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 Introduction  [[!meta title="Xen HowTo"]]
 ============  
   
 [![[Xen  Xen is a Type 1 hypervisor which supports running multiple guest operating
 screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)  systems on a single physical machine. One uses the Xen kernel to control the
   CPU, memory and console, a dom0 operating system which mediates access to
 Xen is a hypervisor (or virtual machine monitor) for x86 hardware  other hardware (e.g., disks, network, USB), and one or more domU operating
 (i686-class or higher), which supports running multiple guest  systems which operate in an unprivileged virtualized environment. IO requests
 operating systems on a single physical machine.  Xen is a Type 1 or  from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
 bare-metal hypervisor; one uses the Xen kernel to control the CPU,  fulfilled.
 memory and console, a dom0 operating system which mediates access to  
 other hardware (e.g., disks, network, USB), and one or more domU  Xen supports different styles of guest:
 operating systems which operate in an unprivileged virtualized  
 environment.  IO requests from the domU systems are forwarded by the  [[!table data="""
 hypervisor (Xen) to the dom0 to be fulfilled.  Style of guest  |Supported by NetBSD
   PV              |Yes (dom0, domU)
 Xen supports two styles of guests.  The original is Para-Virtualized  HVM             |Yes (domU)
 (PV) which means that the guest OS does not attempt to access hardware  PVHVM           |No
 directly, but instead makes hypercalls to the hypervisor.  This is  PVH             |No
 analogous to a user-space program making system calls.  (The dom0  """]]
 operating system uses PV calls for some functions, such as updating  
 memory mapping page tables, but has direct hardware access for disk  In Para-Virtualized (PV) mode, the guest OS does not attempt to access
 and network.)   PV guests must be specifically coded for Xen.  hardware directly, but instead makes hypercalls to the hypervisor; PV
   guests must be specifically coded for Xen. In HVM mode, no guest
 The more recent style is HVM, which means that the guest does not have  modification is required; however, hardware support is required, such
 code for Xen and need not be aware that it is running under Xen.  as VT-x on Intel CPUs and SVM on AMD CPUs.
 Attempts to access hardware registers are trapped and emulated.  This  
 style is less efficient but can run unmodified guests.  
   
 Generally any machine that runs NetBSD/amd64 will work with Xen and PV  
 guests.  In theory i386 computers (without x86_64/amd64 support) can  
 be used for Xen <= 4.2, but we have no recent reports of this working  
 (this is a hint).  For HVM guests, hardware support is needed, but it  
 is common on recent machines.  For Intel CPUs, one needs the VT-x  
 extension, shown in "cpuctl identify 0" as VMX.  For AMD CPUs, one  
 needs the AMD-V extensions, shown in "cpuctl identify 0" as SVM.  
 There are further features for IOMMU virtualization, Intel's VT-d and  
 AMD's AMD-Vi.  TODO: Explain whether Xen on NetBSD makes use of these  
 features.  TODO: Review by someone who really understands this.  
   
 Note that a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this  
 is because the FreeBSD dom0 does not run in PV mode.  
   
 At boot, the dom0 kernel is loaded as a module with Xen as the kernel.  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  The dom0 can start one or more domUs.  (Booting is explained in detail
 in the dom0 section.)  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.  
   
 Xen 3.1 in pkgsrc supports "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.  
   
 NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD  
 7.  Xen 2 has been removed from pkgsrc.  
   
 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  This HOWTO presumes a basic familiarity with the Xen system
 architecture, with installing NetBSD on i386/amd64 hardware, and with  architecture, with installing NetBSD on i386/amd64 hardware, and with
 installing software from pkgsrc.  See also the [Xen  installing software from pkgsrc.  See also the [Xen
 website](http://www.xenproject.org/).  website](http://www.xenproject.org/).
   
 Versions of Xen and NetBSD  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.
 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  Versions and Support
 ---  ====================
   
 In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages  In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
 xenkernel and xentools.  We will refer only to the kernel versions,  xenkernel and xentools.  We will refer only to the kernel versions,
 but note that both packages must be installed together and must have  but note that both packages must be installed together and must have
 matching versions.  matching versions.
   
 xenkernel3 provides Xen 3.1.  It is no longer maintained by Xen, and the last applied security patch was in  Versions available in pkgsrc:
 2011. Thus, it should not be used.  It supports PCI passthrough,  
 which is why people use it anyway. Xen 3.1 supports i386, both PAE and  
 non-PAE.  
   
 xenkernel33 provides Xen 3.3.  It is no longer maintained by Xen, and  
 the last applied security patch was in 2012.  Thus, it should not be  
 used.  Xen 3.3 supports i386, but only in PAE mode.  There are no good  
 reasons to run this version.  
   
