7: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
8: (i686-class or higher), which supports running multiple guest
9: operating systems on a single physical machine. Xen is a Type 1 or
10: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
11: memory and console, a dom0 operating system which mediates access to
12: other hardware (e.g., disks, network, USB), and one or more domU
13: operating systems which operate in an unprivileged virtualized
14: environment. IO requests from the domU systems are forwarded by the
15: hypervisor (Xen) to the dom0 to be fulfilled.
17: Xen supports two styles of guests. The original is Para-Virtualized
18: (PV) which means that the guest OS does not attempt to access hardware
19: directly, but instead makes hypercalls to the hypervisor. This is
20: analogous to a user-space program making system calls. (The dom0
21: operating system uses PV calls for some functions, such as updating
22: memory mapping page tables, but has direct hardware access for disk
23: and network.) PV guests must be specifically coded for Xen.
25: The more recent style is HVM, which means that the guest does not have
26: code for Xen and need not be aware that it is running under Xen.
27: Attempts to access hardware registers are trapped and emulated. This
28: style is less efficient but can run unmodified guests.
30: Generally any amd64 machine will work with Xen and PV guests. In
31: theory i386 computers without amd64 support can be used for Xen <=
32: 4.2, but we have no recent reports of this working (this is a hint).
33: For HVM guests, hardware support is needed, but it is common on recent
34: machines. For Intel CPUs, one needs the VT-x extension, shown in
35: "cpuctl identify 0" as VMX. For AMD CPus, one needs the AMD-V
36: extensions, shown in "cpuctl identify 0" as SVM. There are further
37: features for IOMMU virtualization, Intel's VT-d and AMD's AMD-Vi.
38: TODO: Explain whether Xen on NetBSD makes use of these features.
39: TODO: Review by someone who really understands this.
41: Note a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this is
42: because the FreeBSD dom0 does not run in PV mode.
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: Some versions of Xen 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. This HOWTO presumes familiarity with installing NetBSD
73: on i386/amd64 hardware and installing software from pkgsrc.
74: See also the [Xen website](http://www.xenproject.org/).
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.
87: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
88: xenkernel and xentools. We will refer only to the kernel versions,
89: but note that both packages must be installed together and must have
90: matching versions.
92: xenkernel3 provides Xen 3.1. It is no longer maintained by Xen, and the last applied security patch was in
93: 2011. Thus, it should not be used. It supports PCI passthrough,
94: which is why people use it anyway. Xen 3.1 supports i386, both PAE and
97: xenkernel33 provides Xen 3.3. It is no longer maintained by Xen, and
98: the last applied security patch was in 2012. Thus, it should not be
99: used. Xen 3.3 supports i386, but only in PAE mode. There are no good
100: reasons to run this version.
102: xenkernel41 provides Xen 4.1. It is no longer maintained by Xen, but
103: as of 2016-12 received backported security patches. Xen 4.1 supports
104: i386, but only in PAE mode. There are no good reasons to run this
107: xenkernel42 provides Xen 4.2. It is no longer maintained by Xen, but
108: as of 2016-12 received backported security patches. Xen 4.2 supports
109: i386, but only in PAE mode. The only reason to run this is if you
110: need to use xm instead of xl, or if you need to run an i386 dom0
111: (because your hardware is i386 only).
113: xenkernel45 provides Xen 4.5. As of 2016-12, security patches were
114: released by Xen and applied to pkgsrc. Xen 4.5 requires an amd64
115: dom0, but domUs can be amd64 or i386 PAE. TODO: It is either a
116: conservative choice or somewhat old.
118: xenkernel46 provides Xen 4.6. It is new to pkgsrc as of 2016-05. As
119: of 2016-12, security patches were released by Xen and applied to
120: pkgsrc. Xen 4.6 requires an amd64 dom0, but domUs can be amd64 or
121: i386 PAE. TODO: It is either a somewhat aggressive choice or the
122: standard choice
124: Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in
127: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
129: Note that NetBSD support is called XEN3. It works with Xen 3 and Xen
130: 4 because the hypercall interface has been stable.
132: Xen command program
135: Early Xen used a program called xm to manipulate the system from the
136: dom0. Starting in 4.1, a replacement program with similar behavior
137: called xl is provided, but it does not work well in 4.1. In 4.2, both
138: xm and xl work fine. 4.4 is the last version that has xm. You must
139: choose one or the other, because it affects which daemons you run.
140: However, the rc.d scripts provided by xentools packages expect a
141: particular version, and you should use the version used by the
147: The netbsd-6, netbsd-7, and -current branches are all reasonable
148: choices, with more or less the same considerations for non-Xen use.
