--- wikisrc/ports/xen/howto.mdwn 2015/02/10 17:38:14 1.88 +++ wikisrc/ports/xen/howto.mdwn 2020/11/15 14:59:54 1.185 @@ -1,409 +1,213 @@ -Introduction -============ +[[!meta title="Xen HowTo"]] -[![[Xen -screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png) +Xen is a Type 1 hypervisor which supports running multiple guest operating +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 +other hardware (e.g., disks, network, USB), and one or more domU operating +systems which operate in an unprivileged virtualized environment. IO requests +from the domU systems are forwarded by the Xen hypervisor to the dom0 to be +fulfilled. -Xen is a hypervisor (or virtual machine monitor) for x86 hardware -(i686-class or higher), which supports running multiple guest -operating systems on a single physical machine. Xen is a Type 1 or -bare-metal hypervisor; one uses the Xen kernel to control the CPU, -memory and console, a dom0 operating system which mediates access to -other hardware (e.g., disks, network, USB), and one or more domU -operating systems which operate in an unprivileged virtualized -environment. IO requests from the domU systems are forwarded by the -hypervisor (Xen) to the dom0 to be fulfilled. - -Xen supports two styles of guests. The original is Para-Virtualized -(PV) which means that the guest OS does not attempt to access hardware -directly, but instead makes hypercalls to the hypervisor. This is -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 -and network.) PV guests must be specifically coded for Xen. - -The more recent style is HVM, which means that the guest does not have -code for Xen and need not be aware that it is running under Xen. -Attempts to access hardware registers are trapped and emulated. This -style is less efficient but can run unmodified guests. - -Generally any amd64 machine will work with Xen and PV guests. In -theory i386 computers without 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, the VT or VMX cpu feature (Intel) or SVM/HVM/VT -(amd64) is needed; "cpuctl identify 0" will show this. TODO: Clean up -and check the above features. +This HOWTO presumes a basic familiarity with the Xen system +architecture, with installing NetBSD on amd64 hardware, and with +installing software from pkgsrc. See also the [Xen +website](http://www.xenproject.org/). + +[[!toc]] + +# Overview + +The basic concept of Xen is that the hypervisor (xenkernel) runs on +the hardware, and runs a privileged domain ("dom0") that can access +disks/networking/etc. One then runs additonal unprivileged domains +(each a "domU"), presumably to do something useful. + +This HOWTO addresses how to run a NetBSD dom0 (and hence also build +xen itself). It also addresses how to run domUs in that environment, +and how to deal with having a domU in a Xen environment run by someone +else and/or not running NetBSD. + +## Guest Styles + +Xen supports different styles of guests. + +[[!table data=""" +Style of guest |Supported by NetBSD +PV |Yes (dom0, domU) +HVM |Yes (domU) +PVHVM |current-only (domU) +PVH |current-only (domU, dom0 not yet) +"""]] + +In Para-Virtualized (PV) mode, the guest OS does not attempt to access +hardware directly, but instead makes hypercalls to the hypervisor; PV +guests must be specifically coded for Xen. +See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)). + +In HVM mode, no guest modification is required; however, hardware +support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs. +The dom0 runs qemu to emulate hardware. + +In PVHVM mode, the guest runs as HVM, but additionally can use PV +drivers for efficiency. +See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM). + +There have been two PVH modes: original PVH and PVHv2. Original PVH +was based on PV mode and is no longer relevant at all. PVHv2 is +basically lightweight HVM with PV drivers. A critical feature of it +is that qemu is not needed; the hypervisor can do the emulation that +is required. Thus, a dom0 can be PVHv2. +The source code uses PVH and config files use pvh; this refers to PVHv2. +See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu). -At boot, the dom0 kernel is loaded as a module with Xen as the kernel. +At system 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. - -NetBSD used to support Xen2; this has been removed. - -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. +## CPU Architecture -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/). - -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 runs on x86_64 hardware (the NetBSD amd64 port). + +There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD. + +The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.) -Xen ---- +The domU can be i386PAE or amd64. +i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64. -In NetBSD, xen is provided in pkgsrc, via matching pairs of packages +## Xen Versions + +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. - -xenkernel45 provides Xen 4.5. This is new to pkgsrc as of 2015-01 and -not yet recommended for other than experimental/testing