michaelanthoni.com

So the other day I noticed my /var partition filled up in on my Dom0. One of the symtoms was not allowing me to start up any more DomU’s. So I tracked the disk usage to /var/lib/xen/save. There were files of each of my running dom u’s here which were the culprit.

Apparently, on a Debian system, upon a shutdown of the Dom0, Xen attempts to take a snapshot of the running DomU instead of issuing a shutdown command across all the DomU’s. This snapshot is stored in - you guessed it - /var/lib/xen/save - and is controlled by the XENDOMAINS_SAVE parameter in /etc/default/xendomains. In order to disable this future and always execute a shutdown of DomU’s during a shutdown of the Dom0, you can set XENDOMAINS_SAVE=”". The corresponding restore command is controlled by XENDOMAINS_RESTORE parameter. It is also safe to delete these files provided you have a newer instance of the DomU.

After realizing this I changed the path of where the running domains are stored to in case of a shutdown to a partition with sufficient space to hold the running instances. I also set the XENDOMAINS_RESTORE=true.

Thanks to the helpful individuals on the xen-users mailing lists for the info.

Heres a quick little script for automating the creation of Dom-U’s and there corresponding configuration files. Nothing to fancy, but it helps for users who may be unfamiliar with the process or just need to fire up a new Dom-U quickly without going thru an installation process.

This script assumes that when you first build a Dom-U either by d’bootstrapping or windows installation or whatever it may be, you shut the Dom-U down and move the “template” to /home/xen/templates and that your running Dom-U’s are running from /home/xen/domains . Lastly make sure the template configuration file has the <> strings so sed can replace them with your intended variables. This can be extended as you see fit, if you need to change values for networking, kernel, etc… Happy cloning.

./clone.sh

#!/bin/bash

function syntax {
           echo "Syntax: ./clone.sh source_image destination_image memory(mb)"
           echo " where source_image is the name of the directory in this folder                                                              "
           echo "  destination_image is the name of your new DomU "
           echo "  and memory(mb) is the ammount of memory you want to provision                                                              ."
           echo ""
           echo "Example: ./clone.sh debian_etch_x86 v-debian-etch-x 512"
           echo "Example: ./clone.sh winxp_pro_x86 v-winxp-pro-x 512"
}

if [ $1 ]; then
        if [ $2 ]; then
                if [ $3 ]; then
                        echo "Cloning Template $1 to DomU $2 with $3 MB of memor                                                              y."

                        echo "Copyig Disk Images... This will take a few minutes                                                              ..."
                        cp -R /home/xen/templates/$1 /home/xen/domains/$2

                        echo "Creating Configuration file."
                        sed 's/<domU>/'"$2"'/' /home/xen/templates/$1/$1.cfg > /                                                              home/xen/domains/$2/$2.cfg.tmp
                        sed 's/<domU-mem>/'"$3"'/' /home/xen/domains/$2/$2.cfg.t                                                              mp > /home/xen/domains/$2/$2.cfg
                        echo "Cleaning up temporary files..."
                        rm /home/xen/domains/$2/$2.cfg.tmp
                        rm /home/xen/domains/$2/$1.cfg
                        echo "All Done."
                else
                        syntax
                fi
        else
                syntax
        fi
else
        syntax
fi

./template.cfg

kernel = ‘/boot/vmlinuz-2.6.18-5-xen-vserver-amd64′
ramdisk = ‘/boot/initrd.img-2.6.18-5-xen-vserver-amd64′
memory = ‘<domU-mem>’
root = ‘/dev/sda1 ro’
disk = [ ‘file:/home/xen/domains/<domU>/disk.img,sda1,w’,
‘file:/home/xen/domains/<domU>/swap.img,sda2,w’ ]
name = ‘<domU>’
dhcp = ‘dhcp’
vif = [ ” ]
on_poweroff = ‘destroy’
on_reboot = ‘restart’
on_crash = ‘restart’