1: [[!meta title="Xen HowTo"]]
9: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
10: (i686-class or higher), which supports running multiple guest
11: operating systems on a single physical machine. Xen is a Type 1 or
12: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
13: memory and console, a dom0 operating system which mediates access to
14: other hardware (e.g., disks, network, USB), and one or more domU
15: operating systems which operate in an unprivileged virtualized
16: environment. IO requests from the domU systems are forwarded by the
17: hypervisor (Xen) to the dom0 to be fulfilled.
19: Xen supports two styles of guests. The original is Para-Virtualized
20: (PV) which means that the guest OS does not attempt to access hardware
21: directly, but instead makes hypercalls to the hypervisor. This is
22: analogous to a user-space program making system calls. (The dom0
23: operating system uses PV calls for some functions, such as updating
24: memory mapping page tables, but has direct hardware access for disk
25: and network.) PV guests must be specifically coded for Xen.
27: The more recent style is HVM, which means that the guest does not have
28: code for Xen and need not be aware that it is running under Xen.
29: Attempts to access hardware registers are trapped and emulated. This
30: style is less efficient but can run unmodified guests.
32: Generally any machine that runs NetBSD/amd64 will work with Xen and PV
33: guests. In theory i386 computers (without x86_64/amd64 support) can
34: be used for Xen <= 4.2, but we have no recent reports of this working
35: (this is a hint). For HVM guests, hardware support is needed, but it
36: is common on recent machines. For Intel CPUs, one needs the VT-x
37: extension, shown in "cpuctl identify 0" as VMX. For AMD CPUs, one
38: needs the AMD-V extensions, shown in "cpuctl identify 0" as SVM.
39: There are further features for IOMMU virtualization, Intel's VT-d and
40: AMD's AMD-Vi. TODO: Explain whether Xen on NetBSD makes use of these
41: features. TODO: Review by someone who really understands this.
43: Note that a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this
44: is because the FreeBSD dom0 does not run in PV mode.
46: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
47: The dom0 can start one or more domUs. (Booting is explained in detail
48: in the dom0 section.)
50: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
51: and that Xen kernels and tools are available in pkgsrc. This HOWTO
52: attempts to address both the case of running a NetBSD dom0 on hardware
53: and running domUs under it (NetBSD and other), and also running NetBSD
54: as a domU in a VPS.
56: Xen 3.1 in pkgsrc used to support "PCI passthrough", which means that
57: specific PCI devices can be made available to a specific domU instead
58: of the dom0. This can be useful to let a domU run X11, or access some
59: network interface or other peripheral.
61: NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD
62: 7. Xen 2 has been removed from pkgsrc.
67: Installing NetBSD/Xen is not extremely difficult, but it is more
68: complex than a normal installation of NetBSD.
69: In general, this HOWTO is occasionally overly restrictive about how
70: things must be done, guiding the reader to stay on the established
71: path when there are no known good reasons to stray.
73: This HOWTO presumes a basic familiarity with the Xen system
74: architecture, with installing NetBSD on i386/amd64 hardware, and with
75: installing software from pkgsrc. See also the [Xen
78: Versions of Xen and NetBSD
81: Most of the installation concepts and instructions are independent
82: of Xen version and NetBSD version. This section gives advice on
83: which version to choose. Versions not in pkgsrc and older unsupported
84: versions of NetBSD are intentionally ignored.
86: The term "amd64" is used to refer to both the NetBSD port and to the
87: hardware architecture on which it runs. (Such hardware is made by
88: both Intel and AMD, and in 2016 a normal PC has this CPU
91: Xen versions
94: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
95: xenkernel and xentools. We will refer only to the kernel versions,
96: but note that both packages must be installed together and must have
97: matching versions.
99: Versions available in pkgsrc:
101: [[!table data="""
102: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
103: 4.2 |xenkernel42 |32bit, 64bit |Yes
104: 4.5 |xenkernel45 |64bit |Yes
105: 4.6 |xenkernel46 |64bit |Partially
106: 4.8 |xenkernel48 |64bit |No
107: 4.11 |xenkernel411 |64bit |No
110: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
112: Note: Xen 4.2 was the last version to support 32bit CPUs.
114: Xen command program
117: Early Xen used a program called xm to manipulate the system from the
118: dom0. Starting in 4.1, a replacement program with similar behavior
119: called xl is provided, but it does not work well in 4.1. In 4.2, both
120: xm and xl work fine. 4.4 is the last version that has xm.
122: You must make a global choice to use xm or xl, because it affects not
123: only which command you use, but the command used by rc.d scripts
124: (specifically xendomains) and which daemons should be run. The
125: xentools packages provide xl for 4.2 and up.