use. - -Ideally newer versions of Xen will be added to pkgsrc. - -Note that NetBSD support is called XEN3. It works with Xen 3 and Xen -4 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, 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 -choose one or the other, because it affects which daemons you run. - -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.) - -Architecture ------------- - -Xen itself can run on i386 or amd64 machines. (Practically, almost -any computer where one would want to run Xen supports amd64.) If -using an i386 NetBSD kernel for the dom0, PAE is required (PAE -versions are built by default). While i386 dom0 works fine, amd64 is -recommended as more normal. - -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. - -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.) - -Recommendation --------------- - -Therefore, this HOWTO recommends running xenkernel42 (and xentools42), -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. - -Build problems --------------- - -Ideally, all versions of Xen in pkgsrc would build on all versions of -NetBSD on both i386 and amd64. However, that isn't the case. Besides -aging code and aging compilers, qemu (included in xentools for HVM -support) is difficult to build. The following are known to work or FAIL: - - xenkernel3 netbsd-5 amd64 - xentools3 netbsd-5 amd64 - xentools3=hvm netbsd-5 amd64 ???? - xenkernel33 netbsd-5 amd64 - xentools33 netbsd-5 amd64 - xenkernel41 netbsd-5 amd64 - xentools41 netbsd-5 amd64 - xenkernel42 netbsd-5 amd64 - xentools42 netbsd-5 amd64 - - xenkernel3 netbsd-6 i386 FAIL - xentools3 netbsd-6 i386 - xentools3-hvm netbsd-6 i386 FAIL (dependencies fail) - xenkernel33 netbsd-6 i386 - xentools33 netbsd-6 i386 - xenkernel41 netbsd-6 i386 - xentools41 netbsd-6 i386 - xenkernel42 netbsd-6 i386 - xentools42 netbsd-6 i386 *MIXED - - (all 3 and 33 seem to FAIL) - xenkernel41 netbsd-7 i386 - xentools41 netbsd-7 i386 - xenkernel42 netbsd-7 i386 - xentools42 netbsd-7 i386 ??FAIL - -(*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds, -but it does not build for gdt.) - -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. - -For experimenting with Xen, a machine with as little as 1G of RAM and -100G of disk can work. For running many domUs in productions, far -more will be needed. - -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. 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 +Versions available in pkgsrc: -Installation of NetBSD ----------------------- +[[!table data=""" +Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream +4.11 |xenkernel411 |x86_64 |No +4.13 |xenkernel413 |x86_64 |No +"""]] -First, -[install NetBSD/amd64](/guide/inst/) -just as you would if you were not using Xen. -However, the partitioning approach is very important. +See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/). -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. 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 comunicate 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 filesystem, /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 +Older Xen had a python-based management tool called xm, now replaced +by xl. - menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M +## NetBSD versions -which specifies that the dom0 should have 256M, leaving the rest to be -allocated for domUs. To use a serial console, use +Xen has been supported in NetBSD for a long time, at least since 2005. +Initially Xen was PV only. - menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1 +NetBSD 8 and up support PV and HVM modes. -which will use the first serial port for Xen (which counts starting -from 1), forcing speed/parity, and also for NetBSD (which counts -starting at 0). In an attempt to add performance, one can also add +Support for PVHVM and PVH is available only in NetBSD-current. - dom0_max_vcpus=1 dom0_vcpus_pin +NetBSD as a dom0 does not run SMP, because some drivers are not yet +safe for this. \todo Link to more information about what needs work. -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. +NetBSD, when run as a domU, can and does typically run SMP. -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. +Note: NetBSD support is called XEN3. However, it does support Xen 4, +because the hypercall interface has remained identical. -Now, reboot so that you are running a DOM0 kernel under Xen, rather -than GENERIC without Xen. +# Creating a dom0 -Using grub (historic) ---------------------- +In order to install a NetBSD as a dom0, one must first install a normal +NetBSD system, and then pivot the install to a dom0 install by changing +the kernel and boot configuration. -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.) +In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with +512M it worked reliably. This does not make sense, but if you see +"not ELF" after Xen boots, try increasing dom0 RAM. -Configuring Xen ---------------- +## Installation of NetBSD -Xen logs will be in /var/log/xen. +[Install NetBSD/amd64](/guide/inst/) +just as you would if