Introduction

The process of customizing or "remastering" Ubuntu installation CDs is not especially complex, but it is a little tedious and finicky.

The Ubuntu installation CD (since Ubuntu 6.06, the 'alternative install' or 'server' CD) has three main parts: a boot-loader (ISOLINUX on AMD64/x86 systems, yaboot on PowerPC) and its configuration (which starts everything up); debian-installer (also known as d-i, which in this case is really a specialized miniature Ubuntu system); and a Debian-style repository structure, which is what takes up disk space in the directories "pool" and "dists". Building a new CD may involve modifications to all three parts.

This page shows a simple recipe for customizing the CD. It assumes that you copy the contents of the installation CD to /opt/cd-image/ on your local system and create a couple of other dirs in /opt/. Modify as needed.

You might speed up the development cycle by using a virtual Ubuntu session, for example, using VirtualBox. You can then use the .ISO file to test rather than burning a CD. If you do, please note that you need to perform ALL operations described here on the GUEST system. Note that with VirtualBox, during an installation (Host key)-F4 will display the installation output and (Host key)-F1 will return you to the general status screen. Note that the host key is set to the right Ctrl key by default.

This guide is for the 'Alternative Install' or 'Server Install' CDs. There is a page referring to customization of the Desktop (Live) CD, and another guide on how to create a Live CD without using an existing CD at all.

Get the Alternate CD image

Use the "complete list of download mirrors" http://www.ubuntu.com/getubuntu/downloadmirrors#mirrors Then select correct Ubuntu version and from the next page start downloading the .iso file from "Alternate install CD" section. Server version should also work.

Copy the CD to your hard drive

Copy the entire installation CD to a directory on your hard drive. This guide will assume your CD image is in /opt/cd-image/, but you can put it wherever you like. It will take around 1GB of hard drive space.

If you have an ISO file, you can mount it and copy files out of it without burning it to CD: mount -o loop /path/to/iso /some/mountpoint. Use "Gmount-iso" program for a GUI method of mounting iso files. You can also try "ISO Master" to access the iso file directly without mounting.

You can use rsync to copy the CD:

rsync -av /cdrom/ /opt/cd-image

or just

mkdir -p /opt/cd-image
cp -rT /cdrom /opt/cd-image

Note: the -p option for mkdir creates the leadin directories if they don't already exist. In this example, /opt is created if it doesn't already exist.

Be sure to catch the folder .disk - if you try and copy /cdrom/*, it will ignore the .disk folder, as Bash expands the * to mean "everything it can see".

If you use a filemanager program like Nautilus, be sure to launch it with "gksu nautilus" and mark "Show Hidden Files" from "View" menu or you miss some important files. After the copy is done, change file ownership from "root" if you don't plan to do the rest of the work with sudo.

Modify installer behaviour using a Preseed file

When the CD boots up, a Linux kernel is started and the installation tasks are initiated. The installer's default behavior can be modified through the use of a "preseed" file, which feeds d-i answers to questions normally asked by debconf, or in other contexts. If you look in the preseed folder in the install CD, you'll see that certain options (e.g. "server", "expert", "oem") already have preseed files assigned to them. The installation guide has a detailed appendix on preseeding.

Suppose you are installing Ubuntu on a bunch of identical computers, and you already know the answers to certain questions (what country and time zone you're in, what keyboard you have, how the network should be configured, how you want to partition the hard disk, etc). You can "preseed" the answers to these questions in a very simple configuration file.

Changing isolinux.cfg to identify your preseed

We will create a preseed file called 'firewall.seed', which will live in the /preseed folder of the CD-ROM. We tell d-i where to find this file by modifying the boot-loader configuration file, located in isolinux/isolinux.cfg (or in 8.10 or later, isolinux/text.cfg), to pass appropriate parameters on the kernel command line. In /opt/cd-image/isolinux/isolinux.cfg, add a new section labeled like this:

LABEL firewall
  menu label ^Firewall installation
  kernel /install/vmlinuz
  append  preseed/file=/cdrom/preseed/firewall.seed debian-installer/locale=en_NZ console-setup/layoutcode=us initrd=/install/initrd.gz ramdisk_size=16384 root=/dev/ram rw quiet --

If you want to set the default selected menu item to your custom seed, change the DEFAULT line to read 'DEFAULT firewall'.

