File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
Revision 1.150: download - view: text, annotated - select for diffs
Thu Jul 26 11:08:33 2018 UTC (4 years ago) by maxv
Branches: MAIN
CVS tags: HEAD
Improve the table, remove more duplicated noise (eg "Recommendation",
already said in other sections).

    1: [[!meta title="Xen HowTo"]]
    3: Introduction
    4: ============
    6: [![[Xen
    7: screenshot]](](
    9: Xen is a hypervisor for x86 hardware, which supports running multiple guest
   10: operating systems on a single physical machine.  Xen is a Type 1 or
   11: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
   12: memory and console, a dom0 operating system which mediates access to
   13: other hardware (e.g., disks, network, USB), and one or more domU
   14: operating systems which operate in an unprivileged virtualized
   15: environment.  IO requests from the domU systems are forwarded by the
   16: Xen hypervisor to the dom0 to be fulfilled.
   18: Xen supports different styles of guest:
   20: [[!table data="""
   21: Style of guest	|Supported by NetBSD
   22: PV		|Yes (dom0, domU)
   23: HVM		|Yes (domU)
   24: PVHVM		|No
   25: PVH		|No
   26: """]]
   28: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
   29: hardware directly, but instead makes hypercalls to the hypervisor; PV
   30: guests must be specifically coded for Xen. In HVM mode, no guest
   31: modification is required; however, hardware support is required, such
   32: as VT-x on Intel CPUs and SVM on AMD CPUs.
   34: There are further features for IOMMU virtualization, Intel's VT-d and
   35: AMD's AMD-Vi.  TODO: Explain whether Xen on NetBSD makes use of these
   36: features.  TODO: Review by someone who really understands this.
   38: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   39: The dom0 can start one or more domUs.  (Booting is explained in detail
   40: in the dom0 section.)
   42: This HOWTO presumes a basic familiarity with the Xen system
   43: architecture, with installing NetBSD on i386/amd64 hardware, and with
   44: installing software from pkgsrc.  See also the [Xen
   45: website](
   47: This HOWTO attempts to address both the case of running a NetBSD dom0
   48: on hardware and running domUs under it (NetBSD and other), and also
   49: running NetBSD as a domU in a VPS.
   51: Versions of Xen and NetBSD
   52: ==========================
   54: Most of the installation concepts and instructions are independent
   55: of Xen version and NetBSD version.  This section gives advice on
   56: which version to choose.  Versions not in pkgsrc and older unsupported
   57: versions of NetBSD are intentionally ignored.
   59: The term "amd64" is used to refer to both the NetBSD port and to the
   60: hardware architecture on which it runs.  Such hardware is generally
   61: made by both Intel and AMD, and common on PC computers.
   63: Xen versions
   64: ------------
   66: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   67: xenkernel and xentools.  We will refer only to the kernel versions,
   68: but note that both packages must be installed together and must have
   69: matching versions.
   71: Versions available in pkgsrc:
   73: [[!table data="""
   74: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
   75: 4.2		|xenkernel42	|32bit, 64bit		|Yes
   76: 4.5		|xenkernel45	|64bit			|Yes
   77: 4.6		|xenkernel46	|64bit			|Partially
   78: 4.8		|xenkernel48	|64bit			|No
   79: 4.11		|xenkernel411	|64bit			|No
   80: """]]
   82: See also the [Xen Security Advisory page](
   84: Note: Xen 4.2 was the last version to support 32bit CPUs.
   86: Xen command program
   87: -------------------
   89: Early Xen used a program called xm to manipulate the system from the
   90: dom0.  Starting in 4.1, a replacement program with similar behavior
   91: called xl is provided, but it does not work well in 4.1.  In 4.2, both
   92: xm and xl work fine.  4.4 is the last version that has xm.
   94: You must make a global choice to use xm or xl, because it affects not
   95: only which command you use, but the command used by rc.d scripts
   96: (specifically xendomains) and which daemons should be run.  The
   97: xentools packages provide xl for 4.2 and up.
   99: In 4.2, you can choose to use xm by simply changing the ctl_command
  100: variable and setting xend=YES in rc.conf.
  102: With xl, virtual devices are configured in parallel, which can cause
  103: problems if they are written assuming serial operation (e.g., updating
  104: firewall rules without explicit locking).  There is now locking for
  105: the provided scripts, which works for normal casses (e.g, file-backed
  106: xbd, where a vnd must be allocated).  But, as of 201612, it has not
  107: been adequately tested for a complex custom setup with a large number
  108: of interfaces.
  110: NetBSD versions
  111: ---------------
  113: The netbsd-7, netbsd-8, and -current branches are all reasonable
  114: choices, with more or less the same considerations for non-Xen use.
  115: NetBSD 8 is recommended as the stable version of the most recent
  116: release for production use.
