File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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Tue Dec 20 15:07:56 2016 UTC (4 years, 4 months ago) by gdt
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CVS tags: HEAD
Explain that FreeBSD needing VT-x does not apply

    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: Note a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this is
   42: because the FreeBSD dom0 does not run in PV mode.
   44: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   45: The dom0 can start one or more domUs.  (Booting is explained in detail
   46: in the dom0 section.)
   48: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   49: and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   50: attempts to address both the case of running a NetBSD dom0 on hardware
   51: and running domUs under it (NetBSD and other), and also running NetBSD
   52: as a domU in a VPS.
   54: Some versions of Xen support "PCI passthrough", which means that
   55: specific PCI devices can be made available to a specific domU instead
   56: of the dom0.  This can be useful to let a domU run X11, or access some
   57: network interface or other peripheral.
   59: NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD
   60: 7.  Xen 2 has been removed from pkgsrc.
   62: Prerequisites
   63: -------------
   65: Installing NetBSD/Xen is not extremely difficult, but it is more
   66: complex than a normal installation of NetBSD.
   67: In general, this HOWTO is occasionally overly restrictive about how
   68: things must be done, guiding the reader to stay on the established
   69: path when there are no known good reasons to stray.
   71: This HOWTO presumes a basic familiarity with the Xen system
   72: architecture.  This HOWTO presumes familiarity with installing NetBSD
   73: on i386/amd64 hardware and installing software from pkgsrc.
   74: See also the [Xen website](
   76: Versions of Xen and NetBSD
   77: ==========================
   79: Most of the installation concepts and instructions are independent
   80: of Xen version and NetBSD version.  This section gives advice on
   81: which version to choose.  Versions not in pkgsrc and older unsupported
   82: versions of NetBSD are intentionally ignored.
   84: Xen
   85: ---
   87: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   88: xenkernel and xentools.  We will refer only to the kernel versions,
   89: but note that both packages must be installed together and must have
   90: matching versions.
   92: xenkernel3 provides Xen 3.1.  It is no longer maintained by Xen, and the last applied security patch was in
   93: 2011. Thus, it should not be used.  It supports PCI passthrough,
   94: which is why people use it anyway. Xen 3.1 supports i386, both PAE and
   95: non-PAE.
   97: xenkernel33 provides Xen 3.3.  It is no longer maintained by Xen, and
   98: the last applied security patch was in 2012.  Thus, it should not be
   99: used.  Xen 3.3 supports i386, but only in PAE mode.  There are no good
  100: reasons to run this version.
  102: xenkernel41 provides Xen 4.1.  It is no longer maintained by Xen, but
  103: as of 2016-12 received backported security patches.  Xen 4.1 supports
  104: i386, but only in PAE mode.  There are no good reasons to run this
  105: version.
  107: xenkernel42 provides Xen 4.2.  It is no longer maintained by Xen, but
  108: as of 2016-12 received backported security patches.  Xen 4.2 supports
  109: i386, but only in PAE mode.  The only reason to run this is if you
  110: need to use xm instead of xl, or if you need to run an i386 dom0
  111: (because your hardware is i386 only).
  113: xenkernel45 provides Xen 4.5.  As of 2016-12, security patches were
  114: released by Xen and applied to pkgsrc.  Xen 4.5 requires an amd64
  115: dom0, but domUs can be amd64 or i386 PAE.  TODO: It is either a
  116: conservative choice or somewhat old.
  118: xenkernel46 provides Xen 4.6.  It is new to pkgsrc as of 2016-05.  As
  119: of 2016-12, security patches were released by Xen and applied to
  120: pkgsrc.  Xen 4.6 requires an amd64 dom0, but domUs can be amd64 or
  121: i386 PAE.  TODO: It is either a somewhat aggressive choice or the
  122: standard choice
  124: Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in
  125: pkgsrc.
  127: See also the [Xen Security Advisory page](
  129: Note that NetBSD support is called XEN3.  It works with Xen 3 and Xen
  130: 4 because the hypercall interface has been stable.
  132: Xen command program
  133: -------------------
  135: Early Xen used a program called xm to manipulate the system from the
  136: dom0.  Starting in 4.1, a replacement program with similar behavior
  137: called xl is provided, but it does not work well in 4.1.  In 4.2, both
  138: xm and xl work fine.  4.4 is the last version that has xm.  You must
  139: choose one or the other, because it affects which daemons you run.
  140: However, the rc.d scripts provided by xentools packages expect a
  141: particular version, and you should use the version used by the
  142: scripts.
  144: NetBSD
  145: ------
  147: The netbsd-6, netbsd-7, and -current branches are all reasonable
  148: choices, with more or less the same considerations for non-Xen use.