you were not using Xen. -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. -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. Running xl without xencommons=YES (and starting it) -will result in a hang (so don't do that; follow the HOWTO!). +## Installation of Xen -The installation of NetBSD should already have created devices for xen -(xencons, xenevt), but if they are not present, create them: +We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as +dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc. - cd /dev && sh MAKEDEV xen +Once this is done, install the Xen kernel itself: -TODO: Give 3.1 advice (or remove it from pkgsrc). +[[!template id=programlisting text=""" +# cp /usr/pkg/xen48-kernel/xen.gz / +"""]] -For 3.3 (and thus xm), add to rc.conf (but note that you should have -installed 4.1 or 4.2): +Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel +can either be compiled manually, or downloaded from the NetBSD FTP, for +example at: - xend=YES - xenbackendd=YES +[[!template id=programlisting text=""" +ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz +"""]] -For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf: +Add a line to /boot.cfg to boot Xen: - xencommons=YES - xend=YES +[[!template id=filecontent name="/boot.cfg" text=""" +menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M +"""]] -(If you are using xentools41 from before 2014-12-26, change -rc.d/xendomains to use xm rather than xl.) +This specifies that the dom0 should have 512MB of ram, leaving the rest +to be allocated for domUs. To use a serial console, use: -For 4.2 with xm, add to rc.conf +[[!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 +"""]] - xencommons=YES - xend=YES +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). -For 4.2 with xl, add to rc.conf: +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. Xen has +[many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html), +and other than dom0 memory and max_vcpus, they are generally not +necessary. + +Copy the boot scripts into `/etc/rc.d`: + +[[!template id=programlisting text=""" +# cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/ +"""]] + +Enable `xencommons`: + +[[!template id=filecontent name="/etc/rc.conf" text=""" +xencommons=YES +"""]] - xencommons=YES - TODO: explain if there is a xend replacement +Now, reboot so that you are running a DOM0 kernel under Xen, rather +than GENERIC without Xen. -For 4.5 (and thus with xl), add to rc.conf: +TODO: Recommend for/against xen-watchdog. - xencommons=YES - TODO: explain if there is a xend replacement +Once the reboot is done, use `xl` to inspect Xen's boot messages, +available resources, and running domains. For example: -TODO: Recommend for/against xen-watchdog. +[[!template id=programlisting text=""" +# xl dmesg +... xen's boot info ... +# xl info +... available memory, etc ... +# xl list +Name Id Mem(MB) CPU State Time(s) Console +Domain-0 0 64 0 r---- 58.1 +"""]] -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, -available resources, and running domains. An example with xm follows: - - # xm dmesg - [xen's boot info] - # xm info - [available memory, etc.] - # xm list - Name Id Mem(MB) CPU State Time(s) Console - Domain-0 0 64 0 r---- 58.1 - -With xl, the commands are the same, and the output may be slightly -different. TODO: add example output for xl before the xm example, -after confirming on 4.2 and resolving the TODO about rc.conf. +Xen logs will be in /var/log/xen. ### 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. Certainly all domUs should be shutdown first, following the sort order of the rc.d scripts. However, the dom0 sets up state with xenstored, @@ -413,200 +217,141 @@ make this work, one should not expect to (and thus xencommons). There is currently no reason to expect that this will get fixed any time soon. -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, one should be able to run anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as 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 There are (at least) two additional things different about NetBSD as a dom0 kernel compared to hardware. -One is that modules are not usable in DOM0 kernels, so one must -compile in what's needed. It's not really that modules cannot work, -but that modules must be built for XEN3_DOM0 because some of the -defines change and the normal module builds don't do this. Basically, -enabling Xen changes the kernel ABI, and the module build system -doesn't cope with this. +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 +system does this automatically. 