  118: For developing Xen, netbsd-current may be appropriate.
  120: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  121: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  122: need SMP for dom0 functions; the lack of support is really a problem
  123: when using a dom0 as a normal computer.)
  125: Note: NetBSD support is called XEN3. However, it does support Xen 4,
  126: because the hypercall interface has remained identical.
  128: Architecture
  129: ------------
  131: Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen
  132: versions).  (Practically, almost any computer where one would want to
  133: run Xen today supports amd64.)
  135: Xen, the dom0 system, and each domU system can be either i386 or
  136: amd64.  When building a xenkernel package, one obtains an i386 Xen
  137: kernel on an i386 host, and an amd64 Xen kernel on an amd64 host.  If
  138: the Xen kernel is i386, then the dom0 kernel and all domU kernels must
  139: be i386.  With an amd64 Xen kernel, an amd64 dom0 kernel is known to
  140: work, and an i386 dom0 kernel should in theory work.  An amd64
  141: Xen/dom0 is known to support both i386 and amd64 domUs.
  143: i386 dom0 and domU kernels must be PAE (except for an i386 Xen 3.1
  144: kernel, where one can use non-PAE for dom0 and all domUs); PAE kernels
  145: are included in the NetBSD default build.  (Note that emacs (at least)
  146: fails if run on i386 with PAE when built without, and vice versa,
  147: presumably due to bugs in the undump code.)
  149: Because of the above, the standard approach is to use an amd64 Xen
  150: kernel and NetBSD/amd64 for the dom0.  For domUs, NetBSD/i386 (with
  151: the PAE kernel) and NetBSD/amd64 are in widespread use, and there is
  152: little to no Xen-specific reason to prefer one over the other.
  154: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
  155: (or obtain from pre-built packages) an amd64 Xen kernel and install
  156: that on the system.  (One must also use a PAE i386 kernel, but this is
  157: also required with an i386 Xen kernel.).  Almost no one in the
  158: NetBSD/Xen community does this, and the standard, well-tested,
  159: approach is to use an amd64 dom0.
  161: A [posting on
  162: xen-devel](
  163: explained that PV system call overhead was higher on amd64, and thus
  164: there is some notion that i386 guests are faster.  It goes on to
  165: caution that the total situation is complex and not entirely
  166: understood. On top of that caution, the post is about Linux, not
  167: NetBSD.  TODO: Include link to benchmarks, if someone posts them.
  169: NetBSD as a dom0
  170: ================
  172: NetBSD can be used as a dom0 and works very well.  The following
  173: sections address installation, updating NetBSD, and updating Xen.
  174: Note that it doesn't make sense to talk about installing a dom0 OS
  175: without also installing Xen itself.  We first address installing
  176: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  177: NetBSD install to a dom0 install by just changing the kernel and boot
  178: configuration.
  180: For experimenting with Xen, a machine with as little as 1G of RAM and
  181: 100G of disk can work.  For running many domUs in productions, far
  182: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
  183: half-dozen domUs of 512M and 32G each.  Basically, the RAM and disk
  184: have to be bigger than the sum of the RAM/disk needs of the dom0 and
  185: all the domUs.
  187: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  188: 512M it worked reliably.  This does not make sense, but if you see
  189: "not ELF" after Xen boots, try increasing dom0 RAM.
  191: Styles of dom0 operation
  192: ------------------------
  194: There are two basic ways to use Xen.  The traditional method is for
  195: the dom0 to do absolutely nothing other than providing support to some
  196: number of domUs.  Such a system was probably installed for the sole
  197: purpose of hosting domUs, and sits in a server room on a UPS.
  199: The other way is to put Xen under a normal-usage computer, so that the
  200: dom0 is what the computer would have been without Xen, perhaps a
  201: desktop or laptop.  Then, one can run domUs at will.  Purists will
  202: deride this as less secure than the previous approach, and for a
  203: computer whose purpose is to run domUs, they are right.  But Xen and a
  204: dom0 (without domUs) is not meaningfully less secure than the same
  205: things running without Xen.  One can boot Xen or boot regular NetBSD
  206: alternately with little problems, simply refraining from starting the
  207: Xen daemons when not running Xen.
  209: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  210: limit the performance of the Xen/dom0 workstation approach.  In theory
  211: the only issue is that the "backend drivers" are not yet MPSAFE:
  214: Installation of NetBSD
  215: ----------------------
  217: First,
  218: [install NetBSD/amd64](/guide/inst/)
  219: just as you would if you were not using Xen.
  220: However, the partitioning approach is very important.
  222: If you want to use RAIDframe for the dom0, there are no special issues
  223: for Xen.  Typically one provides RAID storage for the dom0, and the
  224: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  225: over a RAID1 header to find /boot from a file system within a RAID
  226: partition; this is no different when booting Xen.