149: Therefore, netbsd-7 is recommended as the stable version of the most
150: recent release for production use. In addition, netbsd-7 and -current
151: have a important scheduler fix (in November of 2015) affecting
152: contention between dom0 and domUs; see
153: https://releng.netbsd.org/cgi-bin/req-7.cgi?show=1040 for a
154: description. For those wanting to learn Xen or without production
155: stability concerns, netbsd-7 is still likely most appropriate, but
156: -current is also a reasonable choice. (Xen runs ok on netbsd-5, but
157: the xentools packages are likely difficult to build, and netbsd-5 is
158: not supported.)
160: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
161: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
162: need SMP for dom0 functions; the lack of support is really a problem
163: when using a dom0 as a normal computer.)
168: Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen
169: versions). (Practically, almost any computer where one would want to
170: run Xen today supports amd64.)
172: Xen, the dom0 kernel, and each domU kernel can be either i386 or
173: amd64. When building a xenkernel package, one obtains i386 on an i386
174: host, and amd64 on an amd64 host. If the Xen kernel is i386, then the
175: dom0 kernel and all domU kernels must be i386. With an amd64 Xen
176: kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0
177: kernel should in theory work. An amd64 Xen/dom0 is known to support
178: both i386PAE and amd64 domUs.
180: i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are
181: built by default. (Note that emacs (at least) fails if run on i386
182: with PAE when built without, and vice versa, presumably due to bugs in
183: the undump code.)
185: Because of the above, the standard approach is to use amd64 for the
188: Xen 4.2 is the last version to support i386 as a host. TODO: Clarify
189: if this is about the CPU, the Xen kernel, or the dom0 kernel having to
190: be amd64.
196: Mostly, NetBSD as a dom0 or domU is quite stable.
197: However, there are some open PRs indicating problems.
199: - [PR 48125](http://gnats.netbsd.org/48125)
200: - [PR 47720](http://gnats.netbsd.org/47720)
202: Note also that there are issues with sparse vnd(4) instances, but
203: these are not about Xen -- they just are noticed with sparse vnd(4)
204: instances in support of virtual disks in a dom0.
209: Therefore, this HOWTO recommends running xenkernel45 or xenkernel46,
210: xl, the NetBSD 7 stable branch, and to use an amd64 kernel as the
211: dom0. Either the i386PAE or amd64 version of NetBSD may be used as
214: Build problems
217: Ideally, all versions of Xen in pkgsrc would build on all versions of
218: NetBSD on both i386 and amd64. However, that isn't the case. Besides
219: aging code and aging compilers, qemu (included in xentools for HVM
220: support) is difficult to build. The following are known to work or FAIL:
222: xenkernel3 netbsd-5 amd64
223: xentools3 netbsd-5 amd64
224: xentools3=hvm netbsd-5 amd64 ????
225: xenkernel33 netbsd-5 amd64
226: xentools33 netbsd-5 amd64
227: xenkernel41 netbsd-5 amd64
228: xentools41 netbsd-5 amd64
229: xenkernel42 netbsd-5 amd64
230: xentools42 netbsd-5 amd64
232: xenkernel3 netbsd-6 i386 FAIL
233: xentools3 netbsd-6 i386
234: xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
235: xenkernel33 netbsd-6 i386
236: xentools33 netbsd-6 i386
237: xenkernel41 netbsd-6 i386
238: xentools41 netbsd-6 i386
239: xenkernel42 netbsd-6 i386
240: xentools42 netbsd-6 i386 *MIXED
242: (all 3 and 33 seem to FAIL)
243: xenkernel41 netbsd-7 i386
244: xentools41 netbsd-7 i386
245: xenkernel42 netbsd-7 i386
246: xentools42 netbsd-7 i386 ??FAIL
248: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
249: but it does not build for gdt.)
251: NetBSD as a dom0
254: NetBSD can be used as a dom0 and works very well. The following
255: sections address installation, updating NetBSD, and updating Xen.
256: Note that it doesn't make sense to talk about installing a dom0 OS
257: without also installing Xen itself. We first address installing
258: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
259: NetBSD install to a dom0 install by just changing the kernel and boot
262: For experimenting with Xen, a machine with as little as 1G of RAM and
263: 100G of disk can work. For running many domUs in productions, far
264: more will be needed.
266: Styles of dom0 operation
269: There are two basic ways to use Xen. The traditional method is for
270: the dom0 to do absolutely nothing other than providing support to some
271: number of domUs. Such a system was probably installed for the sole
272: purpose of hosting domUs, and sits in a server room on a UPS.
