Level: Intermediate Mayank Sharma (geekybodhi@gmail.com), Freelance technical writer
28 Feb 2007 Though Fedora Linux® is a popular and mature Linux
distribution, and many people have created Live CD distributions based on Fedora,
the Fedora project itself didn't released its first official Live CD until December
2006. Learn how to build your own custom and easy-to-use Live CDs using a rewrite of
Pilgrim, the Fedora Live CD creation tool.
In December 2006, the Fedora Linux distribution released its first official Live
CD, which, thanks to an intelligent selection of applications, nicely advertises
the best features of Fedora. In addition to many applications, the Live CD has
several games, uses the Compiz 3D desktop, and is accessible by non-English
speaking users. But what stole the show for me was David Zeuthen's livecd tools,
which make creating and maintaining a custom Fedora-based Live CD a walk in the
park.
Zeuthen is the developer of Pilgrim, which creates system images that can
run off USB flash drives for the One Laptop Per Child project (OLPC; see Resources for a link to more information). The livecd
tools used for creating the Fedora Live CD is a rewrite of Pilgrim in Python. It
can be used for creating live CDs out of Red Hat Enterprise Linux, CentOS, and
other downstream Fedora distributions.
Before getting down to making your own Live CD, you need to understand how a
Fedora release is assembled, distributed, and maintained. The Fedora project keeps
packages in two publicly accessible repositories. The repository maintained by
official Fedora developers is called the "core" repository, while the one
maintained by contributors and the community is called the "extras" repository. A
repository is simply a collection of packages. Apart from the core and extras,
there are several third-party repositories such as Livna and FreshRPM.
A Fedora Core distribution contains all the packages in the core repository, the
latest being Fedora Core 6. The first official Fedora Live CD is based on packages
in Fedora Core 6 and the extras repository. The livecd tools have been submitted
for inclusion in Fedora's extras repository, which will be merged with the core
repository by the time Fedora 7 is released.
What makes the livecd tools special?
The biggest advantage of the livecd tools approach to creating Live CDs is the
design that separates the tools from the Live CD. To cook a Live CD, all you need
is a set of configuration files. These configuration files contain a list of
packages that you need on the Live CD and also describe the type of system
configuration that will happen once the Live CD is booted.
To assist the custom Live CD maintainer, these configuration files are packaged
as RPMs and kept in a repository of their own. As the Fedora distribution and its
repositories move from version to version, you can keep updating these
configuration files to pull the relevant packages.
Zeuthen has made available three such RPMs that you can base your custom Live CDs
on. These RPMs follow an inheritance scheme that assists in creating derivative
versions. The fedora-livecd package is a minimal Live CD with no user
interface. The fedora-livecd-gnome package is based on the fedora-base
package and includes a GNOME desktop. The fedora-livecd-desktop packages
builds on top of the fedora-gnome package and gives a GNOME desktop with lots of
applications and other things.
Figure 1, from Zeuthen, explains this better.
Figure 1. Relationship among livecd
tools packages
Zeuthen also suggests that in the future it might also help other official Fedora
Special Interest Groups (SIGs) to roll their own distributions derived from these
RPMs.
Figure 2. Possible organization of
derivative packages
This might sound a little obscure, but once you get your hands dirty, you'll
appreciate this approach.
Setting up the base
The first step is to get the livecd-tools RPM that is available from Zeuthen's Fedora home
page. Just grab and install the livecd-tools-001-1.i386.rpm like so:
Listing 1. Installing the Live CD
tools
$ su -
<Enter root password>
# wget -c http://people.redhat.com/davidz/livecd/i386/livecd-tools-001-1.i386.rpm
# rpm -ivh livecd-tools-001-1.i386.rpm |
You should now have the livecd-creator command, which
you can invoke without any options to get a simple list of commands.
Listing 2. Options provided by the
livecd-creator command
$ livecd-creator
No packages specified.
usage: livecd-creator [--help]
[--repo=<name1>,<url1> ...] [--repo=<name2>,<url2>]
--package=<p1> [--package=<p2> ...]
[--exclude-package=<e1>] --exclude-package=<e2> ...]