  228: There are 4 styles of providing backing storage for the virtual disks
  229: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  231: With raw partitions, one has a disklabel (or gpt) partition sized for
  232: each virtual disk to be used by the domU.  (If you are able to predict
  233: how domU usage will evolve, please add an explanation to the HOWTO.
  234: Seriously, needs tend to change over time.)
  236: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  237: for domU disks.  This is almost as efficient as raw disk partitions
  238: and more flexible.  Hence raw disk partitions should typically not
  239: be used.
  241: One can use files in the dom0 file system, typically created by dd'ing
  242: /dev/zero to create a specific size.  This is somewhat less efficient,
  243: but very convenient, as one can cp the files for backup, or move them
  244: between dom0 hosts.
  246: Finally, in theory one can place the files backing the domU disks in a
  247: SAN.  (This is an invitation for someone who has done this to add a
  248: HOWTO page.)
  250: Installation of Xen
  251: -------------------
  253: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  254: pkgsrc (or another matching pair).  See [the pkgsrc
  255: documentation]( for help with
  256: pkgsrc.  Ensure that your packages are recent; the HOWTO does not
  257: contemplate old builds.
  260: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  261: recent versions have HVM support integrated in the main xentools
  262: package.  It is entirely reasonable to run only PV guests.
  264: Next you need to install the selected Xen kernel itself, which is
  265: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  266: For debugging, one may copy xen-debug.gz; this is conceptually similar
  267: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  268: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  269: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  270: of a NetBSD build.  If using i386, use
  271: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  272: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  273: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  274: typically are) left compressed.
  276: In a dom0, kernfs is mandatory for xend to communicate with the
  277: kernel, so ensure that /kern is in fstab.  (A standard NetBSD install
  278: should already mount /kern.)
  280: Because you already installed NetBSD, you have a working boot setup
  281: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  282: beginning of your root file system, have /boot, and likely also
  283: /boot.cfg.  (If not, fix before continuing!)
  285: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  286: example.  The basic line is
  288:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  290: which specifies that the dom0 should have 512M, leaving the rest to be
  291: allocated for domUs.  To use a serial console, use
  293:         menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  295: which will use the first serial port for Xen (which counts starting
  296: from 1, unlike NetBSD which counts starting from 0), forcing
  297: speed/parity.  Because the NetBSD command line lacks a
  298: "console=pc" argument, it will use the default "xencons" console device,
  299: which directs the console I/O through Xen to the same console device Xen
  300: itself uses (in this case, the serial port).
  302: In an attempt to add performance, one can also add
  304:         dom0_max_vcpus=1 dom0_vcpus_pin
  306: to force only one vcpu to be provided (since NetBSD dom0 can't use
  307: more) and to pin that vcpu to a physical CPU.  TODO: benchmark this.
  309: Xen has [many boot
  310: options](,
  311: and other than dom0 memory and max_vcpus, they are generally not
  312: necessary.
  314: As with non-Xen systems, you should have a line to boot /netbsd (a
  315: kernel that works without Xen).  Consider a line to boot /netbsd.ok (a
  316: fallback version of the non-Xen kernel, updated manually when you are
  317: sure /netbsd is ok).  Consider also a line to boot fallback versions
  318: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
  319: to resolve Xen booting issues.
  321: Probably you want a default=N line to choose Xen in the absence of
  322: intervention.
  324: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  325: than GENERIC without Xen.
  327: Using grub (historic)
  328: ---------------------
  330: Before NetBSD's native bootloader could support Xen, the use of
  331: grub was recommended.  If necessary, see the
  332: [old grub information](/ports/xen/howto-grub).
  334: The [HowTo on Installing into
  335: RAID-1](
  336: explains how to set up booting a dom0 with Xen using grub with
  337: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  338: boot.  Now, just create a system with RAID-1, and alter /boot.cfg as
  339: described above.)
  341: Configuring Xen
  342: ---------------
  344: Xen logs will be in /var/log/xen.
  346: Now, you have a system that will boot Xen and the dom0 kernel, but not
  347: do anything else special.  Make sure that you have rebooted into Xen.
  348: There will be no domUs, and none can be started because you still have
  349: to configure the dom0 daemons.
  351: The daemons which should be run vary with Xen version and with whether
  352: one is using xm or xl.  The Xen 3.1, 3.3 and 4.1 packages use xm.  Xen
  353: 4.2 and up packages use xl.  To use xm with 4.2, edit xendomains to
  354: use xm instead.
  356: For 3.1 and 3.3, you should enable xend and xenbackendd:
  358:         xend=YES
  359:         xenbackendd=YES
  361: For 4.1 and up, you should enable xencommons.  Not enabling xencommons
  362: will result in a hang; it is necessary to hit ^C on the console to let
  363: the machine finish booting.  If you are using xm (default in 4.1, or
  364: if you changed xendomains in 4.2), you should also enable xend:
  366:         xend=YES # only if using xm, and only installed <= 4.2
  367:         xencommons=YES
  369: TODO: Recommend for/against xen-watchdog.