274: The other way is to put Xen under a normal-usage computer, so that the
275: dom0 is what the computer would have been without Xen, perhaps a
276: desktop or laptop. Then, one can run domUs at will. Purists will
277: deride this as less secure than the previous approach, and for a
278: computer whose purpose is to run domUs, they are right. But Xen and a
279: dom0 (without domUs) is not meaningfully less secure than the same
280: things running without Xen. One can boot Xen or boot regular NetBSD
281: alternately with little problems, simply refraining from starting the
282: Xen daemons when not running Xen.
284: Note that NetBSD as dom0 does not support multiple CPUs. This will
285: limit the performance of the Xen/dom0 workstation approach. In theory
286: the only issue is that the "backend drivers" are not yet MPSAFE:
289: Installation of NetBSD
293: [install NetBSD/amd64](/guide/inst/)
294: just as you would if you were not using Xen.
295: However, the partitioning approach is very important.
297: If you want to use RAIDframe for the dom0, there are no special issues
298: for Xen. Typically one provides RAID storage for the dom0, and the
299: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
300: over a RAID1 header to find /boot from a file system within a RAID
301: partition; this is no different when booting Xen.
303: There are 4 styles of providing backing storage for the virtual disks
304: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
306: With raw partitions, one has a disklabel (or gpt) partition sized for
307: each virtual disk to be used by the domU. (If you are able to predict
308: how domU usage will evolve, please add an explanation to the HOWTO.
309: Seriously, needs tend to change over time.)
311: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
312: for domU disks. This is almost as efficient as raw disk partitions
313: and more flexible. Hence raw disk partitions should typically not
314: be used.
316: One can use files in the dom0 file system, typically created by dd'ing
317: /dev/zero to create a specific size. This is somewhat less efficient,
318: but very convenient, as one can cp the files for backup, or move them
319: between dom0 hosts.
321: Finally, in theory one can place the files backing the domU disks in a
322: SAN. (This is an invitation for someone who has done this to add a
323: HOWTO page.)
325: Installation of Xen
328: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
329: pkgsrc (or another matching pair).
330: See [the pkgsrc
331: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
333: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
334: recent versions have HVM support integrated in the main xentools
335: package. It is entirely reasonable to run only PV guests.
337: Next you need to install the selected Xen kernel itself, which is
338: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
339: For debugging, one may copy xen-debug.gz; this is conceptually similar
340: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
341: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
342: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
343: of a NetBSD build. If using i386, use
344: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
345: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
346: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
347: typically are) left compressed.
349: In a dom0 kernel, kernfs is mandatory for xend to communicate with the
350: kernel, so ensure that /kern is in fstab. TODO: Say this is default,
351: or file a PR and give a reference.
353: Because you already installed NetBSD, you have a working boot setup
354: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
355: beginning of your root file system, /boot present, and likely
356: /boot.cfg. (If not, fix before continuing!)
358: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
359: example. The basic line is
361: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
363: which specifies that the dom0 should have 256M, leaving the rest to be
364: allocated for domUs. To use a serial console, use
366: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
368: which will use the first serial port for Xen (which counts starting
369: from 1), forcing speed/parity, and also for NetBSD (which counts
370: starting at 0). In an attempt to add performance, one can also add
372: dom0_max_vcpus=1 dom0_vcpus_pin
374: to force only one vcpu to be provided (since NetBSD dom0 can't use
375: more) and to pin that vcpu to a physical CPU. TODO: benchmark this.
377: Xen has [many boot
379: and other than dom0 memory and max_vcpus, they are generally not
382: As with non-Xen systems, you should have a line to boot /netbsd (a
383: kernel that works without Xen) and fallback versions of the non-Xen
384: kernel, Xen, and the dom0 kernel.
386: Now, reboot so that you are running a DOM0 kernel under Xen, rather
387: than GENERIC without Xen.
389: Using grub (historic)
392: Before NetBSD's native bootloader could support Xen, the use of
393: grub was recommended. If necessary, see the
394: [old grub information](/ports/xen/howto-grub/).
396: The [HowTo on Installing into
398: explains how to set up booting a dom0 with Xen using grub with
399: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
402: Configuring Xen
405: Xen logs will be in /var/log/xen.
407: Now, you have a system that will boot Xen and the dom0 kernel, but not
408: do anything else special. Make sure that you have rebooted into Xen.
409: There will be no domUs, and none can be started because you still have
410: to configure the dom0 daemons.
412: The daemons which should be run vary with Xen version and with whether
413: one is using xm or xl. The Xen 3.1 and 3.3 packages use xm. Xen 4.1
414: and higher packages use xl. While is is possible to use xm with some
415: 4.x versions (TODO: 4.1 and 4.2?), the pkgsrc-provided rc.d scripts do
416: not support this as of 2014-12-26, and thus the HOWTO does not support
417: it either. (Make sure your packages are reasonably recent.)
