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 <table>  
 <tbody>  
 <tr class="odd">  
 <td align="left"><a href="../../about/disclaimer.html#bsd-daemon"></a></td>  
 <td align="left"><h1>Table Of Contents</h1>  
 <ul>  
 <li>Introduction</li>  
 <li>Installing NetBSD as privileged domain (Dom0)</li>  
 <li>Creating an unprivileged NetBSD domain (DomU)</li>  
 <li>Creating an unprivileged Linux domain (DomU)</li>  
 <li>Creating an unprivileged Solaris domain (DomU)</li>  
 <li>Using PCI devices in guest domains</li>  
 <li>Links and further information</li>  
 </ul></td>  
 </tr>  
 </tbody>  
 </table>  
   
 Introduction  Introduction
 ------------  ============
   
 [![[Xen  [![[Xen
 screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)  screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](../../gallery/in-Action/hubertf-xen.png)
   
 Xen is a virtual machine monitor for x86 hardware (requires i686-class  Xen is a virtual machine monitor or hypervisor for x86 hardware
 CPUs), which supports running multiple guest operating systems on a  (i686-class or higher), which supports running multiple guest
 single machine. Guest OSes (also called "domains") require a modified  operating systems on a single physical machine.  With Xen, one uses
 kernel which supports Xen hypercalls in replacement to access to the  the Xen kernel to control the CPU, memory and console, a dom0
 physical hardware. At boot, the Xen kernel (also known as the Xen  operating system which mediates access to other hardware (e.g., disks,
 hypervisor) is loaded (via the bootloader) along with the guest kernel  network, USB), and one or more domU operating systems which operate in
 for the first domain (called *domain0*). The Xen kernel has to be loaded  an unprivileged virtualized environment.  IO requests from the domU
 using the multiboot protocol. You would use the NetBSD boot loader for  systems are forwarded by the hypervisor (Xen) to the dom0 to be
 this, or alternatively the `grub` boot loader (`grub` has some  fulfilled.
 limitations, detailed below). *domain0* has special privileges to access  
 the physical hardware (PCI and ISA devices), administrate other domains  Xen supports two styles of guests.  The original is Para-Virtualized
 and provide virtual devices (disks and network) to other domains that  (PV) which means that the guest OS does not attempt to access hardware
 lack those privileges. For more details, see [](http://www.xen.org/).  directly, but instead makes hypercalls to the hypervisor.  This is
   analogous to a user-space program making system calls.  (The dom0
 NetBSD can be used for both *domain0 (Dom0)* and further, unprivileged  operating system uses PV calls for some functions, such as updating
 (DomU) domains. (Actually there can be multiple privileged domains  memory mapping page tables, but has direct hardware access for disk
 accessing different parts of the hardware, all providing virtual devices  and network.)   PV guests must be specifically coded for Xen.
 to unprivileged domains. We will only talk about the case of a single  
 privileged domain, *domain0*). *domain0* will see physical devices much  The more recent style is HVM, which means that the guest does not have
 like a regular i386 or amd64 kernel, and will own the physical console  code for Xen and need not be aware that it is running under Xen.
 (VGA or serial). Unprivileged domains will only see a character-only  Attempts to access hardware registers are trapped and emulated.  This
 virtual console, virtual disks (`xbd`) and virtual network interfaces  style is less efficient but can run unmodified guests.
 (`xennet`) provided by a privileged domain (usually *domain0*). xbd  
 devices are connected to a block device (i.e., a partition of a disk,  Generally any amd64 machine will work with Xen and PV guests.  In
 raid, ccd, ... device) in the privileged domain. xennet devices are  theory i386 computers without amd64 support can be used for Xen <=
 connected to virtual devices in the privileged domain, named  4.2, but we have no recent reports of this working (this is a hint).
 xvif\<domain number\>.\<if number for this domain\>, e.g., xvif1.0. Both  For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT
 xennet and xvif devices are seen as regular Ethernet devices (they can  (amd64) is needed; "cpuctl identify 0" will show this.  TODO: Clean up
 be seen as a crossover cable between 2 PCs) and can be assigned  and check the above features.
 addresses (and be routed or NATed, filtered using IPF, etc ...) or be  
 added as part of a bridge.  At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   The dom0 can start one or more domUs.  (Booting is explained in detail
   in the dom0 section.)
   
   NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   attempts to address both the case of running a NetBSD dom0 on hardware
   and running domUs under it (NetBSD and other), and also running NetBSD
   as a domU in a VPS.
   
   Some versions of Xen support "PCI passthrough", which means that
   specific PCI devices can be made available to a specific domU instead
   of the dom0.  This can be useful to let a domU run X11, or access some
   network interface or other peripheral.
   
   Prerequisites
   -------------
   
   Installing NetBSD/Xen is not extremely difficult, but it is more
   complex than a normal installation of NetBSD.
   In general, this HOWTO is occasionally overly restrictive about how
   things must be done, guiding the reader to stay on the established
   path when there are no known good reasons to stray.
   
   This HOWTO presumes a basic familiarity with the Xen system
   architecture.  This HOWTO presumes familiarity with installing NetBSD
   on i386/amd64 hardware and installing software from pkgsrc.
   See also the [Xen website](http://www.xenproject.org/).
   
   History
   -------
   
   NetBSD used to support Xen2; this has been removed.
   
   Before NetBSD's native bootloader could support Xen, the use of
   grub was recommended.  If necessary, see the
   [old grub information](/ports/xen/howto-grub/).
   
   Versions of Xen and NetBSD
   ==========================
   
   Most of the installation concepts and instructions are independent
   of Xen version and NetBSD version.  This section gives advice on
   which version to choose.  Versions not in pkgsrc and older unsupported
   versions of NetBSD are intentionally ignored.
   
   Xen
   ---
   
   In NetBSD, xen is provided in pkgsrc, via matching pairs of packages
   xenkernel and xentools.  We will refer only to the kernel versions,
   but note that both packages must be installed together and must have
   matching versions.
   
   xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3.  These no longer
   receive security patches and should not be used.  Xen 3.1 supports PCI
   passthrough.  Xen 3.1 supports non-PAE on i386.
   
   xenkernel41 provides Xen 4.1.  This is no longer maintained by Xen,
   but as of 2014-12 receives backported security patches.  It is a
   reasonable although trailing-edge choice.
   
   xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as
   of 2014-12.
   
   Ideally newer versions of Xen will be added to pkgsrc.
   
   Note that NetBSD support is called XEN3.  It works with 3.1 through
   4.2 because the hypercall interface has been stable.
   
   Xen command program
   -------------------
   
   Early Xen used a program called "xm" to manipulate the system from the
   dom0.  Starting in 4.1, a replacement program with similar behavior
   called "xl" is provided.  In 4.2 and later, "xl" is preferred.  4.4 is
   the last version that has "xm".
   
   NetBSD
   ------
   
   The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
   reasonable choices, with more or less the same considerations for
   non-Xen use.  Therefore, netbsd-6 is recommended as the stable version
   of the most recent release for production use.  For those wanting to
   learn Xen or without production stability concerns, netbsd-7 is likely
   most appropriate.
   
   As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
   no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
   need SMP; the lack of support is really a problem when using a dom0 as
   a normal computer.)
   
 Installing NetBSD as privileged domain (Dom0)  Architecture
 ---------------------------------------------  ------------
   