  371: After you have configured the daemons and either started them (in the
  372: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  373: available resources, and running domains.  An example with xl follows:
  375:         # xl dmesg
  376: 	[xen's boot info]
  377:         # xl info
  378: 	[available memory, etc.]
  379:         # xl list
  380:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  381:         Domain-0           0       64    0  r----     58.1
  383: ### Issues with xencommons
  385: xencommons starts xenstored, which stores data on behalf of dom0 and
  386: domUs.  It does not currently work to stop and start xenstored.
  387: Certainly all domUs should be shutdown first, following the sort order
  388: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  389: and is not notified when xenstored exits, leading to not recreating
  390: the state when the new xenstored starts.  Until there's a mechanism to
  391: make this work, one should not expect to be able to restart xenstored
  392: (and thus xencommons).  There is currently no reason to expect that
  393: this will get fixed any time soon.
  395: ### No-longer needed advice about devices
  397: The installation of NetBSD should already have created devices for xen
  398: (xencons, xenevt, xsd_kva), but if they are not present, create them:
  400:         cd /dev && sh MAKEDEV xen
  402: anita (for testing NetBSD)
  403: --------------------------
  405: With the setup so far (assuming 4.2/xl), one should be able to run
  406: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  407: root, because anita must create a domU):
  409:         anita --vmm=xl test file:///usr/obj/i386/
  411: Alternatively, one can use --vmm=xm to use xm-based domU creation
  412: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  414: Xen-specific NetBSD issues
  415: --------------------------
  417: There are (at least) two additional things different about NetBSD as a
  418: dom0 kernel compared to hardware.
  420: One is that the module ABI is different because some of the #defines
  421: change, so one must build modules for Xen.  As of netbsd-7, the build
  422: system does this automatically.  TODO: check this.  (Before building
  423: Xen modules was added, it was awkward to use modules to the point
  424: where it was considered that it did not work.)
  426: The other difference is that XEN3_DOM0 does not have exactly the same
  427: options as GENERIC.  While it is debatable whether or not this is a
  428: bug, users should be aware of this and can simply add missing config
  429: items if desired.
  431: Updating NetBSD in a dom0
  432: -------------------------
  434: This is just like updating NetBSD on bare hardware, assuming the new
  435: version supports the version of Xen you are running.  Generally, one
  436: replaces the kernel and reboots, and then overlays userland binaries
  437: and adjusts /etc.
  439: Note that one must update both the non-Xen kernel typically used for
  440: rescue purposes and the DOM0 kernel used with Xen.
  442: Converting from grub to /boot
  443: -----------------------------
  445: These instructions were [TODO: will be] used to convert a system from
  446: grub to /boot.  The system was originally installed in February of
  447: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  448: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  449: 4.1 and grub, much like the message linked earlier in the grub
  450: section.
  452:         # Install MBR bootblocks on both disks. 
  453:         fdisk -i /dev/rwd0d
  454:         fdisk -i /dev/rwd1d
  455:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  456:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  457:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  458:         # Install secondary boot loader
  459:         cp -p /usr/mdec/boot /
  460:         # Create boot.cfg following earlier guidance:
  461:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  462:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  463:         menu=GENERIC:boot
  464:         menu=GENERIC single-user:boot -s
  465:         menu=GENERIC.ok:boot netbsd.ok
  466:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  467:         menu=Drop to boot prompt:prompt
  468:         default=1
  469:         timeout=30
  471: TODO: actually do this and fix it if necessary.
  473: Upgrading Xen versions
  474: ---------------------
  476: Minor version upgrades are trivial.  Just rebuild/replace the
  477: xenkernel version and copy the new xen.gz to / (where /boot.cfg
  478: references it), and reboot.
  480: Major version upgrades are conceptually not difficult, but can run
  481: into all the issues found when installing Xen.  Assuming migration
  482: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
  483: install the xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz
  484: to /.
  486: Ensure that the contents of /etc/rc.d/xen* are correct.  Specifically,
  487: they must match the package you just installed and not be left over
  488: from some previous installation.
  490: Enable the correct set of daemons; see the configuring section above.
  491: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
  493: Ensure that the domU config files are valid for the new version.
  494: Specifically, for 4.x remove autorestart=True, and ensure that disks
  495: are specified with numbers as the second argument, as the examples
  496: above show, and not NetBSD device names.
  498: Hardware known to work
  499: ----------------------
  501: Arguably, this section is misplaced, and there should be a page of
  502: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
  503: assumption that NetBSD/xen runs fine on any modern hardware that
  504: NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU (and
  505: sometimes RAM) pairs/triples to aid those choosing a motherboard.
