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    1: Introduction
    2: ============
    4: [![[Xen
    5: screenshot]](](
    7: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
    8: (i686-class or higher), which supports running multiple guest
    9: operating systems on a single physical machine.  Xen is a Type 1 or
   10: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
   11: memory and console, a dom0 operating system which mediates access to
   12: other hardware (e.g., disks, network, USB), and one or more domU
   13: operating systems which operate in an unprivileged virtualized
   14: environment.  IO requests from the domU systems are forwarded by the
   15: hypervisor (Xen) to the dom0 to be fulfilled.
   17: Xen supports two styles of guests.  The original is Para-Virtualized
   18: (PV) which means that the guest OS does not attempt to access hardware
   19: directly, but instead makes hypercalls to the hypervisor.  This is
   20: analogous to a user-space program making system calls.  (The dom0
   21: operating system uses PV calls for some functions, such as updating
   22: memory mapping page tables, but has direct hardware access for disk
   23: and network.)   PV guests must be specifically coded for Xen.
   25: The more recent style is HVM, which means that the guest does not have
   26: code for Xen and need not be aware that it is running under Xen.
   27: Attempts to access hardware registers are trapped and emulated.  This
   28: style is less efficient but can run unmodified guests.
   30: Generally any amd64 machine will work with Xen and PV guests.  In
   31: theory i386 computers without amd64 support can be used for Xen <=
   32: 4.2, but we have no recent reports of this working (this is a hint).
   33: For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT
   34: (amd64) is needed; "cpuctl identify 0" will show this.  TODO: Clean up
   35: and check the above features.
   37: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   38: The dom0 can start one or more domUs.  (Booting is explained in detail
   39: in the dom0 section.)
   41: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   42: and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   43: attempts to address both the case of running a NetBSD dom0 on hardware
   44: and running domUs under it (NetBSD and other), and also running NetBSD
   45: as a domU in a VPS.
   47: Some versions of Xen support "PCI passthrough", which means that
   48: specific PCI devices can be made available to a specific domU instead
   49: of the dom0.  This can be useful to let a domU run X11, or access some
   50: network interface or other peripheral.
   52: NetBSD used to support Xen2; this has been removed.
   54: Prerequisites
   55: -------------
   57: Installing NetBSD/Xen is not extremely difficult, but it is more
   58: complex than a normal installation of NetBSD.
   59: In general, this HOWTO is occasionally overly restrictive about how
   60: things must be done, guiding the reader to stay on the established
   61: path when there are no known good reasons to stray.
   63: This HOWTO presumes a basic familiarity with the Xen system
   64: architecture.  This HOWTO presumes familiarity with installing NetBSD
   65: on i386/amd64 hardware and installing software from pkgsrc.
   66: See also the [Xen website](
   68: Versions of Xen and NetBSD
   69: ==========================
   71: Most of the installation concepts and instructions are independent
   72: of Xen version and NetBSD version.  This section gives advice on
   73: which version to choose.  Versions not in pkgsrc and older unsupported
   74: versions of NetBSD are intentionally ignored.
   76: Xen
   77: ---
   79: In NetBSD, xen is provided in pkgsrc, via matching pairs of packages
   80: xenkernel and xentools.  We will refer only to the kernel versions,
   81: but note that both packages must be installed together and must have
   82: matching versions.
   84: xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3.  These no longer
   85: receive security patches and should not be used.  Xen 3.1 supports PCI
   86: passthrough.  Xen 3.1 supports non-PAE on i386.
   88: xenkernel41 provides Xen 4.1.  This is no longer maintained by Xen,
   89: but as of 2014-12 receives backported security patches.  It is a
   90: reasonable although trailing-edge choice.
   92: xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as
   93: of 2014-12.
   95: xenkernel45 provides Xen 4.5.  This is new to pkgsrc as of 2015-01 and
   96: not yet recommended for other than experimental/testing use.
   98: See also the [Xen Security Advisory page](
  100: Ideally newer versions of Xen will be added to pkgsrc.
  102: Note that NetBSD support is called XEN3.  It works with Xen 3 and Xen
  103: 4 because the hypercall interface has been stable.
  105: Xen command program
  106: -------------------
  108: Early Xen used a program called xm to manipulate the system from the
  109: dom0.  Starting in 4.1, a replacement program with similar behavior
  110: called xl is provided, but it does not work well in 4.1.  In 4.2, both
  111: xm and xl work fine.  4.4 is the last version that has xm.  You must
  112: choose one or the other, because it affects which daemons you run.
  114: NetBSD
  115: ------
  117: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
  118: reasonable choices, with more or less the same considerations for
  119: non-Xen use.  Therefore, netbsd-6 is recommended as the stable version
  120: of the most recent release for production use.  For those wanting to
  121: learn Xen or without production stability concerns, netbsd-7 is likely
  122: most appropriate.