[--base-on=<path-to-iso-file>]
[--fslabel=<label>]
--help : Print usage and exit
--repo : Path to yum repository
--package : Include this package
--exclude-package : Exclude this package
--base-on : Add packages to an existing live CD iso9660 image
--fslabel : File system label (default: livecd-YYYYMMDD-HHMI) |
Creating a local
repository of core packages
You also need to have access to RPMs of the tools that you want on your custom
Live CD. If you are on a fast Internet connection, livecd-creator can download them and the packages they depend upon
before creating the Live CD. The other option is to copy all the packages from
Fedora Core 6 installation CDs or DVD and create a local "core" repository. To
create a local repository, you'll need the createrepo tool.
Listing 3. Installing the createrepo
tool
# wget -c http://tqmcube.com/files/createrepo-0.4.3-5.1.noarch.rpm
# rpm -ivh createrepo-0.4.3-5.1.noarch.rpm |
Now, create the local repository by first copying all the RPMS from Core 6's five
CDs or single DVD and then using the createrepo tool.
Listing 4. Creating a local
repository
# mkdir /var/www/html/repo/core/
# cp <PATH TO RPMs> /var/www/html/repo/core/
# createrepo /var/www/html/repo/core/
|
This last command will take some time to complete and will create a repodata
directory. The livecd-creator command uses this
directory to get to the packages.
Creating a local
repository of configuration packages
Since you'll be using Zeuthen's packages to base your Live CD on, you'll need to
create a local repository for them as well.
Listing 5. Creating a repository of the
LiveCD packages
# mkdir base_packages
# cd base_packages
# wget -c http://people.redhat.com/davidz/livecd/i386/fedora-livecd-6-1.i386.rpm
# wget -c http://people.redhat.com/davidz/livecd/i386/fedora-livecd-gnome-6-1.i386.rpm
# wget -c http://people.redhat.com/davidz/livecd/i386/fedora-livecd-desktop-6-1.i386.rpm
# createrepo /root/base_packages |
As before, this last command will produce the repodata directory to help livecd-creator locate the configuration packages.
Spinning CDs
Now that you have your repositories set, you can easily create custom Live CDs.
The livecd-creator command produces ISO images that can
be burned to CD-Rs. But I'd recommend using virtualization software to test the
ISO without actually burning them onto physical media. There are several freely
available, such as VMware Player, QEMU, and VirtualBox.
A minimal Live CD
To get the hang of the livecd-creator command, begin
by creating a minimal Live CD:
Listing 6. Creating a minimal Live
CD
# livecd-creator --repo=c6,file:///var/www/html/repo/core --package=bash \
--package=kernel --package=grub --fslabel=Fedora-minimal-LiveCD |
This command asks livecd-creator to grab three
packages -- bash, grub, and the kernel -- from the local repository and include
them in a Live CD called Fedora-minimal-LiveCD. The livecd-creator command uses Fedora's YUM to install these packages and
will thus also install other applications that the specified packages depend upon.
The command will take some time to complete, since it will create a working
space, then install the specified packages and their dependencies, relabel the
working space for SELinux, Fedora's security mechanism, compress the whole working
space, configure the Live CD bootloader, GRUB, and finally create the ISO image.
Congratulations! You've just created your first Live CD. Of course, you'll not be
able do much with it, since it lacks the configuration files.
A Live CD with GNOME
Now that you know how the livecd-creator command
works, you can use it to create a Live CD that includes GNOME.
Listing 7. Creating a Live CD with
GNOME
# livecd-creator --repo=c6,file:///var/www/html/repo/core \
--repo=lcd6,file:///root/base_packages \
--package=fedora-livecd-gnome \
--repo=e6,http://download.fedora.redhat.com/pub/fedora/linux/extras/6/i386 \
--fslabel=My-Fedora-LiveCD-1 |
Here, you use the local repository for base packages and specify which
configuration package you need to base your CD on. You also specify that any
package that is required by fedora-livecd-gnome should be fetched from your local
core repository. There are some packages in fedora-livecd-gnome that are not in
the core repository. These packages will be fetched from the extras repository at
the given URL. Finally, it will create an ISO called My-Fedora-LiveCD-1.iso.
If livecd-creator is unable to find a package -- for
example, if it's not in the specified repositories -- the command will simply skip
the package and still create the Live CD. Unless the missing package is an
essential package like the kernel, you'll still end up with a usable Live CD.
