File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
Revision 1.117: download - view: text, annotated - select for diffs
Tue Dec 20 15:05:36 2016 UTC (5 years, 1 month ago) by gdt
Branches: MAIN
CVS tags: HEAD
Recommend recent netbsd-7

Add link to 2015-11 pullup of scheduler fix.
Add link to another HOWTO.

    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, 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: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   42: The dom0 can start one or more domUs.  (Booting is explained in detail
   43: in the dom0 section.)
   45: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   46: and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   47: attempts to address both the case of running a NetBSD dom0 on hardware
   48: and running domUs under it (NetBSD and other), and also running NetBSD
   49: as a domU in a VPS.
   51: Some versions of Xen support "PCI passthrough", which means that
   52: specific PCI devices can be made available to a specific domU instead
   53: of the dom0.  This can be useful to let a domU run X11, or access some
   54: network interface or other peripheral.
   56: NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD
   57: 7.  Xen 2 has been removed from pkgsrc.
   59: Prerequisites
   60: -------------
   62: Installing NetBSD/Xen is not extremely difficult, but it is more
   63: complex than a normal installation of NetBSD.
   64: In general, this HOWTO is occasionally overly restrictive about how
   65: things must be done, guiding the reader to stay on the established
   66: path when there are no known good reasons to stray.
   68: This HOWTO presumes a basic familiarity with the Xen system
   69: architecture.  This HOWTO presumes familiarity with installing NetBSD
   70: on i386/amd64 hardware and installing software from pkgsrc.
   71: See also the [Xen website](
   73: Versions of Xen and NetBSD
   74: ==========================
   76: Most of the installation concepts and instructions are independent
   77: of Xen version and NetBSD version.  This section gives advice on
   78: which version to choose.  Versions not in pkgsrc and older unsupported
   79: versions of NetBSD are intentionally ignored.
   81: Xen
   82: ---
   84: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   85: xenkernel and xentools.  We will refer only to the kernel versions,
   86: but note that both packages must be installed together and must have
   87: matching versions.
   89: xenkernel3 provides Xen 3.1.  It is no longer maintained by Xen, and the last applied security patch was in
   90: 2011. Thus, it should not be used.  It supports PCI passthrough,
   91: which is why people use it anyway. Xen 3.1 supports i386, both PAE and
   92: non-PAE.
   94: xenkernel33 provides Xen 3.3.  It is no longer maintained by Xen, and
   95: the last applied security patch was in 2012.  Thus, it should not be
   96: used.  Xen 3.3 supports i386, but only in PAE mode.  There are no good
   97: reasons to run this version.
   99: xenkernel41 provides Xen 4.1.  It is no longer maintained by Xen, but
  100: as of 2016-12 received backported security patches.  Xen 4.1 supports
  101: i386, but only in PAE mode.  There are no good reasons to run this
  102: version.
  104: xenkernel42 provides Xen 4.2.  It is no longer maintained by Xen, but
  105: as of 2016-12 received backported security patches.  Xen 4.2 supports
  106: i386, but only in PAE mode.  The only reason to run this is if you
  107: need to use xm instead of xl, or if you need to run an i386 dom0
  108: (because your hardware is i386 only).
  110: xenkernel45 provides Xen 4.5.  As of 2016-12, security patches were
  111: released by Xen and applied to pkgsrc.  Xen 4.5 requires an amd64
  112: dom0, but domUs can be amd64 or i386 PAE.  TODO: It is either a
  113: conservative choice or somewhat old.
  115: xenkernel46 provides Xen 4.6.  It is new to pkgsrc as of 2016-05.  As
  116: of 2016-12, security patches were released by Xen and applied to
  117: pkgsrc.  Xen 4.6 requires an amd64 dom0, but domUs can be amd64 or
  118: i386 PAE.  TODO: It is either a somewhat aggressive choice or the
  119: standard choice
  121: Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in
  122: pkgsrc.
  124: See also the [Xen Security Advisory page](
  126: Note that NetBSD support is called XEN3.  It works with Xen 3 and Xen
  127: 4 because the hypercall interface has been stable.
  129: Xen command program
  130: -------------------
  132: Early Xen used a program called xm to manipulate the system from the
  133: dom0.  Starting in 4.1, a replacement program with similar behavior
  134: called xl is provided, but it does not work well in 4.1.  In 4.2, both
  135: xm and xl work fine.  4.4 is the last version that has xm.  You must
  136: choose one or the other, because it affects which daemons you run.
  137: However, the rc.d scripts provided by xentools packages expect a
  138: particular version, and you should use the version used by the
  139: scripts.
  141: NetBSD
  142: ------
  144: The netbsd-6, netbsd-7, and -current branches are all reasonable
  145: choices, with more or less the same considerations for non-Xen use.