 xenkernel41 provides Xen 4.1.  It is no longer maintained by Xen, but  
 as of 2016-12 received backported security patches.  Xen 4.1 supports  
 i386, but only in PAE mode.  There are no good reasons to run this  
 version.  
   
 xenkernel42 provides Xen 4.2.  It is no longer maintained by Xen, but  
 as of 2016-12 received backported security patches.  Xen 4.2 supports  
 i386, but only in PAE mode.  The only reason to run this is if you  
 need to use xm instead of xl, or if you need to run an i386 dom0  
 (because your hardware is i386 only).  
   
 xenkernel45 provides Xen 4.5.  As of 2016-12, security patches were  
 released by Xen and applied to pkgsrc.  Xen 4.5 requires using a dom0  
 running NetBSD's amd64 port (Intel or AMD hardware is fine), but domUs  
 can be amd64 or i386 PAE.  While slightly old, n4.5 has been tested and  
 run by others, so it is the conservative choice.  
   
 xenkernel46 provides Xen 4.6.  It is new to pkgsrc as of 2016-05.  As  
 of 2016-12, security patches were released by Xen and applied to  
 pkgsrc.  Xen 4.6 similarly requires a NetBSD/amd64 dom0, but domUs can  
 be amd64 or i386 PAE.  For new installations, 4.6 is probably the  
 appropriate choice and it will likely soon be the standard approach.  
   
 Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in  [[!table data="""
 pkgsrc.  Xen Version     |Package Name   |Xen CPU Support        |EOL'ed By Upstream
   4.2             |xenkernel42    |32bit, 64bit           |Yes
   4.5             |xenkernel45    |64bit                  |Yes
   4.6             |xenkernel46    |64bit                  |Partially
   4.8             |xenkernel48    |64bit                  |No
   4.11            |xenkernel411   |64bit                  |No
   """]]
   
 See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).  See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
   
 Note that NetBSD support is called XEN3.  It works with Xen 3 and Xen  Multiprocessor (SMP) support in NetBSD differs depending on the domain:
 4 because the hypercall interface has been stable.  
   
 Xen command program  [[!table data="""
 -------------------  Domain          |Supports SMP
   dom0            |No
 Early Xen used a program called xm to manipulate the system from the  domU            |Yes
 dom0.  Starting in 4.1, a replacement program with similar behavior  """]]
 called xl is provided, but it does not work well in 4.1.  In 4.2, both  
 xm and xl work fine.  4.4 is the last version that has xm.  
   
 You must make a global choice to use xm or xl, because it affects not  
 only which command you use, but the command used by rc.d scripts  
 (specifically xendomains) and which daemons should be run.  The  
 xentools packages provide xm for 3.1, 3.3 and 4.1 and xl for 4.2 and up.  
   
 In 4.2, you can choose to use xm by simply changing the ctl_command  
 variable.  
   
 With xl, virtual devices are configured in parallel, which can cause  
 problems if they are written assuming serial operation (e.g., updating  
 firewall rules without explicit locking).  There is now locking for  
 the provided scripts, which works for normal casses (e.g, file-backed  
 xbd, where a vnd must be allocated).  But, as of 201612, it has not  
 been adequately tested for a complex custom setup with a large number  
 of interfaces.  
   
 NetBSD  
 ------  
   
 The netbsd-6, netbsd-7, and -current branches are all reasonable  Note: NetBSD support is called XEN3. However, it does support Xen 4,
 choices, with more or less the same considerations for non-Xen use.  because the hypercall interface has remained identical.
 Therefore, netbsd-7 is recommended as the stable version of the most  
 recent release for production use.  In addition, netbsd-7 and -current  
 have a important scheduler fix (in November of 2015) affecting  
 contention between dom0 and domUs; see  
 https://releng.netbsd.org/cgi-bin/req-7.cgi?show=1040 for a  
 description.  For those wanting to learn Xen or without production  
 stability concerns, netbsd-7 is still likely most appropriate, but  
 -current is also a reasonable choice.  (Xen runs ok on netbsd-5, but  
 the xentools packages are likely difficult to build, and netbsd-5 is  
 not supported.)  
   
 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 for dom0 functions; the lack of support is really a problem  
 when using a dom0 as a normal computer.)  
   
 Architecture  Architecture
 ------------  ------------
   
 Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen  Xen itself runs on x86_64 hardware.
 versions).  (Practically, almost any computer where one would want to  
 run Xen today supports amd64.)  
   
 Xen, the dom0 kernel, and each domU kernel can be either i386 or  
 amd64.  When building a xenkernel package, one obtains i386 on an i386  
 host, and amd64 on an amd64 host.  If the Xen kernel is i386, then the  
 dom0 kernel and all domU kernels must be i386.  With an amd64 Xen  
 kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0  
 kernel should in theory work.  An amd64 Xen/dom0 is known to support  
 both i386PAE and amd64 domUs.  
   
 i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are  
 built by default.  (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.)  
   