 First do a NetBSD/i386 or NetBSD/amd64  Xen itself can run on i386 or amd64 machines.  (Practically, almost
 [installation](../../docs/guide/en/chap-inst.html) of the 5.1 release  any computer where one would want to run Xen supports amd64.)  If
 (or newer) as you usually do on x86 hardware. The binary releases are  using an i386 NetBSD kernel for the dom0, PAE is required (PAE
 available from [](ftp://ftp.NetBSD.org/pub/NetBSD/). Binary snapshots  versions are built by default).  While i386 dom0 works fine, amd64 is
 for current and the stable branches are available on daily autobuilds.  recommended as more normal.
 If you plan to use the `grub` boot loader, when partitioning the disk  
 you have to make the root partition smaller than 512Mb, and formatted as  
 FFSv1 with 8k block/1k fragments. If the partition is larger than this,  
 uses FFSv2 or has different block/fragment sizes, grub may fail to load  
 some files. Also keep in mind that you'll probably want to provide  
 virtual disks to other domains, so reserve some partitions for these  
 virtual disks. Alternatively, you can create large files in the file  
 system, map them to vnd(4) devices and export theses vnd devices to  
 other domains.  
   
 Next step is to install the Xen packages via pkgsrc or from binary  
 packages. See [the pkgsrc  
 documentation](http://www.NetBSD.org/docs/pkgsrc/) if you are unfamiliar  
 with pkgsrc and/or handling of binary packages. Xen 3.1, 3.3, 4.1 and  
 4.2 are available. 3.1 supports PCI pass-through while other versions do  
 not. You'll need either `sysutils/xentools3` and `sysutils/xenkernel3`  
 for Xen 3.1, `sysutils/xentools33` and `sysutils/xenkernel33` for Xen  
 3.3, `sysutils/xentools41` and `sysutils/xenkernel41` for Xen 4.1. or  
 `sysutils/xentools42` and `sysutils/xenkernel42` for Xen 4.2. You'll  
 also need `sysutils/grub` if you plan do use the grub boot loader. If  
 using Xen 3.1, you may also want to install `sysutils/xentools3-hvm`  
 which contains the utilities to run unmodified guests OSes using the  
 *HVM* support (for later versions this is included in  
 `sysutils/xentools`). Note that your CPU needs to support this. Intel  
 CPUs must have the 'VT' instruction, AMD CPUs the 'SVM' instruction. You  
 can easily find out if your CPU support HVM by using NetBSD's cpuctl  
 command:  
   
     # cpuctl identify 0  
     cpu0: Intel Core 2 (Merom) (686-class), id 0x6f6  
     cpu0: features 0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>  
     cpu0: features 0xbfebfbff<PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX>  
     cpu0: features 0xbfebfbff<FXSR,SSE,SSE2,SS,HTT,TM,SBF>  
     cpu0: features2 0x4e33d<SSE3,DTES64,MONITOR,DS-CPL,,TM2,SSSE3,CX16,xTPR,PDCM,DCA>  
     cpu0: features3 0x20100800<SYSCALL/SYSRET,XD,EM64T>  
     cpu0: "Intel(R) Xeon(R) CPU            5130  @ 2.00GHz"  
     cpu0: I-cache 32KB 64B/line 8-way, D-cache 32KB 64B/line 8-way  
     cpu0: L2 cache 4MB 64B/line 16-way  
     cpu0: ITLB 128 4KB entries 4-way  
     cpu0: DTLB 256 4KB entries 4-way, 32 4MB entries 4-way  
     cpu0: Initial APIC ID 0  
     cpu0: Cluster/Package ID 0  
     cpu0: Core ID 0  
     cpu0: family 06 model 0f extfamily 00 extmodel 00  
   
 Depending on your CPU, the feature you are looking for is called HVM,  
 SVM or VMX.  
   
 Next you need to copy the selected Xen kernel itself. pkgsrc installed  
 them under `/usr/pkg/xen*-kernel/`. The file you're looking for is  
 `xen.gz`. Copy it to your root file system. `xen-debug.gz` is a kernel  
 with more consistency checks and more details printed on the serial  
 console. It is useful for debugging crashing guests if you use a serial  
 console. It is not useful with a VGA console.  
   
 You'll then need a NetBSD/Xen kernel for *domain0* on your root file  
 system. The XEN3PAE\_DOM0 kernel or XEN3\_DOM0 provided as part of the  
 i386 or amd64 binaries is suitable for this, but you may want to  
 customize it. Keep your native kernel around, as it can be useful for  
 recovery. *Note:* the *domain0* kernel must support KERNFS and `/kern`  
 must be mounted because *xend* needs access to `/kern/xen/privcmd`.  
   