419: For "xm" (3.1 and 3.3), you should enable xend and xenbackendd (but
420: note that you should be using 4.x):
425: For "xl" (4.x), you should enabled xend and xencommons (xenstored).
426: Trying to boot 4.x without xencommons=YES will result in a hang; it is
427: necessary to hit ^C on the console to let the machine finish booting.
428: TODO: explain why xend is installed by the package.
432: The installation of NetBSD should already have created devices for xen
433: (xencons, xenevt), but if they are not present, create them:
435: cd /dev && sh MAKEDEV xen
437: TODO: Recommend for/against xen-watchdog.
439: After you have configured the daemons and either started them (in the
440: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
441: available resources, and running domains. An example with xl follows:
443: # xl dmesg
444: [xen's boot info]
445: # xl info
446: [available memory, etc.]
447: # xl list
448: Name Id Mem(MB) CPU State Time(s) Console
449: Domain-0 0 64 0 r---- 58.1
451: ### Issues with xencommons
453: xencommons starts xenstored, which stores data on behalf of dom0 and
454: domUs. It does not currently work to stop and start xenstored.
455: Certainly all domUs should be shutdown first, following the sort order
456: of the rc.d scripts. However, the dom0 sets up state with xenstored,
457: and is not notified when xenstored exits, leading to not recreating
458: the state when the new xenstored starts. Until there's a mechanism to
459: make this work, one should not expect to be able to restart xenstored
460: (and thus xencommons). There is currently no reason to expect that
461: this will get fixed any time soon.
463: anita (for testing NetBSD)
466: With the setup so far (assuming 4.2/xl), one should be able to run
467: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
468: root, because anita must create a domU):
470: anita --vmm=xl test file:///usr/obj/i386/
472: Alternatively, one can use --vmm=xm to use xm-based domU creation
473: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
475: Xen-specific NetBSD issues
478: There are (at least) two additional things different about NetBSD as a
479: dom0 kernel compared to hardware.
481: One is that the module ABI is different because some of the #defines
482: change, so one must build modules for Xen. As of netbsd-7, the build
483: system does this automatically. TODO: check this. (Before building
484: Xen modules was added, it was awkward to use modules to the point
485: where it was considered that it did not work.)
487: The other difference is that XEN3_DOM0 does not have exactly the same
488: options as GENERIC. While it is debatable whether or not this is a
489: bug, users should be aware of this and can simply add missing config
490: items if desired.
492: Updating NetBSD in a dom0
495: This is just like updating NetBSD on bare hardware, assuming the new
496: version supports the version of Xen you are running. Generally, one
497: replaces the kernel and reboots, and then overlays userland binaries
498: and adjusts /etc.
500: Note that one must update both the non-Xen kernel typically used for
501: rescue purposes and the DOM0 kernel used with Xen.
503: Converting from grub to /boot
506: These instructions were [TODO: will be] used to convert a system from
507: grub to /boot. The system was originally installed in February of
508: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
509: over time. Before these commands, it was running NetBSD 6 i386, Xen
510: 4.1 and grub, much like the message linked earlier in the grub
513: # Install MBR bootblocks on both disks.
514: fdisk -i /dev/rwd0d
515: fdisk -i /dev/rwd1d
516: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
517: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
518: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
519: # Install secondary boot loader
520: cp -p /usr/mdec/boot /
521: # Create boot.cfg following earlier guidance:
522: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
523: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
525: menu=GENERIC single-user:boot -s
526: menu=GENERIC.ok:boot netbsd.ok
527: menu=GENERIC.ok single-user:boot netbsd.ok -s
528: menu=Drop to boot prompt:prompt
532: TODO: actually do this and fix it if necessary.
534: Upgrading Xen versions
537: Minor version upgrades are trivial. Just rebuild/replace the
538: xenkernel version and copy the new xen.gz to / (where /boot.cfg
539: references it), and reboot.
541: Major version upgrades are conceptually not difficult, but can run
542: into all the issues found when installing Xen. Assuming migration
543: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
544: install the xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz
545: to /.
547: Ensure that the contents of /etc/rc.d/xen* are correct. Specifically,
548: they must match the package you just installed and not be left over
549: from some previous installation.
551: Enable the correct set of daemons; see the configuring section above.
552: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
554: Ensure that the domU config files are valid for the new version.
555: Specifically, for 4.x remove autorestart=True, and ensure that disks
556: are specified with numbers as the second argument, as the examples
557: above show, and not NetBSD device names.