  124: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  125: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  126: need SMP; the lack of support is really a problem when using a dom0 as
  127: a normal computer.)
  129: Architecture
  130: ------------
  132: Xen itself can run on i386 or amd64 machines.  (Practically, almost
  133: any computer where one would want to run Xen supports amd64.)  If
  134: using an i386 NetBSD kernel for the dom0, PAE is required (PAE
  135: versions are built by default).  While i386 dom0 works fine, amd64 is
  136: recommended as more normal.
  138: Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
  139: if this is about the CPU having to be amd64, or about the dom0 kernel
  140: having to be amd64.
  142: One can then run i386 domUs and amd64 domUs, in any combination.  If
  143: running an i386 NetBSD kernel as a domU, the PAE version is required.
  144: (Note that emacs (at least) fails if run on i386 with PAE when built
  145: without, and vice versa, presumably due to bugs in the undump code.)
  147: Stability
  148: ---------
  150: Mostly, NetBSD as a dom0 or domU is quite stable.
  151: However, there are some open PRs indicating problems.
  153:  - [PR 48125](
  154:  - [PR 47720](
  156: Note also that there are issues with sparse vnd(4) instances, but
  157: these are not about Xen.
  159: Recommendation
  160: --------------
  162: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
  163: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
  164: dom0.  Either the i386 or amd64 of NetBSD may be used as domUs.
  166: Build problems
  167: --------------
  169: Ideally, all versions of Xen in pkgsrc would build on all versions of
  170: NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
  171: aging code and aging compilers, qemu (included in xentools for HVM
  172: support) is difficult to build.  The following are known to work or FAIL:
  174:         xenkernel3 netbsd-5 amd64
  175:         xentools3 netbsd-5 amd64
  176:         xentools3=hvm netbsd-5 amd64 ????
  177:         xenkernel33 netbsd-5 amd64
  178:         xentools33 netbsd-5 amd64
  179:         xenkernel41 netbsd-5 amd64
  180:         xentools41 netbsd-5 amd64
  181:         xenkernel42 netbsd-5 amd64
  182:         xentools42 netbsd-5 amd64
  184:         xenkernel3 netbsd-6 i386 FAIL
  185:         xentools3 netbsd-6 i386
  186:         xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
  187:         xenkernel33 netbsd-6 i386
  188:         xentools33 netbsd-6 i386
  189:         xenkernel41 netbsd-6 i386
  190:         xentools41 netbsd-6 i386
  191:         xenkernel42 netbsd-6 i386
  192:         xentools42 netbsd-6 i386 *MIXED
  194: 	(all 3 and 33 seem to FAIL)
  195:         xenkernel41 netbsd-7 i386
  196:         xentools41 netbsd-7 i386
  197:         xenkernel42 netbsd-7 i386
  198:         xentools42 netbsd-7 i386 ??FAIL
  200: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
  201: but it does not build for gdt.)
  203: NetBSD as a dom0
  204: ================
  206: NetBSD can be used as a dom0 and works very well.  The following
  207: sections address installation, updating NetBSD, and updating Xen.
  208: Note that it doesn't make sense to talk about installing a dom0 OS
  209: without also installing Xen itself.  We first address installing
  210: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  211: NetBSD install to a dom0 install by just changing the kernel and boot
  212: configuration.
  214: For experimenting with Xen, a machine with as little as 1G of RAM and
  215: 100G of disk can work.  For running many domUs in productions, far
  216: more will be needed.
  218: Styles of dom0 operation
  219: ------------------------
  221: There are two basic ways to use Xen.  The traditional method is for
  222: the dom0 to do absolutely nothing other than providing support to some
  223: number of domUs.  Such a system was probably installed for the sole
  224: purpose of hosting domUs, and sits in a server room on a UPS.
  226: The other way is to put Xen under a normal-usage computer, so that the
  227: dom0 is what the computer would have been without Xen, perhaps a
  228: desktop or laptop.  Then, one can run domUs at will.  Purists will
  229: deride this as less secure than the previous approach, and for a
  230: computer whose purpose is to run domUs, they are right.  But Xen and a
  231: dom0 (without domUs) is not meaningfully less secure than the same
  232: things running without Xen.  One can boot Xen or boot regular NetBSD
  233: alternately with little problems, simply refraining from starting the
  234: Xen daemons when not running Xen.
  236: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  237: limit the performance of the Xen/dom0 workstation approach.  In theory
  238: the only issue is that the "backend drivers" are not yet MPSAFE:
  241: Installation of NetBSD
  242: ----------------------
  244: First,
  245: [install NetBSD/amd64](/guide/inst/)
  246: just as you would if you were not using Xen.
  247: However, the partitioning approach is very important.