  149: Therefore, netbsd-7 is recommended as the stable version of the most
  150: recent release for production use.  In addition, netbsd-7 and -current
  151: have a important scheduler fix (in November of 2015) affecting
  152: contention between dom0 and domUs; see
  153: for a
  154: description.  For those wanting to learn Xen or without production
  155: stability concerns, netbsd-7 is still likely most appropriate, but
  156: -current is also a reasonable choice.  (Xen runs ok on netbsd-5, but
  157: the xentools packages are likely difficult to build, and netbsd-5 is
  158: not supported.)
  160: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  161: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  162: need SMP for dom0 functions; the lack of support is really a problem
  163: when using a dom0 as a normal computer.)
  165: Architecture
  166: ------------
  168: Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen
  169: versions).  (Practically, almost any computer where one would want to
  170: run Xen today supports amd64.)
  172: Xen, the dom0 kernel, and each domU kernel can be either i386 or
  173: amd64.  When building a xenkernel package, one obtains i386 on an i386
  174: host, and amd64 on an amd64 host.  If the Xen kernel is i386, then the
  175: dom0 kernel and all domU kernels must be i386.  With an amd64 Xen
  176: kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0
  177: kernel should in theory work.  An amd64 Xen/dom0 is known to support
  178: both i386PAE and amd64 domUs.
  180: i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are
  181: built by default.  (Note that emacs (at least) fails if run on i386
  182: with PAE when built without, and vice versa, presumably due to bugs in
  183: the undump code.)
  185: Because of the above, the standard approach is to use amd64 for the
  186: dom0.
  188: Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
  189: if this is about the CPU, the Xen kernel, or the dom0 kernel having to
  190: be amd64.
  193: Stability
  194: ---------
  196: Mostly, NetBSD as a dom0 or domU is quite stable.
  197: However, there are some open PRs indicating problems.
  199:  - [PR 48125](
  200:  - [PR 47720](
  202: Note also that there are issues with sparse vnd(4) instances, but
  203: these are not about Xen -- they just are noticed with sparse vnd(4)
  204: instances in support of virtual disks in a dom0.
  206: Recommendation
  207: --------------
  209: Therefore, this HOWTO recommends running xenkernel45 or xenkernel46,
  210: xl, the NetBSD 7 stable branch, and to use an amd64 kernel as the
  211: dom0.  Either the i386PAE or amd64 version of NetBSD may be used as
  212: domUs.
  214: Build problems
  215: --------------
  217: Ideally, all versions of Xen in pkgsrc would build on all versions of
  218: NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
  219: aging code and aging compilers, qemu (included in xentools for HVM
  220: support) is difficult to build.  The following are known to work or FAIL:
  222:         xenkernel3 netbsd-5 amd64
  223:         xentools3 netbsd-5 amd64
  224:         xentools3=hvm netbsd-5 amd64 ????
  225:         xenkernel33 netbsd-5 amd64
  226:         xentools33 netbsd-5 amd64
  227:         xenkernel41 netbsd-5 amd64
  228:         xentools41 netbsd-5 amd64
  229:         xenkernel42 netbsd-5 amd64
  230:         xentools42 netbsd-5 amd64
  232:         xenkernel3 netbsd-6 i386 FAIL
  233:         xentools3 netbsd-6 i386
  234:         xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
  235:         xenkernel33 netbsd-6 i386
  236:         xentools33 netbsd-6 i386
  237:         xenkernel41 netbsd-6 i386
  238:         xentools41 netbsd-6 i386
  239:         xenkernel42 netbsd-6 i386
  240:         xentools42 netbsd-6 i386 *MIXED
  242: 	(all 3 and 33 seem to FAIL)
  243:         xenkernel41 netbsd-7 i386
  244:         xentools41 netbsd-7 i386
  245:         xenkernel42 netbsd-7 i386
  246:         xentools42 netbsd-7 i386 ??FAIL
  248: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
  249: but it does not build for gdt.)
  251: NetBSD as a dom0
  252: ================
  254: NetBSD can be used as a dom0 and works very well.  The following
  255: sections address installation, updating NetBSD, and updating Xen.
  256: Note that it doesn't make sense to talk about installing a dom0 OS
  257: without also installing Xen itself.  We first address installing
  258: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  259: NetBSD install to a dom0 install by just changing the kernel and boot
  260: configuration.
  262: For experimenting with Xen, a machine with as little as 1G of RAM and
  263: 100G of disk can work.  For running many domUs in productions, far
  264: more will be needed.
  266: Styles of dom0 operation
  267: ------------------------
  269: There are two basic ways to use Xen.  The traditional method is for
  270: the dom0 to do absolutely nothing other than providing support to some
  271: number of domUs.  Such a system was probably installed for the sole
  272: purpose of hosting domUs, and sits in a server room on a UPS.
  274: The other way is to put Xen under a normal-usage computer, so that the
  275: dom0 is what the computer would have been without Xen, perhaps a
  276: desktop or laptop.  Then, one can run domUs at will.  Purists will
  277: deride this as less secure than the previous approach, and for a
  278: computer whose purpose is to run domUs, they are right.  But Xen and a
  279: dom0 (without domUs) is not meaningfully less secure than the same
  280: things running without Xen.  One can boot Xen or boot regular NetBSD
  281: alternately with little problems, simply refraining from starting the
  282: Xen daemons when not running Xen.