559: Hardware known to work
562: Arguably, this section is misplaced, and there should be a page of
563: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
564: assumption that NetBSD/xen runs fine on any modern hardware that
565: NetBSD/amd64 runs well on. Until then, we give motherboard/CPU/RAM
566: triples to aid those choosing a motherboard. Note that Xen systems
567: usually do not run X, so a listing here does not imply that X works at
570: Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
571: Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
572: ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
574: Older hardware:
576: Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
578: Running Xen under qemu
581: The astute reader will note that this section is somewhat twisted.
582: However, it can be useful to run Xen under qemu either because the
583: version of NetBSD as a dom0 does not run on the hardware in use, or to
584: generate automated test cases involving Xen.
586: In 2015-01, the following combination was reported to mostly work:
588: host OS: NetBSD/amd64 6.1.4
589: qemu: 2.2.0 from pkgsrc
590: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
591: dom0 kernel: NetBSD/amd64 6.1.5
592: Xen tools: xentools42-4.2.5 from pkgsrc
594: See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0
597: Unprivileged domains (domU)
600: This section describes general concepts about domUs. It does not
601: address specific domU operating systems or how to install them. The
602: config files for domUs are typically in /usr/pkg/etc/xen, and are
603: typically named so that the file name, domU name and the domU's host
604: name match.
606: The domU is provided with CPU and memory by Xen, configured by the
607: dom0. The domU is provided with disk and network by the dom0,
608: mediated by Xen, and configured in the dom0.
610: Entropy in domUs can be an issue; physical disks and network are on
611: the dom0. NetBSD's /dev/random system works, but is often challenged.
613: Config files
616: There is no good order to present config files and the concepts
617: surrounding what is being configured. We first show an example config
618: file, and then in the various sections give details.
620: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
621: for a large number of well-commented examples, mostly for running
624: The following is an example minimal domain configuration file
625: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
626: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
627: i386 domU). The domU serves as a network file server.
629: # -*- mode: python; -*-
631: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
632: memory = 1024
633: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
634: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
635: 'file:/n0/xen/foo-wd1,0x1,w' ]
637: The domain will have the same name as the file. The kernel has the
638: host/domU name in it, so that on the dom0 one can update the various
639: domUs independently. The vif line causes an interface to be provided,
640: with a specific mac address (do not reuse MAC addresses!), in bridge
641: mode. Two disks are provided, and they are both writable; the bits
642: are stored in files and Xen attaches them to a vnd(4) device in the
643: dom0 on domain creation. The system treats xbd0 as the boot device
644: without needing explicit configuration.
646: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
647: that "xm create" takes the name of a config file, while other commands
648: take the name of a domain. To create the domain, connect to the
649: console, create the domain while attaching the console, shutdown the
650: domain, and see if it has finished stopping, do (or xl with Xen >=
653: xm create foo
654: xm console foo
655: xm create -c foo
656: xm shutdown foo
657: xm list
659: Typing ^] will exit the console session. Shutting down a domain is
660: equivalent to pushing the power button; a NetBSD domU will receive a
661: power-press event and do a clean shutdown. Shutting down the dom0
662: will trigger controlled shutdowns of all configured domUs.
664: domU kernels
667: On a physical computer, the BIOS reads sector 0, and a chain of boot
668: loaders finds and loads a kernel. Normally this comes from the root
669: file system. With Xen domUs, the process is totally different. The
670: normal path is for the domU kernel to be a file in the dom0's
671: file system. At the request of the dom0, Xen loads that kernel into a
672: new domU instance and starts execution. While domU kernels can be
673: anyplace, reasonable places to store domU kernels on the dom0 are in /
674: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
675: config files), or in /u0/xen (where the vdisks are).
677: Note that loading the domU kernel from the dom0 implies that boot
678: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
679: See the VPS section near the end for discussion of alternate ways to
680: obtain domU kernels.
682: CPU and memory
685: A domain is provided with some number of vcpus, less than the number
686: of CPUs seen by the hypervisor. (For a dom0, this is controlled by
687: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
688: from the config file by the "vcpus = N" directive.
690: A domain is provided with memory; this is controlled in the config
691: file by "memory = N" (in megabytes). In the straightforward case, the
692: sum of the the memory allocated to the dom0 and all domUs must be less
693: than the available memory.
695: Xen also provides a "balloon" driver, which can be used to let domains
696: use more memory temporarily. TODO: Explain better, and explain how
697: well it works with NetBSD.