127: In 4.2, you can choose to use xm by simply changing the ctl_command
128: variable and setting xend=YES in rc.conf.
130: With xl, virtual devices are configured in parallel, which can cause
131: problems if they are written assuming serial operation (e.g., updating
132: firewall rules without explicit locking). There is now locking for
133: the provided scripts, which works for normal casses (e.g, file-backed
134: xbd, where a vnd must be allocated). But, as of 201612, it has not
135: been adequately tested for a complex custom setup with a large number
136: of interfaces.
138: NetBSD versions
141: The netbsd-7, netbsd-8, and -current branches are all reasonable
142: choices, with more or less the same considerations for non-Xen use.
143: NetBSD 8 is recommended as the stable version of the most recent
144: release for production use.
146: For developing Xen, netbsd-current may be appropriate.
148: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
149: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
150: need SMP for dom0 functions; the lack of support is really a problem
151: when using a dom0 as a normal computer.)
153: Note: NetBSD support is called XEN3. However, it does support Xen 4,
154: because the hypercall interface has remained identical.
159: Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen
160: versions). (Practically, almost any computer where one would want to
161: run Xen today supports amd64.)
163: Xen, the dom0 system, and each domU system can be either i386 or
164: amd64. When building a xenkernel package, one obtains an i386 Xen
165: kernel on an i386 host, and an amd64 Xen kernel on an amd64 host. If
166: the Xen kernel is i386, then the dom0 kernel and all domU kernels must
167: be i386. With an amd64 Xen kernel, an amd64 dom0 kernel is known to
168: work, and an i386 dom0 kernel should in theory work. An amd64
169: Xen/dom0 is known to support both i386 and amd64 domUs.
171: i386 dom0 and domU kernels must be PAE (except for an i386 Xen 3.1
172: kernel, where one can use non-PAE for dom0 and all domUs); PAE kernels
173: are included in the NetBSD default build. (Note that emacs (at least)
174: fails if run on i386 with PAE when built without, and vice versa,
175: presumably due to bugs in the undump code.)
177: Because of the above, the standard approach is to use an amd64 Xen
178: kernel and NetBSD/amd64 for the dom0. For domUs, NetBSD/i386 (with
179: the PAE kernel) and NetBSD/amd64 are in widespread use, and there is
180: little to no Xen-specific reason to prefer one over the other.
182: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
183: (or obtain from pre-built packages) an amd64 Xen kernel and install
184: that on the system. (One must also use a PAE i386 kernel, but this is
185: also required with an i386 Xen kernel.). Almost no one in the
186: NetBSD/Xen community does this, and the standard, well-tested,
187: approach is to use an amd64 dom0.
189: A [posting on
191: explained that PV system call overhead was higher on amd64, and thus
192: there is some notion that i386 guests are faster. It goes on to
193: caution that the total situation is complex and not entirely
194: understood. On top of that caution, the post is about Linux, not
195: NetBSD. TODO: Include link to benchmarks, if someone posts them.
200: Therefore, this HOWTO recommends running xenkernel46, xl, the NetBSD 7
201: stable branch, and therefore to use an amd64 kernel as the dom0.
202: Either the i386PAE or amd64 version of NetBSD may be used as domUs.
204: A tentative replacement recommendation is xenkernel48, xl, and NetBSD
207: Because bugs are fixed quite often, and because of Xen security
208: advisories, it is good to stay up to date with NetBSD (tracking a
209: stable branch), with the Xen kernel (tracking a Xen version via
210: pkgsrc), and with the Xen tools. Specifically, NetBSD (-7 and
211: -current) got an important fix affecting dom0/domU timesharing in
212: November, 2015, and xentools46 got a fix to enable Ubuntu guests to
213: boot in December, 2016.
215: NetBSD as a dom0
218: NetBSD can be used as a dom0 and works very well. The following
219: sections address installation, updating NetBSD, and updating Xen.
220: Note that it doesn't make sense to talk about installing a dom0 OS
221: without also installing Xen itself. We first address installing
222: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
223: NetBSD install to a dom0 install by just changing the kernel and boot
226: For experimenting with Xen, a machine with as little as 1G of RAM and
227: 100G of disk can work. For running many domUs in productions, far
228: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
229: half-dozen domUs of 512M and 32G each. Basically, the RAM and disk
230: have to be bigger than the sum of the RAM/disk needs of the dom0 and
231: all the domUs.
233: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
234: 512M it worked reliably. This does not make sense, but if you see
235: "not ELF" after Xen boots, try increasing dom0 RAM.
237: Styles of dom0 operation
240: There are two basic ways to use Xen. The traditional method is for
241: the dom0 to do absolutely nothing other than providing support to some
242: number of domUs. Such a system was probably installed for the sole
243: purpose of hosting domUs, and sits in a server room on a UPS.