  284: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  285: limit the performance of the Xen/dom0 workstation approach.  In theory
  286: the only issue is that the "backend drivers" are not yet MPSAFE:
  289: Installation of NetBSD
  290: ----------------------
  292: First,
  293: [install NetBSD/amd64](/guide/inst/)
  294: just as you would if you were not using Xen.
  295: However, the partitioning approach is very important.
  297: If you want to use RAIDframe for the dom0, there are no special issues
  298: for Xen.  Typically one provides RAID storage for the dom0, and the
  299: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  300: over a RAID1 header to find /boot from a file system within a RAID
  301: partition; this is no different when booting Xen.
  303: There are 4 styles of providing backing storage for the virtual disks
  304: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  306: With raw partitions, one has a disklabel (or gpt) partition sized for
  307: each virtual disk to be used by the domU.  (If you are able to predict
  308: how domU usage will evolve, please add an explanation to the HOWTO.
  309: Seriously, needs tend to change over time.)
  311: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  312: for domU disks.  This is almost as efficient as raw disk partitions
  313: and more flexible.  Hence raw disk partitions should typically not
  314: be used.
  316: One can use files in the dom0 file system, typically created by dd'ing
  317: /dev/zero to create a specific size.  This is somewhat less efficient,
  318: but very convenient, as one can cp the files for backup, or move them
  319: between dom0 hosts.
  321: Finally, in theory one can place the files backing the domU disks in a
  322: SAN.  (This is an invitation for someone who has done this to add a
  323: HOWTO page.)
  325: Installation of Xen
  326: -------------------
  328: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  329: pkgsrc (or another matching pair).
  330: See [the pkgsrc
  331: documentation]( for help with pkgsrc.
  333: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  334: recent versions have HVM support integrated in the main xentools
  335: package.  It is entirely reasonable to run only PV guests.
  337: Next you need to install the selected Xen kernel itself, which is
  338: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  339: For debugging, one may copy xen-debug.gz; this is conceptually similar
  340: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  341: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  342: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  343: of a NetBSD build.  If using i386, use
  344: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  345: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  346: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  347: typically are) left compressed.
  349: In a dom0 kernel, kernfs is mandatory for xend to communicate with the
  350: kernel, so ensure that /kern is in fstab.  TODO: Say this is default,
  351: or file a PR and give a reference.
  353: Because you already installed NetBSD, you have a working boot setup
  354: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  355: beginning of your root file system, /boot present, and likely
  356: /boot.cfg.  (If not, fix before continuing!)
  358: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  359: example.  The basic line is
  361:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  363: which specifies that the dom0 should have 256M, leaving the rest to be
  364: allocated for domUs.  To use a serial console, use
  366:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
  368: which will use the first serial port for Xen (which counts starting
  369: from 1), forcing speed/parity, and also for NetBSD (which counts
  370: starting at 0).  In an attempt to add performance, one can also add
  372:         dom0_max_vcpus=1 dom0_vcpus_pin
  374: to force only one vcpu to be provided (since NetBSD dom0 can't use
  375: more) and to pin that vcpu to a physical CPU.  TODO: benchmark this.
  377: Xen has [many boot
  378: options](,
  379: and other than dom0 memory and max_vcpus, they are generally not
  380: necessary.
  382: As with non-Xen systems, you should have a line to boot /netbsd (a
  383: kernel that works without Xen) and fallback versions of the non-Xen
  384: kernel, Xen, and the dom0 kernel.
  386: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  387: than GENERIC without Xen.
  389: Using grub (historic)
  390: ---------------------
  392: Before NetBSD's native bootloader could support Xen, the use of
  393: grub was recommended.  If necessary, see the
  394: [old grub information](/ports/xen/howto-grub/).
  396: The [HowTo on Installing into
  397: RAID-1](
  398: explains how to set up booting a dom0 with Xen using grub with
  399: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  400: boot.)
  402: Configuring Xen
  403: ---------------
  405: Xen logs will be in /var/log/xen.
  407: Now, you have a system that will boot Xen and the dom0 kernel, but not
  408: do anything else special.  Make sure that you have rebooted into Xen.
  409: There will be no domUs, and none can be started because you still have
  410: to configure the dom0 daemons.
  412: The daemons which should be run vary with Xen version and with whether
  413: one is using xm or xl.  The Xen 3.1 and 3.3 packages use xm.  Xen 4.1
  414: and higher packages use xl.  While is is possible to use xm with some
  415: 4.x versions (TODO: 4.1 and 4.2?), the pkgsrc-provided rc.d scripts do
  416: not support this as of 2014-12-26, and thus the HOWTO does not support
  417: it either.  (Make sure your packages are reasonably recent.)