  249: If you want to use RAIDframe for the dom0, there are no special issues
  250: for Xen.  Typically one provides RAID storage for the dom0, and the
  251: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  252: over a RAID1 header to find /boot from a filesystem within a RAID
  253: partition; this is no different when booting Xen.
  255: There are 4 styles of providing backing storage for the virtual disks
  256: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  258: With raw partitions, one has a disklabel (or gpt) partition sized for
  259: each virtual disk to be used by the domU.  (If you are able to predict
  260: how domU usage will evolve, please add an explanation to the HOWTO.
  261: Seriously, needs tend to change over time.)
  263: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  264: for domU disks.  This is almost as efficient as raw disk partitions
  265: and more flexible.  Hence raw disk partitions should typically not
  266: be used.
  268: One can use files in the dom0 filesystem, typically created by dd'ing
  269: /dev/zero to create a specific size.  This is somewhat less efficient,
  270: but very convenient, as one can cp the files for backup, or move them
  271: between dom0 hosts.
  273: Finally, in theory one can place the files backing the domU disks in a
  274: SAN.  (This is an invitation for someone who has done this to add a
  275: HOWTO page.)
  277: Installation of Xen
  278: -------------------
  280: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  281: pkgsrc (or another matching pair).
  282: See [the pkgsrc
  283: documentation]( for help with pkgsrc.
  285: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  286: recent versions have HVM support integrated in the main xentools
  287: package.  It is entirely reasonable to run only PV guests.
  289: Next you need to install the selected Xen kernel itself, which is
  290: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  291: For debugging, one may copy xen-debug.gz; this is conceptually similar
  292: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  293: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  294: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  295: of a NetBSD build.  If using i386, use
  296: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  297: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  298: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  299: typically are) left compressed.
  301: In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
  302: kernel, so ensure that /kern is in fstab.  TODO: Say this is default,
  303: or file a PR and give a reference.
  305: Because you already installed NetBSD, you have a working boot setup
  306: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  307: beginning of your root filesystem, /boot present, and likely
  308: /boot.cfg.  (If not, fix before continuing!)
  310: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  311: example.  The basic line is
  313:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  315: which specifies that the dom0 should have 256M, leaving the rest to be
  316: allocated for domUs.  To use a serial console, use
  318:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
  320: which will use the first serial port for Xen (which counts starting
  321: from 1), forcing speed/parity, and also for NetBSD (which counts
  322: starting at 0).  In an attempt to add performance, one can also add
  324:         dom0_max_vcpus=1 dom0_vcpus_pin
  326: to force only one vcpu to be provided (since NetBSD dom0 can't use
  327: more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.
  329: Xen has [many boot
  330: options](,
  331: and other tham dom0 memory and max_vcpus, they are generally not
  332: necessary.
  334: As with non-Xen systems, you should have a line to boot /netbsd (a
  335: kernel that works without Xen) and fallback versions of the non-Xen
  336: kernel, Xen, and the dom0 kernel.
  338: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  339: than GENERIC without Xen.
  341: Using grub (historic)
  342: ---------------------
  344: Before NetBSD's native bootloader could support Xen, the use of
  345: grub was recommended.  If necessary, see the
  346: [old grub information](/ports/xen/howto-grub/).
  348: The [HowTo on Installing into
  349: RAID-1](
  350: explains how to set up booting a dom0 with Xen using grub with
  351: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  352: boot.)
  354: Configuring Xen
  355: ---------------
  357: Xen logs will be in /var/log/xen.
  359: Now, you have a system that will boot Xen and the dom0 kernel, but not
  360: do anything else special.  Make sure that you have rebooted into Xen.
  361: There will be no domUs, and none can be started because you still have
  362: to configure the dom0 tools.  The daemons which should be run vary
  363: with Xen version and with whether one is using xm or xl.  Note that
  364: xend is for supporting "xm", and should only be used if you plan on
  365: using "xm".  Do NOT enable xend if you plan on using "xl" as it will
  366: cause problems.  Running xl without xencommons=YES (and starting it)
  367: will result in a hang (so don't do that; follow the HOWTO!).
  369: The installation of NetBSD should already have created devices for xen
  370: (xencons, xenevt), but if they are not present, create them:
  372:         cd /dev && sh MAKEDEV xen
  374: TODO: Give 3.1 advice (or remove it from pkgsrc).
  376: For 3.3 (and thus xm), add to rc.conf (but note that you should have
  377: installed 4.1 or 4.2):
  379:         xend=YES
  380:         xenbackendd=YES
  382: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
  384:         xencommons=YES
  385:         xend=YES
  387: (If you are using xentools41 from before 2014-12-26, change
  388: rc.d/xendomains to use xm rather than xl.)