 Because of the above, the standard approach is to use amd64 for the  
 dom0.  
   
 Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify  
 if this is about the CPU, the Xen kernel, or the dom0 kernel having to  
 be amd64.  
   
   The dom0 system, plus each domU, can be either i386PAE or amd64.
   i386 without PAE is not supported.
   
 Stability  The standard approach is to use NetBSD/amd64 for the dom0.
 ---------  
   
 Mostly, NetBSD as a dom0 or domU is quite stable.  To use an i386PAE dom0, one must build or obtain a 64bit Xen kernel and
 However, there are some open PRs indicating problems.  install it on the system.
   
  - [PR 48125](http://gnats.netbsd.org/48125)  For domUs, i386PAE is considered as
  - [PR 47720](http://gnats.netbsd.org/47720)  [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html)
   than amd64.
 Note also that there are issues with sparse vnd(4) instances, but  
 these are not about Xen -- they just are noticed with sparse vnd(4)  
 instances in support of virtual disks in a dom0.  
   
 Recommendation  
 --------------  
   
 Therefore, this HOWTO recommends running xenkernel45 or xenkernel46,  
 xl, the NetBSD 7 stable branch, and to use an amd64 kernel as the  
 dom0.  Either the i386PAE or amd64 version of NetBSD may be used as  
 domUs.  
   
 Status  
 ------  
   
 Ideally, all versions of Xen in pkgsrc would build on all supported  
 versions of NetBSD/amd64, to the point where this section would be  
 silly.  However, that has not always been the case.  Besides aging  
 code and aging compilers, qemu (included in xentools for HVM support)  
 is difficult to build.  Note that there is intentionally no data for  
 4.5+ up for i386, and often omits xentools info if the corresponding  
 kernel fails.  
   
 The following table gives status, with the date last checked  
 (generally on the most recent quarterly branch).  The first code is  
 "builds" if it builds ok, and "FAIL" for a failure to build.  The  
 second code/date only appears for xenkernel* and is "works" if it runs  
 ok as a dom0, and "FAIL" if it won't boot or run a domU.  
   
         xenkernel3 netbsd-6 i386 FAIL 201612  
         xenkernel33 netbsd-6 i386 FAIL 201612  
         xenkernel41 netbsd-6 i386 builds 201612  
         xenkernel42 netbsd-6 i386 builds 201612  
         xentools3 netbsd-6 i386 FAIL 201612  
         xentools33 netbsd-6 i386 FAIL 201612  
         xentools41 netbsd-6 i386 builds 201612  
         xentools42 netbsd-6 i386 FAIL 201612  
   
         xenkernel3 netbsd-7 i386 FAIL 201412  
         xenkernel33 netbsd-7 i386 FAIL 201412  
         xenkernel41 netbsd-7 i386 builds 201412  
         xenkernel42 netbsd-7 i386 builds 201412  
         xentools41 netbsd-7 i386 builds 201412  
         xentools42 netbsd-7 i386 ??FAIL 201412  
   
         xenkernel3 netbsd-6 amd64 FAIL 201612  
         xenkernel33 netbsd-6 amd64 FAIL 201612  
         xenkernel41 netbsd-6 amd64 builds 201612 works 201612  
         xenkernel42 netbsd-6 amd64 builds 201612 works 201612  
         xenkernel45 netbsd-6 amd64 builds 201612  
         xenkernel46 netbsd-6 amd64 builds 201612  
         xentools41 netbsd-6 amd64 builds 201612  
         xentools42 netbsd-6 amd64 builds 201612  
         xentools45 netbsd-6 amd64 builds 201612  
         xentools46 netbsd-6 amd64 FAIL 201612  
   
         xenkernel3 netbsd-7 amd64 builds 201612  
         xenkernel33 netbsd-7 amd64 builds 201612  
         xenkernel41 netbsd-7 amd64 builds 201612  
         xenkernel42 netbsd-7 amd64 builds 201612  
         xenkernel45 netbsd-7 amd64 builds 201612  
         xenkernel46 netbsd-7 amd64 builds 201612  
         xentools3 netbsd-7 amd64 builds 201612  
         xentools3-hvm netbsd-7 amd64 builds 201612  
         xentools33 netbsd-7 amd64 FAIL 201612  
         xentools41 netbsd-7 amd64 builds 201612  
         xentools42 netbsd-7 amd64 builds 201612  
         xentools45 netbsd-7 amd64 builds 201612  
         xentools46 netbsd-7 amd64 builds 201612  
   
 NetBSD as a dom0  NetBSD as a dom0
 ================  ================
   
 NetBSD can be used as a dom0 and works very well.  The following  NetBSD can be used as a dom0 and works very well.  The following
 sections address installation, updating NetBSD, and updating Xen.  sections address installation, updating NetBSD, and updating Xen.
   