699: Virtual disks
702: With the file/vnd style, typically one creates a directory,
703: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
704: domUs. Then, for each domU disk, one writes zeros to a file that then
705: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
706: for the first virtual disk for the domU called foo. Writing zeros to
707: the file serves two purposes. One is that preallocating the contents
708: improves performance. The other is that vnd on sparse files has
709: failed to work. TODO: give working/notworking NetBSD versions for
710: sparse vnd. Note that the use of file/vnd for Xen is not really
711: different than creating a file-backed virtual disk for some other
712: purpose, except that xentools handles the vnconfig commands. To
713: create an empty 4G virtual disk, simply do
715: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
717: Do not use qemu-img-xen, because this will create sparse file. There
718: have been recent (2015) reports of sparse vnd(4) devices causing
719: lockups, but there is apparently no PR.
721: With the lvm style, one creates logical devices. They are then used
722: similarly to vnds. TODO: Add an example with lvm.
724: In domU config files, the disks are defined as a sequence of 3-tuples.
725: The first element is "method:/path/to/disk". Common methods are
726: "file:" for file-backed vnd. and "phy:" for something that is already
727: a (TODO: character or block) device.
729: The second element is an artifact of how virtual disks are passed to
730: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
731: are given a device name to associate with the disk, and values like
732: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
733: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
734: second argument. The name given is converted to a major/minor by
735: calling stat(2) on the name in /dev and this is passed to the domU.
736: In the general case, the dom0 and domU can be different operating
737: systems, and it is an unwarranted assumption that they have consistent
738: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
739: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
740: for the second works fine and avoids this issue. For a GNU/Linux
741: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
744: The third element is "w" for writable disks, and "r" for read-only
747: Virtual Networking
750: Xen provides virtual Ethernets, each of which connects the dom0 and a
751: domU. For each virtual network, there is an interface "xvifN.M" in
752: the dom0, and in domU index N, a matching interface xennetM (NetBSD
753: name). The interfaces behave as if there is an Ethernet with two
754: adapters connected. From this primitive, one can construct various
755: configurations. We focus on two common and useful cases for which
756: there are existing scripts: bridging and NAT.
758: With bridging (in the example above), the domU perceives itself to be
759: on the same network as the dom0. For server virtualization, this is
760: usually best. Bridging is accomplished by creating a bridge(4) device
761: and adding the dom0's physical interface and the various xvifN.0
762: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
763: config file. The bridge must be set up already in the dom0; an
764: example /etc/ifconfig.bridge0 is:
768: !brconfig bridge0 add wm0
770: With NAT, the domU perceives itself to be behind a NAT running on the
771: dom0. This is often appropriate when running Xen on a workstation.
772: TODO: NAT appears to be configured by "vif = [ '' ]".
774: The MAC address specified is the one used for the interface in the new
775: domain. The interface in dom0 will use this address XOR'd with
776: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
778: Sizing domains
781: Modern x86 hardware has vast amounts of resources. However, many
782: virtual servers can function just fine on far less. A system with
783: 256M of RAM and a 4G disk can be a reasonable choice. Note that it is
784: far easier to adjust virtual resources than physical ones. For
785: memory, it's just a config file edit and a reboot. For disk, one can
786: create a new file and vnconfig it (or lvm), and then dump/restore,
787: just like updating physical disks, but without having to be there and
788: without those pesky connectors.
790: Starting domains automatically
793: To start domains foo at bar at boot and shut them down cleanly on dom0
794: shutdown, in rc.conf add:
796: xendomains="foo bar"
798: Note that earlier versions of the xentools41 xendomains rc.d script
799: used xl, when one should use xm with 4.1.
801: Creating specific unprivileged domains (domU)
804: Creating domUs is almost entirely independent of operating system. We
805: have already presented the basics of config files. Note that you must
806: have already completed the dom0 setup so that "xl list" (or "xm list")
809: Creating an unprivileged NetBSD domain (domU)
812: See the earlier config file, and adjust memory. Decide on how much
813: storage you will provide, and prepare it (file or lvm).
815: While the kernel will be obtained from the dom0 file system, the same
816: file should be present in the domU as /netbsd so that tools like
817: savecore(8) can work. (This is helpful but not necessary.)
819: The kernel must be specifically for Xen and for use as a domU. The
820: i386 and amd64 provide the following kernels:
822: i386 XEN3_DOMU
823: i386 XEN3PAE_DOMU
824: amd64 XEN3_DOMU
826: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
827: use the PAE version of the i386 kernel.
829: This will boot NetBSD, but this is not that useful if the disk is
830: empty. One approach is to unpack sets onto the disk outside of xen
831: (by mounting it, just as you would prepare a physical disk for a
832: system you can't run the installer on).
