471: options as GENERIC. While it is debatable whether or not this is a
472: bug, users should be aware of this and can simply add missing config
473: items if desired.
475: Updating NetBSD in a dom0
478: This is just like updating NetBSD on bare hardware, assuming the new
479: version supports the version of Xen you are running. Generally, one
480: replaces the kernel and reboots, and then overlays userland binaries
481: and adjusts /etc.
483: Note that one must update both the non-Xen kernel typically used for
484: rescue purposes and the DOM0 kernel used with Xen.
486: Converting from grub to /boot
489: These instructions were [TODO: will be] used to convert a system from
490: grub to /boot. The system was originally installed in February of
491: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
492: over time. Before these commands, it was running NetBSD 6 i386, Xen
493: 4.1 and grub, much like the message linked earlier in the grub
496: # Install MBR bootblocks on both disks.
497: fdisk -i /dev/rwd0d
498: fdisk -i /dev/rwd1d
499: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
500: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
501: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
502: # Install secondary boot loader
503: cp -p /usr/mdec/boot /
504: # Create boot.cfg following earlier guidance:
505: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
506: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
508: menu=GENERIC single-user:boot -s
509: menu=GENERIC.ok:boot netbsd.ok
510: menu=GENERIC.ok single-user:boot netbsd.ok -s
511: menu=Drop to boot prompt:prompt
515: TODO: actually do this and fix it if necessary.
517: Upgrading Xen versions
520: Minor version upgrades are trivial. Just rebuild/replace the
521: xenkernel version and copy the new xen.gz to / (where /boot.cfg
522: references it), and reboot.
524: Major version upgrades are conceptually not difficult, but can run
525: into all the issues found when installing Xen. Assuming migration
526: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
527: install the xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz
528: to /.
530: Ensure that the contents of /etc/rc.d/xen* are correct. Specifically,
531: they must match the package you just installed and not be left over
532: from some previous installation.
534: Enable the correct set of daemons; see the configuring section above.
535: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
537: Ensure that the domU config files are valid for the new version.
538: Specifically, for 4.x remove autorestart=True, and ensure that disks
539: are specified with numbers as the second argument, as the examples
540: above show, and not NetBSD device names.
542: Hardware known to work
545: Arguably, this section is misplaced, and there should be a page of
546: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
547: assumption that NetBSD/xen runs fine on any modern hardware that
548: NetBSD/amd64 runs well on. Until then, we give motherboard/CPU (and
549: sometimes RAM) pairs/triples to aid those choosing a motherboard.
550: Note that Xen systems usually do not run X, so a listing here does not
551: imply that X works at all.
553: Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
554: Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
555: ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
557: Older hardware:
559: Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
560: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E6850 @ 3.00GHz"
561: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz"
563: Running Xen under qemu
566: The astute reader will note that this section is somewhat twisted.
567: However, it can be useful to run Xen under qemu either because the
568: version of NetBSD as a dom0 does not run on the hardware in use, or to
569: generate automated test cases involving Xen.
571: In 2015-01, the following combination was reported to mostly work:
573: host OS: NetBSD/amd64 6.1.4
574: qemu: 2.2.0 from pkgsrc
575: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
576: dom0 kernel: NetBSD/amd64 6.1.5
577: Xen tools: xentools42-4.2.5 from pkgsrc
579: See [PR 47720](https://gnats.netbsd.org/47720) for a problem with dom0
582: Unprivileged domains (domU)
585: This section describes general concepts about domUs. It does not
586: address specific domU operating systems or how to install them. The
587: config files for domUs are typically in /usr/pkg/etc/xen, and are
588: typically named so that the file name, domU name and the domU's host
589: name match.
591: The domU is provided with CPU and memory by Xen, configured by the
592: dom0. The domU is provided with disk and network by the dom0,
593: mediated by Xen, and configured in the dom0.
595: Entropy in domUs can be an issue; physical disks and network are on
596: the dom0. NetBSD's /dev/random system works, but is often challenged.
598: Config files
601: There is no good order to present config files and the concepts
602: surrounding what is being configured. We first show an example config
603: file, and then in the various sections give details.