  390: For 4.2 with xm, add to rc.conf
  392:         xencommons=YES
  393:         xend=YES
  395: For 4.2 with xl, add to rc.conf:
  397:         xencommons=YES
  398:         TODO: explain if there is a xend replacement
  400: For 4.5 (and thus with xl), add to rc.conf:
  402:         xencommons=YES
  403:         TODO: explain if there is a xend replacement
  405: TODO: Recommend for/against xen-watchdog.
  407: After you have configured the daemons and either started them (in the
  408: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  409: available resources, and running domains.  An example with xm follows:
  411:         # xm dmesg
  412: 	[xen's boot info]
  413:         # xm info
  414: 	[available memory, etc.]
  415:         # xm list
  416:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  417:         Domain-0           0       64    0  r----     58.1
  419: With xl, the commands are the same, and the output may be slightly
  420: different.  TODO: add example output for xl before the xm example,
  421: after confirming on 4.2 and resolving the TODO about rc.conf.
  423: ### Issues with xencommons
  425: xencommons starts xenstored, which stores data on behalf of dom0 and
  426: domUs.  It does not currently work to stop and start xenstored.
  427: Certainly all domUs should be shutdown first, following the sort order
  428: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  429: and is not notified when xenstored exits, leading to not recreating
  430: the state when the new xenstored starts.  Until there's a mechanism to
  431: make this work, one should not expect to be able to restart xenstored
  432: (and thus xencommons).  There is currently no reason to expect that
  433: this will get fixed any time soon.
  435: anita (for testing NetBSD)
  436: --------------------------
  438: With the setup so far (assuming 4.2/xl), one should be able to run
  439: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  440: root, because anita must create a domU):
  442:         anita --vmm=xl test file:///usr/obj/i386/
  444: Alternatively, one can use --vmm=xm to use xm-based domU creation
  445: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  447: Xen-specific NetBSD issues
  448: --------------------------
  450: There are (at least) two additional things different about NetBSD as a
  451: dom0 kernel compared to hardware.
  453: One is that modules are not usable in DOM0 kernels, so one must
  454: compile in what's needed.  It's not really that modules cannot work,
  455: but that modules must be built for XEN3_DOM0 because some of the
  456: defines change and the normal module builds don't do this.  Basically,
  457: enabling Xen changes the kernel ABI, and the module build system
  458: doesn't cope with this.
  460: The other difference is that XEN3_DOM0 does not have exactly the same
  461: options as GENERIC.  While it is debatable whether or not this is a
  462: bug, users should be aware of this and can simply add missing config
  463: items if desired.
  465: Updating NetBSD in a dom0
  466: -------------------------
  468: This is just like updating NetBSD on bare hardware, assuming the new
  469: version supports the version of Xen you are running.  Generally, one
  470: replaces the kernel and reboots, and then overlays userland binaries
  471: and adjusts /etc.
  473: Note that one must update both the non-Xen kernel typically used for
  474: rescue purposes and the DOM0 kernel used with Xen.
  476: Converting from grub to /boot
  477: -----------------------------
  479: These instructions were [TODO: will be] used to convert a system from
  480: grub to /boot.  The system was originally installed in February of
  481: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  482: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  483: 4.1 and grub, much like the message linked earlier in the grub
  484: section.
  486:         # Install mbr bootblocks on both disks. 
  487:         fdisk -i /dev/rwd0d
  488:         fdisk -i /dev/rwd1d
  489:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  490:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  491:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  492:         # Install secondary boot loader
  493:         cp -p /usr/mdec/boot /
  494:         # Create boog.cfg following earlier guidance:
  495:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  496:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
  497:         menu=GENERIC:boot
  498:         menu=GENERIC single-user:boot -s
  499:         menu=GENERIC.ok:boot netbsd.ok
  500:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  501:         menu=Drop to boot prompt:prompt
  502:         default=1
  503:         timeout=30
  505: TODO: actually do this and fix it if necessary.
  507: Updating Xen versions
  508: ---------------------
  510: Updating Xen is conceptually not difficult, but can run into all the
  511: issues found when installing Xen.  Assuming migration from 4.1 to 4.2,
  512: remove the xenkernel41 and xentools41 packages and install the
  513: xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz to /.
  515: Ensure that the contents of /etc/rc.d/xen* are correct.  Enable the
  516: correct set of daemons.  Ensure that the domU config files are valid
  517: for the new version.
  519: Hardware known to work
  520: ----------------------
  522: Arguably, this section is misplaced, and there should be a page of
  523: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
  524: assumption that NetBSD/xen runs fine on any modern hardware that
  525: NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU/RAM
  526: triples to aid those choosing a motherboard.  Note that Xen systems
  527: usually do not run X, so a listing here does not imply that X works at
  528: all.
  530:         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
  531:         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
  532:         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
  534: Older hardware:
  536:         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
  538: Running Xen under qemu
  539: ----------------------
  541: The astute reader will note that this section is somewhat twisted.