  146: Therefore, netbsd-7 is recommended as the stable version of the most
  147: recent release for production use.  In addition, netbsd-7 and -current
  148: have a important scheduler fix (in November of 2015) affecting
  149: contention between dom0 and domUs; see
  150: for a
  151: description.  For those wanting to learn Xen or without production
  152: stability concerns, netbsd-7 is still likely most appropriate, but
  153: -current is also a reasonable choice.  (Xen runs ok on netbsd-5, but
  154: the xentools packages are likely difficult to build, and netbsd-5 is
  155: not supported.)
  157: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  158: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  159: need SMP for dom0 functions; the lack of support is really a problem
  160: when using a dom0 as a normal computer.)
  162: Architecture
  163: ------------
  165: Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen
  166: versions).  (Practically, almost any computer where one would want to
  167: run Xen today supports amd64.)
  169: Xen, the dom0 kernel, and each domU kernel can be either i386 or
  170: amd64.  When building a xenkernel package, one obtains i386 on an i386
  171: host, and amd64 on an amd64 host.  If the Xen kernel is i386, then the
  172: dom0 kernel and all domU kernels must be i386.  With an amd64 Xen
  173: kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0
  174: kernel should in theory work.  An amd64 Xen/dom0 is known to support
  175: both i386PAE and amd64 domUs.
  177: i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are
  178: built by default.  (Note that emacs (at least) fails if run on i386
  179: with PAE when built without, and vice versa, presumably due to bugs in
  180: the undump code.)
  182: Because of the above, the standard approach is to use amd64 for the
  183: dom0.
  185: Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
  186: if this is about the CPU, the Xen kernel, or the dom0 kernel having to
  187: be amd64.
  190: Stability
  191: ---------
  193: Mostly, NetBSD as a dom0 or domU is quite stable.
  194: However, there are some open PRs indicating problems.
  196:  - [PR 48125](
  197:  - [PR 47720](
  199: Note also that there are issues with sparse vnd(4) instances, but
  200: these are not about Xen -- they just are noticed with sparse vnd(4)
  201: instances in support of virtual disks in a dom0.
  203: Recommendation
  204: --------------
  206: Therefore, this HOWTO recommends running xenkernel45 or xenkernel46,
  207: xl, the NetBSD 7 stable branch, and to use an amd64 kernel as the
  208: dom0.  Either the i386PAE or amd64 version of NetBSD may be used as
  209: domUs.
  211: Build problems
  212: --------------
  214: Ideally, all versions of Xen in pkgsrc would build on all versions of
  215: NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
  216: aging code and aging compilers, qemu (included in xentools for HVM
  217: support) is difficult to build.  The following are known to work or FAIL:
  219:         xenkernel3 netbsd-5 amd64
  220:         xentools3 netbsd-5 amd64
  221:         xentools3=hvm netbsd-5 amd64 ????
  222:         xenkernel33 netbsd-5 amd64
  223:         xentools33 netbsd-5 amd64
  224:         xenkernel41 netbsd-5 amd64
  225:         xentools41 netbsd-5 amd64
  226:         xenkernel42 netbsd-5 amd64
  227:         xentools42 netbsd-5 amd64
  229:         xenkernel3 netbsd-6 i386 FAIL
  230:         xentools3 netbsd-6 i386
  231:         xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
  232:         xenkernel33 netbsd-6 i386
  233:         xentools33 netbsd-6 i386
  234:         xenkernel41 netbsd-6 i386
  235:         xentools41 netbsd-6 i386
  236:         xenkernel42 netbsd-6 i386
  237:         xentools42 netbsd-6 i386 *MIXED
  239: 	(all 3 and 33 seem to FAIL)
  240:         xenkernel41 netbsd-7 i386
  241:         xentools41 netbsd-7 i386
  242:         xenkernel42 netbsd-7 i386
  243:         xentools42 netbsd-7 i386 ??FAIL
  245: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
  246: but it does not build for gdt.)
  248: NetBSD as a dom0
  249: ================
  251: NetBSD can be used as a dom0 and works very well.  The following
  252: sections address installation, updating NetBSD, and updating Xen.
  253: Note that it doesn't make sense to talk about installing a dom0 OS
  254: without also installing Xen itself.  We first address installing
  255: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  256: NetBSD install to a dom0 install by just changing the kernel and boot
  257: configuration.
  259: For experimenting with Xen, a machine with as little as 1G of RAM and
  260: 100G of disk can work.  For running many domUs in productions, far
  261: more will be needed.
  263: Styles of dom0 operation
  264: ------------------------
  266: There are two basic ways to use Xen.  The traditional method is for
  267: the dom0 to do absolutely nothing other than providing support to some
  268: number of domUs.  Such a system was probably installed for the sole
  269: purpose of hosting domUs, and sits in a server room on a UPS.
  271: The other way is to put Xen under a normal-usage computer, so that the
  272: dom0 is what the computer would have been without Xen, perhaps a
  273: desktop or laptop.  Then, one can run domUs at will.  Purists will
  274: deride this as less secure than the previous approach, and for a
  275: computer whose purpose is to run domUs, they are right.  But Xen and a
  276: dom0 (without domUs) is not meaningfully less secure than the same
  277: things running without Xen.  One can boot Xen or boot regular NetBSD
  278: alternately with little problems, simply refraining from starting the
  279: Xen daemons when not running Xen.