605: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
606: for a large number of well-commented examples, mostly for running
609: The following is an example minimal domain configuration file
610: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
611: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
612: i386 domU). The domU serves as a network file server.
614: # -*- mode: python; -*-
616: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
617: memory = 1024
618: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
619: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
620: 'file:/n0/xen/foo-wd1,0x1,w' ]
622: The domain will have the same name as the file. The kernel has the
623: host/domU name in it, so that on the dom0 one can update the various
624: domUs independently. The vif line causes an interface to be provided,
625: with a specific mac address (do not reuse MAC addresses!), in bridge
626: mode. Two disks are provided, and they are both writable; the bits
627: are stored in files and Xen attaches them to a vnd(4) device in the
628: dom0 on domain creation. The system treats xbd0 as the boot device
629: without needing explicit configuration.
631: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
632: that "xm create" takes the name of a config file, while other commands
633: take the name of a domain. To create the domain, connect to the
634: console, create the domain while attaching the console, shutdown the
635: domain, and see if it has finished stopping, do (or xl with Xen >=
638: xm create foo
639: xm console foo
640: xm create -c foo
641: xm shutdown foo
642: xm list
644: Typing ^] will exit the console session. Shutting down a domain is
645: equivalent to pushing the power button; a NetBSD domU will receive a
646: power-press event and do a clean shutdown. Shutting down the dom0
647: will trigger controlled shutdowns of all configured domUs.
649: domU kernels
652: On a physical computer, the BIOS reads sector 0, and a chain of boot
653: loaders finds and loads a kernel. Normally this comes from the root
654: file system. With Xen domUs, the process is totally different. The
655: normal path is for the domU kernel to be a file in the dom0's
656: file system. At the request of the dom0, Xen loads that kernel into a
657: new domU instance and starts execution. While domU kernels can be
658: anyplace, reasonable places to store domU kernels on the dom0 are in /
659: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
660: config files), or in /u0/xen (where the vdisks are).
662: Note that loading the domU kernel from the dom0 implies that boot
663: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
664: See the VPS section near the end for discussion of alternate ways to
665: obtain domU kernels.
667: CPU and memory
670: A domain is provided with some number of vcpus, less than the number
671: of CPUs seen by the hypervisor. (For a dom0, this is controlled by
672: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
673: from the config file by the "vcpus = N" directive.
675: A domain is provided with memory; this is controlled in the config
676: file by "memory = N" (in megabytes). In the straightforward case, the
677: sum of the the memory allocated to the dom0 and all domUs must be less
678: than the available memory.
680: Xen also provides a "balloon" driver, which can be used to let domains
681: use more memory temporarily. TODO: Explain better, and explain how
682: well it works with NetBSD.
684: Virtual disks
687: With the file/vnd style, typically one creates a directory,
688: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
689: domUs. Then, for each domU disk, one writes zeros to a file that then
690: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
691: for the first virtual disk for the domU called foo. Writing zeros to
692: the file serves two purposes. One is that preallocating the contents
693: improves performance. The other is that vnd on sparse files has
694: failed to work. TODO: give working/notworking NetBSD versions for
695: sparse vnd and gnats reference. Note that the use of file/vnd for Xen
696: is not really different than creating a file-backed virtual disk for
697: some other purpose, except that xentools handles the vnconfig
698: commands. To create an empty 4G virtual disk, simply do
700: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
702: Do not use qemu-img-xen, because this will create sparse file. There
703: have been recent (2015) reports of sparse vnd(4) devices causing
704: lockups, but there is apparently no PR.
706: With the lvm style, one creates logical devices. They are then used
707: similarly to vnds. TODO: Add an example with lvm.
709: In domU config files, the disks are defined as a sequence of 3-tuples.
710: The first element is "method:/path/to/disk". Common methods are
711: "file:" for file-backed vnd. and "phy:" for something that is already
712: a (TODO: character or block) device.
714: The second element is an artifact of how virtual disks are passed to
715: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
716: are given a device name to associate with the disk, and values like
717: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
718: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
719: second argument. The name given is converted to a major/minor by
720: calling stat(2) on the name in /dev and this is passed to the domU.
