--- wikisrc/ports/xen/howto.mdwn 2018/08/27 16:54:42 1.157 +++ wikisrc/ports/xen/howto.mdwn 2018/09/05 09:16:10 1.158 @@ -89,31 +89,14 @@ than amd64. 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. +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. 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. -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. - Installation of NetBSD ---------------------- @@ -125,7 +108,6 @@ Installation of Xen We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc. -Ensure that your packages are recent. Once this is done, install the Xen kernel itself: @@ -158,39 +140,23 @@ itself uses (in this case, the serial po 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/4.5-testing/misc/xen-command-line.html), +more) and to pin that vcpu to a physical CPU. Xen has +[many boot options](http://xenbits.xenproject.org/docs/4.8-testing/misc/xen-command-line.html), and other than dom0 memory and max_vcpus, they are generally not necessary. -Now, reboot so that you are running a DOM0 kernel under Xen, rather -than GENERIC without Xen. - -Configuring 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 daemons. - -Since Xen 4.2, the tool which should be used is `xl`. - -For 4.1 and up, you should enable `xencommons`: +Enable `xencommons`: [[!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: +Now, reboot so that you are running a DOM0 kernel under Xen, rather +than GENERIC without Xen. TODO: Recommend for/against xen-watchdog. -After you have configured the daemons and either started them (in the -order given) or rebooted, use `xl` to inspect Xen's boot messages, +Once the reboot is done, use `xl` to inspect Xen's boot messages, available resources, and running domains. For example: [[!template id=programlisting text=""" @@ -311,11 +277,7 @@ the dom0. NetBSD's /dev/random system w 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 /usr/pkg/share/examples/xen/xmexample*, +See /usr/pkg/share/examples/xen/xlexample*, for a large number of well-commented examples, mostly for running GNU/Linux. @@ -359,21 +321,6 @@ equivalent to pushing the power button; power-press event and do a clean shutdown. Shutting down the dom0 will trigger controlled shutdowns of all configured domUs. -domU kernels ------------- - -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 -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 -file system. At the request of the dom0, Xen loads that kernel into a -new domU instance and starts execution. domU kernels can be anyplace. - -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 -------------- @@ -392,50 +339,34 @@ use more memory temporarily. 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 and gnats reference. 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 - -Do not use qemu-img-xen, because this will create sparse file. There -have been recent (2015) reports of sparse vnd(4) devices causing -lockups, but there is apparently no PR. - -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 first element is "method:/path/to/disk". Common methods are + "file:" for file-backed vnd, and "phy:" for something that is already + a 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, 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. + * 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 @@ -449,8 +380,8 @@ Virtual Networking 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 +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. @@ -477,39 +408,25 @@ 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 -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 -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 script -used 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 domU +---------------------- See the earlier config file, and adjust memory. Decide on how much storage you will provide, and prepare it (file or lvm). @@ -580,8 +497,8 @@ not really a Xen-specific issue, but bec 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. @@ -624,8 +541,8 @@ To get the Linux console right, you need to your configuration since not all Linux distributions auto-attach a tty to the xen console. -Creating an unprivileged Solaris domain (domU) ----------------------------------------------- +Creating a Solaris domU +----------------------- See possibly outdated [Solaris domU instructions](/ports/xen/howto-solaris/).