For totally automatic installation with a predefined language (in this example, Estonian), you need to add some more parameters:

LABEL firewall
  menu label ^Firewall installation (Estonian)
  kernel /install/vmlinuz
  append  file=/cdrom/preseed/firewall.seed debian-installer/locale=et_EE console-setup/layoutcode=et localechooser/translation/warn-light=true localechooser/translation/warn-severe=true initrd=/install/initrd.gz ramdisk_size=16384 root=/dev/ram rw quiet
 --

To make the installer autochoose the default option and start installing after a timeout, add this line to isolinux/isolinux.cfg (in all versions).

timeout 10

Timeout values are in tenths of a second, therefore a timeout value of 10 is equal to one second.

You must specify a locale and keyboard on the command line, as these questions are asked before the seed is loaded. You can also set DEBCONF_PRIORITY here to ensure you don't see any unnecessary debconf questions.

(On Ubuntu 6.06 and older, use kbd-chooser/method=us rather than console-setup/layoutcode=us.)

Writing the preseed file

A preseed file has 4 fields per line:

1. identity of the program which will pick up this command
2. name of the variable whose value will be passed
3. variable type
4. value of variable

It looks something like this (from the default ubuntu-server.seed on the 6.06 CD):

• # Always install the server kernel.
  d-i     base-installer/kernel/override-image    string linux-server
  # Don't install usplash.
  d-i     base-installer/kernel/linux/extra-packages-2.6  string
  # Desktop system not installed; don't waste time and disk space copying it.
  d-i     archive-copier/desktop-task     string ubuntu-standard
  d-i     archive-copier/ship-task        string
  # Only install the standard system and language packs.
  d-i     pkgsel/install-pattern  string ~t^ubuntu-standard$
  d-i     pkgsel/language-pack-patterns   string
  # No language support packages.
  d-i     pkgsel/install-language-support boolean false

The version of this file on some Breezy CD images was buggy: it set base-config/package-selection to "~tubuntu-standard" rather than "~t^ubuntu-standard$". Use the new format in preference; the old one will break with Ubuntu 6.06 and newer.)

d-i expects there to be exactly one tab or space between variable type and variable value (any other space is seen as being part of the value)

The easiest way to create a preseed file is to start with an example and modify it:

1. The Ubuntu installation guide (8.04, 9.04, 9.10, 10.04) has examples of many common preseed directives. (Bear in mind that you may need to modify some to work on older versions.)

2. You could check out Debian's wiki page on preseeding the installer - 6.06 and higher are aligned with Etch and newer versions of the Debian installer, although there are some important differences that apply to preseeding.

3. If you can't find the option you're looking for you can generate a comprehensive preseed file based on your own install time choices by using debconf-get-selections

debconf-get-selections usage:

sudo apt-get install debconf-utils    # It is part of the debconf-utils package.
debconf-get-selections --installer > somefile.txt
debconf-get-selections >> somefile.txt

This will output a list of all debconf options you've chosen throughout your install; you can pick options out of this and put them into your preseed file.

debconf-get-selections prints 2 spaces between variable type and variable value. You need to change this to one space before putting the line in a preseed file.

Installing extra packages in your preseed file

base-config has been removed from debian-installer since Ubuntu 6.06.

In Ubuntu 6.06 and older:

d-i     pkgsel/install-pattern          string ~t^ubuntu-standard$|~n^openssh-server$

In Ubuntu 8.04 and newer: (packages may be separated with commas and/or spaces and continued to another line with a back-slash):

d-i     pkgsel/include  string  gstreamer0.10-plugins-base \
 gstreamer0.10-plugins-good \
 gstreamer0.10-plugins-ugly \
 gstreamer0.10-plugins-bad

The installer can not install packages which rely on services that would normally be running in an installed system, but which are not running in the environment of the Debian installer. One example of this would be packages which create or modify a database at installation time, and require a postgresql or mysql server to be running. In this case, you will need to use a postinst script, start the necessary database server in the /target chroot, and then call "apt-install" (if outside the chroot environment) or apt-get (inside the chroot).