  506: Note that Xen systems usually do not run X, so a listing here does not
  507: imply that X works at all.
  509:         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
  510:         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
  511:         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
  513: Older hardware:
  515:         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
  516:         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz"
  517:         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz"
  519: Running Xen under qemu
  520: ----------------------
  522: The astute reader will note that this section is somewhat twisted.
  523: However, it can be useful to run Xen under qemu either because the
  524: version of NetBSD as a dom0 does not run on the hardware in use, or to
  525: generate automated test cases involving Xen.
  527: In 2015-01, the following combination was reported to mostly work:
  529:         host OS: NetBSD/amd64 6.1.4
  530:         qemu: 2.2.0 from pkgsrc
  531:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  532:         dom0 kernel: NetBSD/amd64 6.1.5
  533:         Xen tools: xentools42-4.2.5 from pkgsrc
  535: See [PR 47720]( for a problem with dom0
  536: shutdown.
  538: Unprivileged domains (domU)
  539: ===========================
  541: This section describes general concepts about domUs.  It does not
  542: address specific domU operating systems or how to install them.  The
  543: config files for domUs are typically in /usr/pkg/etc/xen, and are
  544: typically named so that the file name, domU name and the domU's host
  545: name match.
  547: The domU is provided with CPU and memory by Xen, configured by the
  548: dom0.  The domU is provided with disk and network by the dom0,
  549: mediated by Xen, and configured in the dom0.
  551: Entropy in domUs can be an issue; physical disks and network are on
  552: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  554: Config files
  555: ------------
  557: There is no good order to present config files and the concepts
  558: surrounding what is being configured.  We first show an example config
  559: file, and then in the various sections give details.
  561: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  562: for a large number of well-commented examples, mostly for running
  563: GNU/Linux.
  565: The following is an example minimal domain configuration file
  566: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  567: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  568: i386 domU).  The domU serves as a network file server.
  570:         # -*- mode: python; -*-
  572:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  573:         memory = 1024
  574:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  575:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  576:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  578: The domain will have the same name as the file.  The kernel has the
  579: host/domU name in it, so that on the dom0 one can update the various
  580: domUs independently.  The vif line causes an interface to be provided,
  581: with a specific mac address (do not reuse MAC addresses!), in bridge
  582: mode.  Two disks are provided, and they are both writable; the bits
  583: are stored in files and Xen attaches them to a vnd(4) device in the
  584: dom0 on domain creation.  The system treats xbd0 as the boot device
  585: without needing explicit configuration.
  587: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  588: that "xm create" takes the name of a config file, while other commands
  589: take the name of a domain.  To create the domain, connect to the
  590: console, create the domain while attaching the console, shutdown the
  591: domain, and see if it has finished stopping, do (or xl with Xen >=
  592: 4.2):
  594:         xm create foo
  595:         xm console foo
  596:         xm create -c foo
  597:         xm shutdown foo
  598:         xm list
  600: Typing ^] will exit the console session.  Shutting down a domain is
  601: equivalent to pushing the power button; a NetBSD domU will receive a
  602: power-press event and do a clean shutdown.  Shutting down the dom0
  603: will trigger controlled shutdowns of all configured domUs.
  605: domU kernels
  606: ------------
  608: On a physical computer, the BIOS reads sector 0, and a chain of boot
  609: loaders finds and loads a kernel.  Normally this comes from the root
  610: file system.  With Xen domUs, the process is totally different.  The
  611: normal path is for the domU kernel to be a file in the dom0's
  612: file system.  At the request of the dom0, Xen loads that kernel into a
  613: new domU instance and starts execution.  While domU kernels can be
  614: anyplace, reasonable places to store domU kernels on the dom0 are in /
  615: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  616: config files), or in /u0/xen (where the vdisks are).
  618: Note that loading the domU kernel from the dom0 implies that boot
  619: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  620: See the VPS section near the end for discussion of alternate ways to
  621: obtain domU kernels.
  623: CPU and memory
  624: --------------
  626: A domain is provided with some number of vcpus, less than the number
  627: of CPUs seen by the hypervisor.  (For a dom0, this is controlled by
  628: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  629: from the config file by the "vcpus = N" directive.
  631: A domain is provided with memory; this is controlled in the config
  632: file by "memory = N" (in megabytes).  In the straightforward case, the
  633: sum of the the memory allocated to the dom0 and all domUs must be less
  634: than the available memory.
  636: Xen also provides a "balloon" driver, which can be used to let domains
  637: use more memory temporarily.  TODO: Explain better, and explain how
  638: well it works with NetBSD.