 Next you need to get a bootloader to load the `xen.gz` kernel, and the  
 NetBSD *domain0* kernel as a module. This can be `grub` or NetBSD's boot  
 loader. Below is a detailled example for grub, see the boot.cfg(5)  
 manual page for an example using the latter.  
   
 This is also where you'll specify the memory allocated to *domain0*, the  
 console to use, etc ...  
   
 Here is a commented `/grub/menu.lst` file:  
   
     #Grub config file for NetBSD/xen. Copy as /grub/menu.lst and run  
     # grub-install /dev/rwd0d (assuming your boot device is wd0).  
     #  
     # The default entry to load will be the first one  
     default=0  
   
     # boot the default entry after 10s if the user didn't hit keyboard  
     timeout=10  
   
     # Configure serial port to use as console. Ignore if you'll use VGA only  
     serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1  
   
     # Let the user select which console to use (serial or VGA), default  
     # to serial after 10s  
     terminal --timeout=10 serial console  
   
     # An entry for NetBSD/xen, using /netbsd as the domain0 kernel, and serial  
     # console. Domain0 will have 64MB RAM allocated.  
     # Assume NetBSD is installed in the first MBR partition.  
     title Xen 3 / NetBSD (hda0, serial)  
       root(hd0,0)  
       kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1  
       module (hd0,a)/netbsd bootdev=wd0a ro console=ttyS0  
   
     # Same as above, but using VGA console  
     # We can use console=tty0 (Linux syntax) or console=pc (NetBSD syntax)  
     title Xen 3 / NetBSD (hda0, vga)  
       root(hd0,0)  
       kernel (hd0,a)/xen.gz dom0_mem=65536  
       module (hd0,a)/netbsd bootdev=wd0a ro console=tty0  
   
     # NetBSD/xen using a backup domain0 kernel (in case you installed a  
     # nonworking kernel as /netbsd  
     title Xen 3 / NetBSD (hda0, backup, serial)  
       root(hd0,0)  
       kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1  
       module (hd0,a)/netbsd.backup bootdev=wd0a ro console=ttyS0  
     title Xen 3 / NetBSD (hda0, backup, VGA)  
       root(hd0,0)  
       kernel (hd0,a)/xen.gz dom0_mem=65536  
       module (hd0,a)/netbsd.backup bootdev=wd0a ro console=tty0  
   
     #Load a regular NetBSD/i386 kernel. Can be useful if you end up with a  
     #nonworking /xen.gz  
     title NetBSD 5.1  
       root (hd0,a)  
       kernel --type=netbsd /netbsd-GENERIC  
   
     #Load the NetBSD bootloader, letting it load the NetBSD/i386 kernel.  
     #May be better than the above, as grub can't pass all required infos  
     #to the NetBSD/i386 kernel (e.g. console, root device, ...)  
     title NetBSD chain  
       root        (hd0,0)  
       chainloader +1  
   
     ## end of grub config file.  Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
             if this is about the CPU having to be amd64, or about the dom0 kernel
   having to be amd64.
   
 Install grub with the following command:  One can then run i386 domUs and amd64 domUs, in any combination.  If
   running an i386 NetBSD kernel as a domU, the PAE version is required.
   (Note that emacs (at least) fails if run on i386 with PAE when built
   without, and vice versa, presumably due to bugs in the undump code.)
   