245: The other way is to put Xen under a normal-usage computer, so that the
246: dom0 is what the computer would have been without Xen, perhaps a
247: desktop or laptop. Then, one can run domUs at will. Purists will
248: deride this as less secure than the previous approach, and for a
249: computer whose purpose is to run domUs, they are right. But Xen and a
250: dom0 (without domUs) is not meaningfully less secure than the same
251: things running without Xen. One can boot Xen or boot regular NetBSD
252: alternately with little problems, simply refraining from starting the
253: Xen daemons when not running Xen.
255: Note that NetBSD as dom0 does not support multiple CPUs. This will
256: limit the performance of the Xen/dom0 workstation approach. In theory
257: the only issue is that the "backend drivers" are not yet MPSAFE:
260: Installation of NetBSD
264: [install NetBSD/amd64](/guide/inst/)
265: just as you would if you were not using Xen.
266: However, the partitioning approach is very important.
268: If you want to use RAIDframe for the dom0, there are no special issues
269: for Xen. Typically one provides RAID storage for the dom0, and the
270: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
271: over a RAID1 header to find /boot from a file system within a RAID
272: partition; this is no different when booting Xen.
274: There are 4 styles of providing backing storage for the virtual disks
275: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
277: With raw partitions, one has a disklabel (or gpt) partition sized for
278: each virtual disk to be used by the domU. (If you are able to predict
279: how domU usage will evolve, please add an explanation to the HOWTO.
280: Seriously, needs tend to change over time.)
282: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
283: for domU disks. This is almost as efficient as raw disk partitions
284: and more flexible. Hence raw disk partitions should typically not
285: be used.
287: One can use files in the dom0 file system, typically created by dd'ing
288: /dev/zero to create a specific size. This is somewhat less efficient,
289: but very convenient, as one can cp the files for backup, or move them
290: between dom0 hosts.
292: Finally, in theory one can place the files backing the domU disks in a
293: SAN. (This is an invitation for someone who has done this to add a
294: HOWTO page.)
296: Installation of Xen
299: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
300: pkgsrc (or another matching pair). See [the pkgsrc
301: documentation](https://www.NetBSD.org/docs/pkgsrc/) for help with
302: pkgsrc. Ensure that your packages are recent; the HOWTO does not
303: contemplate old builds.
306: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
307: recent versions have HVM support integrated in the main xentools
308: package. It is entirely reasonable to run only PV guests.
310: Next you need to install the selected Xen kernel itself, which is
311: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
312: For debugging, one may copy xen-debug.gz; this is conceptually similar
313: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
314: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
315: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
316: of a NetBSD build. If using i386, use
317: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
318: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
319: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
320: typically are) left compressed.
322: In a dom0, kernfs is mandatory for xend to communicate with the
323: kernel, so ensure that /kern is in fstab. (A standard NetBSD install
324: should already mount /kern.)
326: Because you already installed NetBSD, you have a working boot setup
327: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
328: beginning of your root file system, have /boot, and likely also
329: /boot.cfg. (If not, fix before continuing!)
331: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
332: example. The basic line is
334: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
336: which specifies that the dom0 should have 512M, leaving the rest to be
337: allocated for domUs. To use a serial console, use
339: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
341: which will use the first serial port for Xen (which counts starting
342: from 1, unlike NetBSD which counts starting from 0), forcing
343: speed/parity. Because the NetBSD command line lacks a
344: "console=pc" argument, it will use the default "xencons" console device,
345: which directs the console I/O through Xen to the same console device Xen
346: itself uses (in this case, the serial port).
348: In an attempt to add performance, one can also add
350: dom0_max_vcpus=1 dom0_vcpus_pin
352: to force only one vcpu to be provided (since NetBSD dom0 can't use
353: more) and to pin that vcpu to a physical CPU. TODO: benchmark this.
355: Xen has [many boot
357: and other than dom0 memory and max_vcpus, they are generally not
360: As with non-Xen systems, you should have a line to boot /netbsd (a
361: kernel that works without Xen). Consider a line to boot /netbsd.ok (a
362: fallback version of the non-Xen kernel, updated manually when you are
363: sure /netbsd is ok). Consider also a line to boot fallback versions
364: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
365: to resolve Xen booting issues.
367: Probably you want a default=N line to choose Xen in the absence of
370: Now, reboot so that you are running a DOM0 kernel under Xen, rather
371: than GENERIC without Xen.
373: Using grub (historic)
376: Before NetBSD's native bootloader could support Xen, the use of
377: grub was recommended. If necessary, see the
378: [old grub information](/ports/xen/howto-grub).
380: The [HowTo on Installing into
382: explains how to set up booting a dom0 with Xen using grub with
383: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
384: boot. Now, just create a system with RAID-1, and alter /boot.cfg as
385: described above.)