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 bug, users should be aware of this and can simply add missing config items if desired. -Updating NetBSD in a dom0 -------------------------- +## 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. +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. -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 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 4.1 and grub, much like the message linked earlier in the grub section. - # Install mbr bootblocks on both disks. - fdisk -i /dev/rwd0d - fdisk -i /dev/rwd1d - # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components. - installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1 - installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1 - # Install secondary boot loader - cp -p /usr/mdec/boot / - # Create boog.cfg following earlier guidance: - menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M - menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M - menu=GENERIC:boot - menu=GENERIC single-user:boot -s - menu=GENERIC.ok:boot netbsd.ok - menu=GENERIC.ok single-user:boot netbsd.ok -s - menu=Drop to boot prompt:prompt - default=1 - timeout=30 - -TODO: actually do this and fix it if necessary. - -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. - - -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: +[[!template id=programlisting text=""" +# Install MBR bootblocks on both disks. +fdisk -i /dev/rwd0d +fdisk -i /dev/rwd1d +# Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components. +installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1 +installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1 +# Install secondary boot loader +cp -p /usr/mdec/boot / +# Create boot.cfg following earlier guidance: +menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M +menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M +menu=GENERIC:boot +menu=GENERIC single-user:boot -s +menu=GENERIC.ok:boot netbsd.ok +menu=GENERIC.ok single-user:boot netbsd.ok -s +menu=Drop to boot prompt:prompt +default=1 +timeout=30 +"""]] + +## Upgrading Xen versions + +Minor version upgrades are trivial. Just rebuild/replace the +xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg` +references it), and reboot. - 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 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 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 name match. -The domU is provided with cpu and memory by Xen, configured by the +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. -Config files ------------- +## Config files -There is no good order to present config files and the concepts -surrounding what is being configured. We first show an example config -file, and then in the various sections give details. - -See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*, -for a large number of well-commented examples, mostly for running +See /usr/pkg/share/examples/xen/xlexample* +for a small number of well-commented examples, mostly for running GNU/Linux. -The following is an example minimal domain configuration file -"/usr/pkg/etc/xen/foo". It is (with only a name change) an actual -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 following is an example minimal domain configuration file. The domU +serves as a network file server. + +[[!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 the same name as the file. The kernel has the +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 -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 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 -dom0 on domain creation. The system treates xbd0 as the boot device +dom0 on domain creation. The system treats xbd0 as the boot device without needing explicit configuration. -By default xm looks for domain config files in /usr/pkg/etc/xen. Note -that "xm create" takes the name of a config file, while other commands -take the name of a domain. To create the domain, connect to the -console, create the domain while attaching the console, shutdown the -domain, and see if it has finished stopping, do (or xl with Xen >= -4.2): - - xm create foo - xm console foo - xm create -c foo - xm shutdown foo - xm list +By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note +that "xl create" takes the name of a config file, while other commands +take the name of a domain. + +Examples of commands: + +[[!template id=programlisting text=""" +xl create /usr/pkg/etc/xen/foo +xl console domU-id +xl create -c /usr/pkg/etc/xen/foo +xl shutdown domU-id +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 power-press event and do a clean shutdown. Shutting down the dom0 will trigger controlled shutdowns of all configured domUs. -domU kernels ------------- +## CPU and memory -On a physical computer, the BIOS reads sector 0, and a chain of boot -loaders finds and loads a kernel. Normally this comes from the root -filesystem. With Xen domUs, the process is totally different. The -normal path is for the domU kernel to be a file in the dom0's -filesystem. At the request of the dom0, Xen loads that kernel into a -new domU instance and starts execution. While domU kernels can be -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 -blocks, /boot, /boot.cfg, and so on are all ignored in the domU. -See the VPS section near the end for discussion of alternate ways to -obtain domU kernels. - -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 +A domain is provided with some number of vcpus, up to the number +of CPUs seen