Xen

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Install of Xen Source (paravirtualizer) on Debian Sarge

Install of Xen

I used the binary distribution of xen 2.0.7 altough I also tried to compile a custom kernel as I had question about hardware support which I didn't find in the pached kernel. I posted it on the xen-users ML, no answer yet.

To be documented (note are offline)

update grub's menu.lst and rename /lib/tls in /lib/tls.disabled as it is not natively supported by xen and need a real emulation which will reduced performance a lot (this step has to be done in all unpriviledged guest too (enforce it ?)

Xen topology

Xen uses a para-vitualisation hypervisor running in ring 0 (x86 CPU).
The kernel runs in ring1 and user-app in ring3.
Hardware management is done inside a privileged kernel named domain0 (guest OSes are called domainX).
Xen uses a xend daemon in dom0 to manage network, cpu, memory and export standard devices to the domX guest (generally eth0, a root fs and some swap space).
xend also manages bridging the real eth0 and sets up a xen-br0 device
xend is not running by default on dom0 at startup

Invoking 


update-rc.d xend defaults 80

does the job as dmesg says 


eth0: link up, 100Mbps, full-duplex, lpa 0x45E1
eth0: Promiscuous mode enabled.
device eth0 entered promiscuous mode
xen-br0: port 1(eth0) entering learning state
xen-br0: topology change detected, propagating
xen-br0: port 1(eth0) entering forwarding state

and 


ns1:/home/skycode# xm list
Name              Id  Mem(MB)  CPU  State  Time(s)  Console
Domain-0           0      251    0  r----     13.0

So domain0 is now running (in a small 4Go partition, the rest of the disk is left for LVM)

setting-up LVM for the hosts 


apt-get install lvm2

Partitioning the free space left on the disk 


ns1:/home/skycode# fdisk /dev/hda

The number of cylinders for this disk is set to 9964.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/hda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1               1         486     3903763+  83  Linux
/dev/hda2   *         487         608      979965   82  Linux swap / Solaris

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 3
First cylinder (609-9964, default 609):
Using default value 609
Last cylinder or +size or +sizeM or +sizeK (609-9964, default 9964):
Using default value 9964

Command (m for help): p

Disk /dev/hda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1               1         486     3903763+  83  Linux
/dev/hda2   *         487         608      979965   82  Linux swap / Solaris
/dev/hda3             609        9964    75152070   83  Linux

Command (m for help): t
Partition number (1-4): 3
Hex code (type L to list codes): 8e
Changed system type of partition 3 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/hda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1               1         486     3903763+  83  Linux
/dev/hda2   *         487         608      979965   82  Linux swap / Solaris
/dev/hda3             609        9964    75152070   8e  Linux LVM

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

reboot :-)

Create physical volumes 

pvcreate /dev/hda3</pre>
add it to a volume groupvgcreate volg0 /dev/hda3
  Volume group "volg0" successfully created

Create 2 partition (root and swap for the first test domain) 

ns1:/home/skycode# lvcreate -L 2G -n test0root volg0
  Logical volume "test0root" created
ns1:/home/skycode# lvcreate -L 256M -n test0swap volg0
  Logical volume "test0swap" created
ns1:/home/skycode# mke2fs -j /dev/volg0/test0root
mke2fs 1.37 (21-Mar-2005)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
262144 inodes, 524288 blocks
26214 blocks (5.00%) reserved for the super user
First data block=0
16 block groups
32768 blocks per group, 32768 fragments per group
16384 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912

Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 38 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
ns1:/home/skycode# mkswap /dev/volg0/test0swap
Setting up swapspace version 1, size = 268431 kB
no label, UUID=451e4e02-5d9f-4524-922a-c7432e844b21
ns1:/home/skycode#

Install a minimal debian sarge with debootstrap and back-it up for futur installs 


ns1:/home/skycode# debootstrap --arch i386 sarge /mnt/xen_install http://www.uk.debian.org/debian/
Lots of output ...
ns1:/home/skycode# cd /mnt/xen_install/
ns1:/mnt/xen_install# mkdir /var/xen_images
ns1:/mnt/xen_install# tar -jpcf /var/xen_images/debian-sarge-pre-config.tar.bz2 .

Now it's config time

fstab 

 ns1:/mnt/xen_install/etc# cat fstab
 # Fstab for virtual domain  root is exported by dom0 as sda1
 # And swap as sda2
 #
 # Exxoss - brewed on March 24th 2006
 
 /dev/sda1       /       ext3    defaults        0       1
 /dev/sda2       swap    swap    defaults        0       0
 proc            /proc   proc    defaults        0       0

hostname 


ns1:/mnt/xen_install/etc# cat hostname
test0

hosts 


ns1:/mnt/xen_install/etc# cat hosts
127.0.0.1       localhost

Network interfaces 

 ns1:/mnt/xen_install/etc# cat network/interfaces
 # Used by ifup(8) and ifdown(8). See the interfaces(5) manpage or
 # /usr/share/doc/ifupdown/examples for more information.
 
 #
 # Exxoss - brewed march 24th 2006
 # virtual domain interface config file
 # dom0 export a NIC as eth0
 #
 
 # Loopback device
 auto lo
 iface lo inet loopback
 
 # eth0 device
 auto eth0
 iface eth0 inet static
         address 192.168.1.111
         netmask 255.255.255.0
         gateway 192.168.1.1

sources.list 

 ns1:/mnt/xen_install/etc# cat apt/sources.list
 #deb file:///cdrom/ sarge main
 
 deb http://ftp.debian.skynet.be/ftp/debian/ stable main contrib
deb-src http://ftp.debian.skynet.be/ftp/debian/ stable main contrib

deb http://security.debian.org/ stable/updates main contrib

lib/tls (again) 


ns1:/mnt/xen_install/etc# cd ..
ns1:/mnt/xen_install# mv lib/tls lib/tls.disabled

umount /mnt/xen_install

Configure xen for the new dom

in /etc/xen/test0.conf 

 ns1:/etc/xen# cat /etc/xen/test0.conf
 #
 # Test Xen domU config file
 #
 
 name="test0"
 memory=256
 kernel="/boot/vmlinuz-2.6-xenU"
 nics=1
 disk=[%27phy%3Avolg0 'phy:volg0][%27phy%3Avolg0/test0root%2Csda1%2Cw%27%2C%20%27phy%3Avolg0 /test0root,sda1,w', 'phy:volg0]test0swap,sda2,w'[%27phy%3Avolg0/test0root%2Csda1%2Cw%27%2C%20%27phy%3Avolg0/test0swap%2Csda2%2Cw%27?action=create ?]
root="/dev/sda1 ro"
ns1:/etc/xen#

xm (xend ctl tool) commands

Create a new domain <pre>xm create /etc/xen/test0.conf -c</pre>

Logout from console to dom0 : Ctrl-]

list runing domains <pre> xm list </pre>

stop a runing domain <pre> xm shutdown domain </pre>

Tests

what happens if I try to allocate more meory to a domain than I have available

it fail rturning an error code (12)

set the cpu time limit

use cpu_weight in config file like cpu_weight=5

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