721: In the general case, the dom0 and domU can be different operating
722: systems, and it is an unwarranted assumption that they have consistent
723: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
724: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
725: for the second works fine and avoids this issue. For a GNU/Linux
726: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
729: The third element is "w" for writable disks, and "r" for read-only
732: Note that NetBSD by default creates only vnd. If you need more
733: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
736: Note that NetBSD by default creates only xbd. If you need more
737: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
739: Virtual Networking
742: Xen provides virtual Ethernets, each of which connects the dom0 and a
743: domU. For each virtual network, there is an interface "xvifN.M" in
744: the dom0, and in domU index N, a matching interface xennetM (NetBSD
745: name). The interfaces behave as if there is an Ethernet with two
746: adapters connected. From this primitive, one can construct various
747: configurations. We focus on two common and useful cases for which
748: there are existing scripts: bridging and NAT.
750: With bridging (in the example above), the domU perceives itself to be
751: on the same network as the dom0. For server virtualization, this is
752: usually best. Bridging is accomplished by creating a bridge(4) device
753: and adding the dom0's physical interface and the various xvifN.0
754: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
755: config file. The bridge must be set up already in the dom0; an
756: example /etc/ifconfig.bridge0 is:
760: !brconfig bridge0 add wm0
762: With NAT, the domU perceives itself to be behind a NAT running on the
763: dom0. This is often appropriate when running Xen on a workstation.
764: TODO: NAT appears to be configured by "vif = [ '' ]".
766: The MAC address specified is the one used for the interface in the new
767: domain. The interface in dom0 will use this address XOR'd with
768: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
770: Sizing domains
773: Modern x86 hardware has vast amounts of resources. However, many
774: virtual servers can function just fine on far less. A system with
775: 512M of RAM and a 4G disk can be a reasonable choice. Note that it is
776: far easier to adjust virtual resources than physical ones. For
777: memory, it's just a config file edit and a reboot. For disk, one can
778: create a new file and vnconfig it (or lvm), and then dump/restore,
779: just like updating physical disks, but without having to be there and
780: without those pesky connectors.
782: Starting domains automatically
785: To start domains foo at bar at boot and shut them down cleanly on dom0
786: shutdown, in rc.conf add:
788: xendomains="foo bar"
790: Note that earlier versions of the xentools41 xendomains rc.d script
791: used xl, when one should use xm with 4.1.
793: Creating specific unprivileged domains (domU)
796: Creating domUs is almost entirely independent of operating system. We
797: have already presented the basics of config files. Note that you must
798: have already completed the dom0 setup so that "xl list" (or "xm list")
801: Creating an unprivileged NetBSD domain (domU)
804: See the earlier config file, and adjust memory. Decide on how much
805: storage you will provide, and prepare it (file or lvm).
807: While the kernel will be obtained from the dom0 file system, the same
808: file should be present in the domU as /netbsd so that tools like
809: savecore(8) can work. (This is helpful but not necessary.)
811: The kernel must be specifically for Xen and for use as a domU. The
812: i386 and amd64 provide the following kernels:
814: i386 XEN3_DOMU
815: i386 XEN3PAE_DOMU
816: amd64 XEN3_DOMU
818: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
819: use the PAE version of the i386 kernel.
821: This will boot NetBSD, but this is not that useful if the disk is
822: empty. One approach is to unpack sets onto the disk outside of xen
823: (by mounting it, just as you would prepare a physical disk for a
824: system you can't run the installer on).
826: A second approach is to run an INSTALL kernel, which has a miniroot
827: and can load sets from the network. To do this, copy the INSTALL
828: kernel to / and change the kernel line in the config file to:
830: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
832: Then, start the domain as "xl create -c configname".
834: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
835: line should be used in the config file.
837: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
839: After booting the domain, the option to install via CDROM may be
840: selected. The CDROM device should be changed to `xbd1d`.
842: Once done installing, "halt -p" the new domain (don't reboot or halt,
843: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
844: config file), switch the config file back to the XEN3_DOMU kernel,
845: and start the new domain again. Now it should be able to use "root on
846: xbd0a" and you should have a, functional NetBSD domU.
848: TODO: check if this is still accurate.