  640: Virtual disks
  641: -------------
  643: With the file/vnd style, typically one creates a directory,
  644: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  645: domUs.  Then, for each domU disk, one writes zeros to a file that then
  646: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  647: for the first virtual disk for the domU called foo.  Writing zeros to
  648: the file serves two purposes.  One is that preallocating the contents
  649: improves performance.  The other is that vnd on sparse files has
  650: failed to work.  TODO: give working/notworking NetBSD versions for
  651: sparse vnd and gnats reference.  Note that the use of file/vnd for Xen
  652: is not really different than creating a file-backed virtual disk for
  653: some other purpose, except that xentools handles the vnconfig
  654: commands.  To create an empty 4G virtual disk, simply do
  656:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  658: Do not use qemu-img-xen, because this will create sparse file.  There
  659: have been recent (2015) reports of sparse vnd(4) devices causing
  660: lockups, but there is apparently no PR.
  662: With the lvm style, one creates logical devices.  They are then used
  663: similarly to vnds.  TODO: Add an example with lvm.
  665: In domU config files, the disks are defined as a sequence of 3-tuples.
  666: The first element is "method:/path/to/disk".  Common methods are
  667: "file:" for file-backed vnd. and "phy:" for something that is already
  668: a (TODO: character or block) device.
  670: The second element is an artifact of how virtual disks are passed to
  671: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  672: are given a device name to associate with the disk, and values like
  673: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  674: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  675: second argument.  The name given is converted to a major/minor by
  676: calling stat(2) on the name in /dev and this is passed to the domU.
  677: In the general case, the dom0 and domU can be different operating
  678: systems, and it is an unwarranted assumption that they have consistent
  679: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  680: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  681: for the second works fine and avoids this issue.  For a GNU/Linux
  682: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  683: /dev/hda1.
  685: The third element is "w" for writable disks, and "r" for read-only
  686: disks.
  688: Note that NetBSD by default creates only vnd[0123].  If you need more
  689: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  690: dom0.
  692: Note that NetBSD by default creates only xbd[0123].  If you need more
  693: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  695: Virtual Networking
  696: ------------------
  698: Xen provides virtual Ethernets, each of which connects the dom0 and a
  699: domU.  For each virtual network, there is an interface "xvifN.M" in
  700: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  701: name).  The interfaces behave as if there is an Ethernet with two
  702: adapters connected.  From this primitive, one can construct various
  703: configurations.  We focus on two common and useful cases for which
  704: there are existing scripts: bridging and NAT.
  706: With bridging (in the example above), the domU perceives itself to be
  707: on the same network as the dom0.  For server virtualization, this is
  708: usually best.  Bridging is accomplished by creating a bridge(4) device
  709: and adding the dom0's physical interface and the various xvifN.0
  710: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  711: config file.  The bridge must be set up already in the dom0; an
  712: example /etc/ifconfig.bridge0 is:
  714:         create
  715:         up
  716:         !brconfig bridge0 add wm0
  718: With NAT, the domU perceives itself to be behind a NAT running on the
  719: dom0.  This is often appropriate when running Xen on a workstation.
  720: TODO: NAT appears to be configured by "vif = [ '' ]".
  722: The MAC address specified is the one used for the interface in the new
  723: domain.  The interface in dom0 will use this address XOR'd with
  724: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  726: Sizing domains
  727: --------------
  729: Modern x86 hardware has vast amounts of resources.  However, many
  730: virtual servers can function just fine on far less.  A system with
  731: 512M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  732: far easier to adjust virtual resources than physical ones.  For
  733: memory, it's just a config file edit and a reboot.  For disk, one can
  734: create a new file and vnconfig it (or lvm), and then dump/restore,
  735: just like updating physical disks, but without having to be there and
  736: without those pesky connectors.
  738: Starting domains automatically
  739: ------------------------------
  741: To start domains foo at bar at boot and shut them down cleanly on dom0
  742: shutdown, in rc.conf add:
  744:         xendomains="foo bar"
  746: Note that earlier versions of the xentools41 xendomains rc.d script
  747: used xl, when one should use xm with 4.1.
  749: Creating specific unprivileged domains (domU)
  750: =============================================
  752: Creating domUs is almost entirely independent of operating system.  We
  753: have already presented the basics of config files.  Note that you must
  754: have already completed the dom0 setup so that "xl list" (or "xm list")
  755: works.
  757: Creating an unprivileged NetBSD domain (domU)
  758: ---------------------------------------------
  760: See the earlier config file, and adjust memory.  Decide on how much
  761: storage you will provide, and prepare it (file or lvm).
  763: While the kernel will be obtained from the dom0 file system, the same
  764: file should be present in the domU as /netbsd so that tools like
  765: savecore(8) can work.   (This is helpful but not necessary.)
  767: The kernel must be specifically for Xen and for use as a domU.  The
  768: i386 and amd64 provide the following kernels:
  770:         i386 XEN3_DOMU
  771:         i386 XEN3PAE_DOMU
  772:         amd64 XEN3_DOMU
  774: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  775: use the PAE version of the i386 kernel.