  419: For "xm" (3.1 and 3.3), you should enable xend and xenbackendd (but
  420: note that you should be using 4.x):
  422:         xend=YES
  423:         xenbackendd=YES
  425: For "xl" (4.x), you should enabled xend and xencommons (xenstored).
  426: Trying to boot 4.x without xencommons=YES will result in a hang; it is
  427: necessary to hit ^C on the console to let the machine finish booting.
  428: TODO: explain why xend is installed by the package.
  430:         xencommons=YES
  432: The installation of NetBSD should already have created devices for xen
  433: (xencons, xenevt), but if they are not present, create them:
  435:         cd /dev && sh MAKEDEV xen
  437: TODO: Recommend for/against xen-watchdog.
  439: After you have configured the daemons and either started them (in the
  440: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  441: available resources, and running domains.  An example with xl follows:
  443:         # xl dmesg
  444: 	[xen's boot info]
  445:         # xl info
  446: 	[available memory, etc.]
  447:         # xl list
  448:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  449:         Domain-0           0       64    0  r----     58.1
  451: ### Issues with xencommons
  453: xencommons starts xenstored, which stores data on behalf of dom0 and
  454: domUs.  It does not currently work to stop and start xenstored.
  455: Certainly all domUs should be shutdown first, following the sort order
  456: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  457: and is not notified when xenstored exits, leading to not recreating
  458: the state when the new xenstored starts.  Until there's a mechanism to
  459: make this work, one should not expect to be able to restart xenstored
  460: (and thus xencommons).  There is currently no reason to expect that
  461: this will get fixed any time soon.
  463: anita (for testing NetBSD)
  464: --------------------------
  466: With the setup so far (assuming 4.2/xl), one should be able to run
  467: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  468: root, because anita must create a domU):
  470:         anita --vmm=xl test file:///usr/obj/i386/
  472: Alternatively, one can use --vmm=xm to use xm-based domU creation
  473: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  475: Xen-specific NetBSD issues
  476: --------------------------
  478: There are (at least) two additional things different about NetBSD as a
  479: dom0 kernel compared to hardware.
  481: One is that the module ABI is different because some of the #defines
  482: change, so one must build modules for Xen.  As of netbsd-7, the build
  483: system does this automatically.  TODO: check this.  (Before building
  484: Xen modules was added, it was awkward to use modules to the point
  485: where it was considered that it did not work.)
  487: The other difference is that XEN3_DOM0 does not have exactly the same
  488: options as GENERIC.  While it is debatable whether or not this is a
  489: bug, users should be aware of this and can simply add missing config
  490: items if desired.
  492: Updating NetBSD in a dom0
  493: -------------------------
  495: This is just like updating NetBSD on bare hardware, assuming the new
  496: version supports the version of Xen you are running.  Generally, one
  497: replaces the kernel and reboots, and then overlays userland binaries
  498: and adjusts /etc.
  500: Note that one must update both the non-Xen kernel typically used for
  501: rescue purposes and the DOM0 kernel used with Xen.
  503: Converting from grub to /boot
  504: -----------------------------
  506: These instructions were [TODO: will be] used to convert a system from
  507: grub to /boot.  The system was originally installed in February of
  508: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  509: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  510: 4.1 and grub, much like the message linked earlier in the grub
  511: section.
  513:         # Install MBR bootblocks on both disks. 
  514:         fdisk -i /dev/rwd0d
  515:         fdisk -i /dev/rwd1d
  516:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  517:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  518:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  519:         # Install secondary boot loader
  520:         cp -p /usr/mdec/boot /
  521:         # Create boot.cfg following earlier guidance:
  522:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  523:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
  524:         menu=GENERIC:boot
  525:         menu=GENERIC single-user:boot -s
  526:         menu=GENERIC.ok:boot netbsd.ok
  527:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  528:         menu=Drop to boot prompt:prompt
  529:         default=1
  530:         timeout=30
  532: TODO: actually do this and fix it if necessary.
  534: Upgrading Xen versions
  535: ---------------------
  537: Minor version upgrades are trivial.  Just rebuild/replace the
  538: xenkernel version and copy the new xen.gz to / (where /boot.cfg
  539: references it), and reboot.
  541: Major version upgrades are conceptually not difficult, but can run
  542: into all the issues found when installing Xen.  Assuming migration
  543: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
  544: install the xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz
  545: to /.
  547: Ensure that the contents of /etc/rc.d/xen* are correct.  Specifically,
  548: they must match the package you just installed and not be left over
  549: from some previous installation.
  551: Enable the correct set of daemons; see the configuring section above.
  552: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
  554: Ensure that the domU config files are valid for the new version.
  555: Specifically, for 4.x remove autorestart=True, and ensure that disks
  556: are specified with numbers as the second argument, as the examples
  557: above show, and not NetBSD device names.