     # grub --no-floppy  Recommendation
   --------------
   
     grub> root (hd0,a)  Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
      Filesystem type is ffs, partition type 0xa9  xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
   dom0.  Either the i386 or amd64 of NetBSD may be used as domUs.
   
     grub> setup (hd0)  Build problems
      Checking if "/boot/grub/stage1" exists... no  --------------
      Checking if "/grub/stage1" exists... yes  
      Checking if "/grub/stage2" exists... yes  Ideally, all versions of Xen in pkgsrc would build on all versions of
      Checking if "/grub/ffs_stage1_5" exists... yes  NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
      Running "embed /grub/ffs_stage1_5 (hd0)"...  14 sectors are embedded.  aging code and aging compilers, qemu (included in xentools for HVM
     succeeded  support) is difficult to build.  The following are known to fail:
      Running "install /grub/stage1 (hd0) (hd0)1+14 p (hd0,0,a)/grub/stage2 /grub/menu.lst"...  
      succeeded          xenkernel3 netbsd-6 i386
     Done.          xentools42 netbsd-6 i386 
             
   The following are known to work:
   
           xenkernel41 netbsd-5 amd64
           xentools41 netbsd-5 amd64
           xenkernel41 netbsd-6 i386
           xentools41 netbsd-6 i386
   
   NetBSD as a dom0
   ================
   
   NetBSD can be used as a dom0 and works very well.  The following
   sections address installation, updating NetBSD, and updating Xen.
   Note that it doesn't make sense to talk about installing a dom0 OS
   without also installing Xen itself.  We first address installing
   NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
   NetBSD install to a dom0 install by just changing the kernel and boot
   configuration.
   
   Styles of dom0 operation
   ------------------------
   
   There are two basic ways to use Xen.  The traditional method is for
   the dom0 to do absolutely nothing other than providing support to some
   number of domUs.  Such a system was probably installed for the sole
   purpose of hosting domUs, and sits in a server room on a UPS.
   
   The other way is to put Xen under a normal-usage computer, so that the
   dom0 is what the computer would have been without Xen, perhaps a
   desktop or laptop.  Then, one can run domUs at will.  Purists will
   deride this as less secure than the previous approach, and for a
   computer whose purpose is to run domUs, they are right.  But Xen and a
   dom0 (without domUs) is not meaingfully less secure than the same
   things running without Xen.  One can boot Xen or boot regular NetBSD
   alternately with little problems, simply refraining from starting the
   Xen daemons when not running Xen.
   
   Note that NetBSD as dom0 does not support multiple CPUs.  This will
   limit the performance of the Xen/dom0 workstation approach.
   
   Installation of NetBSD
   ----------------------
   
   First,
   [install NetBSD/amd64](/guide/inst/)
   just as you would if you were not using Xen.
   However, the partitioning approach is very important.
   
   If you want to use RAIDframe for the dom0, there are no special issues
   for Xen.  Typically one provides RAID storage for the dom0, and the
   domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
   over a RAID1 header to find /boot from a filesystem within a RAID
   partition; this is no different when booting Xen.
   
   There are 4 styles of providing backing storage for the virtual disks
   used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,
   
   With raw partitions, one has a disklabel (or gpt) partition sized for
   each virtual disk to be used by the domU.  (If you are able to predict
   how domU usage will evolve, please add an explanation to the HOWTO.
   Seriously, needs tend to change over time.)
   
   One can use [lvm(8)](/guide/lvm/) to create logical devices to use
   for domU disks.  This is almost as efficient as raw disk partitions
   and more flexible.  Hence raw disk partitions should typically not
   be used.
   
   One can use files in the dom0 filesystem, typically created by dd'ing
   /dev/zero to create a specific size.  This is somewhat less efficient,
   but very convenient, as one can cp the files for backup, or move them
   between dom0 hosts.
   
   Finally, in theory one can place the files backing the domU disks in a
   SAN.  (This is an invitation for someone who has done this to add a
   HOWTO page.)
   
   Installation of Xen
   -------------------
   
   In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
   pkgsrc (or another matching pair).
   See [the pkgsrc
   documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
   
   For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
   recent versions have HVM support integrated in the main xentools
   package.  It is entirely reasonable to run only PV guests.
   
   Next you need to install the selected Xen kernel itself, which is
   installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
   For debugging, one may copy xen-debug.gz; this is conceptually similar
   to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
   useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
   in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
   of a NetBSD build.  Both xen and NetBSD may be left compressed.  (If
   using i386, use releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.)
   