  542: However, it can be useful to run Xen under qemu either because the
  543: version of NetBSD as a dom0 does not run on the hardware in use, or to
  544: generate automated test cases involving Xen.
  546: In 2015-01, the following combination was reported to mostly work:
  548:         host OS: NetBSD/amd64 6.1.4
  549:         qemu: 2.2.0 from pkgsrc
  550:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  551:         dom0 kernel: NetBSD/amd64 6.1.5
  552:         Xen tools: xentools42-4.2.5 from pkgsrc
  554: See [PR 47720]( for a problem with dom0
  555: shutdown.
  557: Unprivileged domains (domU)
  558: ===========================
  560: This section describes general concepts about domUs.  It does not
  561: address specific domU operating systems or how to install them.  The
  562: config files for domUs are typically in /usr/pkg/etc/xen, and are
  563: typically named so that the file name, domU name and the domU's host
  564: name match.
  566: The domU is provided with cpu and memory by Xen, configured by the
  567: dom0.  The domU is provided with disk and network by the dom0,
  568: mediated by Xen, and configured in the dom0.
  570: Entropy in domUs can be an issue; physical disks and network are on
  571: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  573: Config files
  574: ------------
  576: There is no good order to present config files and the concepts
  577: surrounding what is being configured.  We first show an example config
  578: file, and then in the various sections give details.
  580: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  581: for a large number of well-commented examples, mostly for running
  582: GNU/Linux.
  584: The following is an example minimal domain configuration file
  585: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  586: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  587: i386 domU).  The domU serves as a network file server.
  589:         # -*- mode: python; -*-
  591:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  592:         memory = 1024
  593:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  594:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  595:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  597: The domain will have the same name as the file.  The kernel has the
  598: host/domU name in it, so that on the dom0 one can update the various
  599: domUs independently.  The vif line causes an interface to be provided,
  600: with a specific mac address (do not reuse MAC addresses!), in bridge
  601: mode.  Two disks are provided, and they are both writable; the bits
  602: are stored in files and Xen attaches them to a vnd(4) device in the
  603: dom0 on domain creation.  The system treates xbd0 as the boot device
  604: without needing explicit configuration.
  606: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  607: that "xm create" takes the name of a config file, while other commands
  608: take the name of a domain.  To create the domain, connect to the
  609: console, create the domain while attaching the console, shutdown the
  610: domain, and see if it has finished stopping, do (or xl with Xen >=
  611: 4.2):
  613:         xm create foo
  614:         xm console foo
  615:         xm create -c foo
  616:         xm shutdown foo
  617:         xm list
  619: Typing ^] will exit the console session.  Shutting down a domain is
  620: equivalent to pushing the power button; a NetBSD domU will receive a
  621: power-press event and do a clean shutdown.  Shutting down the dom0
  622: will trigger controlled shutdowns of all configured domUs.
  624: domU kernels
  625: ------------
  627: On a physical computer, the BIOS reads sector 0, and a chain of boot
  628: loaders finds and loads a kernel.  Normally this comes from the root
  629: filesystem.  With Xen domUs, the process is totally different.  The
  630: normal path is for the domU kernel to be a file in the dom0's
  631: filesystem.  At the request of the dom0, Xen loads that kernel into a
  632: new domU instance and starts execution.  While domU kernels can be
  633: anyplace, reasonable places to store domU kernels on the dom0 are in /
  634: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  635: config files), or in /u0/xen (where the vdisks are).
  637: Note that loading the domU kernel from the dom0 implies that boot
  638: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  639: See the VPS section near the end for discussion of alternate ways to
  640: obtain domU kernels.
  642: CPU and memory
  643: --------------
  645: A domain is provided with some number of vcpus, less than the number
  646: of cpus seen by the hypervisor.  (For a dom0, this is controlled by
  647: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  648: from the config file by the "vcpus = N" directive.
  650: A domain is provided with memory; this is controlled in the config
  651: file by "memory = N" (in megabytes).  In the straightforward case, the
  652: sum of the the memory allocated to the dom0 and all domUs must be less
  653: than the available memory.
  655: Xen also provides a "balloon" driver, which can be used to let domains
  656: use more memory temporarily.  TODO: Explain better, and explain how
  657: well it works with NetBSD.
  659: Virtual disks
  660: -------------
  662: With the file/vnd style, typically one creates a directory,
  663: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  664: domUs.  Then, for each domU disk, one writes zeros to a file that then
  665: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  666: for the first virtual disk for the domU called foo.  Writing zeros to
  667: the file serves two purposes.  One is that preallocating the contents
  668: improves performance.  The other is that vnd on sparse files has
  669: failed to work.  TODO: give working/notworking NetBSD versions for
  670: sparse vnd.  Note that the use of file/vnd for Xen is not really
  671: different than creating a file-backed virtual disk for some other
  672: purpose, except that xentools handles the vnconfig commands.  To
  673: create an empty 4G virtual disk, simply do
  675:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  677: Do not use qemu-img-xen, because this will create sparse file.  There
  678: have been recent (2015) reports of sparse vnd(4) devices causing
  679: lockups, but there is apparently no PR.
