Difference between revisions of "Xen Dom0"

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So before anything else verify that you can '''reliably''' log into your Alpine box through [[Setting_up_a_ssh-server|SSH]], because with some video chipset (intel in my case) xen will blank your screen so you will have to use SSH.
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This guide will show you how to have your 'sys' install of Alpine run as a Xen Dom0. You can start either from an existing standard install or install a new copy of Alpine with the Alpine Xen ISO.
  
Then upgrade your setup to [[Upgrading_to_Edge|Edge/testing]] (as of the date of writing, Xen is only available in Edge). Install Xen:
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== Install Xen ==
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=== New installation ===
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==== Writing the medium ====
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{{Warning|This will erase '''everything''' on the drive you point it at. Check and double check that <code>/dev/sdx</code> is the correct USB device you want to write to, using the commands <code>lsblk</code> and <code>blkid</code>.}}
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First download Alpine's [https://www.alpinelinux.org/downloads/ Xen install ISO], and either [[Burning ISOs|burn the ISO to a CD/DVD]] or write it to a USB storage device with the following command, where <code>3.12.0</code> should be replaced with the release number of your downloaded ISO and <code>/dev/sdx</code> should be replaced with the drive letter of your USB:
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<pre>dd if=alpine-xen-3.12.0-x86_64.iso of=/dev/sdx</pre>
  
{{Cmd|apk add xen}}
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==== Installation ====
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Now boot from your CD or USB, and type 'root' when prompted for a username. After you have logged in run <code>setup-xen-dom0</code>, then continue with a standard [[Install to disk|Alpine installation]] until you get to the prompt asking to choose your network card.
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What you'll want to do is select what is to be your internet-facing interface, and when asked to bridge it type 'yes'. Then you can configure the networking settings of your bridge device, <code>br0</code>, as you would have configured your internet-facing interface.
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{{Note|You cannot bridge a WiFi interface in the automatic installation script due to incompatible protocols. Make sure you pick an ethernet interface for this.}}
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Now continue with your installation to disk until you reach the 'reboot' prompt. There are a few more things to do before you can boot without errors:
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<pre>
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# xen-hypervisor isn't installed by default with Xen so we must install it manually
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apk add xen-hypervisor
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apk add bridge
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</pre>
  
Modify your extlinux.cfg (credits: http://lists.alpinelinux.org/alpine-devel/1406.html)
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Now you can safely reboot after removing your install medium, making sure to pick the <code>Alpine Linux v3.12, with Xen 4.13.1 and Linux lts</code> boot option in your GRUB menu, with 3.12 and 4.13.1 replaced with your Linux and Xen version numbers, respectively.
since video card is not working for now, we will use a serial console:
 
  
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After this, [[Enable Community Repository|enable the Alpine community repository]] and install the firmware to be used for Xen's virtual machines:
 
<pre>
 
<pre>
SERIAL 0 115200
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apk add seabios ovmf
DEFAULT menu.c32
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</pre>
PROMPT 0
 
MENU TITLE Alpine/Linux Boot Menu
 
MENU HIDDEN
 
MENU AUTOBOOT Alpine will be booted automatically in # seconds.
 
TIMEOUT 50
 
LABEL 0
 
  MENU DEFAULT
 
  MENU LABEL Linux 2.6.38.8-vs2.3.0.37-rc17
 
  KERNEL vmlinuz-2.6.38.8-vs2.3.0.37-rc17
 
  APPEND initrd=initramfs-2.6.38.8-vs2.3.0.37-rc17 root=UUID=f40e340b-ea49-445b-81c0-4d7104b56662 modules=sd-mod,usb-storage,ext4 quiet
 
  
LABEL 1
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Now you are ready to configure GRUB.
  MENU LABEL Linux 2.6.36.3-scst
 
  KERNEL vmlinuz-2.6.36.3-scst
 
  APPEND initrd=initramfs-2.6.36.3-scst root=UUID=f40e340b-ea49-445b-81c0-4d7104b56662 modules=sd-mod,usb-storage,ext4 quiet
 
  
LABEL 2
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=== Existing installation ===
  MENU LABEL Linux 2.6.38.8-grsec
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First you must [[Enable Community Repository|enable the Alpine community repository]], then install Xen and the seabios (BIOS) and ovmf (UEFI) firmwares for its virtual machines.
  KERNEL vmlinuz-2.6.38.8-grsec
 