   In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
   kernel, so ensure that /kern is in fstab.
   
   Because you already installed NetBSD, you have a working boot setup
   with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
   beginning of your root filesystem, /boot present, and likely
   /boot.cfg.  (If not, fix before continuing!)
   
   See boot.cfg(5) for an example.  The basic line is
   
           menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
   
   which specifies that the dom0 should have 256M, leaving the rest to be
   allocated for domUs.  In an attempt to add performance, one can also
   add
   
           dom0_max_vcpus=1 dom0_vcpus_pin
   
   to force only one vcpu to be provided (since NetBSD dom0 can't use
   more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.
   
   As with non-Xen systems, you should have a line to boot /netbsd (a
   kernel that works without Xen) and fallback versions of the non-Xen
   kernel, Xen, and the dom0 kernel.
   
   The [HowTo on Installing into
   RAID-1](http://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html)
   explains how to set up booting a dom0 with Xen using grub with
   NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
   boot.)
   
   Configuring Xen
   ---------------
   
   Now, you have a system that will boot Xen and the dom0 kernel, and
   just run the dom0 kernel.  There will be no domUs, and none can be
   started because you still have to configure the dom0 tools.  The
   daemons which should be run vary with Xen version and with whether one
   is using xm or xl.  Note that xend is for supporting "xm", and should
   only be used if you plan on using "xm".  Do NOT enable xend if you
   plan on using "xl" as it will cause problems.
   
   TODO: Give 3.1 advice (or remove it from pkgsrc).
   
   For 3.3 (and thus xm), add to rc.conf (but note that you should have
   installed 4.1 or 4.2):
   
           xend=YES
           xenbackendd=YES
   
   For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
   
           xend=YES
           xencommons=YES
   
   TODO: Explain why if xm is preferred on 4.1, rc.d/xendomains has xl.
   Or fix the package.
   
 Creating an unprivileged NetBSD domain (DomU)  For 4.2 with xm, add to rc.conf
   
           xend=YES
           xencommons=YES
   
   For 4.2 with xl (preferred), add to rc.conf:
   
           TODO: explain if there is a xend replacement
           xencommons=YES
   
   TODO: Recommend for/against xen-watchdog.
   
   After you have configured the daemons and rebooted, run the following
   to inspect Xen's boot messages, available resources, and running
   domains:
   
           xm dmesg
           xm info
           xm list
   
   Updating NetBSD in a dom0
   -------------------------
   
   This is just like updating NetBSD on bare hardware, assuming the new
   version supports the version of Xen you are running.  Generally, one
   replaces the kernel and reboots, and then overlays userland binaries
   and adjusts /etc.
   
   Note that one must update both the non-Xen kernel typically used for
   rescue purposes and the DOM0 kernel used with Xen.
   
   To convert from grub to /boot, install an mbr bootblock with fdisk,
   bootxx_ with installboot, /boot and /boot.cfg.  This really should be
   no different than completely reinstalling boot blocks on a non-Xen
   system.
   
   Updating Xen versions
   ---------------------
   
   Updating Xen is conceptually not difficult, but can run into all the
   issues found when installing Xen.  Assuming migration from 4.1 to 4.2,
   remove the xenkernel41 and xentools41 packages and install the
   xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz to /.
   
   Ensure that the contents of /etc/rc.d/xen* are correct.  Enable the
   correct set of daemons.  Ensure that the domU config files are valid
   for the new version.
   
   
   Unprivileged domains (domU)
   ===========================
   
   This section describes general concepts about domUs.  It does not
   address specific domU operating systems or how to install them.  The
   config files for domUs are typically in /usr/pkg/etc/xen, and are
   typically named so that the file anme, domU name and the domU's host
   name match.
   
   The domU is provided with cpu and memory by Xen, configured by the
   dom0.  The domU is provided with disk and network by the dom0,
   mediated by Xen, and configured in the dom0.
   