  777: This will boot NetBSD, but this is not that useful if the disk is
  778: empty.  One approach is to unpack sets onto the disk outside of xen
  779: (by mounting it, just as you would prepare a physical disk for a
  780: system you can't run the installer on).
  782: A second approach is to run an INSTALL kernel, which has a miniroot
  783: and can load sets from the network.  To do this, copy the INSTALL
  784: kernel to / and change the kernel line in the config file to:
  786:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  788: Then, start the domain as "xl create -c configname".
  790: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  791: line should be used in the config file.
  793:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  795: After booting the domain, the option to install via CDROM may be
  796: selected.  The CDROM device should be changed to `xbd1d`.
  798: Once done installing, "halt -p" the new domain (don't reboot or halt,
  799: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  800: config file), switch the config file back to the XEN3_DOMU kernel,
  801: and start the new domain again. Now it should be able to use "root on
  802: xbd0a" and you should have a, functional NetBSD domU.
  804: TODO: check if this is still accurate.
  805: When the new domain is booting you'll see some warnings about *wscons*
  806: and the pseudo-terminals. These can be fixed by editing the files
  807: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  808: `/etc/ttys`, except *console*, like this:
  810:     console "/usr/libexec/getty Pc"         vt100   on secure
  811:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  812:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  813:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  814:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  816: Finally, all screens must be commented out from `/etc/wscons.conf`.
  818: It is also desirable to add
  820:         powerd=YES
  822: in rc.conf. This way, the domain will be properly shut down if
  823: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  825: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  826: file system.  However, various programs (e.g. netstat) will use that
  827: kernel to look up symbols to read from kernel virtual memory.  If
  828: /netbsd is not the running kernel, those lookups will fail.  (This is
  829: not really a Xen-specific issue, but because the domU kernel is
  830: obtained from the dom0, it is far more likely to be out of sync or
  831: missing with Xen.)
  833: Creating an unprivileged Linux domain (domU)
  834: --------------------------------------------
  836: Creating unprivileged Linux domains isn't much different from
  837: unprivileged NetBSD domains, but there are some details to know.
  839: First, the second parameter passed to the disk declaration (the '0x1' in
  840: the example below)
  842:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  844: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  845: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  846: So, hda1 which has major 3 and minor 1 on a Linux system will have
  847: device number 0x301.  Alternatively, devices names can be used (hda,
  848: hdb, ...)  as xentools has a table to map these names to devices
  849: numbers.  To export a partition to a Linux guest we can use:
  851:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  852:         root = "/dev/hda1 ro"
  854: and it will appear as /dev/hda on the Linux system, and be used as root
  855: partition.
  857: To install the Linux system on the partition to be exported to the
  858: guest domain, the following method can be used: install
  859: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  860: that will be the root partition of your Linux domain, and mount it.
  861: Then copy the files from a working Linux system, make adjustments in
  862: `/etc` (fstab, network config).  It should also be possible to extract
  863: binary packages such as .rpm or .deb directly to the mounted partition
  864: using the appropriate tool, possibly running under NetBSD's Linux
  865: emulation.  Once the file system has been populated, umount it.  If
  866: desirable, the file system can be converted to ext3 using tune2fs -j.
  867: It should now be possible to boot the Linux guest domain, using one of
  868: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  870: To get the Linux console right, you need to add:
  872:     extra = "xencons=tty1"
  874: to your configuration since not all Linux distributions auto-attach a
  875: tty to the xen console.
  877: Creating an unprivileged Solaris domain (domU)
  878: ----------------------------------------------
  880: See possibly outdated
  881: [Solaris domU instructions](/ports/xen/howto-solaris/).
  884: PCI passthrough: Using PCI devices in guest domains
  885: ---------------------------------------------------
  887: The dom0 can give other domains access to selected PCI
  888: devices. This can allow, for example, a non-privileged domain to have
  889: access to a physical network interface or disk controller.  However,
  890: keep in mind that giving a domain access to a PCI device most likely
  891: will give the domain read/write access to the whole physical memory,
  892: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  893: device.  Also, it's not possible to export ISA devices to non-dom0
  894: domains, which means that the primary VGA adapter can't be exported.
  895: A guest domain trying to access the VGA registers will panic.
  897: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  898: not been ported to later versions at this time.
  900: For a PCI device to be exported to a domU, is has to be attached to
  901: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  902: pciback.hide boot parameter will attach to "pciback" instead of the
  903: usual driver.  The list of devices is specified as "(bus:dev.func)",
  904: where bus and dev are 2-digit hexadecimal numbers, and func a
  905: single-digit number:
  907:         pciback.hide=(00:0a.0)(00:06.0)
  909: pciback devices should show up in the dom0's boot messages, and the
  910: devices should be listed in the `/kern/xen/pci` directory.