Installing language support

A different mechanism is used to install additional languages. Preseed the detailed locale question asked by the installer in expert mode. See the first column of /usr/share/i18n/SUPPORTED for the locale names you can use here. For example, to add support for Bengali and Tamil, use this line:

d-i localechooser/supported-locales multiselect bn_IN, ta_IN

Running a Final Script

You can run a script in the final part of the installation. The following example runs a script that has been copied onto the installation CD in the setup/install folder. This script runs in the target environment, thus can run scripts in any language (e.g. Python or Perl) that has been installed on the target system.

d-i preseed/late_command string chroot /target bash /cdrom/setup/install/settings.sh

The above command may not work on 8.10 or later; to copy the script to the target and then execute it, try this:

d-i preseed/late_command string cp /cdrom/finisher/finisher.sh /target/root/; chroot /target chmod +x /root/finisher.sh; chroot /target bash /root/finisher.sh

Generally, a script run from the seed file via late_command, cannot interact with the user. If you need to interact, there are generally three options:

• Create a custom UDEB that interacts with debconf, and include it with the CD.
• Create a 'firstrun' script that executes the first time the system boots, and disables itself on completion.

• Access debconf directly within your script.

A preseed script run via late_command that attempts to run "chroot /target apt-get ..." (or similar) may run into problems (e.g. file descriptor 3 not found in the postinst stage of some packages, dash being one example). This is caused by your script inheriting environment variables from the already running installer. To solve this, clear the environment variables in your script before calling apt-get:

unset DEBCONF_REDIR
unset DEBCONF_FRONTEND
unset DEBIAN_HAS_FRONTEND
unset DEBIAN_FRONTEND

Modify pool structure to include more packages

Probably the prime motivation to build your own install CDs is to modify which packages are installed; in particular you may want to add some packages to the CD.

The easiest way to do this is to build an 'extras' repository structure, containing only your extra .debs, and merge these into the CD file hierarchy before rebuilding the .ISO image. This guide will step you through how to do this.

This requires you to generate the Packages files that defines what files are in your repository; the Release file that indexes your Packages files, and the signed Release.gpg file, approving the repository as being official.

Create an "Extras" component

The following examples reference Ubuntu 8.04 ("hardy"). Substitute your version where appropriate.

Create directories for your new component (substituting your version where appropriate):

cd /opt/cd-image
mkdir -p dists/hardy/extras/binary-i386/pool/extras/

Put all the extra .debs you want on your CD into pool/extras.

Create the file dists/hardy/extras/binary-i386/Release with the following content:

Archive: hardy
Version: 8.04
Component: extras
Origin: Ubuntu
Label: Ubuntu
Architecture: i386

On the scripts page there is a useful script that will strip out all of the packages from your CD image that are not currently installed. You will need to run apt-ftparchive (below) to generate the Packages file.

Generating a new ubuntu-keyring .deb to sign your CD

In order to sign the Release file, we need to use GPG. The install system will then check the signature against the public keys held in the package ubuntu-keyring. You do not have a private key that matches one of the ones in the shipped ubuntu-keyring, so we need to build a custom version of the ubuntu-keyring package. Install the gnupg package if you do not have it already.

To create a signing key, enter gpg --gen-key. Accept the defaults, (for this use, it is probably OK to use "No expiry"). For your Real Name and E-mail address, you might like to use something like "XXX Signing Key" and "packages@xxx.example.org". Enter an appropriate passphrase.

In another directory (I use /opt/build/), we will download the source for the ubuntu-keyring package, unpack it, add our own GPG key, and rebuild the package. These steps import the 2 Ubuntu public signing keys into your main keyring, then exports them, along with your own public signing key, into a replacement keyring. "YOURKEYID" should be replaced with the 8-digit hexadecimal code that gpg tells you when you do the --list-keys command. "Signing Key Name" is what you used in the previous step, when running gpg --gen-key.

To clarify, below is an example 'gpg --list-keys' response. In this example, "YOURKEYID" immediately follows the '/' on the line beginning with 'pub' (which in this example is '437D05B5'.)

gpg --list-keys
pub   1024D/437D05B5 2006-09-08
uid                  XXX Signing Key <packages@xxx.example.org>
sub   2048g/79164387 2006-09-08