  559: Hardware known to work
  560: ----------------------
  562: Arguably, this section is misplaced, and there should be a page of
  563: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
  564: assumption that NetBSD/xen runs fine on any modern hardware that
  565: NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU/RAM
  566: triples to aid those choosing a motherboard.  Note that Xen systems
  567: usually do not run X, so a listing here does not imply that X works at
  568: all.
  570:         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
  571:         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
  572:         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
  574: Older hardware:
  576:         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
  578: Running Xen under qemu
  579: ----------------------
  581: The astute reader will note that this section is somewhat twisted.
  582: However, it can be useful to run Xen under qemu either because the
  583: version of NetBSD as a dom0 does not run on the hardware in use, or to
  584: generate automated test cases involving Xen.
  586: In 2015-01, the following combination was reported to mostly work:
  588:         host OS: NetBSD/amd64 6.1.4
  589:         qemu: 2.2.0 from pkgsrc
  590:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  591:         dom0 kernel: NetBSD/amd64 6.1.5
  592:         Xen tools: xentools42-4.2.5 from pkgsrc
  594: See [PR 47720]( for a problem with dom0
  595: shutdown.
  597: Unprivileged domains (domU)
  598: ===========================
  600: This section describes general concepts about domUs.  It does not
  601: address specific domU operating systems or how to install them.  The
  602: config files for domUs are typically in /usr/pkg/etc/xen, and are
  603: typically named so that the file name, domU name and the domU's host
  604: name match.
  606: The domU is provided with CPU and memory by Xen, configured by the
  607: dom0.  The domU is provided with disk and network by the dom0,
  608: mediated by Xen, and configured in the dom0.
  610: Entropy in domUs can be an issue; physical disks and network are on
  611: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  613: Config files
  614: ------------
  616: There is no good order to present config files and the concepts
  617: surrounding what is being configured.  We first show an example config
  618: file, and then in the various sections give details.
  620: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  621: for a large number of well-commented examples, mostly for running
  622: GNU/Linux.
  624: The following is an example minimal domain configuration file
  625: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  626: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  627: i386 domU).  The domU serves as a network file server.
  629:         # -*- mode: python; -*-
  631:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  632:         memory = 1024
  633:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  634:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  635:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  637: The domain will have the same name as the file.  The kernel has the
  638: host/domU name in it, so that on the dom0 one can update the various
  639: domUs independently.  The vif line causes an interface to be provided,
  640: with a specific mac address (do not reuse MAC addresses!), in bridge
  641: mode.  Two disks are provided, and they are both writable; the bits
  642: are stored in files and Xen attaches them to a vnd(4) device in the
  643: dom0 on domain creation.  The system treats xbd0 as the boot device
  644: without needing explicit configuration.
  646: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  647: that "xm create" takes the name of a config file, while other commands
  648: take the name of a domain.  To create the domain, connect to the
  649: console, create the domain while attaching the console, shutdown the
  650: domain, and see if it has finished stopping, do (or xl with Xen >=
  651: 4.2):
  653:         xm create foo
  654:         xm console foo
  655:         xm create -c foo
  656:         xm shutdown foo
  657:         xm list
  659: Typing ^] will exit the console session.  Shutting down a domain is
  660: equivalent to pushing the power button; a NetBSD domU will receive a
  661: power-press event and do a clean shutdown.  Shutting down the dom0
  662: will trigger controlled shutdowns of all configured domUs.
  664: domU kernels
  665: ------------
  667: On a physical computer, the BIOS reads sector 0, and a chain of boot
  668: loaders finds and loads a kernel.  Normally this comes from the root
  669: file system.  With Xen domUs, the process is totally different.  The
  670: normal path is for the domU kernel to be a file in the dom0's
  671: file system.  At the request of the dom0, Xen loads that kernel into a
  672: new domU instance and starts execution.  While domU kernels can be
  673: anyplace, reasonable places to store domU kernels on the dom0 are in /
  674: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  675: config files), or in /u0/xen (where the vdisks are).
  677: Note that loading the domU kernel from the dom0 implies that boot
  678: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  679: See the VPS section near the end for discussion of alternate ways to
  680: obtain domU kernels.
  682: CPU and memory
  683: --------------
  685: A domain is provided with some number of vcpus, less than the number
  686: of CPUs seen by the hypervisor.  (For a dom0, this is controlled by
  687: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  688: from the config file by the "vcpus = N" directive.
  690: A domain is provided with memory; this is controlled in the config
  691: file by "memory = N" (in megabytes).  In the straightforward case, the
  692: sum of the the memory allocated to the dom0 and all domUs must be less
  693: than the available memory.
  695: Xen also provides a "balloon" driver, which can be used to let domains
  696: use more memory temporarily.  TODO: Explain better, and explain how
  697: well it works with NetBSD.