  281: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  282: limit the performance of the Xen/dom0 workstation approach.  In theory
  283: the only issue is that the "backend drivers" are not yet MPSAFE:
  286: Installation of NetBSD
  287: ----------------------
  289: First,
  290: [install NetBSD/amd64](/guide/inst/)
  291: just as you would if you were not using Xen.
  292: However, the partitioning approach is very important.
  294: If you want to use RAIDframe for the dom0, there are no special issues
  295: for Xen.  Typically one provides RAID storage for the dom0, and the
  296: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  297: over a RAID1 header to find /boot from a file system within a RAID
  298: partition; this is no different when booting Xen.
  300: There are 4 styles of providing backing storage for the virtual disks
  301: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  303: With raw partitions, one has a disklabel (or gpt) partition sized for
  304: each virtual disk to be used by the domU.  (If you are able to predict
  305: how domU usage will evolve, please add an explanation to the HOWTO.
  306: Seriously, needs tend to change over time.)
  308: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  309: for domU disks.  This is almost as efficient as raw disk partitions
  310: and more flexible.  Hence raw disk partitions should typically not
  311: be used.
  313: One can use files in the dom0 file system, typically created by dd'ing
  314: /dev/zero to create a specific size.  This is somewhat less efficient,
  315: but very convenient, as one can cp the files for backup, or move them
  316: between dom0 hosts.
  318: Finally, in theory one can place the files backing the domU disks in a
  319: SAN.  (This is an invitation for someone who has done this to add a
  320: HOWTO page.)
  322: Installation of Xen
  323: -------------------
  325: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  326: pkgsrc (or another matching pair).
  327: See [the pkgsrc
  328: documentation]( for help with pkgsrc.
  330: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  331: recent versions have HVM support integrated in the main xentools
  332: package.  It is entirely reasonable to run only PV guests.
  334: Next you need to install the selected Xen kernel itself, which is
  335: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  336: For debugging, one may copy xen-debug.gz; this is conceptually similar
  337: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  338: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  339: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  340: of a NetBSD build.  If using i386, use
  341: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  342: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  343: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  344: typically are) left compressed.
  346: In a dom0 kernel, kernfs is mandatory for xend to communicate with the
  347: kernel, so ensure that /kern is in fstab.  TODO: Say this is default,
  348: or file a PR and give a reference.
  350: Because you already installed NetBSD, you have a working boot setup
  351: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  352: beginning of your root file system, /boot present, and likely
  353: /boot.cfg.  (If not, fix before continuing!)
  355: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  356: example.  The basic line is
  358:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  360: which specifies that the dom0 should have 256M, leaving the rest to be
  361: allocated for domUs.  To use a serial console, use
  363:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
  365: which will use the first serial port for Xen (which counts starting
  366: from 1), forcing speed/parity, and also for NetBSD (which counts
  367: starting at 0).  In an attempt to add performance, one can also add
  369:         dom0_max_vcpus=1 dom0_vcpus_pin
  371: to force only one vcpu to be provided (since NetBSD dom0 can't use
  372: more) and to pin that vcpu to a physical CPU.  TODO: benchmark this.
  374: Xen has [many boot
  375: options](,
  376: and other than dom0 memory and max_vcpus, they are generally not
  377: necessary.
  379: As with non-Xen systems, you should have a line to boot /netbsd (a
  380: kernel that works without Xen) and fallback versions of the non-Xen
  381: kernel, Xen, and the dom0 kernel.
  383: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  384: than GENERIC without Xen.
  386: Using grub (historic)
  387: ---------------------
  389: Before NetBSD's native bootloader could support Xen, the use of
  390: grub was recommended.  If necessary, see the
  391: [old grub information](/ports/xen/howto-grub/).
  393: The [HowTo on Installing into
  394: RAID-1](
  395: explains how to set up booting a dom0 with Xen using grub with
  396: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  397: boot.)
  399: Configuring Xen
  400: ---------------
  402: Xen logs will be in /var/log/xen.
  404: Now, you have a system that will boot Xen and the dom0 kernel, but not
  405: do anything else special.  Make sure that you have rebooted into Xen.
  406: There will be no domUs, and none can be started because you still have
  407: to configure the dom0 daemons.
  409: The daemons which should be run vary with Xen version and with whether
  410: one is using xm or xl.  The Xen 3.1 and 3.3 packages use xm.  Xen 4.1
  411: and higher packages use xl.  While is is possible to use xm with some
  412: 4.x versions (TODO: 4.1 and 4.2?), the pkgsrc-provided rc.d scripts do
  413: not support this as of 2014-12-26, and thus the HOWTO does not support
  414: it either.  (Make sure your packages are reasonably recent.)