  681: With the lvm style, one creates logical devices.  They are then used
  682: similarly to vnds.  TODO: Add an example with lvm.
  684: In domU config files, the disks are defined as a sequence of 3-tuples.
  685: The first element is "method:/path/to/disk".  Common methods are
  686: "file:" for file-backed vnd. and "phy:" for something that is already
  687: a (TODO: character or block) device.
  689: The second element is an artifact of how virtual disks are passed to
  690: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  691: are given a device name to associate with the disk, and values like
  692: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  693: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  694: second argument.  The name given is converted to a major/minor by
  695: calling stat(2) on the name in /dev and this is passed to the domU.
  696: In the general case, the dom0 and domU can be different operating
  697: systems, and it is an unwarranted assumption that they have consistent
  698: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  699: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  700: for the second works fine and avoids this issue.  For a GNU/Linux
  701: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  702: /dev/hda1.
  704: The third element is "w" for writable disks, and "r" for read-only
  705: disks.
  707: Virtual Networking
  708: ------------------
  710: Xen provides virtual ethernets, each of which connects the dom0 and a
  711: domU.  For each virtual network, there is an interface "xvifN.M" in
  712: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  713: name).  The interfaces behave as if there is an Ethernet with two
  714: adaptors connected.  From this primitive, one can construct various
  715: configurations.  We focus on two common and useful cases for which
  716: there are existing scripts: bridging and NAT.
  718: With bridging (in the example above), the domU perceives itself to be
  719: on the same network as the dom0.  For server virtualization, this is
  720: usually best.  Bridging is accomplished by creating a bridge(4) device
  721: and adding the dom0's physical interface and the various xvifN.0
  722: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  723: config file.  The bridge must be set up already in the dom0; an
  724: example /etc/ifconfig.bridge0 is:
  726:         create
  727:         up
  728:         !brconfig bridge0 add wm0
  730: With NAT, the domU perceives itself to be behind a NAT running on the
  731: dom0.  This is often appropriate when running Xen on a workstation.
  732: TODO: NAT appears to be configured by "vif = [ '' ]".
  734: The MAC address specified is the one used for the interface in the new
  735: domain.  The interface in dom0 will use this address XOR'd with
  736: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  738: Sizing domains
  739: --------------
  741: Modern x86 hardware has vast amounts of resources.  However, many
  742: virtual servers can function just fine on far less.  A system with
  743: 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  744: far easier to adjust virtual resources than physical ones.  For
  745: memory, it's just a config file edit and a reboot.  For disk, one can
  746: create a new file and vnconfig it (or lvm), and then dump/restore,
  747: just like updating physical disks, but without having to be there and
  748: without those pesky connectors.
  750: Starting domains automatically
  751: ------------------------------
  753: To start domains foo at bar at boot and shut them down cleanly on dom0
  754: shutdown, in rc.conf add:
  756:         xendomains="foo bar"
  758: Note that earlier versions of the xentools41 xendomains rc.d scripth
  759: usd xl, when one should use xm with 4.1.
  761: Creating specific unprivileged domains (domU)
  762: =============================================
  764: Creating domUs is almost entirely independent of operating system.  We
  765: have already presented the basics of config files.  Note that you must
  766: have already completed the dom0 setup so that "xl list" (or "xm list")
  767: works.
  769: Creating an unprivileged NetBSD domain (domU)
  770: ---------------------------------------------
  772: See the earlier config file, and adjust memory.  Decide on how much
  773: storage you will provide, and prepare it (file or lvm).
  775: While the kernel will be obtained from the dom0 filesystem, the same
  776: file should be present in the domU as /netbsd so that tools like
  777: savecore(8) can work.   (This is helpful but not necessary.)
  779: The kernel must be specifically for Xen and for use as a domU.  The
  780: i386 and amd64 provide the following kernels:
  782:         i386 XEN3_DOMU
  783:         i386 XEN3PAE_DOMU
  784:         amd64 XEN3_DOMU
  786: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  787: use the PAE version of the i386 kernel.
  789: This will boot NetBSD, but this is not that useful if the disk is
  790: empty.  One approach is to unpack sets onto the disk outside of xen
  791: (by mounting it, just as you would prepare a physical disk for a
  792: system you can't run the installer on).
  794: A second approach is to run an INSTALL kernel, which has a miniroot
  795: and can load sets from the network.  To do this, copy the INSTALL
  796: kernel to / and change the kernel line in the config file to:
  798:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  800: Then, start the domain as "xl create -c configname".