   Entropy in domUs can be an issue; physical disks and network are on
   the dom0.  NetBSD's /dev/random system works, but is often challenged.
   
   CPU and memory
   --------------
   
   A domain is provided with some number of vcpus, less than the
   number of cpus seen by the hypervisor.  For a dom0, this is controlled
   by the boot argument "dom0_max_vcpus=1".  For a domU, it is controlled
   from the config file.
   
   A domain is provided with memory, In the straightforward case, the sum
   of the the memory allocated to the dom0 and all domUs must be less
   than the available memory.
   
   Xen also provides a "balloon" driver, which can be used to let domains
   use more memory temporarily.  TODO: Explain better, and explain how
   well it works with NetBSD.
   
   Virtual disks
   -------------
   
   With the file/vnd style, typically one creates a directory,
   e.g. /u0/xen, on a disk large enough to hold virtual disks for all
   domUs.  Then, for each domU disk, one writes zeros to a file that then
   serves to hold the virtual disk's bits; a suggested name is foo-xbd0
   for the first virtual disk for the domU called foo.  Writing zeros to
   the file serves two purposes.  One is that preallocating the contents
   improves performance.  The other is that vnd on sparse files has
   failed to work.  TODO: give working/notworking NetBSD versions for
   sparse vnd.  Note that the use of file/vnd for Xen is not really
   different than creating a file-backed virtual disk for some other
   purpose, except that xentools handles the vnconfig commands.
   
   With the lvm style, one creates logical devices.  They are then used
   similarly to vnds.
   
   Virtual Networking
   ------------------
   
   TODO: explain xvif concept, and that it's general.
   
   There are two normal styles: bridging and NAT.
   
   With bridging, the domU perceives itself to be on the same network as
   the dom0.  For server virtualization, this is usually best.
   
   With NAT, the domU perceives itself to be behind a NAT running on the
   dom0.  This is often appropriate when running Xen on a workstation.
   
   One can construct arbitrary other configurations, but there is no
   script support.
   
   Sizing domains
   --------------
   
   Modern x86 hardware has vast amounts of resources.  However, many
   virtual servers can function just fine on far less.  A system with
   256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
   far easier to adjust virtual resources than physical ones.  For
   memory, it's just a config file edit and a reboot.  For disk, one can
   create a new file and vnconfig it (or lvm), and then dump/restore,
   just like updating physical disks, but without having to be there and
   without those pesky connectors.
   
   Config files
   ------------
   
   TODO: give example config files.   Use both lvm and vnd.
   
   TODO: explain the mess with 3 arguments for disks and how to cope (0x1).
   
   Starting domains
   ----------------
   
   TODO: Explain "xm start" and "xl start".  Explain rc.d/xendomains.
   
   TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm
   on 4.1.
   
   Creating specific unprivileged domains (domU)
   =============================================
   
   Creating domUs is almost entirely independent of operating system.  We
   first explain NetBSD, and then differences for Linux and Solaris.
   
   Creating an unprivileged NetBSD domain (domU)
 ---------------------------------------------  ---------------------------------------------
   
 Once you have *domain0* running, you need to start the xen tool daemon  Once you have *domain0* running, you need to start the xen tool daemon
Line 237  PKG\_SYSCONFDIR for its parameters. By d Line 491  PKG\_SYSCONFDIR for its parameters. By d
 will be executed in the new domain (this kernel is in the *domain0* file  will be executed in the new domain (this kernel is in the *domain0* file
 system, not on the new domain virtual disk; but please note, you should  system, not on the new domain virtual disk; but please note, you should
 install the same kernel into *domainU* as `/netbsd` in order to make  install the same kernel into *domainU* as `/netbsd` in order to make
 your system tools, like MAN.SAVECORE.8, work). A suitable kernel is  your system tools, like savecore(8), work). A suitable kernel is
 provided as part of the i386 and amd64 binary sets: XEN3\_DOMU.  provided as part of the i386 and amd64 binary sets: XEN3\_DOMU.
   