387: Configuring Xen
390: Xen logs will be in /var/log/xen.
392: Now, you have a system that will boot Xen and the dom0 kernel, but not
393: do anything else special. Make sure that you have rebooted into Xen.
394: There will be no domUs, and none can be started because you still have
395: to configure the dom0 daemons.
397: The daemons which should be run vary with Xen version and with whether
398: one is using xm or xl. The Xen 3.1, 3.3 and 4.1 packages use xm. Xen
399: 4.2 and up packages use xl. To use xm with 4.2, edit xendomains to
400: use xm instead.
402: For 3.1 and 3.3, you should enable xend and xenbackendd:
407: For 4.1 and up, you should enable xencommons. Not enabling xencommons
408: will result in a hang; it is necessary to hit ^C on the console to let
409: the machine finish booting. If you are using xm (default in 4.1, or
410: if you changed xendomains in 4.2), you should also enable xend:
412: xend=YES # only if using xm, and only installed <= 4.2
415: TODO: Recommend for/against xen-watchdog.
417: After you have configured the daemons and either started them (in the
418: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
419: available resources, and running domains. An example with xl follows:
421: # xl dmesg
422: [xen's boot info]
423: # xl info
424: [available memory, etc.]
425: # xl list
426: Name Id Mem(MB) CPU State Time(s) Console
427: Domain-0 0 64 0 r---- 58.1
429: ### Issues with xencommons
431: xencommons starts xenstored, which stores data on behalf of dom0 and
432: domUs. It does not currently work to stop and start xenstored.
433: Certainly all domUs should be shutdown first, following the sort order
434: of the rc.d scripts. However, the dom0 sets up state with xenstored,
435: and is not notified when xenstored exits, leading to not recreating
436: the state when the new xenstored starts. Until there's a mechanism to
437: make this work, one should not expect to be able to restart xenstored
438: (and thus xencommons). There is currently no reason to expect that
439: this will get fixed any time soon.
441: ### No-longer needed advice about devices
443: The installation of NetBSD should already have created devices for xen
444: (xencons, xenevt, xsd_kva), but if they are not present, create them:
446: cd /dev && sh MAKEDEV xen
448: anita (for testing NetBSD)
451: With the setup so far (assuming 4.2/xl), one should be able to run
452: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
453: root, because anita must create a domU):
455: anita --vmm=xl test file:///usr/obj/i386/
457: Alternatively, one can use --vmm=xm to use xm-based domU creation
458: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
460: Xen-specific NetBSD issues
463: There are (at least) two additional things different about NetBSD as a
464: dom0 kernel compared to hardware.
466: One is that the module ABI is different because some of the #defines
467: change, so one must build modules for Xen. As of netbsd-7, the build
468: system does this automatically. TODO: check this. (Before building
469: Xen modules was added, it was awkward to use modules to the point
470: where it was considered that it did not work.)
472: The other difference is that XEN3_DOM0 does not have exactly the same
473: options as GENERIC. While it is debatable whether or not this is a
474: bug, users should be aware of this and can simply add missing config
475: items if desired.
477: Updating NetBSD in a dom0
480: This is just like updating NetBSD on bare hardware, assuming the new
481: version supports the version of Xen you are running. Generally, one
482: replaces the kernel and reboots, and then overlays userland binaries
483: and adjusts /etc.
485: Note that one must update both the non-Xen kernel typically used for
486: rescue purposes and the DOM0 kernel used with Xen.
488: Converting from grub to /boot
491: These instructions were [TODO: will be] used to convert a system from
492: grub to /boot. The system was originally installed in February of
493: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
494: over time. Before these commands, it was running NetBSD 6 i386, Xen
495: 4.1 and grub, much like the message linked earlier in the grub
498: # Install MBR bootblocks on both disks.
499: fdisk -i /dev/rwd0d
500: fdisk -i /dev/rwd1d
501: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
502: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
503: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
504: # Install secondary boot loader
505: cp -p /usr/mdec/boot /
506: # Create boot.cfg following earlier guidance:
507: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
508: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
510: menu=GENERIC single-user:boot -s
511: menu=GENERIC.ok:boot netbsd.ok
512: menu=GENERIC.ok single-user:boot netbsd.ok -s
513: menu=Drop to boot prompt:prompt
517: TODO: actually do this and fix it if necessary.
519: Upgrading Xen versions
522: Minor version upgrades are trivial. Just rebuild/replace the
523: xenkernel version and copy the new xen.gz to / (where /boot.cfg
524: references it), and reboot.
526: Major version upgrades are conceptually not difficult, but can run
527: into all the issues found when installing Xen. Assuming migration
528: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
529: install the xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz
530: to /.