  802: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  803: line should be used in the config file.
  805:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  807: After booting the domain, the option to install via CDROM may be
  808: selected.  The CDROM device should be changed to `xbd1d`.
  810: Once done installing, "halt -p" the new domain (don't reboot or halt,
  811: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  812: config file), switch the config file back to the XEN3_DOMU kernel,
  813: and start the new domain again. Now it should be able to use "root on
  814: xbd0a" and you should have a, functional NetBSD domU.
  816: TODO: check if this is still accurate.
  817: When the new domain is booting you'll see some warnings about *wscons*
  818: and the pseudo-terminals. These can be fixed by editing the files
  819: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  820: `/etc/ttys`, except *console*, like this:
  822:     console "/usr/libexec/getty Pc"         vt100   on secure
  823:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  824:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  825:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  826:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  828: Finally, all screens must be commented out from `/etc/wscons.conf`.
  830: It is also desirable to add
  832:         powerd=YES
  834: in rc.conf. This way, the domain will be properly shut down if
  835: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  837: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  838: filesystem.  However, various programs (e.g. netstat) will use that
  839: kernel to look up symbols to read from kernel virtual memory.  If
  840: /netbsd is not the running kernel, those lookups will fail.  (This is
  841: not really a Xen-specific issue, but because the domU kernel is
  842: obtained from the dom0, it is far more likely to be out of sync or
  843: missing with Xen.)
  845: Creating an unprivileged Linux domain (domU)
  846: --------------------------------------------
  848: Creating unprivileged Linux domains isn't much different from
  849: unprivileged NetBSD domains, but there are some details to know.
  851: First, the second parameter passed to the disk declaration (the '0x1' in
  852: the example below)
  854:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  856: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  857: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  858: So, hda1 which has major 3 and minor 1 on a Linux system will have
  859: device number 0x301.  Alternatively, devices names can be used (hda,
  860: hdb, ...)  as xentools has a table to map these names to devices
  861: numbers.  To export a partition to a Linux guest we can use:
  863:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  864:         root = "/dev/hda1 ro"
  866: and it will appear as /dev/hda on the Linux system, and be used as root
  867: partition.
  869: To install the Linux system on the partition to be exported to the
  870: guest domain, the following method can be used: install
  871: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  872: that will be the root partition of your Linux domain, and mount it.
  873: Then copy the files from a working Linux system, make adjustments in
  874: `/etc` (fstab, network config).  It should also be possible to extract
  875: binary packages such as .rpm or .deb directly to the mounted partition
  876: using the appropriate tool, possibly running under NetBSD's Linux
  877: emulation.  Once the filesystem has been populated, umount it.  If
  878: desirable, the filesystem can be converted to ext3 using tune2fs -j.
  879: It should now be possible to boot the Linux guest domain, using one of
  880: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  882: To get the linux console right, you need to add:
  884:     extra = "xencons=tty1"
  886: to your configuration since not all linux distributions auto-attach a
  887: tty to the xen console.
  889: Creating an unprivileged Solaris domain (domU)
  890: ----------------------------------------------
  892: See possibly outdated
  893: [Solaris domU instructions](/ports/xen/howto-solaris/).
  896: PCI passthrough: Using PCI devices in guest domains
  897: ---------------------------------------------------
  899: The dom0 can give other domains access to selected PCI
  900: devices. This can allow, for example, a non-privileged domain to have
  901: access to a physical network interface or disk controller.  However,
  902: keep in mind that giving a domain access to a PCI device most likely
  903: will give the domain read/write access to the whole physical memory,
  904: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  905: device.  Also, it's not possible to export ISA devices to non-dom0
  906: domains, which means that the primary VGA adapter can't be exported.
  907: A guest domain trying to access the VGA registers will panic.
  909: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  910: not been ported to later versions at this time.
  912: For a PCI device to be exported to a domU, is has to be attached to
  913: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  914: pciback.hide boot parameter will attach to "pciback" instead of the
  915: usual driver.  The list of devices is specified as "(bus:dev.func)",
  916: where bus and dev are 2-digit hexadecimal numbers, and func a
  917: single-digit number:
  919:         pciback.hide=(00:0a.0)(00:06.0)
  921: pciback devices should show up in the dom0's boot messages, and the
  922: devices should be listed in the `/kern/xen/pci` directory.
  924: PCI devices to be exported to a domU are listed in the "pci" array of
  925: the domU's config file, with the format "0000:bus:dev.func".
  927:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  929: In the domU an "xpci" device will show up, to which one or more pci
  930: busses will attach.  Then the PCI drivers will attach to PCI busses as
  931: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  932: or any PCI drivers built in by default; you have to build your own
  933: kernel to use PCI devices in a domU.  Here's a kernel config example;
  934: note that only the "xpci" lines are unusual.