  416: For "xm" (3.1 and 3.3), you should enable xend and xenbackendd (but
  417: note that you should be using 4.x):
  419:         xend=YES
  420:         xenbackendd=YES
  422: For "xl" (4.x), you should enabled xend and xencommons (xenstored).
  423: Trying to boot 4.x without xencommons=YES will result in a hang; it is
  424: necessary to hit ^C on the console to let the machine finish booting.
  425: TODO: explain why xend is installed by the package.
  427:         xencommons=YES
  429: The installation of NetBSD should already have created devices for xen
  430: (xencons, xenevt), but if they are not present, create them:
  432:         cd /dev && sh MAKEDEV xen
  434: TODO: Recommend for/against xen-watchdog.
  436: After you have configured the daemons and either started them (in the
  437: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  438: available resources, and running domains.  An example with xl follows:
  440:         # xl dmesg
  441: 	[xen's boot info]
  442:         # xl info
  443: 	[available memory, etc.]
  444:         # xl list
  445:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  446:         Domain-0           0       64    0  r----     58.1
  448: ### Issues with xencommons
  450: xencommons starts xenstored, which stores data on behalf of dom0 and
  451: domUs.  It does not currently work to stop and start xenstored.
  452: Certainly all domUs should be shutdown first, following the sort order
  453: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  454: and is not notified when xenstored exits, leading to not recreating
  455: the state when the new xenstored starts.  Until there's a mechanism to
  456: make this work, one should not expect to be able to restart xenstored
  457: (and thus xencommons).  There is currently no reason to expect that
  458: this will get fixed any time soon.
  460: anita (for testing NetBSD)
  461: --------------------------
  463: With the setup so far (assuming 4.2/xl), one should be able to run
  464: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  465: root, because anita must create a domU):
  467:         anita --vmm=xl test file:///usr/obj/i386/
  469: Alternatively, one can use --vmm=xm to use xm-based domU creation
  470: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  472: Xen-specific NetBSD issues
  473: --------------------------
  475: There are (at least) two additional things different about NetBSD as a
  476: dom0 kernel compared to hardware.
  478: One is that the module ABI is different because some of the #defines
  479: change, so one must build modules for Xen.  As of netbsd-7, the build
  480: system does this automatically.  TODO: check this.  (Before building
  481: Xen modules was added, it was awkward to use modules to the point
  482: where it was considered that it did not work.)
  484: The other difference is that XEN3_DOM0 does not have exactly the same
  485: options as GENERIC.  While it is debatable whether or not this is a
  486: bug, users should be aware of this and can simply add missing config
  487: items if desired.
  489: Updating NetBSD in a dom0
  490: -------------------------
  492: This is just like updating NetBSD on bare hardware, assuming the new
  493: version supports the version of Xen you are running.  Generally, one
  494: replaces the kernel and reboots, and then overlays userland binaries
  495: and adjusts /etc.
  497: Note that one must update both the non-Xen kernel typically used for
  498: rescue purposes and the DOM0 kernel used with Xen.
  500: Converting from grub to /boot
  501: -----------------------------
  503: These instructions were [TODO: will be] used to convert a system from
  504: grub to /boot.  The system was originally installed in February of
  505: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  506: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  507: 4.1 and grub, much like the message linked earlier in the grub
  508: section.
  510:         # Install MBR bootblocks on both disks. 
  511:         fdisk -i /dev/rwd0d
  512:         fdisk -i /dev/rwd1d
  513:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  514:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  515:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  516:         # Install secondary boot loader
  517:         cp -p /usr/mdec/boot /
  518:         # Create boot.cfg following earlier guidance:
  519:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  520:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
  521:         menu=GENERIC:boot
  522:         menu=GENERIC single-user:boot -s
  523:         menu=GENERIC.ok:boot netbsd.ok
  524:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  525:         menu=Drop to boot prompt:prompt
  526:         default=1
  527:         timeout=30
  529: TODO: actually do this and fix it if necessary.
  531: Upgrading Xen versions
  532: ---------------------
  534: Minor version upgrades are trivial.  Just rebuild/replace the
  535: xenkernel version and copy the new xen.gz to / (where /boot.cfg
  536: references it), and reboot.
  538: Major version upgrades are conceptually not difficult, but can run
  539: into all the issues found when installing Xen.  Assuming migration
  540: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
  541: install the xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz
  542: to /.
  544: Ensure that the contents of /etc/rc.d/xen* are correct.  Specifically,
  545: they must match the package you just installed and not be left over
  546: from some previous installation.
  548: Enable the correct set of daemons; see the configuring section above.
  549: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
  551: Ensure that the domU config files are valid for the new version.
  552: Specifically, for 4.x remove autorestart=True, and ensure that disks
  553: are specified with numbers as the second argument, as the examples
  554: above show, and not NetBSD device names.