Here is an example, which you will need to customize to suit your own setup:

cd /opt/build
sudo apt-get install fakeroot   # requires the fakeroot package which may not be installed on your system.
apt-get source ubuntu-keyring
cd ubuntu-keyring-2008.03.04/keyrings
gpg --import < ubuntu-archive-keyring.gpg
gpg --list-keys "Signing Key Name"
gpg --export FBB75451 437D05B5 YOURKEYID > ubuntu-archive-keyring.gpg
cd ..    # you are now on ubuntu-keyring-2008.03.04
dpkg-buildpackage -rfakeroot -m"Your Name <your.email@your.host>" -kYOURKEYID
cd ..  # you are now on the directory where you started, in the example, /opt/build
cp ubuntu-keyring*deb /opt/cd-image/pool/main/u/ubuntu-keyring

You will end up with a udeb file for the installer, and a .deb file for the system. Both files need to be copied into the main component of your CD, because the CD will not check the extras directory.

Building the repository with apt-ftparchive

apt-ftparchive builds the Packages and Packages.gz files, needed by the installer. In order to use apt-ftparchive we will need to provide it with some configuration and some index files.

If you will be adding .deb files to pool/universe (eg. customizing xubuntu) you will also need to wget extra.universe and universe files.

We will put the index files in /opt/indices:

mkdir -p /opt/indices /opt/apt-ftparchive
cd /opt/indices/
DIST=hardy
for SUFFIX in extra.main main main.debian-installer restricted restricted.debian-installer; do
  wget http://archive.ubuntu.com/ubuntu/indices/override.$DIST.$SUFFIX
done

Create the files apt-ftparchive-deb.conf, apt-ftparchive-udeb.conf, apt-ftparchive-extras.conf, and release.conf in a directory (/opt/apt-ftparchive), substituting /opt/cd-image/ for the path to your CD image directory, and /opt/indices/ for the location of the index files, if they differ.

The .conf files shown here are sufficient if you are ONLY making changes to .deb files under pool/main and pool/restricted. If you are adding security updates to a Xubuntu customized CD, though, you will be updating .deb files under pool/universe also, so you will need to add lines to apt-ftparchive-deb.conf for universe, similar to the lines shown for main. You will also need to run extraoverride.pl for universe as well as for main - see below.

/opt/apt-ftparchive/apt-ftparchive-deb.conf:

• Dir {
    ArchiveDir "/opt/cd-image/";
  };
  
  TreeDefault {
    Directory "pool/";
  };
  
  BinDirectory "pool/main" {
    Packages "dists/hardy/main/binary-i386/Packages";
    BinOverride "/opt/indices/override.hardy.main";
    ExtraOverride "/opt/indices/override.hardy.extra.main";
  };
  
  BinDirectory "pool/restricted" {
   Packages "dists/hardy/restricted/binary-i386/Packages";
   BinOverride "/opt/indices/override.hardy.restricted";
  };
  
  Default {
    Packages {
      Extensions ".deb";
      Compress ". gzip";
    };
  };
  
  Contents {
    Compress "gzip";
  };

The ExtraOverride component above is needed to add the Task: line to main packages, referenced from the preseed file with ~t<task name>. This is not supplied - but can be extracted from the existing main Packages file with the simple perl script below.

• # extraoverride.pl
  # generate ExtraOverride file
  # use as follows :-
  # extraoverride.pl < /opt/cd-image/dists/hardy/main/binary-i386/Packages >> /opt/indices/override.hardy.extra.main
  
  while (<>) {
          chomp;
          next if /^ /;
          if (/^$/ && defined($task)) {
                  print "$package Task $task\n";
                  undef $package;
                  undef $task;
          }
          ($key, $value) = split /: /, $_, 2;
          if ($key eq 'Package') {
                  $package = $value;
          }
          if ($key eq 'Task') {
                  $task = $value;
          }
  }

If customizing Xubuntu, and adding new .deb files to pool/universe, run this script for the universe repository also.