 Note that it doesn't make sense to talk about installing a dom0 OS  Note that it doesn't make sense to talk about installing a dom0 OS
 without also installing Xen itself.  We first address installing  without also installing Xen itself.  We first address installing
 NetBSD, which is not yet a dom0, and then adding Xen, pivoting the  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  NetBSD install to a dom0 install by just changing the kernel and boot
 configuration.  configuration.
   
 For experimenting with Xen, a machine with as little as 1G of RAM and  In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
 100G of disk can work.  For running many domUs in productions, far  512M it worked reliably.  This does not make sense, but if you see
 more will be needed.  "not ELF" after Xen boots, try increasing dom0 RAM.
   
 Styles of dom0 operation  Styles of dom0 operation
 ------------------------  ------------------------
Line 307  purpose of hosting domUs, and sits in a  Line 112  purpose of hosting domUs, and sits in a 
   
 The other way is to put Xen under a normal-usage computer, so that the  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  dom0 is what the computer would have been without Xen, perhaps a
 desktop or laptop.  Then, one can run domUs at will.  Purists will  desktop or laptop.  Then, one can run domUs at 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 meaningfully 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.  In theory  
 the only issue is that the "backend drivers" are not yet MPSAFE:  
   http://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html  
   
 Installation of NetBSD  Installation of NetBSD
 ----------------------  ----------------------
   
 First,  [Install NetBSD/amd64](/guide/inst/)
 [install NetBSD/amd64](/guide/inst/)  
 just as you would if you were not using Xen.  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 file system 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 file system, 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  Installation of Xen
 -------------------  -------------------
   
 In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from  We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as
 pkgsrc (or another matching pair).  See [the pkgsrc  dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
 documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with  Ensure that your packages are recent.
 pkgsrc.  Ensure that your packages are recent; the HOWTO does not  
 contemplate old builds.  
   
   
 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.  If using i386, use  
 releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen  
 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you  
 should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and  
 typically are) left compressed.  
   
 In a dom0 kernel, kernfs is mandatory for xend to communicate with the  
 kernel, so ensure that /kern is in fstab.  TODO: Say this is default,  
 or file a PR and give a reference.  
   
 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 file system, /boot present, and likely  
 /boot.cfg.  (If not, fix before continuing!)  
   
 Add a line to to /boot.cfg to boot Xen.  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  Once this is done, install the Xen kernel itself:
   
 which specifies that the dom0 should have 256M, leaving the rest to be  [[!template id=programlisting text="""
 allocated for domUs.  To use a serial console, use  # cp /usr/pkg/xen48-kernel/xen.gz /
   """]]
   
         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1  Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory, copied from
   `releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz` of a NetBSD build.
   
 which will use the first serial port for Xen (which counts starting  Add a line to /boot.cfg to boot Xen:
 from 1), forcing speed/parity, and also for NetBSD (which counts  
 starting at 0).  In an attempt to add performance, one can also add  [[!template id=filecontent name="/boot.cfg" text="""
   menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
   """]]
   
         dom0_max_vcpus=1 dom0_vcpus_pin  which specifies that the dom0 should have 512MB of ram, leaving the rest
   to be allocated for domUs.  To use a serial console, use
   
   [[!template id=filecontent name="/boot.cfg" text="""
   menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
   """]]
   
   which will use the first serial port for Xen (which counts starting
   from 1, unlike NetBSD which counts starting from 0), forcing
   speed/parity.  Because the NetBSD command line lacks a
   "console=pc" argument, it will use the default "xencons" console device,
   which directs the console I/O through Xen to the same console device Xen
   itself uses (in this case, the serial port).
   
   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  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.  more) and to pin that vcpu to a physical CPU.
   
 Xen has [many boot  Xen has [many boot
 options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),  options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),
 and other than dom0 memory and max_vcpus, they are generally not  and other than dom0 memory and max_vcpus, they are generally not
 necessary.  necessary.
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  
 kernel that works without Xen).  Consider a line to boot /netbsd.ok (a  
 fallback version of the non-Xen kernel, updated manually when you are  
 sure /netbsd is ok).  Consider also a line to boot fallback versions  
 of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used  
 to resolve Xen booting issues.  
   
 Probably you want a default=N line to choose Xen in the absence of  
 intervention.  
   
 Now, reboot so that you are running a DOM0 kernel under Xen, rather  Now, reboot so that you are running a DOM0 kernel under Xen, rather
 than GENERIC without Xen.  than GENERIC without Xen.
   
