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== Concise instructions for installing a CentOS VM on Xen ==

Before you begin, please read this entire guide and visit the other links to make sure this method (using rpmstrap) is what you prefer. The other way involves the use of yum's --installroot option and rpm's --root option.

* http://lists.xensource.com/archives/html/xen-users/2005-04/msg00329.html
* http://wiki.sisuite.org/BuildingLinuxChroots

Prepare your storage. You can use partitions, LVM volumes or simple file-based images. I choose file-based for the flexibility.

Choosing a suitably large partition (/usr) I linked it into /opt/xen
  mkdir /usr/xen
  ln -s /usr/xen /opt/xen

Prepare file-based image (note: this is a meager setup of 1GB root / and 128MB swap, you'll likely want much more for a real-world VM)
  mkdir -p /opt/xen/domains/vm02
  cd /opt/xen/domains/vm02
  dd if=/dev/zero of=diskimage bs=1024k count=1024
  dd if=/dev/zero of=swapimage bs=1024k count=128
  mkfs.ext3 diskimage
  mkswap swapimage
  mkdir /mnt/disk
  mount -o loop diskimage /mnt/disk

Alternatively, you may want to use LVM to more flexibly manage your virtual disks. In this example /dev/sdb1 is an available (empty) SCSI disk device partition.
  pvcreate /dev/sdb1
  vgcreate vg01 /dev/sdb1
  # Create an 8GB partition for /
  lvcreate -L 8192 -nvol01 vg01 
  # Create a 512M partition for swap
  lvcreate -L 512 -nvol02 vg01
  mkfs.ext3 /dev/vg01/vol01
  mkswap /dev/vg01/vol02
  mkdir /mnt/disk
  mount /dev/vg01/vol01 /mnt/disk

Now setup prepare a few things, an empty fstab to appease some RPMs, a resolv.conf and mounted proc filesystem.
  cd /mnt/disk
  mkdir -p etc
  touch etc/fstab
  cp /etc/resolv.conf etc/
  mkdir proc
  mount -t proc proc ./proc

You will need the rpmstrap program. See http://hackers.progeny.com/~sam/rpmstrap/releases/
The latest release support centos3, centos4 and quite a few other distros such as fedora!
  cd /tmp/
  wget http://rpmstrap.pimpscript.net/releases/rpmstrap-0.5.2.tar.bz2
  tar xjvf rpmstrap-0.5.2.tar.bz2
  cd rpmstrap-0.5.2
  ./install.sh

In this example, we bootstrap a [http://www.centos.org/ centos4.3] system into place. It is easy enough to replace centos4.3 with centos4 or even centos3.

http://mark.foster.cc/image/icons/important.gif /tmp/centos4-rpms should NOT exist or your downloaded rpms will go into an unexpected subfolder.

http://mark.foster.cc/image/icons/info.gif You will need the latest Centos 4.3 rpmstrap file 
http://svn.samhart.net/rpmstrap/trunk/lib/scripts/. Download the script that do you need.

 wget 'http://svn.samhart.net/rpmstrap/trunk/lib/scripts/centos4'
 mv centos4 /usr/lib/rpmstrap/scripts/centos43

Now proceed with the rpmstrap process.
  cd /
  mkdir /tmp/centos4-rpms 
  mkdir /var/lib/rpm
  rpmstrap --verbose --download-only centos43 /tmp/centos4-rpms 
  rpm --root /mnt/disk --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-4
  rpmstrap --verbose --local-source /tmp/centos4-rpms/rpmstrap*/ centos43 /mnt/disk

http://mark.foster.cc/image/icons/important.gif I get a nasty error here...
  rpmstrap: debug: Installing glibc-common-2.3.4-2.19.i386.rpm to /mnt/disk...
  error: %post(glibc-common-2.3.4-2.19.i386) scriptlet failed, exit status 255

To fix, I disabled selinux as per http://trac.samhart.net/trac/ticket/24
and also put selinux=0 in the grub.conf kernel line ... rebooted then made sure that proc was mounted.

http://mark.foster.cc/image/icons/important.gif I get this nasty error here...
  error: can't create transaction lock on /mnt/disk/var/lock/rpm/transaction

To fix, I created the /mnt/disk/var/lock/rpm directory and continued installation with:
  mkdir -p /mnt/disk/var/lock/rpm
  rpm --root /mnt/disk --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-4
  rpmstrap --verbose --local-source /tmp/centos4-rpms/rpmstrap*/ centos43 /mnt/disk

Continue install:
  chroot /mnt/disk /bin/bash
  cd /etc
  nano fstab

Create an fstab file. You'll have to use cat or nano because the rpmstrap centos4 suite does not install vi.

  /dev/sdb1     /     ext3     errors=remount-ro     0     1
  /dev/sdb2     none  swap     sw                    0     0
  proc          /proc proc     defaults              0     0
  none          /dev/pts       devpts gid=5,mode=620 0     0
  none          /dev/shm       tmpfs  defaults       0     0 

Make some necessary devices
  cd /dev
  MAKEDEV null console zero random hda hdb sda sdb

Logout and unmount <tt>/mnt/disk</tt>
  exit
  cd /mnt/disk
  umount proc
  umount /mnt/disk

Now you can setup the VM configuration in '''/etc/xen/vm02'''

  kernel = "/boot/vmlinuz-2.6.11-xenU"
  memory = 96
  name = "vm02"
  dhcp = "dhcp"
  disk = [ 'file:/opt/xen/domains/vm02/diskimage,sdb1,w','file:/opt/xen/domains/vm02/swapimage,sdb2,w' ]
  # or if you use LVM
  # disk = [ 'phy:/dev/vg01/vol01,sdb1,w','phy:/dev/vg01/vol02,sdb2,w' ]
  root = "/dev/sdb1 ro"
  

Start it (-c also puts you into the console so you can watch it boot)
  xm create -c vm02
  > Using config file "/etc/xen/vm02".
  > Started domain vm02, console on port 9602

You can use CTL-] to break out of the console, just like telnet.

Login as root, update the system and set the root password.
  mv /lib/tls /lib/tls.disabled
  rpm --import /usr/share/doc/centos-release-4/RPM-GPG-KEY
  yum update
  yum install passwd
  passwd root
  reboot




[[Category:Linux]]
[[Category:Virtualization]]
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