by the hypervisor. For a domU, it is controlled from the config file by the "vcpus = N" directive. A domain is provided with memory; this is controlled in the config @@ -615,61 +360,54 @@ sum of the the memory allocated to the d 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. +use more memory temporarily. -Virtual disks -------------- +## 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. To -create an empty 4G virtual disk, simply do - - dd if=/dev/zero of=foo-xbd0 bs=1m count=4096 - -With the lvm style, one creates logical devices. They are then used -similarly to vnds. TODO: Add an example with lvm. - -In domU config files, the disks are defined as a sequence of 3-tuples. -The first element is "method:/path/to/disk". Common methods are -"file:" for file-backed vnd. and "phy:" for something that is already -a (TODO: character or block) device. - -The second element is an artifact of how virtual disks are passed to -Linux, and a source of confusion with NetBSD Xen usage. Linux domUs -are given a device name to associate with the disk, and values like -"hda1" or "sda1" are common. In a NetBSD domU, the first disk appears -as xbd0, the second as xbd1, and so on. However, xm/xl demand a -second argument. The name given is converted to a major/minor by -calling stat(2) on the name in /dev and this is passed to the domU. -In the general case, the dom0 and domU can be different operating -systems, and it is an unwarranted assumption that they have consistent -numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD -as both dom0 and domU, using values of 0x0 for the first disk and 0x1 -for the second works fine and avoids this issue. For a GNU/Linux -guest, one can create /dev/hda1 in /dev, or to pass 0x301 for -/dev/hda1. +In domU config files, the disks are defined as a sequence of 3-tuples: -The third element is "w" for writable disks, and "r" for read-only -disks. + * The first element is "method:/path/to/disk". Common methods are + "file:" for a file-backed vnd, and "phy:" for something that is already + a device, such as an LVM logical volume. + + * The second element is an artifact of how virtual disks are passed to + Linux, and a source of confusion with NetBSD Xen usage. Linux domUs + are given a device name to associate with the disk, and values like + "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears + as xbd0, the second as xbd1, and so on. However, xl demands a + second argument. The name given is converted to a major/minor by + calling stat(2) on the name in /dev and this is passed to the domU. + In the general case, the dom0 and domU can be different operating + systems, and it is an unwarranted assumption that they have consistent + numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD + as both dom0 and domU, using values of 0x0 for the first disk and 0x1 + for the second works fine and avoids this issue. For a GNU/Linux + guest, one can create /dev/hda1 in /dev, or to pass 0x301 for + /dev/hda1. + + * The third element is "w" for writable disks, and "r" for read-only + disks. + +Example: +[[!template id=filecontent name="/usr/pkg/etc/xen/foo" text=""" +disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ] +"""]] + +Note that NetBSD by default creates only vnd[0123]. If you need more +than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the +dom0. + +Note that NetBSD by default creates only xbd[0123]. If you need more +virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU. Virtual Networking ------------------ -Xen provides virtual ethernets, each of which connects the dom0 and a +Xen provides virtual Ethernets, each of which connects the dom0 and a domU. For each virtual network, there is an interface "xvifN.M" in -the dom0, and in domU index N, a matching interface xennetM (NetBSD -name). The interfaces behave as if there is an Ethernet with two -adaptors connected. From this primitive, one can construct various +the dom0, and a matching interface xennetM (NetBSD name) in domU index N. +The interfaces behave as if there is an Ethernet with two +adapters connected. From this primitive, one can construct various configurations. We focus on two common and useful cases for which there are existing scripts: bridging and NAT. @@ -681,9 +419,11 @@ interfaces to the bridge. One specifies config file. The bridge must be set up already in the dom0; an example /etc/ifconfig.bridge0 is: - create - up - !brconfig bridge0 add wm0 +[[!template id=filecontent name="/etc/ifconfig.bridge0" text=""" +create +up +!brconfig bridge0 add wm0 +"""]] 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. @@ -693,56 +433,37 @@ The MAC address specified is the one use domain. The interface in dom0 will use this address XOR'd with 00:00:00:01:00:00. Random MAC addresses are assigned if not given. -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. - Starting domains automatically ------------------------------ -To start domains foo at bar at boot and shut them down cleanly on dom0 -shutdown, in rc.conf add: - - xendomains="foo bar" +To start domains `domU-netbsd` and `domU-linux` at boot and shut them +down cleanly on dom0 shutdown, add the following in rc.conf: -Note that earlier versions of the xentools41 xendomains rc.d scripth -usd xl, when one should use xm with 4.1. +[[!template id=filecontent name="/etc/rc.conf" text=""" +xendomains="domU-netbsd domU-linux" +"""]] -Creating specific unprivileged domains (domU) -============================================= +# Creating a domU Creating domUs is almost entirely independent of operating system. We have already presented the basics of config files. Note that you must -have already completed the dom0 setup so that "xl list" (or "xm list") -works. +have already completed the dom0 setup so that "xl list" works. -Creating an unprivileged NetBSD domain (domU) ---------------------------------------------- +Creating a NetBSD PV domU +-------------------------- See the earlier config file, and adjust memory. Decide on how much -storage you will provide, and prepare it (file or lvm). +storage you will provide, and prepare it (file or LVM). -While the kernel will be obtained from the dom0 filesystem, the same +While the kernel will be obtained from the dom0 file system, the same file should be present in the domU as /netbsd so that tools like savecore(8) can work. (This is helpful but not necessary.) The kernel must be specifically for Xen and for use as a domU. The i386 and amd64 provide the following kernels: - i386 XEN3_DOMU i386 XEN3PAE_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. + amd64 XEN3_DOMU 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 @@ -755,7 +476,7 @@ kernel to / and change the kernel line i kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU" -Then, start the domain as "xl create -c configname". +Then, start the domain as "xl create -c configfile". Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following line should be used in the config file. @@ -790,12 +511,19 @@ It is also desirable to add powerd=YES in rc.conf. This way, the domain will be properly shut down if -`xm shutdown -R` or `xm shutdown -H` is used on the dom0. +`xl shutdown -R` or `xl shutdown -H` is used on the dom0. +\todo Check the translation to xl. -Your domain should be now ready to work, enjoy. +It is not strictly necessary to have a kernel (as /netbsd) in the domU +file system. However, various programs (e.g. netstat) will use that +kernel to look up symbols to read from kernel virtual memory. If +/netbsd is not the running kernel, those lookups will fail. (This is +not really a Xen-specific issue, but because the domU kernel is +obtained from the dom0, it is far more likely to be out of sync or +missing with Xen.) -Creating an unprivileged Linux domain (domU) --------------------------------------------- +Creating a Linux domU +--------------------- Creating unprivileged Linux domains isn't much different from unprivileged NetBSD domains, but there are some details to know. @@ -826,20 +554,31 @@ Then copy the files from a working Linux `/etc` (fstab, network config). It should also be possible to extract binary packages such as .rpm or .deb directly to the mounted partition using the appropriate tool, possibly running under NetBSD's Linux -emulation. Once the filesystem has been populated, umount it. If -desirable, the filesystem can be converted to ext3 using tune2fs -j. +emulation. Once the file system has been populated, umount it. If +desirable, the file system can be converted to ext3 using tune2fs -j. It should now be possible to boot the Linux guest domain, using one of the vmlinuz-\*-xenU kernels available in the Xen binary distribution. -To get the linux console right, you need to add: +To get the Linux console right, you need to add: extra = "xencons=tty1" -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. -Creating an unprivileged Solaris domain (domU) ----------------------------------------------- +## Creating a NetBSD HVM domU + +Use type='hmv', probably. Use a GENERIC kernel within the disk image. + +## Creating a NetBSD PVH domU + +Use type='pvh'. + +\todo Explain where the kernel comes from. + + +Creating a Solaris domU +----------------------- See possibly outdated [Solaris domU instructions](/ports/xen/howto-solaris/). @@ -848,6 +587,10 @@ See possibly outdated PCI passthrough: Using PCI devices in guest domains --------------------------------------------------- +NB: PCI passthrough only works on some Xen versions and as of 2020 it +is not clear that it works on any version in pkgsrc. Reports +confirming or denying this notion should be sent to port-xen@. + The dom0 can give other domains access to selected PCI devices. This can allow, for example, a non-privileged domain to have access to a physical network interface or disk controller. However, @@ -879,7 +622,7 @@ the domU's config file, with the format pci = [ '0000:00:06.0', '0000:00:0a.0' ] In the domU an "xpci" device will show up, to which one or more pci -busses will attach. Then the PCI drivers will attach to PCI busses as +buses will attach. Then the PCI drivers will attach to PCI buses