 Using grub (historic)  
 ---------------------  
   
 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/).  
   
 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  Configuring Xen
 ---------------  ---------------
   
 Xen logs will be in /var/log/xen.  
   
 Now, you have a system that will boot Xen and the dom0 kernel, but not  Now, you have a system that will boot Xen and the dom0 kernel, but not
 do anything else special.  Make sure that you have rebooted into Xen.  do anything else special.  Make sure that you have rebooted into Xen.
 There will be no domUs, and none can be started because you still have  There will be no domUs, and none can be started because you still have
 to configure the dom0 daemons.  to configure the dom0 daemons.
   
 The daemons which should be run vary with Xen version and with whether  Since Xen 4.2, the tool which should be used is `xl`.
 one is using xm or xl.  The Xen 3.1, 3.3 and 4.1 packages use xm.  Xen  
 4.2 and up packages use xl.  To use xm with 4.2, edit xendomains to  
 use xm instead.  
   
 For 3.1 and 3.3, you should enable xend and xenbackendd:  
   
         xend=YES  
         xenbackendd=YES  
   
 For 4.1 and up, you should enable xencommons.  Not enabling xencommons  
 will result in a hang; it is necessary to hit ^C on the console to let  
 the machine finish booting.  If you are using xm (default in 4.1, or  
 if you changed xendomains in 4.2), you should also enable xend:  
   
         xend=YES # only if using xm, and only installed <= 4.2  For 4.1 and up, you should enable `xencommons`:
         xencommons=YES  
   [[!template id=filecontent name="/etc/rc.conf" text="""
   xencommons=YES
   """]]
   
   Not enabling xencommons will result in a hang; it is necessary to hit `^C` on
   the console to let the machine finish booting:
   
 TODO: Recommend for/against xen-watchdog.  TODO: Recommend for/against xen-watchdog.
   
 After you have configured the daemons and either started them (in the  After you have configured the daemons and either started them (in the
 order given) or rebooted, use xm or xl to inspect Xen's boot messages,  order given) or rebooted, use `xl` to inspect Xen's boot messages,
 available resources, and running domains.  An example with xl follows:  available resources, and running domains.  For example:
   
         # xl dmesg  [[!template id=programlisting text="""
         [xen's boot info]  # xl dmesg
         # xl info  ... xen's boot info ...
         [available memory, etc.]  # xl info
         # xl list  ... available memory, etc ...
         Name              Id  Mem(MB)  CPU  State  Time(s)  Console  # xl list
         Domain-0           0       64    0  r----     58.1  Name              Id  Mem(MB)  CPU  State  Time(s)  Console
   Domain-0           0       64    0  r----     58.1
   """]]
   
   Xen logs will be in /var/log/xen.
   
 ### Issues with xencommons  ### Issues with xencommons
   
 xencommons starts xenstored, which stores data on behalf of dom0 and  `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
 domUs.  It does not currently work to stop and start xenstored.  domUs.  It does not currently work to stop and start xenstored.
 Certainly all domUs should be shutdown first, following the sort order  Certainly all domUs should be shutdown first, following the sort order
 of the rc.d scripts.  However, the dom0 sets up state with xenstored,  of the rc.d scripts.  However, the dom0 sets up state with xenstored,
Line 495  make this work, one should not expect to Line 217  make this work, one should not expect to
 (and thus xencommons).  There is currently no reason to expect that  (and thus xencommons).  There is currently no reason to expect that
 this will get fixed any time soon.  this will get fixed any time soon.
   
 ### No-longer needed advice about devices  
   
 The installation of NetBSD should already have created devices for xen  
 (xencons, xenevt, xsd_kva), but if they are not present, create them:  
   
         cd /dev && sh MAKEDEV xen  
   
 anita (for testing NetBSD)  anita (for testing NetBSD)
 --------------------------  --------------------------
   
 With the setup so far (assuming 4.2/xl), one should be able to run  With the setup so far (assuming 4.8/xl), one should be able to run
 anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as  anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
 root, because anita must create a domU):  root, because anita must create a domU):
   
         anita --vmm=xl test file:///usr/obj/i386/  [[!template id=programlisting text="""
   anita --vmm=xl test file:///usr/obj/i386/
   """]]
   
 Alternatively, one can use --vmm=xm to use xm-based domU creation  
 instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.  
       
 Xen-specific NetBSD issues  Xen-specific NetBSD issues
 --------------------------  --------------------------
   
Line 522  dom0 kernel compared to hardware. Line 236  dom0 kernel compared to hardware.
   