834: A second approach is to run an INSTALL kernel, which has a miniroot
835: and can load sets from the network. To do this, copy the INSTALL
836: kernel to / and change the kernel line in the config file to:
838: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
840: Then, start the domain as "xl create -c configname".
842: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
843: line should be used in the config file.
845: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
847: After booting the domain, the option to install via CDROM may be
848: selected. The CDROM device should be changed to `xbd1d`.
850: Once done installing, "halt -p" the new domain (don't reboot or halt,
851: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
852: config file), switch the config file back to the XEN3_DOMU kernel,
853: and start the new domain again. Now it should be able to use "root on
854: xbd0a" and you should have a, functional NetBSD domU.
856: TODO: check if this is still accurate.
857: When the new domain is booting you'll see some warnings about *wscons*
858: and the pseudo-terminals. These can be fixed by editing the files
859: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
860: `/etc/ttys`, except *console*, like this:
862: console "/usr/libexec/getty Pc" vt100 on secure
863: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
864: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
865: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
866: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
868: Finally, all screens must be commented out from `/etc/wscons.conf`.
870: It is also desirable to add
874: in rc.conf. This way, the domain will be properly shut down if
875: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
877: It is not strictly necessary to have a kernel (as /netbsd) in the domU
878: file system. However, various programs (e.g. netstat) will use that
879: kernel to look up symbols to read from kernel virtual memory. If
880: /netbsd is not the running kernel, those lookups will fail. (This is
881: not really a Xen-specific issue, but because the domU kernel is
882: obtained from the dom0, it is far more likely to be out of sync or
883: missing with Xen.)
885: Creating an unprivileged Linux domain (domU)
888: Creating unprivileged Linux domains isn't much different from
889: unprivileged NetBSD domains, but there are some details to know.
891: First, the second parameter passed to the disk declaration (the '0x1' in
892: the example below)
894: disk = [ 'phy:/dev/wd0e,0x1,w' ]
896: does matter to Linux. It wants a Linux device number here (e.g. 0x300
897: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
898: So, hda1 which has major 3 and minor 1 on a Linux system will have
899: device number 0x301. Alternatively, devices names can be used (hda,
900: hdb, ...) as xentools has a table to map these names to devices
901: numbers. To export a partition to a Linux guest we can use:
903: disk = [ 'phy:/dev/wd0e,0x300,w' ]
904: root = "/dev/hda1 ro"
906: and it will appear as /dev/hda on the Linux system, and be used as root
909: To install the Linux system on the partition to be exported to the
910: guest domain, the following method can be used: install
911: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
912: that will be the root partition of your Linux domain, and mount it.
913: Then copy the files from a working Linux system, make adjustments in
914: `/etc` (fstab, network config). It should also be possible to extract
915: binary packages such as .rpm or .deb directly to the mounted partition
916: using the appropriate tool, possibly running under NetBSD's Linux
917: emulation. Once the file system has been populated, umount it. If
918: desirable, the file system can be converted to ext3 using tune2fs -j.
919: It should now be possible to boot the Linux guest domain, using one of
920: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
922: To get the Linux console right, you need to add:
924: extra = "xencons=tty1"
926: to your configuration since not all Linux distributions auto-attach a
927: tty to the xen console.
929: Creating an unprivileged Solaris domain (domU)
932: See possibly outdated
933: [Solaris domU instructions](/ports/xen/howto-solaris/).
936: PCI passthrough: Using PCI devices in guest domains
939: The dom0 can give other domains access to selected PCI
940: devices. This can allow, for example, a non-privileged domain to have
941: access to a physical network interface or disk controller. However,
942: keep in mind that giving a domain access to a PCI device most likely
943: will give the domain read/write access to the whole physical memory,
944: as PCs don't have an IOMMU to restrict memory access to DMA-capable
945: device. Also, it's not possible to export ISA devices to non-dom0
946: domains, which means that the primary VGA adapter can't be exported.
947: A guest domain trying to access the VGA registers will panic.
949: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
950: not been ported to later versions at this time.
952: For a PCI device to be exported to a domU, is has to be attached to
953: the "pciback" driver in dom0. Devices passed to the dom0 via the
954: pciback.hide boot parameter will attach to "pciback" instead of the
955: usual driver. The list of devices is specified as "(bus:dev.func)",
956: where bus and dev are 2-digit hexadecimal numbers, and func a
957: single-digit number:
961: pciback devices should show up in the dom0's boot messages, and the
962: devices should be listed in the `/kern/xen/pci` directory.
964: PCI devices to be exported to a domU are listed in the "pci" array of
965: the domU's config file, with the format "0000:bus:dev.func".