  699: Virtual disks
  700: -------------
  702: With the file/vnd style, typically one creates a directory,
  703: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  704: domUs.  Then, for each domU disk, one writes zeros to a file that then
  705: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  706: for the first virtual disk for the domU called foo.  Writing zeros to
  707: the file serves two purposes.  One is that preallocating the contents
  708: improves performance.  The other is that vnd on sparse files has
  709: failed to work.  TODO: give working/notworking NetBSD versions for
  710: sparse vnd.  Note that the use of file/vnd for Xen is not really
  711: different than creating a file-backed virtual disk for some other
  712: purpose, except that xentools handles the vnconfig commands.  To
  713: create an empty 4G virtual disk, simply do
  715:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  717: Do not use qemu-img-xen, because this will create sparse file.  There
  718: have been recent (2015) reports of sparse vnd(4) devices causing
  719: lockups, but there is apparently no PR.
  721: With the lvm style, one creates logical devices.  They are then used
  722: similarly to vnds.  TODO: Add an example with lvm.
  724: In domU config files, the disks are defined as a sequence of 3-tuples.
  725: The first element is "method:/path/to/disk".  Common methods are
  726: "file:" for file-backed vnd. and "phy:" for something that is already
  727: a (TODO: character or block) device.
  729: The second element is an artifact of how virtual disks are passed to
  730: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  731: are given a device name to associate with the disk, and values like
  732: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  733: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  734: second argument.  The name given is converted to a major/minor by
  735: calling stat(2) on the name in /dev and this is passed to the domU.
  736: In the general case, the dom0 and domU can be different operating
  737: systems, and it is an unwarranted assumption that they have consistent
  738: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  739: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  740: for the second works fine and avoids this issue.  For a GNU/Linux
  741: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  742: /dev/hda1.
  744: The third element is "w" for writable disks, and "r" for read-only
  745: disks.
  747: Virtual Networking
  748: ------------------
  750: Xen provides virtual Ethernets, each of which connects the dom0 and a
  751: domU.  For each virtual network, there is an interface "xvifN.M" in
  752: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  753: name).  The interfaces behave as if there is an Ethernet with two
  754: adapters connected.  From this primitive, one can construct various
  755: configurations.  We focus on two common and useful cases for which
  756: there are existing scripts: bridging and NAT.
  758: With bridging (in the example above), the domU perceives itself to be
  759: on the same network as the dom0.  For server virtualization, this is
  760: usually best.  Bridging is accomplished by creating a bridge(4) device
  761: and adding the dom0's physical interface and the various xvifN.0
  762: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  763: config file.  The bridge must be set up already in the dom0; an
  764: example /etc/ifconfig.bridge0 is:
  766:         create
  767:         up
  768:         !brconfig bridge0 add wm0
  770: With NAT, the domU perceives itself to be behind a NAT running on the
  771: dom0.  This is often appropriate when running Xen on a workstation.
  772: TODO: NAT appears to be configured by "vif = [ '' ]".
  774: The MAC address specified is the one used for the interface in the new
  775: domain.  The interface in dom0 will use this address XOR'd with
  776: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  778: Sizing domains
  779: --------------
  781: Modern x86 hardware has vast amounts of resources.  However, many
  782: virtual servers can function just fine on far less.  A system with
  783: 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  784: far easier to adjust virtual resources than physical ones.  For
  785: memory, it's just a config file edit and a reboot.  For disk, one can
  786: create a new file and vnconfig it (or lvm), and then dump/restore,
  787: just like updating physical disks, but without having to be there and
  788: without those pesky connectors.
  790: Starting domains automatically
  791: ------------------------------
  793: To start domains foo at bar at boot and shut them down cleanly on dom0
  794: shutdown, in rc.conf add:
  796:         xendomains="foo bar"
  798: Note that earlier versions of the xentools41 xendomains rc.d script
  799: used xl, when one should use xm with 4.1.
  801: Creating specific unprivileged domains (domU)
  802: =============================================
  804: Creating domUs is almost entirely independent of operating system.  We
  805: have already presented the basics of config files.  Note that you must
  806: have already completed the dom0 setup so that "xl list" (or "xm list")
  807: works.
  809: Creating an unprivileged NetBSD domain (domU)
  810: ---------------------------------------------
  812: See the earlier config file, and adjust memory.  Decide on how much
  813: storage you will provide, and prepare it (file or lvm).
  815: While the kernel will be obtained from the dom0 file system, the same
  816: file should be present in the domU as /netbsd so that tools like
  817: savecore(8) can work.   (This is helpful but not necessary.)
  819: The kernel must be specifically for Xen and for use as a domU.  The
  820: i386 and amd64 provide the following kernels:
  822:         i386 XEN3_DOMU
  823:         i386 XEN3PAE_DOMU
  824:         amd64 XEN3_DOMU
  826: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  827: use the PAE version of the i386 kernel.
  829: This will boot NetBSD, but this is not that useful if the disk is
  830: empty.  One approach is to unpack sets onto the disk outside of xen
  831: (by mounting it, just as you would prepare a physical disk for a
  832: system you can't run the installer on).