 One is that the module ABI is different because some of the #defines  One is that the module ABI is different because some of the #defines
 change, so one must build modules for Xen.  As of netbsd-7, the build  change, so one must build modules for Xen.  As of netbsd-7, the build
 system does this automatically.  TODO: check this.  (Before building  system does this automatically.
 Xen modules was added, it was awkward to use modules to the point  
 where it was considered that it did not work.)  
   
 The other difference is that XEN3_DOM0 does not have exactly the same  The other difference is that XEN3_DOM0 does not have exactly the same
 options as GENERIC.  While it is debatable whether or not this is a  options as GENERIC.  While it is debatable whether or not this is a
Line 537  Updating NetBSD in a dom0 Line 249  Updating NetBSD in a dom0
 This is just like updating NetBSD on bare hardware, assuming the new  This is just like updating NetBSD on bare hardware, assuming the new
 version supports the version of Xen you are running.  Generally, one  version supports the version of Xen you are running.  Generally, one
 replaces the kernel and reboots, and then overlays userland binaries  replaces the kernel and reboots, and then overlays userland binaries
 and adjusts /etc.  and adjusts `/etc`.
   
 Note that one must update both the non-Xen kernel typically used for  Note that one must update both the non-Xen kernel typically used for
 rescue purposes and the DOM0 kernel used with Xen.  rescue purposes and the DOM0 kernel used with Xen.
Line 545  rescue purposes and the DOM0 kernel used Line 257  rescue purposes and the DOM0 kernel used
 Converting from grub to /boot  Converting from grub to /boot
 -----------------------------  -----------------------------
   
 These instructions were [TODO: will be] used to convert a system from  These instructions were used to convert a system from
 grub to /boot.  The system was originally installed in February of  grub to /boot.  The system was originally installed in February of
 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated  2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
 over time.  Before these commands, it was running NetBSD 6 i386, Xen  over time.  Before these commands, it was running NetBSD 6 i386, Xen
 4.1 and grub, much like the message linked earlier in the grub  4.1 and grub, much like the message linked earlier in the grub
 section.  section.
   
         # Install MBR bootblocks on both disks.   [[!template id=programlisting text="""
         fdisk -i /dev/rwd0d  # Install MBR bootblocks on both disks.
         fdisk -i /dev/rwd1d  fdisk -i /dev/rwd0d
         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.  fdisk -i /dev/rwd1d
         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1  # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1  installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
         # Install secondary boot loader  installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
         cp -p /usr/mdec/boot /  # Install secondary boot loader
         # Create boot.cfg following earlier guidance:  cp -p /usr/mdec/boot /
         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M  # Create boot.cfg following earlier guidance:
         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M  menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
         menu=GENERIC:boot  menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
         menu=GENERIC single-user:boot -s  menu=GENERIC:boot
         menu=GENERIC.ok:boot netbsd.ok  menu=GENERIC single-user:boot -s
         menu=GENERIC.ok single-user:boot netbsd.ok -s  menu=GENERIC.ok:boot netbsd.ok
         menu=Drop to boot prompt:prompt  menu=GENERIC.ok single-user:boot netbsd.ok -s
         default=1  menu=Drop to boot prompt:prompt
         timeout=30  default=1
   timeout=30
 TODO: actually do this and fix it if necessary.  """]]
   
 Upgrading Xen versions  Upgrading Xen versions
 ---------------------  ---------------------
   
 Minor version upgrades are trivial.  Just rebuild/replace the  Minor version upgrades are trivial.  Just rebuild/replace the
 xenkernel version and copy the new xen.gz to / (where /boot.cfg  xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
 references it), and reboot.  references it), and reboot.
   
 Major version upgrades are 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.  Specifically,  
 they must match the package you just installed and not be left over  
 from some previous installation.  
   
 Enable the correct set of daemons; see the configuring section above.  
 (Upgrading from 3.x to 4.x without doing this will result in a hang.)  
   
 Ensure that the domU config files are valid for the new version.  
 Specifically, for 4.x remove autorestart=True, and ensure that disks  
 are specified with numbers as the second argument, as the examples  
 above show, and not NetBSD device names.  
   
 Hardware known to work  
 ----------------------  
   
 Arguably, this section is misplaced, and there should be a page of  
 hardware that runs NetBSD/amd64 well, with the mostly-well-founded  
 assumption that NetBSD/xen runs fine on any modern hardware that  
 NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU (and  
 sometimes RAM) pairs/triples to aid those choosing a motherboard.  
 Note that Xen systems usually do not run X, so a listing here does not  
 imply that X works at all.  
   
         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC  
         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC  
         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC  
   
 Older hardware:  
   
         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2  
         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz"  
         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz"  
   
 Running Xen under qemu  
 ----------------------  
   
 The astute reader will note that this section is somewhat twisted.  
 However, it can be useful to run Xen under qemu either because the  
 version of NetBSD as a dom0 does not run on the hardware in use, or to  
 generate automated test cases involving Xen.  
   