967: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
969: In the domU an "xpci" device will show up, to which one or more pci
970: buses will attach. Then the PCI drivers will attach to PCI buses as
971: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
972: or any PCI drivers built in by default; you have to build your own
973: kernel to use PCI devices in a domU. Here's a kernel config example;
974: note that only the "xpci" lines are unusual.
976: include "arch/i386/conf/XEN3_DOMU"
978: # Add support for PCI buses to the XEN3_DOMU kernel
979: xpci* at xenbus ?
980: pci* at xpci ?
982: # PCI USB controllers
983: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
985: # USB bus support
986: usb* at uhci?
988: # USB Hubs
989: uhub* at usb?
990: uhub* at uhub? port ? configuration ? interface ?
992: # USB Mass Storage
993: umass* at uhub? port ? configuration ? interface ?
994: wd* at umass?
995: # SCSI controllers
996: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
998: # SCSI bus support (for both ahc and umass)
999: scsibus* at scsi?
1001: # SCSI devices
1002: sd* at scsibus? target ? lun ? # SCSI disk drives
1003: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
1006: NetBSD as a domU in a VPS
1009: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
1010: hardware. This section explains how to deal with Xen in a domU as a
1011: virtual private server where you do not control or have access to the
1012: dom0. This is not intended to be an exhaustive list of VPS providers;
1013: only a few are mentioned that specifically support NetBSD.
1015: VPS operators provide varying degrees of access and mechanisms for
1016: configuration. The big issue is usually how one controls which kernel
1017: is booted, because the kernel is nominally in the dom0 file system (to
1018: which VPS users do not normally have access). A second issue is how
1019: to install NetBSD.
1020: A VPS user may want to compile a kernel for security updates, to run
1021: npf, run IPsec, or any other reason why someone would want to change
1022: their kernel.
1024: One approach is to have an administrative interface to upload a kernel,
1025: or to select from a prepopulated list. Other approaches are pygrub
1026: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
1027: kernel from the domU file system. This is closer to a regular physical
1028: computer, where someone who controls a machine can replace the kernel.
1030: A second issue is multiple CPUs. With NetBSD 6, domUs support
1031: multiple vcpus, and it is typical for VPS providers to enable multiple
1032: CPUs for NetBSD domUs.
1037: pygrub runs in the dom0 and looks into the domU file system. This
1038: implies that the domU must have a kernel in a file system in a format
1039: known to pygrub. As of 2014, pygrub seems to be of mostly historical
1045: pvgrub is a version of grub that uses PV operations instead of BIOS
1046: calls. It is booted from the dom0 as the domU kernel, and then reads
1047: /grub/menu.lst and loads a kernel from the domU file system.
1049: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
1050: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
1051: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
1052: page](http://www.panix.com/v-colo/grub.html), which describes only
1053: Linux but should be updated to cover NetBSD :-).
1055: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
1056: their own kernel. See then [prgmr.com NetBSD
1058: (which is in need of updating).
1060: It appears that [grub's FFS
1062: does not support all aspects of modern FFS, but there are also reports
1063: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1064: partition for the kernel with the intent that grub can understand it,
1065: which leads to /netbsd not being the actual kernel. One must remember
1066: to update the special boot partition.
1071: See the [Amazon EC2 page](../amazon_ec2/).
1073: Using npf
1076: In standard kernels, npf is a module, and thus cannot be loaded in a
1077: DOMU kernel.
1079: TODO: Explain how to compile npf into a custom kernel, answering (but
1080: note that the problem was caused by not booting the right kernel)
1081: [this email to
1084: TODO items for improving NetBSD/xen
1087: * Make the NetBSD dom0 kernel work with SMP.
1088: * Test the Xen 4.5 packages adequately to be able to recommend them as
1089: the standard approach.
1090: * Get PCI passthrough working on Xen 4.5
1091: * Get pvgrub into pkgsrc, either via xentools or separately.
1092: * grub
1093: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1094: fragsize/blocksize (UFS2 support may be present; the point is to
1095: make it so that with any UFS1/UFS2 file system setup that works
1096: with NetBSD grub will also work).
1097: See [pkg/40258](http://gnats.netbsd.org/40258).
1098: * Push patches upstream.
1099: * Get UFS2 patches into pvgrub.
1100: * Add support for PV ops to a version of /boot, and make it usable as
1101: a kernel in Xen, similar to pvgrub.
1102: * Solve somehow the issue with modules for GENERIC not being loadable
1103: in a Xen dom0 or domU kernel.
1105: Random pointers
1108: This section contains links from elsewhere not yet integrated into the
1109: HOWTO, and other guides.
1111: * http://www.lumbercartel.ca/library/xen/
1112: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
1113: * https://gmplib.org/~tege/xen.html
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