[[PageOutline]]
= How to Setup an MF/PL Xen server =

This document describes how to set up a debian Xen dom0 with the associated hypervisor for a standard May First/People Link server.  It assumes you're starting with a minimal stock debian install.

== Install the hypervisor ==
 * Install with (change the version number of xen-linux-system-2.6.18-6-xen-686 to match the latest version in debian stable; also: on amd64 machines you don't libc6-xen):
{{{
aptitude install xen-hypervisor xen-linux-system-2.6.18-6-xen-686 libc6-xen
}}}
 * limit the dom0 to 128M of RAM, and make sure both the hypervisor and dom0 kernel use the serial console.  A convenient way to do this on debian is to edit `/boot/grub/menu.lst` so that the following lines are contained within the `AUTOMAGIC KERNELS LIST` section:
{{{
## Xen hypervisor options to use with the default Xen boot option
# xenhopt=dom0_mem=131072 com1=115200,8n1

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0 console=ttyS0,115200n8

}}}
 * run `update-grub` and reboot

== Set up the dom0's network environment ==
 * Install `bridge-utils`:
{{{
aptitude install bridge-utils
}}}
 * Tell Xen to bridge the primary network interface across all domUs -- you can do this by applying the following diff to `/etc/xen/xend-config.sxp`:
{{{
--- xend-config.sxp.orig        2008-03-13 11:23:56.000000000 -0400
+++ xend-config.sxp     2008-03-13 17:40:57.000000000 -0400
@@ -68,7 +68,7 @@
 #
 # use
 #
-# (network-script network-bridge)
+(network-script network-bridge)
 #
 # Your default ethernet device is used as the outgoing interface, by default.
 # To use a different one (e.g. eth1) use
@@ -84,7 +84,7 @@
 # two fake interfaces per guest domain.  To do things like this, write
 # yourself a wrapper script, and call network-bridge from it, as appropriate.
 #
-(network-script network-dummy)
+#(network-script network-dummy)

 # The script used to control virtual interfaces.  This can be overridden on a
 # per-vif basis when creating a domain or a configuring a new vif.  The
}}}
 * Restart xen
{{{
/etc/init.d/xend restart
}}}

== Prepare for convenient domU creation and maintenance ==
 * install `xen-tools`:
{{{
aptitude install xen-tools
}}}
 * Edit `/etc/xen-tools/xen-tools.conf` to adjust for three different things:
  * new domUs should be created with `debootstrap`, since we want debian domUs
  * domU block devices should be pulled from the primary volume group of the domU
  * domUs should use the same kernel as the dom0.
 Here's the example diff from `gramsci`: 
{{{
0 gramsci:/etc/xen-tools# diff -u xen-tools.conf.orig xen-tools.conf
--- xen-tools.conf.orig 2007-05-27 19:59:38.000000000 -0400
+++ xen-tools.conf      2007-05-27 20:01:15.000000000 -0400
@@ -35,6 +35,7 @@
#
##
# lvm = skx-vg
+lvm = vg_gramsci0


#
@@ -61,7 +62,7 @@
##
#
# copy = /path/to/pristine/image
-# debootstrap = 1
+debootstrap = 1
# rpmstrap = 1
# tar = /path/to/img.tar
#
@@ -95,7 +96,7 @@
swap   = 128Mb    # Swap size
# noswap = 1      # Don't use swap at all for the new system.
fs     = ext3     # use the EXT3 filesystem for the disk image.
-dist   = sarge    # Default distribution to install.
+dist   = etch     # Default distribution to install.
image  = sparse   # Specify sparse vs. full disk images.

#
@@ -154,8 +155,8 @@
#
# Default kernel and ramdisk to use for the virtual servers
#
-kernel = /boot/vmlinuz-2.6.16-2-xen-686
-initrd = /boot/initrd.img-2.6.16-2-xen-686
+kernel = /boot/vmlinuz-2.6.18-6-xen-686
+initrd = /boot/initrd.img-2.6.18-6-xen-686

#
#  The architecture to use when using debootstrap or rpmstrap.
1 gramsci:/etc/xen-tools#
}}}

 * make sure there's enough room in the dom0's filesystem for the domUs to all have their state saved to disk -- this is what happens at a normal shutdown when `/etc/init.d/xendomains stop` gets invoked.  In particular, the domU state gets stored in `/var/lib/xen/save`, and the size of the state files is roughly the size of the memory (plus a little bit extra for the state of the processors).  A decent rule of thumb is to allocate the total size of physical memory + 10% for a separate partition on `/var/lib/xen`.  Here's the situation on fred for example:
{{{
0 fred:~# xm info | grep ^total_memory
total_memory           : 8188
0 fred:~# df -h /var/lib/xen
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_fred0-fred_var.lib.xen
                      8.9G  149M  8.3G   2% /var/lib/xen
0 fred:~# 
}}}