/opt/apt-ftparchive/apt-ftparchive-udeb.conf:

• Dir {
    ArchiveDir "/opt/cd-image/";
  };
  
  TreeDefault {
    Directory "pool/";
  };
  
  BinDirectory "pool/main" {
    Packages "dists/hardy/main/debian-installer/binary-i386/Packages";
    BinOverride "/opt/indices/override.hardy.main.debian-installer";
  };
  
  BinDirectory "pool/restricted" {
    Packages "dists/hardy/restricted/debian-installer/binary-i386/Packages";
    BinOverride "/opt/indices/override.hardy.restricted.debian-installer";
  };
  
  Default {
    Packages {
      Extensions ".udeb";
      Compress ". gzip";
    };
  };
  
  Contents {
    Compress "gzip";
  };

/opt/apt-ftparchive/apt-ftparchive-extras.conf:

• Dir {
    ArchiveDir "/opt/cd-image/";
  };
  
  TreeDefault {
    Directory "pool/";
  };
  
  BinDirectory "pool/extras" {
    Packages "dists/hardy/extras/binary-i386/Packages";
  };
  
  Default {
    Packages {
      Extensions ".deb";
      Compress ". gzip";
    };
  };
  
  Contents {
    Compress "gzip";
  };

You need to build the Packages file in dists/hardy/extras/binary-i386/Packages using dpkg-scanpackages. See here for an explanation.

/opt/apt-ftparchive/release.conf

This is the configuration file for apt-ftparchive. Change to suit your distribution version:

• APT::FTPArchive::Release::Origin "Ubuntu";
  APT::FTPArchive::Release::Label "Ubuntu";
  APT::FTPArchive::Release::Suite "hardy";
  APT::FTPArchive::Release::Version "8.04";
  APT::FTPArchive::Release::Codename "hardy";
  APT::FTPArchive::Release::Architectures "i386";
  APT::FTPArchive::Release::Components "main restricted extras";
  APT::FTPArchive::Release::Description "Ubuntu 8.04 LTS";

To build the repository, sign it, and update the MD5SUM file, you can use a script like this:

BUILD=/opt/cd-image
APTCONF=/opt/apt-ftparchive/release.conf
DISTNAME=hardy

pushd $BUILD
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-deb.conf
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-udeb.conf
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-extras.conf
apt-ftparchive -c $APTCONF release $BUILD/dists/$DISTNAME > $BUILD/dists/$DISTNAME/Release

gpg --default-key "YOURKEYID" --output $BUILD/dists/$DISTNAME/Release.gpg -ba $BUILD/dists/$DISTNAME/Release
find . -type f -print0 | xargs -0 md5sum > md5sum.txt
popd

"YOURKEYID" is the key id you put in your own compiled keyring package before.

Burning the CD

At this point, you have a directory which is ready to be collected into an .ISO file and then burnt to a CD.

Building the ISO image

x86 and AMD64

IMAGE=custom.iso
BUILD=/opt/cd-image/

mkisofs -r -V "Custom Ubuntu Install CD" \
            -cache-inodes \
            -J -l -b isolinux/isolinux.bin \
            -c isolinux/boot.cat -no-emul-boot \
            -boot-load-size 4 -boot-info-table \
            -o $IMAGE $BUILD

Power PC

Download the HFS map, then use the following command:

IMAGE=custom.iso
BUILD=/opt/cd-image/

mkisofs -r -V "Custom Ubuntu Install CD" \
            --netatalk -hfs -probe -map hfs.map \
            -chrp-boot -iso-level 2 -part -no-desktop \
            -hfs-bless $BUILD/install \
            -hfs-volid Ubuntu/PowerPC_hardy \
            -o $IMAGE $BUILD

ia64

IMAGE=custom.iso
BUILD=/opt/cd-image/

mkisofs -r -V 'Custom Ubuntu Install CD' \
        -o $IMAGE -no-emul-boot \
        -J -b boot/boot.img -c boot/boot.catalog $BUILD

• $IMAGE is just the location of your iso image.

Burning the image to CD

To detect the location of your CD drive, try cdrecord --scanbus. For a primary IDE CD drive on /dev/hdc:

sudo nice -18 cdrecord dev=ATA:0,1,0 --speed=24 --blank=fast -v -gracetime=2 -tao $IMAGE

You will burn a lot of coasters in experimenting with this process, so please use rewritable media!

Testing

You can now boot off your CD. Select the new menu item you created. If you've used preseeding to stop the CD asking questions, the installation could be totally automatic.

Troubleshooting

• If your CD fails to read, try re-burning it, possibly at a slower speed.
• If you get a red d-i screen, check the error message (use Alt-F2, Alt-F3 etc to cycle through the terminals to read the log), and fix your CD appropriately. The log file is /var/log/syslog , check the last lines.

See also

• Check out some install CD customization scripts that can be used to automate this process.

• An "Unattended Ubuntu" guide in Estonian is also available.