  834: A second approach is to run an INSTALL kernel, which has a miniroot
  835: and can load sets from the network.  To do this, copy the INSTALL
  836: kernel to / and change the kernel line in the config file to:
  838:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  840: Then, start the domain as "xl create -c configname".
  842: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  843: line should be used in the config file.
  845:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  847: After booting the domain, the option to install via CDROM may be
  848: selected.  The CDROM device should be changed to `xbd1d`.
  850: Once done installing, "halt -p" the new domain (don't reboot or halt,
  851: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  852: config file), switch the config file back to the XEN3_DOMU kernel,
  853: and start the new domain again. Now it should be able to use "root on
  854: xbd0a" and you should have a, functional NetBSD domU.
  856: TODO: check if this is still accurate.
  857: When the new domain is booting you'll see some warnings about *wscons*
  858: and the pseudo-terminals. These can be fixed by editing the files
  859: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  860: `/etc/ttys`, except *console*, like this:
  862:     console "/usr/libexec/getty Pc"         vt100   on secure
  863:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  864:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  865:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  866:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  868: Finally, all screens must be commented out from `/etc/wscons.conf`.
  870: It is also desirable to add
  872:         powerd=YES
  874: in rc.conf. This way, the domain will be properly shut down if
  875: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  877: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  878: file system.  However, various programs (e.g. netstat) will use that
  879: kernel to look up symbols to read from kernel virtual memory.  If
  880: /netbsd is not the running kernel, those lookups will fail.  (This is
  881: not really a Xen-specific issue, but because the domU kernel is
  882: obtained from the dom0, it is far more likely to be out of sync or
  883: missing with Xen.)
  885: Creating an unprivileged Linux domain (domU)
  886: --------------------------------------------
  888: Creating unprivileged Linux domains isn't much different from
  889: unprivileged NetBSD domains, but there are some details to know.
  891: First, the second parameter passed to the disk declaration (the '0x1' in
  892: the example below)
  894:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  896: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  897: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  898: So, hda1 which has major 3 and minor 1 on a Linux system will have
  899: device number 0x301.  Alternatively, devices names can be used (hda,
  900: hdb, ...)  as xentools has a table to map these names to devices
  901: numbers.  To export a partition to a Linux guest we can use:
  903:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  904:         root = "/dev/hda1 ro"
  906: and it will appear as /dev/hda on the Linux system, and be used as root
  907: partition.
  909: To install the Linux system on the partition to be exported to the
  910: guest domain, the following method can be used: install
  911: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  912: that will be the root partition of your Linux domain, and mount it.
  913: Then copy the files from a working Linux system, make adjustments in
  914: `/etc` (fstab, network config).  It should also be possible to extract
  915: binary packages such as .rpm or .deb directly to the mounted partition
  916: using the appropriate tool, possibly running under NetBSD's Linux
  917: emulation.  Once the file system has been populated, umount it.  If
  918: desirable, the file system can be converted to ext3 using tune2fs -j.
  919: It should now be possible to boot the Linux guest domain, using one of
  920: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  922: To get the Linux console right, you need to add:
  924:     extra = "xencons=tty1"
  926: to your configuration since not all Linux distributions auto-attach a
  927: tty to the xen console.
  929: Creating an unprivileged Solaris domain (domU)
  930: ----------------------------------------------
  932: See possibly outdated
  933: [Solaris domU instructions](/ports/xen/howto-solaris/).
  936: PCI passthrough: Using PCI devices in guest domains
  937: ---------------------------------------------------
  939: The dom0 can give other domains access to selected PCI
  940: devices. This can allow, for example, a non-privileged domain to have
  941: access to a physical network interface or disk controller.  However,
  942: keep in mind that giving a domain access to a PCI device most likely
  943: will give the domain read/write access to the whole physical memory,
  944: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  945: device.  Also, it's not possible to export ISA devices to non-dom0
  946: domains, which means that the primary VGA adapter can't be exported.
  947: A guest domain trying to access the VGA registers will panic.
  949: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  950: not been ported to later versions at this time.
  952: For a PCI device to be exported to a domU, is has to be attached to
  953: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  954: pciback.hide boot parameter will attach to "pciback" instead of the
  955: usual driver.  The list of devices is specified as "(bus:dev.func)",
  956: where bus and dev are 2-digit hexadecimal numbers, and func a
  957: single-digit number:
  959:         pciback.hide=(00:0a.0)(00:06.0)
  961: pciback devices should show up in the dom0's boot messages, and the
  962: devices should be listed in the `/kern/xen/pci` directory.
  964: PCI devices to be exported to a domU are listed in the "pci" array of
  965: the domU's config file, with the format "0000:bus:dev.func".
  967:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  969: In the domU an "xpci" device will show up, to which one or more pci
  970: buses will attach.  Then the PCI drivers will attach to PCI buses as
  971: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  972: or any PCI drivers built in by default; you have to build your own
  973: kernel to use PCI devices in a domU.  Here's a kernel config example;
  974: note that only the "xpci" lines are unusual.