532: Ensure that the contents of /etc/rc.d/xen* are correct. Specifically,
533: they must match the package you just installed and not be left over
534: from some previous installation.
536: Enable the correct set of daemons; see the configuring section above.
537: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
539: Ensure that the domU config files are valid for the new version.
540: Specifically, for 4.x remove autorestart=True, and ensure that disks
541: are specified with numbers as the second argument, as the examples
542: above show, and not NetBSD device names.
544: Hardware known to work
547: Arguably, this section is misplaced, and there should be a page of
548: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
549: assumption that NetBSD/xen runs fine on any modern hardware that
550: NetBSD/amd64 runs well on. Until then, we give motherboard/CPU (and
551: sometimes RAM) pairs/triples to aid those choosing a motherboard.
552: Note that Xen systems usually do not run X, so a listing here does not
553: imply that X works at all.
555: Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
556: Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
557: ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
559: Older hardware:
561: Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
562: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E6850 @ 3.00GHz"
563: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz"
565: Running Xen under qemu
568: The astute reader will note that this section is somewhat twisted.
569: However, it can be useful to run Xen under qemu either because the
570: version of NetBSD as a dom0 does not run on the hardware in use, or to
571: generate automated test cases involving Xen.
573: In 2015-01, the following combination was reported to mostly work:
575: host OS: NetBSD/amd64 6.1.4
576: qemu: 2.2.0 from pkgsrc
577: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
578: dom0 kernel: NetBSD/amd64 6.1.5
579: Xen tools: xentools42-4.2.5 from pkgsrc
581: See [PR 47720](https://gnats.netbsd.org/47720) for a problem with dom0
584: Unprivileged domains (domU)
587: This section describes general concepts about domUs. It does not
588: address specific domU operating systems or how to install them. The
589: config files for domUs are typically in /usr/pkg/etc/xen, and are
590: typically named so that the file name, domU name and the domU's host
591: name match.
593: The domU is provided with CPU and memory by Xen, configured by the
594: dom0. The domU is provided with disk and network by the dom0,
595: mediated by Xen, and configured in the dom0.
597: Entropy in domUs can be an issue; physical disks and network are on
598: the dom0. NetBSD's /dev/random system works, but is often challenged.
600: Config files
603: There is no good order to present config files and the concepts
604: surrounding what is being configured. We first show an example config
605: file, and then in the various sections give details.
607: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
608: for a large number of well-commented examples, mostly for running
611: The following is an example minimal domain configuration file
612: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
613: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
614: i386 domU). The domU serves as a network file server.
616: # -*- mode: python; -*-
618: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
619: memory = 1024
620: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
621: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
622: 'file:/n0/xen/foo-wd1,0x1,w' ]
624: The domain will have the same name as the file. The kernel has the
625: host/domU name in it, so that on the dom0 one can update the various
626: domUs independently. The vif line causes an interface to be provided,
627: with a specific mac address (do not reuse MAC addresses!), in bridge
628: mode. Two disks are provided, and they are both writable; the bits
629: are stored in files and Xen attaches them to a vnd(4) device in the
630: dom0 on domain creation. The system treats xbd0 as the boot device
631: without needing explicit configuration.
633: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
634: that "xm create" takes the name of a config file, while other commands
635: take the name of a domain. To create the domain, connect to the
636: console, create the domain while attaching the console, shutdown the
637: domain, and see if it has finished stopping, do (or xl with Xen >=
640: xm create foo
641: xm console foo
642: xm create -c foo
643: xm shutdown foo
644: xm list
646: Typing ^] will exit the console session. Shutting down a domain is
647: equivalent to pushing the power button; a NetBSD domU will receive a
648: power-press event and do a clean shutdown. Shutting down the dom0
649: will trigger controlled shutdowns of all configured domUs.
651: domU kernels
654: On a physical computer, the BIOS reads sector 0, and a chain of boot
655: loaders finds and loads a kernel. Normally this comes from the root
656: file system. With Xen domUs, the process is totally different. The
657: normal path is for the domU kernel to be a file in the dom0's
658: file system. At the request of the dom0, Xen loads that kernel into a
659: new domU instance and starts execution. While domU kernels can be
660: anyplace, reasonable places to store domU kernels on the dom0 are in /
661: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
662: config files), or in /u0/xen (where the vdisks are).
664: Note that loading the domU kernel from the dom0 implies that boot
665: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
666: See the VPS section near the end for discussion of alternate ways to
667: obtain domU kernels.
669: CPU and memory
672: A domain is provided with some number of vcpus, less than the number
673: of CPUs seen by the hypervisor. (For a dom0, this is controlled by
674: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
675: from the config file by the "vcpus = N" directive.