  APPEND initrd=initramfs-2.6.38.8-grsec root=UUID=f40e340b-ea49-445b-81c0-4d7104b56662 modules=sd-mod,usb-storage,ext4 quiet
 
  
LABEL 3
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<pre>
  MENU LABEL XEN
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# apk add xen xen-hypervisor seabios ovmf
  KERNEL mboot.c32
 
  APPEND /boot/xen-4.gz loglvl=all guest_loglvl=all com1=115200,8n1 console=com1 dom0_mem=256M --- /boot/vmlinuz-grsec root=UUID=f40e340b-ea49-445b-81c0-4d7104b56662 modules=sd-mod,usb-storage,ext4 console=hvc0 earlyprintk=xen nomodeset --- /boot/initramfs-grsec
 
 
</pre>
 
</pre>
Of course replace root=UUID= with '''your''' UUID in yours.
 
  
xl info won't work
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This will install Xen Hypervisor, xl cli command and all the required packages. The next step is to modify your GRUB configuration to properly boot Xen.
  
Start xecommons:
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The next step is to load the necessary kernel modules for Xen, we will add them to /etc/modules, so they will be loaded automatically on boot:
<pre>
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<pre>echo "xen-netback" >> /etc/modules
alpine:/boot# /etc/init.d/xencommons start
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echo "xen-blkback" >> /etc/modules
Starting xenstored...FATAL: Failed to open evtchn device: No such file or directory
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echo "tun" >> /etc/modules</pre>
</pre>
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Then lastly we add the Xen daemons to the default runlevel.
well this will fail but xl info will work anyway
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<pre>rc-update add xenconsoled
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rc-update add xendomains
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rc-update add xenqemu
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rc-update add xenstored</pre>
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Now reboot.
  
Oh but wait, evtchn device is built in the kernel, so why is there no /dev/xen/evtch file ?
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== GRUB configuration ==
let's start udev ! ;)
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Once running a Xen kernel we will need to edit its command-line options and enable the setting of a default GRUB entry by inserting this at the bottom of <code>/etc/default/grub</code>:
{{Cmd|rc-service udev start}}
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{{Cat|/etc/default/grub|<nowiki># We need to set the amount of RAM we allocate to our Dom0 Alpine install so that
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# our future virtual machines are left with enough memory.
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GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=1024M,max:1024M"
  
That's all folks !
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GRUB_DEFAULT="saved"
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GRUB_SAVEDEFAULT="true"</nowiki>}}
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You can replace 1024M with the amount of memory you want to allocate to your Dom0 operating system.
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After this you need to run the following:
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<pre>grub-mkconfig -o /boot/grub/grub.cfg
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grub-set-default "$(grep ^menuentry /boot/grub/grub.cfg | grep Xen | cut -d \' -f 2 | head -1)"
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</pre>
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What this does is set your default entry in GRUB to the first entry containing 'Xen'. Run this every time you upgrade Alpine or Xen.
  
on going debug:
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== Loop Devices ==
vi /etc/rc.conf
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If you plan to use more than 8 DomU's, you may need to increase the amount of loop-devices in your Dom0.
rc_sys="xen0"
 
why ?
 
  
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In Alpine Linux, you will need to add the ''max_loop'' option to the ''loop'' module, then add the loop module to your initramfs.
  
Commands recap:
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Start by populating <code>/etc/modprobe.d/loop.conf</code> with the module options:
{{Cmd|
 
apk add xen
 
apk add udev
 
rc-service udev start ; rc-service udev-postmount start
 
rc-service xencommons start
 
}}
 
If you want "xm" command
 
{{Cmd|rc-service xend start}}
 
  
So let's install services at boot time :
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<pre>
{{Cmd|
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# touch /etc/modprobe.d/loop.conf
rc-update add udev sysinit
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# echo "options loop max_loop=32" > /etc/modprobe.d/loop.conf
rc-update add udev-postmount default
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</pre>
rc-update add xencommons
 
rc-update add xend
 
}}
 
  
since we use a serial line, let'a add a serial console prompt, modify your /etc/inittab accordinly:
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Now reflect the module options in the initramfs:
  
# Put a getty on the serial port
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<pre>
#ttyS0::respawn:/sbin/getty -L ttyS0 115200 vt100
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# mkinitfs
hvc0::respawn:/sbin/getty -L hvc0 115200 vt100
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# reboot
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</pre>
  
hvc0 is Xen console output, where we have already redirected the kernel messages.
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== See also ==
To switch to Xen console, type three time "Ctrl+a"
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* [[Xen Dom0 on USB or SD]]
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* [https://wiki.gentoo.org/wiki/Xen#Host_configuration_.28domain-0.29|Xen page on Gentoo wiki]
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[[Category:Virtualization]]

Revision as of 08:18, 27 August 2020

This guide will show you how to have your 'sys' install of Alpine run as a Xen Dom0. You can start either from an existing standard install or install a new copy of Alpine with the Alpine Xen ISO.