  556: Hardware known to work
  557: ----------------------
  559: Arguably, this section is misplaced, and there should be a page of
  560: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
  561: assumption that NetBSD/xen runs fine on any modern hardware that
  562: NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU/RAM
  563: triples to aid those choosing a motherboard.  Note that Xen systems
  564: usually do not run X, so a listing here does not imply that X works at
  565: all.
  567:         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
  568:         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
  569:         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
  571: Older hardware:
  573:         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
  575: Running Xen under qemu
  576: ----------------------
  578: The astute reader will note that this section is somewhat twisted.
  579: However, it can be useful to run Xen under qemu either because the
  580: version of NetBSD as a dom0 does not run on the hardware in use, or to
  581: generate automated test cases involving Xen.
  583: In 2015-01, the following combination was reported to mostly work:
  585:         host OS: NetBSD/amd64 6.1.4
  586:         qemu: 2.2.0 from pkgsrc
  587:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  588:         dom0 kernel: NetBSD/amd64 6.1.5
  589:         Xen tools: xentools42-4.2.5 from pkgsrc
  591: See [PR 47720]( for a problem with dom0
  592: shutdown.
  594: Unprivileged domains (domU)
  595: ===========================
  597: This section describes general concepts about domUs.  It does not
  598: address specific domU operating systems or how to install them.  The
  599: config files for domUs are typically in /usr/pkg/etc/xen, and are
  600: typically named so that the file name, domU name and the domU's host
  601: name match.
  603: The domU is provided with CPU and memory by Xen, configured by the
  604: dom0.  The domU is provided with disk and network by the dom0,
  605: mediated by Xen, and configured in the dom0.
  607: Entropy in domUs can be an issue; physical disks and network are on
  608: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  610: Config files
  611: ------------
  613: There is no good order to present config files and the concepts
  614: surrounding what is being configured.  We first show an example config
  615: file, and then in the various sections give details.
  617: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  618: for a large number of well-commented examples, mostly for running
  619: GNU/Linux.
  621: The following is an example minimal domain configuration file
  622: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  623: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  624: i386 domU).  The domU serves as a network file server.
  626:         # -*- mode: python; -*-
  628:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  629:         memory = 1024
  630:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  631:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  632:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  634: The domain will have the same name as the file.  The kernel has the
  635: host/domU name in it, so that on the dom0 one can update the various
  636: domUs independently.  The vif line causes an interface to be provided,
  637: with a specific mac address (do not reuse MAC addresses!), in bridge
  638: mode.  Two disks are provided, and they are both writable; the bits
  639: are stored in files and Xen attaches them to a vnd(4) device in the
  640: dom0 on domain creation.  The system treats xbd0 as the boot device
  641: without needing explicit configuration.
  643: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  644: that "xm create" takes the name of a config file, while other commands
  645: take the name of a domain.  To create the domain, connect to the
  646: console, create the domain while attaching the console, shutdown the
  647: domain, and see if it has finished stopping, do (or xl with Xen >=
  648: 4.2):
  650:         xm create foo
  651:         xm console foo
  652:         xm create -c foo
  653:         xm shutdown foo
  654:         xm list
  656: Typing ^] will exit the console session.  Shutting down a domain is
  657: equivalent to pushing the power button; a NetBSD domU will receive a
  658: power-press event and do a clean shutdown.  Shutting down the dom0
  659: will trigger controlled shutdowns of all configured domUs.
  661: domU kernels
  662: ------------
  664: On a physical computer, the BIOS reads sector 0, and a chain of boot
  665: loaders finds and loads a kernel.  Normally this comes from the root
  666: file system.  With Xen domUs, the process is totally different.  The
  667: normal path is for the domU kernel to be a file in the dom0's
  668: file system.  At the request of the dom0, Xen loads that kernel into a
  669: new domU instance and starts execution.  While domU kernels can be
  670: anyplace, reasonable places to store domU kernels on the dom0 are in /
  671: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  672: config files), or in /u0/xen (where the vdisks are).
  674: Note that loading the domU kernel from the dom0 implies that boot
  675: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  676: See the VPS section near the end for discussion of alternate ways to
  677: obtain domU kernels.
  679: CPU and memory
  680: --------------
  682: A domain is provided with some number of vcpus, less than the number
  683: of CPUs seen by the hypervisor.  (For a dom0, this is controlled by
  684: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  685: from the config file by the "vcpus = N" directive.
  687: A domain is provided with memory; this is controlled in the config
  688: file by "memory = N" (in megabytes).  In the straightforward case, the
  689: sum of the the memory allocated to the dom0 and all domUs must be less
  690: than the available memory.
  692: Xen also provides a "balloon" driver, which can be used to let domains
  693: use more memory temporarily.  TODO: Explain better, and explain how
  694: well it works with NetBSD.
