Ubuntu Live CD Customization From The Scratch

bigluo

This procedure works and can create a bootable Ubuntu
LiveCd
(along with the
automatic hardware detection and configuration) from scratch. You do not need to
start from a pre-existing
LiveCd
.
You may wish to create an Ubuntu Remix and distribute it as a
LiveCd. Here is a way to do that without having to start from an existing Ubuntu
Desktop Cd.

Overview

There are three different areas to think about; the host
system, the disk image and the chroot.

The Host System

This refers to the Ubuntu desktop you are running, the one the
customised LiveCd is being built on. You will need to install the syslinux,
squashfs-tools and mkisofs packages to be able to build the LiveCd Remix using
the current system.

The Disk Image

The disk image is a folder that we will burn to Cd. Just create
a new folder to be the Disk-Image-Folder. The isolinux bootloader binary (taken
from the syslinux package) needs to be copied onto the disk image so it will go
into the disk image folder for now. The isolinux configuration file, which will
allow the Cd to show a boot-menu at boot time, needs to be copied into there
too. You will also copy the kernel from the chroot onto the disk image
(folder).
The disk image will be created in the host environment, outside
of the chroot.

The ChRoot Environment

This is the system that will eventually run from the disk. It
does not need a kernel, nor a boot-loader unless you are planning on installing
it back onto a hard disk (using Ubiquity). The Casper package needs to be
installed into the chroot. Casper is what allows the Live System to perform
hardware autoconfiguration and run from a live environment. Installing the
Casper package will update the kernel's initrd to perform these tasks. The
kernel that is installed into the chroot will be copied out from the chroot and
put into the disk image.
The chroot will end up inside the disk image in the form of a
squashed (compressed) file. For right now, it will be just another folder on
your host system.
The basic steps are to

Create a chroot and install your packages there.

Compress the chroot system into a file.

Create and configure the disk image which will have the bootloader
(isolinux), the kernel, the compressed file-system image and some other stuff.

Burn the Cd and test it out.

Make the ChRoot Environment

From a
command-line

install

debootstrap on the host system. Then make a new folder "work" and inside that
make another directory "chroot". Then run debootstrap
Note: The version of Debootstrap for a release of ubuntu does
not contain the files to bootstrap the next Ubuntu release. For example, you
cannot bootstrap Karmic on an Intrepid system without intalling Karmic's
debootstrap package. Find the version of debootstrap you need
here

and install it using dpkg. The debootstrap package doesn't depend on any other
packages and so installing it "by hand" will not cause any problems on your
system.

sudo apt-get install debootstrap
#alternatively, download the package and run sudo dpkg -i debootstrap_1.0.20_all.deb
mkdir -p work/chroot
cd work
sudo debootstrap --arch=i386 karmic chroot

Note that in the last line "karmic" may need to be replaced
with your host system; "hardy", "jaunty", "gutsy" or whatever. Those 4 lines
should create a directory with a chroot directory within it - then installs a
bare ubuntu system in there. It is important to install custom applications such
as MySQL after linux-generic is installed because such applications require
kernel modules for post-install configurations.

sudo cp /etc/resolv.conf chroot/etc/resolv.conf
sudo cp /etc/apt/sources.list chroot/etc/apt/sources.list

You may edit the sources.list in the chroot to add a line from
a PPA, if you need. You will need to add the PPA's key to your chroot's package
manager. On the PPA's overview page you'll see the PPA's OpenPGP key id. It'll
look something like this: 1024/12345678. Copy it, or make a note of, the portion
after the slash, e.g: 12345678. This key will be added once we enter the
chroot.

sudo chroot chroot
mount -t proc none /proc
mount -t sysfs none /sys
mount -t devpts none /dev/pts
export HOME=/root
export LC_ALL=C
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 12345678  #Substitute "12345678" with the PPA's OpenPGP ID.
apt-get update

There is a current (Karmic, 9.10) issue with services running
in a chroot:
https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/430224
A workaround is to link /sbin/initctl to /bin/true

dpkg-divert --local --rename --add /sbin/initctl
ln -s /bin/true /sbin/initctl

Install packages needed for Live System:
apt-get install --yes ubuntu-standard casper lupin-casper
apt-get install --yes discover1 laptop-detect os-prober
apt-get install --yes linux-generic

Jaunty Jackalope (9.04) seems to hang on the configuration of
the network interfaces unless network-manager is installed. This is no longer a
problem in Karmic 9.10.

apt-get install --no-install-recommends network-manager

Next, you may install more packages as you like, assuming you
have the legal rights to redistribute the packages. This is where you build your
custom system using packages from the Ubuntu archives.

Graphical installer, optional
step

The customised system can be set-up to allow it to be installed
onto machines rather than only ever being a
LiveCd
. Simply install the
Ubiquity packages and an appropriate desktop environment with a window manager.
This step is optional and only needed if you want to allow your customised
Ubuntu system to be installed on other computers.

For the Gtk front-end - Gnome
& Xfce


apt-get install ubiquity-frontend-gtk


For the Qt front-end - KDE


apt-get install ubiquity-frontend-kde

Before exiting the chroot, remove the diversion:

rm /sbin/initctl
dpkg-divert --rename --remove /sbin/initctl

Then just clean up.

apt-get clean
rm -rf /tmp/*
rm /etc/resolv.conf
umount -lf /proc
umount -lf /sys
umount -lf /dev/pts
exit

So far, you have entered the chroot and installed packages,
then cleaned up and left.