as usual. Note that the default NetBSD DOMU kernels do not have "xpci" or any PCI drivers built in by default; you have to build your own kernel to use PCI devices in a domU. Here's a kernel config example; @@ -887,7 +630,7 @@ note that only the "xpci" lines are unus include "arch/i386/conf/XEN3_DOMU" - # Add support for PCI busses to the XEN3_DOMU kernel + # Add support for PCI buses to the XEN3_DOMU kernel xpci* at xenbus ? pci* at xpci ? @@ -915,8 +658,14 @@ note that only the "xpci" lines are unus cd* at scsibus? target ? lun ? # SCSI CD-ROM drives -NetBSD as a domU in a VPS -========================= +# Specific Issues + +## domU + +[NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html) +(However, NetBSD 5 systems should be updated to a supported version.) + +# NetBSD as a domU in a VPS The bulk of the HOWTO is about using NetBSD as a dom0 on your own hardware. This section explains how to deal with Xen in a domU as a @@ -926,37 +675,53 @@ only a few are mentioned that specifical VPS operators provide varying degrees of access and mechanisms for configuration. The big issue is usually how one controls which kernel -is booted, because the kernel is nominally in the dom0 filesystem (to -which VPS users do not normally have acesss). A second issue is how +is booted, because the kernel is nominally in the dom0 file system (to +which VPS users do not normally have access). A second issue is how to install NetBSD. A VPS user may want to compile a kernel for security updates, to run npf, run IPsec, or any other reason why someone would want to change their kernel. -One approach is to have an adminstrative interface to upload a kernel, +One approach is to have an administrative interface to upload a kernel, or to select from a prepopulated list. Other approaches are pygrub (deprecated) and pvgrub, which are ways to have a bootloader obtain a -kernel from the domU filesystem. This is closer to a regular physical +kernel from the domU file system. This is closer to a regular physical computer, where someone who controls a machine can replace the kernel. A second issue is multiple CPUs. With NetBSD 6, domUs support multiple vcpus, and it is typical for VPS providers to enable multiple CPUs for NetBSD domUs. -pygrub -------- +## Complexities due to Xen changes + +Xen has many security advisories and people running Xen systems make +different choices. + +### stub domains + +Some (Linux only?) dom0 systems use something called "stub domains" to +isolate qemu from the dom0 system, as a security and reliabilty +mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel +ends up using PIO for disks rather than DMA. Of course, all of this +is emulated, but emulated PIO is unusably slow. This problem is not +currently understood. -pygrub runs in the dom0 and looks into the domU filesystem. This -implies that the domU must have a kernel in a filesystem in a format -known to pygrub. As of 2014, pygrub seems to be of mostly historical -interest. +### Grant tables -pvgrub ------- +There are multiple versions of using grant tables, and some security +advisories have suggested disabling some versions. Some versions of +NetBSD apparently only use specific versions and this can lead to +"NetBSD current doesn't run on hosting provider X" situations. + +\todo Explain better. + +## Boot methods + +### pvgrub pvgrub is a version of grub that uses PV operations instead of BIOS calls. It is booted from the dom0 as the domU kernel, and then reads -/grub/menu.lst and loads a kernel from the domU filesystem. +/grub/menu.lst and loads a kernel from the domU file system. [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes @@ -975,36 +740,24 @@ does not support all aspects of modern F that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT partition for the kernel with the intent that grub can understand it, which leads to /netbsd not being the actual kernel. One must remember -to update the special boot partiion. +to update the special boot partition. + +### pygrub + +pygrub runs in the dom0 and looks into the domU file system. This +implies that the domU must have a kernel in a file system in a format +known to pygrub. + +pygrub doesn't seem to work to load Linux images under NetBSD dom0, +and is inherently less secure than pvgrub due to running inside dom0. For both these +reasons, pygrub should not be used, and is only still present so that +historical DomU images using it still work. + +As of 2014, pygrub seems to be of mostly historical +interest. New DomUs should use pvgrub. -Amazon ------- +## Specific Providers -TODO: add link to NetBSD amazon howto. +### Amazon -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): -http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html - -TODO items for improving NetBSD/xen -=================================== - -* Package Xen 4.4. -* Get PCI passthrough working on Xen 4.2 (or 4.4). -* 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 filesystem 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. +See the [Amazon EC2 page](/amazon_ec2/).