  696: Virtual disks
  697: -------------
  699: With the file/vnd style, typically one creates a directory,
  700: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  701: domUs.  Then, for each domU disk, one writes zeros to a file that then
  702: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  703: for the first virtual disk for the domU called foo.  Writing zeros to
  704: the file serves two purposes.  One is that preallocating the contents
  705: improves performance.  The other is that vnd on sparse files has
  706: failed to work.  TODO: give working/notworking NetBSD versions for
  707: sparse vnd.  Note that the use of file/vnd for Xen is not really
  708: different than creating a file-backed virtual disk for some other
  709: purpose, except that xentools handles the vnconfig commands.  To
  710: create an empty 4G virtual disk, simply do
  712:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  714: Do not use qemu-img-xen, because this will create sparse file.  There
  715: have been recent (2015) reports of sparse vnd(4) devices causing
  716: lockups, but there is apparently no PR.
  718: With the lvm style, one creates logical devices.  They are then used
  719: similarly to vnds.  TODO: Add an example with lvm.
  721: In domU config files, the disks are defined as a sequence of 3-tuples.
  722: The first element is "method:/path/to/disk".  Common methods are
  723: "file:" for file-backed vnd. and "phy:" for something that is already
  724: a (TODO: character or block) device.
  726: The second element is an artifact of how virtual disks are passed to
  727: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  728: are given a device name to associate with the disk, and values like
  729: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  730: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  731: second argument.  The name given is converted to a major/minor by
  732: calling stat(2) on the name in /dev and this is passed to the domU.
  733: In the general case, the dom0 and domU can be different operating
  734: systems, and it is an unwarranted assumption that they have consistent
  735: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  736: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  737: for the second works fine and avoids this issue.  For a GNU/Linux
  738: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  739: /dev/hda1.
  741: The third element is "w" for writable disks, and "r" for read-only
  742: disks.
  744: Virtual Networking
  745: ------------------
  747: Xen provides virtual Ethernets, each of which connects the dom0 and a
  748: domU.  For each virtual network, there is an interface "xvifN.M" in
  749: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  750: name).  The interfaces behave as if there is an Ethernet with two
  751: adapters connected.  From this primitive, one can construct various
  752: configurations.  We focus on two common and useful cases for which
  753: there are existing scripts: bridging and NAT.
  755: With bridging (in the example above), the domU perceives itself to be
  756: on the same network as the dom0.  For server virtualization, this is
  757: usually best.  Bridging is accomplished by creating a bridge(4) device
  758: and adding the dom0's physical interface and the various xvifN.0
  759: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  760: config file.  The bridge must be set up already in the dom0; an
  761: example /etc/ifconfig.bridge0 is:
  763:         create
  764:         up
  765:         !brconfig bridge0 add wm0
  767: With NAT, the domU perceives itself to be behind a NAT running on the
  768: dom0.  This is often appropriate when running Xen on a workstation.
  769: TODO: NAT appears to be configured by "vif = [ '' ]".
  771: The MAC address specified is the one used for the interface in the new
  772: domain.  The interface in dom0 will use this address XOR'd with
  773: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  775: Sizing domains
  776: --------------
  778: Modern x86 hardware has vast amounts of resources.  However, many
  779: virtual servers can function just fine on far less.  A system with
  780: 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  781: far easier to adjust virtual resources than physical ones.  For
  782: memory, it's just a config file edit and a reboot.  For disk, one can
  783: create a new file and vnconfig it (or lvm), and then dump/restore,
  784: just like updating physical disks, but without having to be there and
  785: without those pesky connectors.
  787: Starting domains automatically
  788: ------------------------------
  790: To start domains foo at bar at boot and shut them down cleanly on dom0
  791: shutdown, in rc.conf add:
  793:         xendomains="foo bar"
  795: Note that earlier versions of the xentools41 xendomains rc.d script
  796: used xl, when one should use xm with 4.1.
  798: Creating specific unprivileged domains (domU)
  799: =============================================
  801: Creating domUs is almost entirely independent of operating system.  We
  802: have already presented the basics of config files.  Note that you must
  803: have already completed the dom0 setup so that "xl list" (or "xm list")
  804: works.
  806: Creating an unprivileged NetBSD domain (domU)
  807: ---------------------------------------------
  809: See the earlier config file, and adjust memory.  Decide on how much
  810: storage you will provide, and prepare it (file or lvm).
  812: While the kernel will be obtained from the dom0 file system, the same
  813: file should be present in the domU as /netbsd so that tools like
  814: savecore(8) can work.   (This is helpful but not necessary.)
  816: The kernel must be specifically for Xen and for use as a domU.  The
  817: i386 and amd64 provide the following kernels:
  819:         i386 XEN3_DOMU
  820:         i386 XEN3PAE_DOMU
  821:         amd64 XEN3_DOMU
  823: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  824: use the PAE version of the i386 kernel.
  826: This will boot NetBSD, but this is not that useful if the disk is
  827: empty.  One approach is to unpack sets onto the disk outside of xen
  828: (by mounting it, just as you would prepare a physical disk for a
  829: system you can't run the installer on).