 Here is an /usr/pkg/etc/xen/nbsd example config file:  Here is an /usr/pkg/etc/xen/nbsd example config file:
Line 347  like this: Line 601  like this:
     !brconfig $int add ex0 up      !brconfig $int add ex0 up
   
 (replace `ex0` with the name of your physical interface). Then bridge0  (replace `ex0` with the name of your physical interface). Then bridge0
 will be created on boot. See the MAN.BRIDGE.4 man page for details.  will be created on boot. See the bridge(4) man page for details.
   
 So, here is a suitable `/usr/pkg/etc/xen/vif-bridge` for xvif?.? (a  So, here is a suitable `/usr/pkg/etc/xen/vif-bridge` for xvif?.? (a
 working vif-bridge is also provided with xentools20) configuring:  working vif-bridge is also provided with xentools20) configuring:
   
     #!/bin/sh      #!/bin/sh
     #============================================================================      #============================================================================
     # $NetBSD: howto.mdwn,v 1.5 2013/11/01 12:27:37 mspo Exp $      # $NetBSD: howto.mdwn,v 1.36 2014/12/24 16:02:49 gdt Exp $
     #      #
     # /usr/pkg/etc/xen/vif-bridge      # /usr/pkg/etc/xen/vif-bridge
     #      #
Line 478  in rc.conf. This way, the domain will be Line 732  in rc.conf. This way, the domain will be
   
 Your domain should be now ready to work, enjoy.  Your domain should be now ready to work, enjoy.
   
 Creating an unprivileged Linux domain (DomU)  Creating an unprivileged Linux domain (domU)
 --------------------------------------------  --------------------------------------------
   
 Creating unprivileged Linux domains isn't much different from  Creating unprivileged Linux domains isn't much different from
Line 522  To get the linux console right, you need Line 776  To get the linux console right, you need
 to your configuration since not all linux distributions auto-attach a  to your configuration since not all linux distributions auto-attach a
 tty to the xen console.  tty to the xen console.
   
 Creating an unprivileged Solaris domain (DomU)  Creating an unprivileged Solaris domain (domU)
 ----------------------------------------------  ----------------------------------------------
   
 Download an Opensolaris [release](http://opensolaris.org/os/downloads/)  Download an Opensolaris [release](http://opensolaris.org/os/downloads/)
Line 659  Restart the guest to verify it works cor Line 913  Restart the guest to verify it works cor
                         
   
 Using PCI devices in guest domains  Using PCI devices in guest domains
 ==================================  ----------------------------------
   
 The domain0 can give other domains access to selected PCI devices. This  The domain0 can give other domains access to selected PCI devices. This
 can allow, for example, a non-privileged domain to have access to a  can allow, for example, a non-privileged domain to have access to a
Line 731  to use PCI devices in a domU. Here's a k Line 985  to use PCI devices in a domU. Here's a k
     sd*     at scsibus? target ? lun ?      # SCSI disk drives      sd*     at scsibus? target ? lun ?      # SCSI disk drives
     cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives      cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
   
 Links and further information  
 =============================  
   
 -   The HowTo on  NetBSD as a domU in a VPS
     Installing into RAID-1  =========================
     gives some hints on using Xen (grub) with NetBSD's RAIDframe  
 -   Harold Gutch wrote documentation on  The bulk of the HOWTO is about using NetBSD as a dom0 on your own
     setting up a Linux DomU with a NetBSD Dom0  hardware.  This section explains how to deal with Xen in a domU as a
 -   An example of how to use NetBSD's native bootloader to load  virtual private server where you do not control or have access to the
     NetBSD/Xen instead of Grub can be found in the i386/amd64 MAN.BOOT.8  dom0.
     and MAN.BOOT.CFG.5 manpages.  
   TODO: Perhaps reference panix, prmgr, amazon as interesting examples.
   
   TODO: Somewhere, discuss pvgrub and py-grub to load the domU kernel
   from the domU filesystem.
Removed from v.1.6  
changed lines
  Added in v.1.37

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