 In 2015-01, the following combination was reported to mostly work:  
   
         host OS: NetBSD/amd64 6.1.4  
         qemu: 2.2.0 from pkgsrc  
         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc  
         dom0 kernel: NetBSD/amd64 6.1.5  
         Xen tools: xentools42-4.2.5 from pkgsrc  
   
 See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0  
 shutdown.  
   
 Unprivileged domains (domU)  Unprivileged domains (domU)
 ===========================  ===========================
   
 This section describes general concepts about domUs.  It does not  This section describes general concepts about domUs.  It does not
 address specific domU operating systems or how to install them.  The  address specific domU operating systems or how to install them.  The
 config files for domUs are typically in /usr/pkg/etc/xen, and are  config files for domUs are typically in `/usr/pkg/etc/xen`, and are
 typically named so that the file name, domU name and the domU's host  typically named so that the file name, domU name and the domU's host
 name match.  name match.
   
Line 661  There is no good order to present config Line 315  There is no good order to present config
 surrounding what is being configured.  We first show an example config  surrounding what is being configured.  We first show an example config
 file, and then in the various sections give details.  file, and then in the various sections give details.
   
 See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,  See /usr/pkg/share/examples/xen/xmexample*,
 for a large number of well-commented examples, mostly for running  for a large number of well-commented examples, mostly for running
 GNU/Linux.  GNU/Linux.
   
 The following is an example minimal domain configuration file  The following is an example minimal domain configuration file. The domU
 "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual  serves as a network file server.
 known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5  
 i386 domU).  The domU serves as a network file server.  
   
         # -*- mode: python; -*-  
   
         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"  
         memory = 1024  
         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]  
         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',  
                  'file:/n0/xen/foo-wd1,0x1,w' ]  
   
 The domain will have the same name as the file.  The kernel has the  [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
   name = "domU-id"
   kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
   memory = 1024
   vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
   disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
            'file:/n0/xen/foo-wd1,0x1,w' ]
   """]]
   
   The domain will have name given in the `name` setting.  The kernel has the
 host/domU name in it, so that on the dom0 one can update the various  host/domU name in it, so that on the dom0 one can update the various
 domUs independently.  The vif line causes an interface to be provided,  domUs independently.  The `vif` line causes an interface to be provided,
 with a specific mac address (do not reuse MAC addresses!), in bridge  with a specific mac address (do not reuse MAC addresses!), in bridge
 mode.  Two disks are provided, and they are both writable; the bits  mode.  Two disks are provided, and they are both writable; the bits
 are stored in files and Xen attaches them to a vnd(4) device in the  are stored in files and Xen attaches them to a vnd(4) device in the
 dom0 on domain creation.  The system treats xbd0 as the boot device  dom0 on domain creation.  The system treats xbd0 as the boot device
 without needing explicit configuration.  without needing explicit configuration.
   
 By default xm looks for domain config files in /usr/pkg/etc/xen.  Note  By default, `xl` looks for domain config files in `/usr/pkg/etc/xen`.  Note
 that "xm create" takes the name of a config file, while other commands  that "xl create" takes the name of a config file, while other commands
 take the name of a domain.  To create the domain, connect to the  take the name of a domain.
 console, create the domain while attaching the console, shutdown the  
 domain, and see if it has finished stopping, do (or xl with Xen >=  Examples of commands:
 4.2):  
   [[!template id=programlisting text="""
         xm create foo  xl create foo
         xm console foo  xl console foo
         xm create -c foo  xl create -c foo
         xm shutdown foo  xl shutdown foo
         xm list  xl list
   """]]
   
 Typing ^] will exit the console session.  Shutting down a domain is  Typing `^]` will exit the console session.  Shutting down a domain is
 equivalent to pushing the power button; a NetBSD domU will receive a  equivalent to pushing the power button; a NetBSD domU will receive a
 power-press event and do a clean shutdown.  Shutting down the dom0  power-press event and do a clean shutdown.  Shutting down the dom0
 will trigger controlled shutdowns of all configured domUs.  will trigger controlled shutdowns of all configured domUs.
Line 713  loaders finds and loads a kernel.  Norma Line 367  loaders finds and loads a kernel.  Norma
 file system.  With Xen domUs, the process is totally different.  The  file system.  With Xen domUs, the process is totally different.  The
 normal path is for the domU kernel to be a file in the dom0's  normal path is for the domU kernel to be a file in the dom0's
 file system.  At the request of the dom0, Xen loads that kernel into a  file system.  At the request of the dom0, Xen loads that kernel into a
 new domU instance and starts execution.  While domU kernels can be  new domU instance and starts execution. domU kernels can be anyplace.
 anyplace, reasonable places to store domU kernels on the dom0 are in /  
 (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the  
 config files), or in /u0/xen (where the vdisks are).  
   
