Ubuntu Gutsy template creation

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This article summarizes the experience of creating Ubunty Gutsy Gibbon (a.k.a. 7.10) template for OpenVZ.

Template creation is based on debootstrap, and the procedure is similar to Debian template creation, but it differs in some subtle details.

Contents

[edit] Prerequisites

[edit] debootstrap

You have to have a debootstrap working for Gutsy, i.e. you should have

  • debootstrap and its dependencies
  • /usr/lib/debootstrap/scripts/gutsy file

The simplest way to have it all is to work on an Ubuntu Gutsy system (be it on a real machine or inside a container). If you don't have debootstrap installed, this is the command to install it:

# apt-get install debootstrap

On a Gentoo Linux, debootstrap is also available, this is how you can install it:

# emerge \>=debootstrap-1.0.0

Note you need at least version 1.0.0, since earlier versions do not have Ubuntu scripts. So, possible you will first need to add it to package.keywords, like this:

# echo dev-util/debootstrap >> /etc/portage.package.keywords

On a Fedora system (at least Fedora 8, not sure about earlier versions):

# yum install debootstrap

[edit] vzctl

You need vzctl-3.0.22 or later to work with Ubuntu Gutsy Gibbon. If vzctl-3.0.18 or earlier is used, you will not be able to run your Ubuntu Gutsy container. See OpenVZ Bug #662 for details.

Note: Older versions of vzctl are working if you install sysvinit (which will remove upstart). The only problem I had was the network did not start, so I added "/etc/init.d/networking restart" to /etc/re.local.

[edit] Creating template

[edit] Running debootstrap

Create a working directory:

[HW]# mkdir gutsy-chroot

Run debootstrap to install a minimal Ubunty Gutsy system into that directory:

[HW]# debootstrap [--arch ARCH] gutsy gutsy-chroot 

If ARCH of CT0 is equal to container, you can skip the --arch option, but if you need to build an OS template for another ARCH, specify it explicitly:

  • for AMD64/x86_64, use amd64
  • for IA64, use ia64
  • for i386 i386

[edit] Preparing/starting a container

Now then you have an installation created by debootstrap, you can run it as a container. In the example below CT ID of 777 is used; of course you can use any other non-allocated ID.

Yellowpin.svg Note: an alternative way is using chroot instead of running a container. This is not recommended because of security concerns.

[edit] Moving installation to container private area

You should move the contents of gutsy-chroot directory into new container private area, like this:

# mv gutsy-chroot /vz/private/777

[edit] Setting container config

An initial config for the container is needed:

# vzctl set 777 --applyconfig vps.basic --save

[edit] Setting container OSTEMPLATE

Also, we need OSTEMPLATE to be set in container configuration file, for the vzctl to work properly.

# echo "OSTEMPLATE=ubuntu-7.10" >> /etc/vz/conf/777.conf

[edit] Setting container IP address

For the container to be able to download updates from the Internet, we need a valid IP address for it:

# vzctl set 777 --ipadd x.x.x.x --save
Yellowpin.svg Note: if you use private IP for the container, you have to set up NAT as described in Using NAT for container with private IPs.

[edit] Setting DNS server for the container

For the container to be able to download updates from the Internet, we also need to specify a DNS for it:

# vzctl set 777 --nameserver x.x.x.x --save

Instead of x.x.x.x, specify the same IP that you have in your /etc/resolv.conf.

[edit] Starting container

Now start the container:

# vzctl start 777

[edit] Modify the installation

You have to do some things in order to modify the installation to better suit the environment it will be run in (i.e. a container).

First, enter a container:

# vzctl enter 777
Warning.svg Warning: Do not run the commands below on the hardware node, they are only to be run within the container!

[edit] Remove unneeded packages

Some packages does not make sense in a container, or are really optional. Remove those:

[container]# dpkg -P ubuntu-minimal wpasupplicant wireless-tools \
  udev pcmciautils initramfs-tools volumeid console-setup \
  xkb-data usbutils mii-diag alsa-base alsa-utils ethtool \
  module-init-tools linux-sound-base console-tools \
  console-terminus busybox-initramfs libvolume-id0 \
  ntpdate eject libasound2 pciutils tasksel tasksel-data \
  laptop-detect
Yellowpin.svg Note: On removing the deb-package "module-init-tools", a fake-modprobe is needed for IPv6 addresses, see below!

Note that the above list of packages may be too extensive. Say, if you want to use tasksel tool, do not remove it — but then you have to let laptop-detect stay.

Clean up after udev:

[container]# rm -fr /lib/udev

[edit] Disable getty

On a usual Linux system, getty is running on a virtual terminals, which a container does not have. So, having getty running doesn't make sense; more to say, it complains it can not open terminal device and this clutters the logs.

So, first of all we stop all getty processes:

[container]# initctl stop tty{1,2,3,4,5,6}

Next, we disable running getty. This can be done in two ways:

First way:

[container]# rm /etc/event.d/tty*

Second way:

[container]# dpkg -P system-services

Second way can be dangerous for future versions of system-services, but it's OK for now since the only service they carry is running gettys.