Apart from the packages mentioned in the configuration RPM, you can add custom
packages with the --package switch. The livecd-creator command can also use multiple repositories
to build your CD.
Listing 8. Creating a Live CD using
multiple repositories
# livecd-creator --repo=c6,file:///var/www/html/repo/core \
--package=openoffice
--repo=lcd6,file:///root/base_packages \
--package=fedora-livecd-gnome \
--repo=e6,http://download.fedora.redhat.com/pub/fedora/linux/extras/6/i386 \
--repo=livna,http://rpm.livna.org/fedora/6/i386 \
--package=vlc \
--fslabel=My-LiveCD-2 |
As in the previous example, this command creates a Live CD with all the packages
from fedora-livecd-gnome. Additionally, it will include the OpenOffice.org office
suite, which is available in the core repository. It will also add the VLC Media
Player from the livna repository. We are calling it My-LiveCD-2, since it contains
packages from third-party repositories and cannot be called a Fedora Live CD.
What if after creating the CD you want to add another application, say
Evolution e-mail client, into this custom CD? No problem. If you have the ISO of the
previous CD available, just ask livecd-creator to use
the packages of this ISO and append the new ones.
Listing 9. Adding new packages to an
existing Live CD ISO
# livecd-creator --repo=c6,file:///var/www/html/repo/core \
--base-on=My-LiveCD-2.iso
--package=evolution
--fslabel=My-LiveCD-New |
This will create a new Live CD based on packages from the previous ISO with the
additional Evolution package.
Creating custom configuration packages
I hope the examples above show you that creating a Live CD is actually a
trivial job. Using Zeuthen's packages, you can go on creating Live CDs, adding
applications from any repository.
But suppose you need to create a Live CD that you can use to write documents and
code as well. You'll want to include OpenOffice.org, Evolution e-mail client,
Beagle desktop search, GAIM instant messenger, Xchat IRC client, GIMP image
manipulator, GCC compiler, GDB debugger, and Doxygen for code documentation.
Either you can specify them with the --package switch
every time you want to assemble the CD, or you can write a configuration file of
your own. The added advantage of using a configuration file is that you can
specify your custom configuration as well.
Anatomy of a
configuration file
Before you create your own configuration file, look at the configuration file
that you've been using to create your Live CDs, fedora-gnome. You can extract the
configuration file from the RPM by right-clicking on
fedora-livecd-gnome-6-1.i386.rpm and selecting the Extract Here option.
This should get you a file called 20-fedora-livecd-gnome.conf available under the
etc/livecd/ directory. The prefix numbers help identify the particular package in
the tree of packages. So 20-* package follows and probably depends upon a 10-*
package, and a 30-* package follows and probably depends upon the 20-* and earlier
packages.
The first part of the file contains a list of applications to install, and the
second part contains the configuration that needs to be done for that particular
environment.
Listing 10. Contents of the
20-fedora-livecd-gnome.conf file
case $1 in
# inquire what packages to install; must print packages to install
pkgadd)
echo "
chkconfig
gdm
gnome-panel
nautilus
metacity
gnome-themes
redhat-artwork
gnome-power-manager
gnome-volume-manager
desktop-printing
gnome-terminal
gedit
.
.
.
.
# run configuration scripts when all packages are installed
post)
# mount livecd
mkdir -p /mnt/livecd
mount -o ro -t iso9660 /dev/livecd /mnt/livecd
# add fedora user with no passwd
useradd -c "Fedora live CD" fedora
passwd -d fedora > /dev/null
.
.
.
. |
As you can see, most of the work such as setting up a user and setting up
networking is done by the fedora-gnome package.
Creating a configuration
file
The best way to create a configuration file is to use the
20-fedora-livecd-gnome.conf and remove the GNOME-specific bits. Let's call our
file 40-fedora-livecd-office-code.conf. This should do the trick:
# cp 20-fedora-livecd-gnome.conf
40-fedora-livecd-office-code.conf
After stripping off the GNOME bits, you can add the list of packages you need.