Install Xen

New installation

Writing the medium

Tango-dialog-warning.png
Warning: This will erase everything on the drive you point it at. Check and double check that /dev/sdx is the correct USB device you want to write to, using the commands lsblk and blkid.


First download Alpine's Xen install ISO, and either burn the ISO to a CD/DVD or write it to a USB storage device with the following command, where 3.12.0 should be replaced with the release number of your downloaded ISO and /dev/sdx should be replaced with the drive letter of your USB:

dd if=alpine-xen-3.12.0-x86_64.iso of=/dev/sdx

Installation

Now boot from your CD or USB, and type 'root' when prompted for a username. After you have logged in run setup-xen-dom0, then continue with a standard Alpine installation until you get to the prompt asking to choose your network card. What you'll want to do is select what is to be your internet-facing interface, and when asked to bridge it type 'yes'. Then you can configure the networking settings of your bridge device, br0, as you would have configured your internet-facing interface.

Note: You cannot bridge a WiFi interface in the automatic installation script due to incompatible protocols. Make sure you pick an ethernet interface for this.

Now continue with your installation to disk until you reach the 'reboot' prompt. There are a few more things to do before you can boot without errors:

# xen-hypervisor isn't installed by default with Xen so we must install it manually
apk add xen-hypervisor
apk add bridge

Now you can safely reboot after removing your install medium, making sure to pick the Alpine Linux v3.12, with Xen 4.13.1 and Linux lts boot option in your GRUB menu, with 3.12 and 4.13.1 replaced with your Linux and Xen version numbers, respectively.

After this, enable the Alpine community repository and install the firmware to be used for Xen's virtual machines:

apk add seabios ovmf

Now you are ready to configure GRUB.

Existing installation

First you must enable the Alpine community repository, then install Xen and the seabios (BIOS) and ovmf (UEFI) firmwares for its virtual machines.

# apk add xen xen-hypervisor seabios ovmf

This will install Xen Hypervisor, xl cli command and all the required packages. The next step is to modify your GRUB configuration to properly boot Xen.

The next step is to load the necessary kernel modules for Xen, we will add them to /etc/modules, so they will be loaded automatically on boot:

echo "xen-netback" >> /etc/modules
echo "xen-blkback" >> /etc/modules
echo "tun" >> /etc/modules

Then lastly we add the Xen daemons to the default runlevel.

rc-update add xenconsoled
rc-update add xendomains
rc-update add xenqemu
rc-update add xenstored

Now reboot.

GRUB configuration

Once running a Xen kernel we will need to edit its command-line options and enable the setting of a default GRUB entry by inserting this at the bottom of /etc/default/grub:

Contents of /etc/default/grub

# We need to set the amount of RAM we allocate to our Dom0 Alpine install so that # our future virtual machines are left with enough memory. GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=1024M,max:1024M" GRUB_DEFAULT="saved" GRUB_SAVEDEFAULT="true"

You can replace 1024M with the amount of memory you want to allocate to your Dom0 operating system. After this you need to run the following:

grub-mkconfig -o /boot/grub/grub.cfg
grub-set-default "$(grep ^menuentry /boot/grub/grub.cfg | grep Xen | cut -d \' -f 2 | head -1)"

What this does is set your default entry in GRUB to the first entry containing 'Xen'. Run this every time you upgrade Alpine or Xen.

Loop Devices

If you plan to use more than 8 DomU's, you may need to increase the amount of loop-devices in your Dom0.

In Alpine Linux, you will need to add the max_loop option to the loop module, then add the loop module to your initramfs.

Start by populating /etc/modprobe.d/loop.conf with the module options:

# touch /etc/modprobe.d/loop.conf
# echo "options loop max_loop=32" > /etc/modprobe.d/loop.conf

Now reflect the module options in the initramfs:

# mkinitfs
# reboot

See also