849: When the new domain is booting you'll see some warnings about *wscons*
850: and the pseudo-terminals. These can be fixed by editing the files
851: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
852: `/etc/ttys`, except *console*, like this:
854: console "/usr/libexec/getty Pc" vt100 on secure
855: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
856: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
857: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
858: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
860: Finally, all screens must be commented out from `/etc/wscons.conf`.
862: It is also desirable to add
866: in rc.conf. This way, the domain will be properly shut down if
867: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
869: It is not strictly necessary to have a kernel (as /netbsd) in the domU
870: file system. However, various programs (e.g. netstat) will use that
871: kernel to look up symbols to read from kernel virtual memory. If
872: /netbsd is not the running kernel, those lookups will fail. (This is
873: not really a Xen-specific issue, but because the domU kernel is
874: obtained from the dom0, it is far more likely to be out of sync or
875: missing with Xen.)
877: Creating an unprivileged Linux domain (domU)
880: Creating unprivileged Linux domains isn't much different from
881: unprivileged NetBSD domains, but there are some details to know.
883: First, the second parameter passed to the disk declaration (the '0x1' in
884: the example below)
886: disk = [ 'phy:/dev/wd0e,0x1,w' ]
888: does matter to Linux. It wants a Linux device number here (e.g. 0x300
889: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
890: So, hda1 which has major 3 and minor 1 on a Linux system will have
891: device number 0x301. Alternatively, devices names can be used (hda,
892: hdb, ...) as xentools has a table to map these names to devices
893: numbers. To export a partition to a Linux guest we can use:
895: disk = [ 'phy:/dev/wd0e,0x300,w' ]
896: root = "/dev/hda1 ro"
898: and it will appear as /dev/hda on the Linux system, and be used as root
901: To install the Linux system on the partition to be exported to the
902: guest domain, the following method can be used: install
903: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
904: that will be the root partition of your Linux domain, and mount it.
905: Then copy the files from a working Linux system, make adjustments in
906: `/etc` (fstab, network config). It should also be possible to extract
907: binary packages such as .rpm or .deb directly to the mounted partition
908: using the appropriate tool, possibly running under NetBSD's Linux
909: emulation. Once the file system has been populated, umount it. If
910: desirable, the file system can be converted to ext3 using tune2fs -j.
911: It should now be possible to boot the Linux guest domain, using one of
912: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
914: To get the Linux console right, you need to add:
916: extra = "xencons=tty1"
918: to your configuration since not all Linux distributions auto-attach a
919: tty to the xen console.
921: Creating an unprivileged Solaris domain (domU)
924: See possibly outdated
925: [Solaris domU instructions](/ports/xen/howto-solaris/).
928: PCI passthrough: Using PCI devices in guest domains
931: The dom0 can give other domains access to selected PCI
932: devices. This can allow, for example, a non-privileged domain to have
933: access to a physical network interface or disk controller. However,
934: keep in mind that giving a domain access to a PCI device most likely
935: will give the domain read/write access to the whole physical memory,
936: as PCs don't have an IOMMU to restrict memory access to DMA-capable
937: device. Also, it's not possible to export ISA devices to non-dom0
938: domains, which means that the primary VGA adapter can't be exported.
939: A guest domain trying to access the VGA registers will panic.
941: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
942: not been ported to later versions at this time.
944: For a PCI device to be exported to a domU, is has to be attached to
945: the "pciback" driver in dom0. Devices passed to the dom0 via the
946: pciback.hide boot parameter will attach to "pciback" instead of the
947: usual driver. The list of devices is specified as "(bus:dev.func)",
948: where bus and dev are 2-digit hexadecimal numbers, and func a
949: single-digit number:
953: pciback devices should show up in the dom0's boot messages, and the
954: devices should be listed in the `/kern/xen/pci` directory.
956: PCI devices to be exported to a domU are listed in the "pci" array of
957: the domU's config file, with the format "0000:bus:dev.func".
959: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
961: In the domU an "xpci" device will show up, to which one or more pci
962: buses will attach. Then the PCI drivers will attach to PCI buses as
963: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
964: or any PCI drivers built in by default; you have to build your own
965: kernel to use PCI devices in a domU. Here's a kernel config example;
966: note that only the "xpci" lines are unusual.