The new file should read like this (please note that I have removed the license
bits to conserve space):
Listing 11. The newly created
40-fedora-live-office.conf file
#!/bin/bash
# livecd configuration for Base Fedora system
# PLEASE ADD LICENSE RELATED NOTE
case $1 in
# inquire what packages to install; prints package list on stdout
pkgadd)
echo "
evolution
evolution-connector
evolution-webcal
gaim
xchat
beagle
gimp
openoffice.org-core
openoffice.org-draw
openoffice.org-calc
openoffice.org-graphicfilter
openoffice.org-math
openoffice.org-writer
openoffice.org-xsltfilter
openoffice.org-impress
gcc
gdb
doxygen
"
;;
# run configuration scripts when all packages are installed
post)
;;
# run when an livecd install is complete to clean up
install-post)
;;
# run when an livecd install is complete; must prints packages to remove
install-pkgrem)
echo "
fedora-livecd-office-code
"
;;
esac |
Do not forget to include the name of the configuration package in the list of
packages to remove before the ISO is created.
Creating the RPM
Before you can actually use this configuration file, you need to create an RPM
out of it. Creating an RPM requires a SPEC file.
You'll need to use Zeuthen's
fedora-livecd.spec and edit it to include information about the new
configuration file.
Basically, a SPEC file contains the list of files that will be included in the
RPM and where will they be placed when the RPM is installed. I won't go into
the details of creating a SPEC file, but you can use a SPEC file I created for
this article. Download it from the Downloads section,
below, and read the comments to understand the changes from Zeuthen's original
file.
Note that my SPEC files points to configuration files of other packages, such as
fedora-live-gnome-fedora-livecd-desktop. Make sure you have all of them available
as well.
Fedora uses the rpmbuild command to create RPMs from a
SPEC file. The rpmbuild command expects all the .conf
configuration files to be under the /usr/src/redhat/SOURCES directory, along with
any other file mentioned as a SOURCE in the SPEC file. Also make sure the
fedora-livecd.spec file is under /usr/src/redhat/SPECS directory.
Listing 12. Creating new RPMs
# cd /usr/src/redhat/SPECS
# rpmbuild -bb fedora-livecd.spec
# ls /usr/src/redhat/RPMS/i386
fedora-livecd-6-2.i386.rpm
fedora-livecd-gnome-6-2.i386.rpm
fedora-livecd-desktop-6-2.i386.rpm
fedora-livecd-office-6-2.i386.rpm |
To separate the custom RPMS from the original, I've versioned them 6-2 instead of
the original 6-1.
Using custom RPMs to
build Live CD
Once the RPMs are at your disposal, the procedure to create a Live CD isn't any
different. Re-create the local repository of packages with the new ones.
Listing 13. Creating the local repository
of configuration packages with the new RPMs
# rm /root/base_packages/*
# cp /usr/src/redhat/RPMS/* /root/base_packages/
# createrepo /root/base_packages |
Now use livecd-creator to use the newly created
packages.
Listing 14. Creating a Live CD using the
new Fedora-Office-Code-LiveCD RPM
# livecd-creator --repo=c6,file:///var/www/html/repo/core \
--repo=lcd6,file:///root/base_packages \
--package=fedora-livecd-office-code \
--repo=e6,http://download.fedora.redhat.com/pub/fedora/linux/extras/6/i386 \
--fslabel=My-Fedora-Office-Code-LiveCD |
Presto! You have your very own custom Live CD from your very own custom
configuration.
Once you get the hang of creating configuration RPMS, you'll be creating Live CDs
in no time. You can customize the Live CDs by tweaking any setting and adding or
removing packages. Add to that the ability to move any data file into the Live CD
environment, as I've shown in my SPEC file.
It's only a matter of time before the Live CD installer, already in testing
stages, is released. One single entry in your configuration file or a --package option will bundle it onto your Live CD, making
it fully installable on the hard disk. How cool is that? Your custom Linux
distribution in no time.
Download | Description | Name | Size | Download method |
|---|
| Sample SPEC file | fedora-livecd-custom.zip | 2KB | HTTP |
|---|
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About the author  | | | Mayank Sharma is a contributing editor at the Open Source Technology Group
(OSTG), a division of VA Linux, and publishes mainly on OSTG's NewsForge and
Linux.com. Also, he contributes a monthly column for Packt Publishing. In
addition, he teaches courses on open source topics at the Indian Institute of
Technology, Delhi, as guest lecturer. |
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