  831: A second approach is to run an INSTALL kernel, which has a miniroot
  832: and can load sets from the network.  To do this, copy the INSTALL
  833: kernel to / and change the kernel line in the config file to:
  835:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  837: Then, start the domain as "xl create -c configname".
  839: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  840: line should be used in the config file.
  842:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  844: After booting the domain, the option to install via CDROM may be
  845: selected.  The CDROM device should be changed to `xbd1d`.
  847: Once done installing, "halt -p" the new domain (don't reboot or halt,
  848: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  849: config file), switch the config file back to the XEN3_DOMU kernel,
  850: and start the new domain again. Now it should be able to use "root on
  851: xbd0a" and you should have a, functional NetBSD domU.
  853: TODO: check if this is still accurate.
  854: When the new domain is booting you'll see some warnings about *wscons*
  855: and the pseudo-terminals. These can be fixed by editing the files
  856: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  857: `/etc/ttys`, except *console*, like this:
  859:     console "/usr/libexec/getty Pc"         vt100   on secure
  860:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  861:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  862:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  863:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  865: Finally, all screens must be commented out from `/etc/wscons.conf`.
  867: It is also desirable to add
  869:         powerd=YES
  871: in rc.conf. This way, the domain will be properly shut down if
  872: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  874: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  875: file system.  However, various programs (e.g. netstat) will use that
  876: kernel to look up symbols to read from kernel virtual memory.  If
  877: /netbsd is not the running kernel, those lookups will fail.  (This is
  878: not really a Xen-specific issue, but because the domU kernel is
  879: obtained from the dom0, it is far more likely to be out of sync or
  880: missing with Xen.)
  882: Creating an unprivileged Linux domain (domU)
  883: --------------------------------------------
  885: Creating unprivileged Linux domains isn't much different from
  886: unprivileged NetBSD domains, but there are some details to know.
  888: First, the second parameter passed to the disk declaration (the '0x1' in
  889: the example below)
  891:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  893: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  894: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  895: So, hda1 which has major 3 and minor 1 on a Linux system will have
  896: device number 0x301.  Alternatively, devices names can be used (hda,
  897: hdb, ...)  as xentools has a table to map these names to devices
  898: numbers.  To export a partition to a Linux guest we can use:
  900:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  901:         root = "/dev/hda1 ro"
  903: and it will appear as /dev/hda on the Linux system, and be used as root
  904: partition.
  906: To install the Linux system on the partition to be exported to the
  907: guest domain, the following method can be used: install
  908: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  909: that will be the root partition of your Linux domain, and mount it.
  910: Then copy the files from a working Linux system, make adjustments in
  911: `/etc` (fstab, network config).  It should also be possible to extract
  912: binary packages such as .rpm or .deb directly to the mounted partition
  913: using the appropriate tool, possibly running under NetBSD's Linux
  914: emulation.  Once the file system has been populated, umount it.  If
  915: desirable, the file system can be converted to ext3 using tune2fs -j.
  916: It should now be possible to boot the Linux guest domain, using one of
  917: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  919: To get the Linux console right, you need to add:
  921:     extra = "xencons=tty1"
  923: to your configuration since not all Linux distributions auto-attach a
  924: tty to the xen console.
  926: Creating an unprivileged Solaris domain (domU)
  927: ----------------------------------------------
  929: See possibly outdated
  930: [Solaris domU instructions](/ports/xen/howto-solaris/).
  933: PCI passthrough: Using PCI devices in guest domains
  934: ---------------------------------------------------
  936: The dom0 can give other domains access to selected PCI
  937: devices. This can allow, for example, a non-privileged domain to have
  938: access to a physical network interface or disk controller.  However,
  939: keep in mind that giving a domain access to a PCI device most likely
  940: will give the domain read/write access to the whole physical memory,
  941: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  942: device.  Also, it's not possible to export ISA devices to non-dom0
  943: domains, which means that the primary VGA adapter can't be exported.
  944: A guest domain trying to access the VGA registers will panic.
  946: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  947: not been ported to later versions at this time.
  949: For a PCI device to be exported to a domU, is has to be attached to
  950: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  951: pciback.hide boot parameter will attach to "pciback" instead of the
  952: usual driver.  The list of devices is specified as "(bus:dev.func)",
  953: where bus and dev are 2-digit hexadecimal numbers, and func a
  954: single-digit number:
  956:         pciback.hide=(00:0a.0)(00:06.0)
  958: pciback devices should show up in the dom0's boot messages, and the
  959: devices should be listed in the `/kern/xen/pci` directory.
  961: PCI devices to be exported to a domU are listed in the "pci" array of
  962: the domU's config file, with the format "0000:bus:dev.func".
  964:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  966: In the domU an "xpci" device will show up, to which one or more pci
  967: buses will attach.  Then the PCI drivers will attach to PCI buses as
  968: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  969: or any PCI drivers built in by default; you have to build your own
  970: kernel to use PCI devices in a domU.  Here's a kernel config example;
  971: note that only the "xpci" lines are unusual.