677: A domain is provided with memory; this is controlled in the config
678: file by "memory = N" (in megabytes). In the straightforward case, the
679: sum of the the memory allocated to the dom0 and all domUs must be less
680: than the available memory.
682: Xen also provides a "balloon" driver, which can be used to let domains
683: use more memory temporarily. TODO: Explain better, and explain how
684: well it works with NetBSD.
686: Virtual disks
689: With the file/vnd style, typically one creates a directory,
690: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
691: domUs. Then, for each domU disk, one writes zeros to a file that then
692: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
693: for the first virtual disk for the domU called foo. Writing zeros to
694: the file serves two purposes. One is that preallocating the contents
695: improves performance. The other is that vnd on sparse files has
696: failed to work. TODO: give working/notworking NetBSD versions for
697: sparse vnd and gnats reference. Note that the use of file/vnd for Xen
698: is not really different than creating a file-backed virtual disk for
699: some other purpose, except that xentools handles the vnconfig
700: commands. To create an empty 4G virtual disk, simply do
702: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
704: Do not use qemu-img-xen, because this will create sparse file. There
705: have been recent (2015) reports of sparse vnd(4) devices causing
706: lockups, but there is apparently no PR.
708: With the lvm style, one creates logical devices. They are then used
709: similarly to vnds. TODO: Add an example with lvm.
711: In domU config files, the disks are defined as a sequence of 3-tuples.
712: The first element is "method:/path/to/disk". Common methods are
713: "file:" for file-backed vnd. and "phy:" for something that is already
714: a (TODO: character or block) device.
716: The second element is an artifact of how virtual disks are passed to
717: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
718: are given a device name to associate with the disk, and values like
719: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
720: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
721: second argument. The name given is converted to a major/minor by
722: calling stat(2) on the name in /dev and this is passed to the domU.
723: In the general case, the dom0 and domU can be different operating
724: systems, and it is an unwarranted assumption that they have consistent
725: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
726: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
727: for the second works fine and avoids this issue. For a GNU/Linux
728: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
731: The third element is "w" for writable disks, and "r" for read-only
734: Note that NetBSD by default creates only vnd. If you need more
735: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
738: Note that NetBSD by default creates only xbd. If you need more
739: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
741: Virtual Networking
744: Xen provides virtual Ethernets, each of which connects the dom0 and a
745: domU. For each virtual network, there is an interface "xvifN.M" in
746: the dom0, and in domU index N, a matching interface xennetM (NetBSD
747: name). The interfaces behave as if there is an Ethernet with two
748: adapters connected. From this primitive, one can construct various
749: configurations. We focus on two common and useful cases for which
750: there are existing scripts: bridging and NAT.
752: With bridging (in the example above), the domU perceives itself to be
753: on the same network as the dom0. For server virtualization, this is
754: usually best. Bridging is accomplished by creating a bridge(4) device
755: and adding the dom0's physical interface and the various xvifN.0
756: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
757: config file. The bridge must be set up already in the dom0; an
758: example /etc/ifconfig.bridge0 is:
762: !brconfig bridge0 add wm0
764: With NAT, the domU perceives itself to be behind a NAT running on the
765: dom0. This is often appropriate when running Xen on a workstation.
766: TODO: NAT appears to be configured by "vif = [ '' ]".
768: The MAC address specified is the one used for the interface in the new
769: domain. The interface in dom0 will use this address XOR'd with
770: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
772: Sizing domains
775: Modern x86 hardware has vast amounts of resources. However, many
776: virtual servers can function just fine on far less. A system with
777: 512M of RAM and a 4G disk can be a reasonable choice. Note that it is
778: far easier to adjust virtual resources than physical ones. For
779: memory, it's just a config file edit and a reboot. For disk, one can
780: create a new file and vnconfig it (or lvm), and then dump/restore,
781: just like updating physical disks, but without having to be there and
782: without those pesky connectors.
784: Starting domains automatically
787: To start domains foo at bar at boot and shut them down cleanly on dom0
788: shutdown, in rc.conf add:
790: xendomains="foo bar"
792: Note that earlier versions of the xentools41 xendomains rc.d script
793: used xl, when one should use xm with 4.1.
795: Creating specific unprivileged domains (domU)
798: Creating domUs is almost entirely independent of operating system. We
799: have already presented the basics of config files. Note that you must
800: have already completed the dom0 setup so that "xl list" (or "xm list")
803: Creating an unprivileged NetBSD domain (domU)
806: See the earlier config file, and adjust memory. Decide on how much
807: storage you will provide, and prepare it (file or lvm).
809: While the kernel will be obtained from the dom0 file system, the same
810: file should be present in the domU as /netbsd so that tools like
811: savecore(8) can work. (This is helpful but not necessary.)