968: include "arch/i386/conf/XEN3_DOMU"
970: # Add support for PCI buses to the XEN3_DOMU kernel
971: xpci* at xenbus ?
972: pci* at xpci ?
974: # PCI USB controllers
975: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
977: # USB bus support
978: usb* at uhci?
980: # USB Hubs
981: uhub* at usb?
982: uhub* at uhub? port ? configuration ? interface ?
984: # USB Mass Storage
985: umass* at uhub? port ? configuration ? interface ?
986: wd* at umass?
987: # SCSI controllers
988: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
990: # SCSI bus support (for both ahc and umass)
991: scsibus* at scsi?
993: # SCSI devices
994: sd* at scsibus? target ? lun ? # SCSI disk drives
995: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
998: NetBSD as a domU in a VPS
1001: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
1002: hardware. This section explains how to deal with Xen in a domU as a
1003: virtual private server where you do not control or have access to the
1004: dom0. This is not intended to be an exhaustive list of VPS providers;
1005: only a few are mentioned that specifically support NetBSD.
1007: VPS operators provide varying degrees of access and mechanisms for
1008: configuration. The big issue is usually how one controls which kernel
1009: is booted, because the kernel is nominally in the dom0 file system (to
1010: which VPS users do not normally have access). A second issue is how
1011: to install NetBSD.
1012: A VPS user may want to compile a kernel for security updates, to run
1013: npf, run IPsec, or any other reason why someone would want to change
1014: their kernel.
1016: One approach is to have an administrative interface to upload a kernel,
1017: or to select from a prepopulated list. Other approaches are pygrub
1018: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
1019: kernel from the domU file system. This is closer to a regular physical
1020: computer, where someone who controls a machine can replace the kernel.
1022: A second issue is multiple CPUs. With NetBSD 6, domUs support
1023: multiple vcpus, and it is typical for VPS providers to enable multiple
1024: CPUs for NetBSD domUs.
1029: pygrub runs in the dom0 and looks into the domU file system. This
1030: implies that the domU must have a kernel in a file system in a format
1031: known to pygrub. As of 2014, pygrub seems to be of mostly historical
1037: pvgrub is a version of grub that uses PV operations instead of BIOS
1038: calls. It is booted from the dom0 as the domU kernel, and then reads
1039: /grub/menu.lst and loads a kernel from the domU file system.
1041: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
1042: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
1043: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
1044: page](http://www.panix.com/v-colo/grub.html), which describes only
1045: Linux but should be updated to cover NetBSD :-).
1047: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
1048: their own kernel. See then [prgmr.com NetBSD
1050: (which is in need of updating).
1052: It appears that [grub's FFS
1054: does not support all aspects of modern FFS, but there are also reports
1055: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1056: partition for the kernel with the intent that grub can understand it,
1057: which leads to /netbsd not being the actual kernel. One must remember
1058: to update the special boot partition.
1063: See the [Amazon EC2 page](/amazon_ec2/).
1065: TODO items for improving NetBSD/xen
1068: * Make the NetBSD dom0 kernel work with SMP.
1069: * Test the Xen 4.5 packages adequately to be able to recommend them as
1070: the standard approach.
1071: * Get PCI passthrough working on Xen 4.5
1072: * Get pvgrub into pkgsrc, either via xentools or separately.
1073: * grub
1074: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1075: fragsize/blocksize (UFS2 support may be present; the point is to
1076: make it so that with any UFS1/UFS2 file system setup that works
1077: with NetBSD grub will also work).
1078: See [pkg/40258](https://gnats.netbsd.org/40258).
1079: * Push patches upstream.
1080: * Get UFS2 patches into pvgrub.
1081: * Add support for PV ops to a version of /boot, and make it usable as
1082: a kernel in Xen, similar to pvgrub.
1084: Random pointers
1087: This section contains links from elsewhere not yet integrated into the
1088: HOWTO, and other guides.
1090: * http://www.lumbercartel.ca/library/xen/
1091: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
1092: * https://gmplib.org/~tege/xen.html
CVSweb for NetBSD wikisrc <wikimaster@NetBSD.org> software: FreeBSD-CVSweb