  976:         include         "arch/i386/conf/XEN3_DOMU"
  978:         # Add support for PCI buses to the XEN3_DOMU kernel
  979:         xpci* at xenbus ?
  980:         pci* at xpci ?
  982:         # PCI USB controllers
  983:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  985:         # USB bus support
  986:         usb*    at uhci?
  988:         # USB Hubs
  989:         uhub*   at usb?
  990:         uhub*   at uhub? port ? configuration ? interface ?
  992:         # USB Mass Storage
  993:         umass*  at uhub? port ? configuration ? interface ?
  994:         wd*     at umass?
  995:         # SCSI controllers
  996:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  998:         # SCSI bus support (for both ahc and umass)
  999:         scsibus* at scsi?
 1001:         # SCSI devices
 1002:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
 1003:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
 1006: NetBSD as a domU in a VPS
 1007: =========================
 1009: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
 1010: hardware.  This section explains how to deal with Xen in a domU as a
 1011: virtual private server where you do not control or have access to the
 1012: dom0.  This is not intended to be an exhaustive list of VPS providers;
 1013: only a few are mentioned that specifically support NetBSD.
 1015: VPS operators provide varying degrees of access and mechanisms for
 1016: configuration.  The big issue is usually how one controls which kernel
 1017: is booted, because the kernel is nominally in the dom0 file system (to
 1018: which VPS users do not normally have access).  A second issue is how
 1019: to install NetBSD.
 1020: A VPS user may want to compile a kernel for security updates, to run
 1021: npf, run IPsec, or any other reason why someone would want to change
 1022: their kernel.
 1024: One approach is to have an administrative interface to upload a kernel,
 1025: or to select from a prepopulated list.  Other approaches are pygrub
 1026: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
 1027: kernel from the domU file system.  This is closer to a regular physical
 1028: computer, where someone who controls a machine can replace the kernel.
 1030: A second issue is multiple CPUs.  With NetBSD 6, domUs support
 1031: multiple vcpus, and it is typical for VPS providers to enable multiple
 1032: CPUs for NetBSD domUs.
 1034: pygrub
 1035: -------
 1037: pygrub runs in the dom0 and looks into the domU file system.  This
 1038: implies that the domU must have a kernel in a file system in a format
 1039: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
 1040: interest.
 1042: pvgrub
 1043: ------
 1045: pvgrub is a version of grub that uses PV operations instead of BIOS
 1046: calls.  It is booted from the dom0 as the domU kernel, and then reads
 1047: /grub/menu.lst and loads a kernel from the domU file system.
 1049: [Panix]( lets users use pvgrub.  Panix reports
 1050: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
 1051: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
 1052: page](, which describes only
 1053: Linux but should be updated to cover NetBSD :-).
 1055: []( also lets users with pvgrub to boot
 1056: their own kernel.  See then [ NetBSD
 1057: HOWTO](
 1058: (which is in need of updating).
 1060: It appears that [grub's FFS
 1061: code](
 1062: does not support all aspects of modern FFS, but there are also reports
 1063: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
 1064: partition for the kernel with the intent that grub can understand it,
 1065: which leads to /netbsd not being the actual kernel.  One must remember
 1066: to update the special boot partition.
 1068: Amazon
 1069: ------
 1071: See the [Amazon EC2 page](../amazon_ec2/).
 1073: Using npf
 1074: ---------
 1076: In standard kernels, npf is a module, and thus cannot be loaded in a
 1077: DOMU kernel.
 1079: TODO: Explain how to compile npf into a custom kernel, answering (but
 1080: note that the problem was caused by not booting the right kernel)
 1081: [this email to
 1082: netbsd-users](
 1084: TODO items for improving NetBSD/xen
 1085: ===================================
 1087: * Make the NetBSD dom0 kernel work with SMP.
 1088: * Test the Xen 4.5 packages adequately to be able to recommend them as
 1089:   the standard approach.
 1090: * Get PCI passthrough working on Xen 4.5
 1091: * Get pvgrub into pkgsrc, either via xentools or separately.
 1092: * grub
 1093:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
 1094:     fragsize/blocksize (UFS2 support may be present; the point is to
 1095:     make it so that with any UFS1/UFS2 file system setup that works
 1096:     with NetBSD grub will also work).
 1097:     See [pkg/40258](
 1098:   * Push patches upstream.
 1099:   * Get UFS2 patches into pvgrub.
 1100: * Add support for PV ops to a version of /boot, and make it usable as
 1101:   a kernel in Xen, similar to pvgrub.
 1102: * Solve somehow the issue with modules for GENERIC not being loadable
 1103:   in a Xen dom0 or domU kernel.
 1105: Random pointers
 1106: ===============
 1108: This section contains links from elsewhere not yet integrated into the
 1109: HOWTO, and other guides.
 1111: *
 1112: *
 1113: *

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