813: The kernel must be specifically for Xen and for use as a domU. The
814: i386 and amd64 provide the following kernels:
816: i386 XEN3_DOMU
817: i386 XEN3PAE_DOMU
818: amd64 XEN3_DOMU
820: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
821: use the PAE version of the i386 kernel.
823: This will boot NetBSD, but this is not that useful if the disk is
824: empty. One approach is to unpack sets onto the disk outside of xen
825: (by mounting it, just as you would prepare a physical disk for a
826: system you can't run the installer on).
828: A second approach is to run an INSTALL kernel, which has a miniroot
829: and can load sets from the network. To do this, copy the INSTALL
830: kernel to / and change the kernel line in the config file to:
832: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
834: Then, start the domain as "xl create -c configname".
836: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
837: line should be used in the config file.
839: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
841: After booting the domain, the option to install via CDROM may be
842: selected. The CDROM device should be changed to `xbd1d`.
844: Once done installing, "halt -p" the new domain (don't reboot or halt,
845: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
846: config file), switch the config file back to the XEN3_DOMU kernel,
847: and start the new domain again. Now it should be able to use "root on
848: xbd0a" and you should have a, functional NetBSD domU.
850: TODO: check if this is still accurate.
851: When the new domain is booting you'll see some warnings about *wscons*
852: and the pseudo-terminals. These can be fixed by editing the files
853: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
854: `/etc/ttys`, except *console*, like this:
856: console "/usr/libexec/getty Pc" vt100 on secure
857: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
858: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
859: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
860: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
862: Finally, all screens must be commented out from `/etc/wscons.conf`.
864: It is also desirable to add
868: in rc.conf. This way, the domain will be properly shut down if
869: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
871: It is not strictly necessary to have a kernel (as /netbsd) in the domU
872: file system. However, various programs (e.g. netstat) will use that
873: kernel to look up symbols to read from kernel virtual memory. If
874: /netbsd is not the running kernel, those lookups will fail. (This is
875: not really a Xen-specific issue, but because the domU kernel is
876: obtained from the dom0, it is far more likely to be out of sync or
877: missing with Xen.)
879: Creating an unprivileged Linux domain (domU)
882: Creating unprivileged Linux domains isn't much different from
883: unprivileged NetBSD domains, but there are some details to know.
885: First, the second parameter passed to the disk declaration (the '0x1' in
886: the example below)
888: disk = [ 'phy:/dev/wd0e,0x1,w' ]
890: does matter to Linux. It wants a Linux device number here (e.g. 0x300
891: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
892: So, hda1 which has major 3 and minor 1 on a Linux system will have
893: device number 0x301. Alternatively, devices names can be used (hda,
894: hdb, ...) as xentools has a table to map these names to devices
895: numbers. To export a partition to a Linux guest we can use:
897: disk = [ 'phy:/dev/wd0e,0x300,w' ]
898: root = "/dev/hda1 ro"
900: and it will appear as /dev/hda on the Linux system, and be used as root
903: To install the Linux system on the partition to be exported to the
904: guest domain, the following method can be used: install
905: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
906: that will be the root partition of your Linux domain, and mount it.
907: Then copy the files from a working Linux system, make adjustments in
908: `/etc` (fstab, network config). It should also be possible to extract
909: binary packages such as .rpm or .deb directly to the mounted partition
910: using the appropriate tool, possibly running under NetBSD's Linux
911: emulation. Once the file system has been populated, umount it. If
912: desirable, the file system can be converted to ext3 using tune2fs -j.
913: It should now be possible to boot the Linux guest domain, using one of
914: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
916: To get the Linux console right, you need to add:
918: extra = "xencons=tty1"
920: to your configuration since not all Linux distributions auto-attach a
921: tty to the xen console.
923: Creating an unprivileged Solaris domain (domU)
926: See possibly outdated
927: [Solaris domU instructions](/ports/xen/howto-solaris/).
930: PCI passthrough: Using PCI devices in guest domains
933: The dom0 can give other domains access to selected PCI
934: devices. This can allow, for example, a non-privileged domain to have
935: access to a physical network interface or disk controller. However,
936: keep in mind that giving a domain access to a PCI device most likely
937: will give the domain read/write access to the whole physical memory,
938: as PCs don't have an IOMMU to restrict memory access to DMA-capable
939: device. Also, it's not possible to export ISA devices to non-dom0
940: domains, which means that the primary VGA adapter can't be exported.
941: A guest domain trying to access the VGA registers will panic.
943: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
944: not been ported to later versions at this time.