[edit] Set sane permissions for /root directory

[container]# chmod 700 /root

[edit] Disable root login

[container]# usermod -L root

[edit] "fake-modprobe" needed for IPv6 addresses

[container]# ln -s /bin/true /sbin/modprobe

On setup IPv6, the command "modprobe -Q IPv6" is called, which fails without the "fake-modprobe"

[edit] Get new security updates

[container]# apt-get update && apt-get upgrade

This didn't show anything for me, but might do something in the future.

[edit] Install some more packages

[container]# apt-get install ssh quota

Feel free to add packages which you want to have in a default template to this command.

[edit] Fix SSH host keys

This is only useful if you installed SSH above. Each individual container should have its own pair of SSH host keys. The code below will wipe out the existing SSH keys and instruct the newly-created container to create new SSH keys on first boot.

rm -f /etc/ssh/ssh_host_*
cat << EOF > /etc/rc2.d/S15ssh_gen_host_keys
#!/bin/sh
ssh-keygen -f /etc/ssh/ssh_host_rsa_key -t rsa -N ''
ssh-keygen -f /etc/ssh/ssh_host_dsa_key -t dsa -N ''
rm -f \$0
EOF
chmod a+x /etc/rc2.d/S15ssh_gen_host_keys

[edit] Disable sync() for syslog

Turn off doing sync() on every write for syslog's log files, to improve overall I/O performance. In Ubuntu this is already done for most log files and levels, so you can omit this step if you know what you are doing.

[container]# sed -i -e 's@\([[:space:]]\)\(/var/log/\)@\1-\2@' /etc/syslog.conf

[edit] Fix /etc/mtab

Link /etc/mtab to /proc/mounts, so df and friends will work:

[container]# rm -f /etc/mtab
[container]# ln -s /proc/mounts /etc/mtab

After that, it would make sense to disable mtab.sh script which messes with /etc/mtab:

[container]# update-rc.d -f mtab.sh remove

[edit] Disable some services

In most of the cases you don't want klogd to run -- the only exception is if you configure iptables to log some events -- so you can disable it:

[container]# update-rc.d -f klogd remove

[edit] Hostname

Set proper hostname:

[container]# echo "localhost" > /etc/hostname

[edit] Set /etc/hosts

[container]# echo "127.0.0.1 localhost.localdomain localhost" > /etc/hosts

[edit] Add ptys to /dev

This is needed in case /dev/pts will not me mounted after container start. In case /dev/ttyp* and /dev/ptyp* files are present, and LEGACY_PTYS support is enabled in the kernel, vzctl will still be able to enter container.

[container]# cd /dev && /sbin/MAKEDEV ptyp

[edit] Remove nameserver(s)

Remove DNS entries:

[container]# > /etc/resolv.conf

[edit] Clean packages

After installing packages, you'll have some junk packages laying around in your cache. Since you don't want your template to have those, this command will wipe them out.

[container]# apt-get clean

[edit] Cleaning up log files

[container]# cd /var/log
[container]# > messages; > auth.log; > kern.log; > bootstrap.log
[container]# > dpkg.log; > syslog; > daemon.log; > apt/term.log
[container]# rm -f *.0 *.1

[edit] Anything else?

Think of what else could be done to better suit your needs.

[edit] Exit from the container

Now everything is done. Exit from the template and go back to the hardware node.

[container]# exit

[edit] Preparing for and packing template cache

The following commands are to be run in the host system (i.e. not inside a container).

We don't need an IP for the container anymore, and we definitely do not need it in template cache, so remove it:

[HW]# vzctl set 777 --ipdel all --save

Stop the container:

[HW]# vzctl stop 777

Change dir to the container private:

[HW]# cd /vz/private/777

Now create a cached OS tarball. In the command below, you'll want to replace <arch> with your architecture (i386, amd64, ia64, etc). Note the space and the dot at the end of the command.

[HW]# tar --numeric-owner -czf /vz/template/cache/ubuntu-7.10-<arch>-minimal.tar.gz .

Look at the resulting tarball to see its size is sane:

# ls -lh /vz/template/cache
-rw-r--r-- 1 root root   53M Nov 15 12:40 ubuntu-7.10-i386-minimal.tar.gz

[edit] Testing template cache

We can now create a container based on the just-created template cache. Be sure to change i386 to your architecture just like you did when you named the tarball above.

[HW]# vzctl create 123456 --ostemplate ubuntu-7.10-<arch>-minimal

Now make sure that your new container it works:

[HW]# vzctl start 123456
[HW]# vzctl exec 123456 ps axf

You should see that a few processes are running.

Other tests that could be done are:

[HW]# vzctl enter 123456
[container]# ps axf
[container]# mount
[container]# dpkg -l
[container]# logout
[HW]#

Feel free to do more tests.

[edit] Final cleanup

Stop and remove the test container you just created:

[HW]# vzctl stop 123456
[HW]# vzctl destroy 123456
[HW]# rm -f /etc/vz/conf/123456.conf.destroyed

Finally, let's remove the container we used for OS template cache creation:

[HW]# vzctl destroy 777
[HW]# rm -f /etc/vz/conf/777.conf.destroyed

[edit] Updating the template cache

See Updating Ubuntu template

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