  912: PCI devices to be exported to a domU are listed in the "pci" array of
  913: the domU's config file, with the format "0000:bus:dev.func".
  915:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  917: In the domU an "xpci" device will show up, to which one or more pci
  918: buses will attach.  Then the PCI drivers will attach to PCI buses as
  919: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  920: or any PCI drivers built in by default; you have to build your own
  921: kernel to use PCI devices in a domU.  Here's a kernel config example;
  922: note that only the "xpci" lines are unusual.
  924:         include         "arch/i386/conf/XEN3_DOMU"
  926:         # Add support for PCI buses to the XEN3_DOMU kernel
  927:         xpci* at xenbus ?
  928:         pci* at xpci ?
  930:         # PCI USB controllers
  931:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  933:         # USB bus support
  934:         usb*    at uhci?
  936:         # USB Hubs
  937:         uhub*   at usb?
  938:         uhub*   at uhub? port ? configuration ? interface ?
  940:         # USB Mass Storage
  941:         umass*  at uhub? port ? configuration ? interface ?
  942:         wd*     at umass?
  943:         # SCSI controllers
  944:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  946:         # SCSI bus support (for both ahc and umass)
  947:         scsibus* at scsi?
  949:         # SCSI devices
  950:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  951:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  954: NetBSD as a domU in a VPS
  955: =========================
  957: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  958: hardware.  This section explains how to deal with Xen in a domU as a
  959: virtual private server where you do not control or have access to the
  960: dom0.  This is not intended to be an exhaustive list of VPS providers;
  961: only a few are mentioned that specifically support NetBSD.
  963: VPS operators provide varying degrees of access and mechanisms for
  964: configuration.  The big issue is usually how one controls which kernel
  965: is booted, because the kernel is nominally in the dom0 file system (to
  966: which VPS users do not normally have access).  A second issue is how
  967: to install NetBSD.
  968: A VPS user may want to compile a kernel for security updates, to run
  969: npf, run IPsec, or any other reason why someone would want to change
  970: their kernel.
  972: One approach is to have an administrative interface to upload a kernel,
  973: or to select from a prepopulated list.  Other approaches are pygrub
  974: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  975: kernel from the domU file system.  This is closer to a regular physical
  976: computer, where someone who controls a machine can replace the kernel.
  978: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  979: multiple vcpus, and it is typical for VPS providers to enable multiple
  980: CPUs for NetBSD domUs.
  982: pygrub
  983: -------
  985: pygrub runs in the dom0 and looks into the domU file system.  This
  986: implies that the domU must have a kernel in a file system in a format
  987: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
  988: interest.
  990: pvgrub
  991: ------
  993: pvgrub is a version of grub that uses PV operations instead of BIOS
  994: calls.  It is booted from the dom0 as the domU kernel, and then reads
  995: /grub/menu.lst and loads a kernel from the domU file system.
  997: [Panix]( lets users use pvgrub.  Panix reports
  998: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  999: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
 1000: page](, which describes only
 1001: Linux but should be updated to cover NetBSD :-).
 1003: []( also lets users with pvgrub to boot
 1004: their own kernel.  See then [ NetBSD
 1005: HOWTO](
 1006: (which is in need of updating).
 1008: It appears that [grub's FFS
 1009: code](
 1010: does not support all aspects of modern FFS, but there are also reports
 1011: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
 1012: partition for the kernel with the intent that grub can understand it,
 1013: which leads to /netbsd not being the actual kernel.  One must remember
 1014: to update the special boot partition.
 1016: Amazon
 1017: ------
 1019: See the [Amazon EC2 page](/amazon_ec2/).
 1021: TODO items for improving NetBSD/xen
 1022: ===================================
 1024: * Make the NetBSD dom0 kernel work with SMP.
 1025: * Test the Xen 4.5 packages adequately to be able to recommend them as
 1026:   the standard approach.
 1027: * Get PCI passthrough working on Xen 4.5
 1028: * Get pvgrub into pkgsrc, either via xentools or separately.
 1029: * grub
 1030:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
 1031:     fragsize/blocksize (UFS2 support may be present; the point is to
 1032:     make it so that with any UFS1/UFS2 file system setup that works
 1033:     with NetBSD grub will also work).
 1034:     See [pkg/40258](
 1035:   * Push patches upstream.
 1036:   * Get UFS2 patches into pvgrub.
 1037: * Add support for PV ops to a version of /boot, and make it usable as
 1038:   a kernel in Xen, similar to pvgrub.
 1040: Random pointers
 1041: ===============
 1043: This section contains links from elsewhere not yet integrated into the
 1044: HOWTO, and other guides.
 1046: *
 1047: *
 1048: *

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