  973:         include         "arch/i386/conf/XEN3_DOMU"
  975:         # Add support for PCI buses to the XEN3_DOMU kernel
  976:         xpci* at xenbus ?
  977:         pci* at xpci ?
  979:         # PCI USB controllers
  980:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  982:         # USB bus support
  983:         usb*    at uhci?
  985:         # USB Hubs
  986:         uhub*   at usb?
  987:         uhub*   at uhub? port ? configuration ? interface ?
  989:         # USB Mass Storage
  990:         umass*  at uhub? port ? configuration ? interface ?
  991:         wd*     at umass?
  992:         # SCSI controllers
  993:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  995:         # SCSI bus support (for both ahc and umass)
  996:         scsibus* at scsi?
  998:         # SCSI devices
  999:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
 1000:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
 1003: NetBSD as a domU in a VPS
 1004: =========================
 1006: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
 1007: hardware.  This section explains how to deal with Xen in a domU as a
 1008: virtual private server where you do not control or have access to the
 1009: dom0.  This is not intended to be an exhaustive list of VPS providers;
 1010: only a few are mentioned that specifically support NetBSD.
 1012: VPS operators provide varying degrees of access and mechanisms for
 1013: configuration.  The big issue is usually how one controls which kernel
 1014: is booted, because the kernel is nominally in the dom0 file system (to
 1015: which VPS users do not normally have access).  A second issue is how
 1016: to install NetBSD.
 1017: A VPS user may want to compile a kernel for security updates, to run
 1018: npf, run IPsec, or any other reason why someone would want to change
 1019: their kernel.
 1021: One approach is to have an administrative interface to upload a kernel,
 1022: or to select from a prepopulated list.  Other approaches are pygrub
 1023: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
 1024: kernel from the domU file system.  This is closer to a regular physical
 1025: computer, where someone who controls a machine can replace the kernel.
 1027: A second issue is multiple CPUs.  With NetBSD 6, domUs support
 1028: multiple vcpus, and it is typical for VPS providers to enable multiple
 1029: CPUs for NetBSD domUs.
 1031: pygrub
 1032: -------
 1034: pygrub runs in the dom0 and looks into the domU file system.  This
 1035: implies that the domU must have a kernel in a file system in a format
 1036: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
 1037: interest.
 1039: pvgrub
 1040: ------
 1042: pvgrub is a version of grub that uses PV operations instead of BIOS
 1043: calls.  It is booted from the dom0 as the domU kernel, and then reads
 1044: /grub/menu.lst and loads a kernel from the domU file system.
 1046: [Panix]( lets users use pvgrub.  Panix reports
 1047: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
 1048: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
 1049: page](, which describes only
 1050: Linux but should be updated to cover NetBSD :-).
 1052: []( also lets users with pvgrub to boot
 1053: their own kernel.  See then [ NetBSD
 1054: HOWTO](
 1055: (which is in need of updating).
 1057: It appears that [grub's FFS
 1058: code](
 1059: does not support all aspects of modern FFS, but there are also reports
 1060: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
 1061: partition for the kernel with the intent that grub can understand it,
 1062: which leads to /netbsd not being the actual kernel.  One must remember
 1063: to update the special boot partition.
 1065: Amazon
 1066: ------
 1068: See the [Amazon EC2 page](../amazon_ec2/).
 1070: Using npf
 1071: ---------
 1073: In standard kernels, npf is a module, and thus cannot be loaded in a
 1074: DOMU kernel.
 1076: TODO: Explain how to compile npf into a custom kernel, answering (but
 1077: note that the problem was caused by not booting the right kernel)
 1078: [this email to
 1079: netbsd-users](
 1081: TODO items for improving NetBSD/xen
 1082: ===================================
 1084: * Make the NetBSD dom0 kernel work with SMP.
 1085: * Test the Xen 4.5 packages adequately to be able to recommend them as
 1086:   the standard approach.
 1087: * Get PCI passthrough working on Xen 4.5
 1088: * Get pvgrub into pkgsrc, either via xentools or separately.
 1089: * grub
 1090:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
 1091:     fragsize/blocksize (UFS2 support may be present; the point is to
 1092:     make it so that with any UFS1/UFS2 file system setup that works
 1093:     with NetBSD grub will also work).
 1094:     See [pkg/40258](
 1095:   * Push patches upstream.
 1096:   * Get UFS2 patches into pvgrub.
 1097: * Add support for PV ops to a version of /boot, and make it usable as
 1098:   a kernel in Xen, similar to pvgrub.
 1099: * Solve somehow the issue with modules for GENERIC not being loadable
 1100:   in a Xen dom0 or domU kernel.
 1102: Random pointers
 1103: ===============
 1105: This section contains links from elsewhere not yet integrated into the
 1106: HOWTO, and other guides.
 1108: *
 1109: *
 1110: *

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