946: For a PCI device to be exported to a domU, is has to be attached to
947: the "pciback" driver in dom0. Devices passed to the dom0 via the
948: pciback.hide boot parameter will attach to "pciback" instead of the
949: usual driver. The list of devices is specified as "(bus:dev.func)",
950: where bus and dev are 2-digit hexadecimal numbers, and func a
951: single-digit number:
955: pciback devices should show up in the dom0's boot messages, and the
956: devices should be listed in the `/kern/xen/pci` directory.
958: PCI devices to be exported to a domU are listed in the "pci" array of
959: the domU's config file, with the format "0000:bus:dev.func".
961: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
963: In the domU an "xpci" device will show up, to which one or more pci
964: buses will attach. Then the PCI drivers will attach to PCI buses as
965: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
966: or any PCI drivers built in by default; you have to build your own
967: kernel to use PCI devices in a domU. Here's a kernel config example;
968: note that only the "xpci" lines are unusual.
970: include "arch/i386/conf/XEN3_DOMU"
972: # Add support for PCI buses to the XEN3_DOMU kernel
973: xpci* at xenbus ?
974: pci* at xpci ?
976: # PCI USB controllers
977: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
979: # USB bus support
980: usb* at uhci?
982: # USB Hubs
983: uhub* at usb?
984: uhub* at uhub? port ? configuration ? interface ?
986: # USB Mass Storage
987: umass* at uhub? port ? configuration ? interface ?
988: wd* at umass?
989: # SCSI controllers
990: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
992: # SCSI bus support (for both ahc and umass)
993: scsibus* at scsi?
995: # SCSI devices
996: sd* at scsibus? target ? lun ? # SCSI disk drives
997: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
1000: NetBSD as a domU in a VPS
1003: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
1004: hardware. This section explains how to deal with Xen in a domU as a
1005: virtual private server where you do not control or have access to the
1006: dom0. This is not intended to be an exhaustive list of VPS providers;
1007: only a few are mentioned that specifically support NetBSD.
1009: VPS operators provide varying degrees of access and mechanisms for
1010: configuration. The big issue is usually how one controls which kernel
1011: is booted, because the kernel is nominally in the dom0 file system (to
1012: which VPS users do not normally have access). A second issue is how
1013: to install NetBSD.
1014: A VPS user may want to compile a kernel for security updates, to run
1015: npf, run IPsec, or any other reason why someone would want to change
1016: their kernel.
1018: One approach is to have an administrative interface to upload a kernel,
1019: or to select from a prepopulated list. Other approaches are pygrub
1020: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
1021: kernel from the domU file system. This is closer to a regular physical
1022: computer, where someone who controls a machine can replace the kernel.
1024: A second issue is multiple CPUs. With NetBSD 6, domUs support
1025: multiple vcpus, and it is typical for VPS providers to enable multiple
1026: CPUs for NetBSD domUs.
1031: pygrub runs in the dom0 and looks into the domU file system. This
1032: implies that the domU must have a kernel in a file system in a format
1033: known to pygrub. As of 2014, pygrub seems to be of mostly historical
1039: pvgrub is a version of grub that uses PV operations instead of BIOS
1040: calls. It is booted from the dom0 as the domU kernel, and then reads
1041: /grub/menu.lst and loads a kernel from the domU file system.
1043: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
1044: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
1045: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
1046: page](http://www.panix.com/v-colo/grub.html), which describes only
1047: Linux but should be updated to cover NetBSD :-).
1049: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
1050: their own kernel. See then [prgmr.com NetBSD
1052: (which is in need of updating).
1054: It appears that [grub's FFS
1056: does not support all aspects of modern FFS, but there are also reports
1057: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1058: partition for the kernel with the intent that grub can understand it,
1059: which leads to /netbsd not being the actual kernel. One must remember
1060: to update the special boot partition.
1065: See the [Amazon EC2 page](/amazon_ec2/).
1067: TODO items for improving NetBSD/xen
1070: * Make the NetBSD dom0 kernel work with SMP.
1071: * Test the Xen 4.5 packages adequately to be able to recommend them as
1072: the standard approach.
1073: * Get PCI passthrough working on Xen 4.5
1074: * Get pvgrub into pkgsrc, either via xentools or separately.
1075: * grub
1076: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1077: fragsize/blocksize (UFS2 support may be present; the point is to
1078: make it so that with any UFS1/UFS2 file system setup that works
1079: with NetBSD grub will also work).
1080: See [pkg/40258](https://gnats.netbsd.org/40258).
1081: * Push patches upstream.
1082: * Get UFS2 patches into pvgrub.
1083: * Add support for PV ops to a version of /boot, and make it usable as
1084: a kernel in Xen, similar to pvgrub.
1086: Random pointers
1089: This section contains links from elsewhere not yet integrated into the
1090: HOWTO, and other guides.
1092: * http://www.lumbercartel.ca/library/xen/
1093: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
1094: * https://gmplib.org/~tege/xen.html
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