  936:         include         "arch/i386/conf/XEN3_DOMU"
  938:         # Add support for PCI busses to the XEN3_DOMU kernel
  939:         xpci* at xenbus ?
  940:         pci* at xpci ?
  942:         # PCI USB controllers
  943:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  945:         # USB bus support
  946:         usb*    at uhci?
  948:         # USB Hubs
  949:         uhub*   at usb?
  950:         uhub*   at uhub? port ? configuration ? interface ?
  952:         # USB Mass Storage
  953:         umass*  at uhub? port ? configuration ? interface ?
  954:         wd*     at umass?
  955:         # SCSI controllers
  956:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  958:         # SCSI bus support (for both ahc and umass)
  959:         scsibus* at scsi?
  961:         # SCSI devices
  962:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  963:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  966: NetBSD as a domU in a VPS
  967: =========================
  969: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  970: hardware.  This section explains how to deal with Xen in a domU as a
  971: virtual private server where you do not control or have access to the
  972: dom0.  This is not intended to be an exhaustive list of VPS providers;
  973: only a few are mentioned that specifically support NetBSD.
  975: VPS operators provide varying degrees of access and mechanisms for
  976: configuration.  The big issue is usually how one controls which kernel
  977: is booted, because the kernel is nominally in the dom0 filesystem (to
  978: which VPS users do not normally have acesss).  A second issue is how
  979: to install NetBSD.
  980: A VPS user may want to compile a kernel for security updates, to run
  981: npf, run IPsec, or any other reason why someone would want to change
  982: their kernel.
  984: One approach is to have an adminstrative interface to upload a kernel,
  985: or to select from a prepopulated list.  Other approaches are pygrub
  986: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  987: kernel from the domU filesystem.  This is closer to a regular physical
  988: computer, where someone who controls a machine can replace the kernel.
  990: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  991: multiple vcpus, and it is typical for VPS providers to enable multiple
  992: CPUs for NetBSD domUs.
  994: pygrub
  995: -------
  997: pygrub runs in the dom0 and looks into the domU filesystem.  This
  998: implies that the domU must have a kernel in a filesystem in a format
  999: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
 1000: interest.
 1002: pvgrub
 1003: ------
 1005: pvgrub is a version of grub that uses PV operations instead of BIOS
 1006: calls.  It is booted from the dom0 as the domU kernel, and then reads
 1007: /grub/menu.lst and loads a kernel from the domU filesystem.
 1009: [Panix]( lets users use pvgrub.  Panix reports
 1010: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
 1011: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
 1012: page](, which describes only
 1013: Linux but should be updated to cover NetBSD :-).
 1015: []( also lets users with pvgrub to boot
 1016: their own kernel.  See then [ NetBSD
 1017: HOWTO](
 1018: (which is in need of updating).
 1020: It appears that [grub's FFS
 1021: code](
 1022: does not support all aspects of modern FFS, but there are also reports
 1023: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
 1024: partition for the kernel with the intent that grub can understand it,
 1025: which leads to /netbsd not being the actual kernel.  One must remember
 1026: to update the special boot partiion.
 1028: Amazon
 1029: ------
 1031: See the [Amazon EC2 page](../amazon_ec2/).
 1033: Using npf
 1034: ---------
 1036: In standard kernels, npf is a module, and thus cannot be loaded in a
 1037: DOMU kernel.
 1039: TODO: Explain how to compile npf into a custom kernel, answering (but
 1040: note that the problem was caused by not booting the right kernel)
 1041: [this email to
 1042: netbsd-users](
 1044: TODO items for improving NetBSD/xen
 1045: ===================================
 1047: * Make the NetBSD dom0 kernel work with SMP.
 1048: * Test the Xen 4.5 packages adequately to be able to recommend them as
 1049:   the standard approach.
 1050: * Get PCI passthrough working on Xen 4.5
 1051: * Get pvgrub into pkgsrc, either via xentools or separately.
 1052: * grub
 1053:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
 1054:     fragsize/blocksize (UFS2 support may be present; the point is to
 1055:     make it so that with any UFS1/UFS2 filesystem setup that works
 1056:     with NetBSD grub will also work).
 1057:     See [pkg/40258](
 1058:   * Push patches upstream.
 1059:   * Get UFS2 patches into pvgrub.
 1060: * Add support for PV ops to a version of /boot, and make it usable as
 1061:   a kernel in Xen, similar to pvgrub.
 1062: * Solve somehow the issue with modules for GENERIC not being loadable
 1063:   in a Xen dom0 or domU kernel.
 1065: Random pointers
 1066: ===============
 1068: TODO: This section contains links from elsewhere not yet integrated
 1069: into the HOWTO.
 1071: *
 1072: *

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