 Note that loading the domU kernel from the dom0 implies that boot  Note that loading the domU kernel from the dom0 implies that boot
 blocks, /boot, /boot.cfg, and so on are all ignored in the domU.  blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
Line 727  CPU and memory Line 378  CPU and memory
 --------------  --------------
   
 A domain is provided with some number of vcpus, less than the number  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  of CPUs seen by the hypervisor. For a domU, it is controlled
 the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled  
 from the config file by the "vcpus = N" directive.  from the config file by the "vcpus = N" directive.
   
 A domain is provided with memory; this is controlled in the config  A domain is provided with memory; this is controlled in the config
Line 737  sum of the the memory allocated to the d Line 387  sum of the the memory allocated to the d
 than the available memory.  than the available memory.
   
 Xen also provides a "balloon" driver, which can be used to let domains  Xen also provides a "balloon" driver, which can be used to let domains
 use more memory temporarily.  TODO: Explain better, and explain how  use more memory temporarily.
 well it works with NetBSD.  
   
 Virtual disks  Virtual disks
 -------------  -------------
Line 814  interfaces to the bridge.  One specifies Line 463  interfaces to the bridge.  One specifies
 config file.  The bridge must be set up already in the dom0; an  config file.  The bridge must be set up already in the dom0; an
 example /etc/ifconfig.bridge0 is:  example /etc/ifconfig.bridge0 is:
   
         create  [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
         up  create
         !brconfig bridge0 add wm0  up
   !brconfig bridge0 add wm0
   """]]
   
 With NAT, the domU perceives itself to be behind a NAT running on the  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.  dom0.  This is often appropriate when running Xen on a workstation.
Line 831  Sizing domains Line 482  Sizing domains
   
 Modern x86 hardware has vast amounts of resources.  However, many  Modern x86 hardware has vast amounts of resources.  However, many
 virtual servers can function just fine on far less.  A system with  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  512M 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  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  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,  create a new file and vnconfig it (or lvm), and then dump/restore,
Line 870  savecore(8) can work.   (This is helpful Line 521  savecore(8) can work.   (This is helpful
 The kernel must be specifically for Xen and for use as a domU.  The  The kernel must be specifically for Xen and for use as a domU.  The
 i386 and amd64 provide the following kernels:  i386 and amd64 provide the following kernels:
   
         i386 XEN3_DOMU  
         i386 XEN3PAE_DOMU          i386 XEN3PAE_DOMU
         amd64 XEN3_DOMU          amd64 XEN3_DOMU
   
 Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must  
 use the PAE version of the i386 kernel.  
   
 This will boot NetBSD, but this is not that useful if the disk is  This will boot NetBSD, but this is not that useful if the disk is
 empty.  One approach is to unpack sets onto the disk outside of xen  empty.  One approach is to unpack sets onto the disk outside of xen
 (by mounting it, just as you would prepare a physical disk for a  (by mounting it, just as you would prepare a physical disk for a
Line 1119  to update the special boot partition. Line 766  to update the special boot partition.
 Amazon  Amazon
 ------  ------
   
 See the [Amazon EC2 page](../amazon_ec2/).  See the [Amazon EC2 page](/amazon_ec2/).
   
 Using npf  
 ---------  
   
 In standard kernels, npf is a module, and thus cannot be loaded in a  
 DOMU kernel.  
   
 TODO: Explain how to compile npf into a custom kernel, answering (but  
 note that the problem was caused by not booting the right kernel)  
 [this email to  
 netbsd-users](http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html).  
   
 TODO items for improving NetBSD/xen  
 ===================================  
   
 * Make the NetBSD dom0 kernel work with SMP.  
 * Test the Xen 4.5 packages adequately to be able to recommend them as  
   the standard approach.  
 * Get PCI passthrough working on Xen 4.5  
 * Get pvgrub into pkgsrc, either via xentools or separately.  
 * grub  
   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary  
     fragsize/blocksize (UFS2 support may be present; the point is to  
     make it so that with any UFS1/UFS2 file system setup that works  
     with NetBSD grub will also work).  
     See [pkg/40258](http://gnats.netbsd.org/40258).  
   * Push patches upstream.  
   * Get UFS2 patches into pvgrub.  
 * Add support for PV ops to a version of /boot, and make it usable as  
   a kernel in Xen, similar to pvgrub.  
 * Solve somehow the issue with modules for GENERIC not being loadable  
   in a Xen dom0 or domU kernel.  
   
 Random pointers  Random pointers
 ===============  ===============

Removed from v.1.132  
changed lines
  Added in v.1.157


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