Create the Cd Image
Directory and Populate it

There are 4 packages that need to be installed on the Host
System which provide the tools to make the Cd image. Syslinux contains
isolinux which makes the Cd bootable. Squashfs-tools will compress the image.
SBM is a tool which is useful to have on the Cd if you cannot get it to boot.
Genisoimage provides mkisofs tool to turn a directory into a CD image. So
install

syslinux, squashfs-tools, mkisofs and sbm.
sudo apt-get install syslinux squashfs-tools genisoimage sbm

This next command makes the image directory and the 3 required
subdirectories.
mkdir -p image/{casper,isolinux,install}
# Same as 'mkdir image image/casper image/isolinux image/install'

You will need a kernel and an initrd that was built with the
Casper scripts. Grab them from your chroot. Use the current version. Note that
as of 9.10, the initrd is in lz not gz format... This may cause problems with
GRUB2.
cp chroot/boot/vmlinuz-2.6.**-**-generic image/casper/vmlinuz
cp chroot/boot/initrd.img-2.6.**-**-generic image/casper/initrd.gz

You need the isolinux binary and the sbm binary.

cp /usr/lib/syslinux/isolinux.bin image/isolinux/
cp /boot/memtest86+.bin image/install/memtest
cp /boot/sbm.img image/install/


Boot Instructions for the Remix
User

To give some boot-time instructions to the user create an
isolinux.txt file in image/isolinux, for example:
splash.rle
************************************************************************
This is an Ubuntu Remix Live CD.
For the default live system, enter "live".  To run memtest86+, enter "memtest"
************************************************************************


Splash Screen

A graphic can be displayed at boot time, but it is optional.
The example text above contains a special character along with the file name of
the splash image (splash.rle). To create that character, do one of the
following:
A. Cut and copy the text above and use any text editor to
modify the text.
or
B. Use the following command
printf "\x18" >emptyfile

and then edit the emptyfile with any text editor. Add the file
name just next to the first character and add the text you want to display at
boot time beneath it and save the file as "isolinux.txt"
or
C. Use vi to edit a text file and press CTRL-V and then CTRL-X
to create that special character. This doesn't work for other text editors such
as nano or gedit.
To create the splash.rle file, create an image 480 pixels wide.
Convert it to 15 colours, indexed (perhaps using TheGIMP) and "Save As" to
change the ending to .bmp which converts the image to a bitmap format. Then
install
the
"netpbm" package and run
bmptoppm splash.bmp > splash.ppm
ppmtolss16 '#ffffff=7'  splash.rle

If you want to use an animated splash screen such as
USplash
or
for a higher resolution console mode please make sure you add 'vga=rrr' after
the keyword splash in the append line in the configuration
file (see item below). Replace the rrr with the console resolution
value.

Boot-loader Configuration

Create an isolinux.cfg file in image/isolinux/ to provide
configuration settings for the boot-loader. Please read
syslinux.doc which should be on the host machine in
/usr/share/doc/syslinux to find out about the configuration options available on
the current set-up. Here is an example of what could be in the file:
DEFAULT live
LABEL live
  menu label ^Start or install Ubuntu
  kernel /casper/vmlinuz
  append  file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.gz quiet splash --
LABEL check
  menu label ^Check CD for defects
  kernel /casper/vmlinuz
  append  boot=casper integrity-check initrd=/casper/initrd.gz quiet splash --
LABEL memtest
  menu label ^Memory test
  kernel /install/memtest
  append -
LABEL hd
  menu label ^Boot from first hard disk
  localboot 0x80
  append -
DISPLAY isolinux.txt
TIMEOUT 300
PROMPT 1
#prompt flag_val
#
# If flag_val is 0, display the "boot:" prompt
# only if the Shift or Alt key is pressed,
# or Caps Lock or Scroll lock is set (this is the default).
# If  flag_val is 1, always display the "boot:" prompt.
#  http://linux.die.net/man/1/syslinux   syslinux manpage

Don't forget to pick the correct extension for your initrd
(initrd.gz or initrd.lz). Now the Cd should be able to boot, at least it will be
after the image is burned


Create manifest:


sudo chroot chroot dpkg-query -W --showformat='${Package} ${Version}\n' | sudo tee image/casper/filesystem.manifest
sudo cp -v image/casper/filesystem.manifest image/casper/filesystem.manifest-desktop
REMOVE='ubiquity casper live-initramfs user-setup discover1 xresprobe os-prober libdebian-installer4'
for i in $REMOVE
do
        sudo sed -i "/${i}/d" image/casper/filesystem.manifest-desktop
done


Compress the chroot

If this Customised Remix is to potentially be installed on some
systems then the /boot folder will be needed. To allow the Customised Cd to be
an installer Cd, compress the entire chroot folder with this command:
sudo mksquashfs chroot image/casper/filesystem.squashfs

However, if it is not going to be installed and is 'only' meant
as a
LiveCd
then the
/boot folder can be excluded to save space on your iso image. The live system
boots from outside the chroot and so the /boot folder is not used.
sudo mksquashfs chroot image/casper/filesystem.squashfs -e boot

It is important to note that if you are building a Karmic
LiveCd
on an earlier system,
you will need the squashfs-tools package
from Karmic or the
LiveCd
will not boot.

Create diskdefines


nano image/README.diskdefines

example:
#define DISKNAME  Ubuntu 9.10 "Karmic Koala" - Release i386 **Remix**
#define TYPE  binary
#define TYPEbinary  1
#define ARCH  i386
#define ARCHi386  1
#define DISKNUM  1
#define DISKNUM1  1
#define TOTALNUM  0
#define TOTALNUM0  1


Recognition as an Ubuntu Remix

Create an empty file named "ubuntu" and a hidden ".disk"
folder. This is needed to make the USB Creator work with this custom iso image.
Without this the image will still boot but the USB creator will not recognize
the image as an Ubuntu Cd and refuse to use it. Also, create the following files
with the pertinent information:
touch image/ubuntu
mkdir image/.disk
cd image/.disk
touch base_installable
echo "full_cd/single" > cd_type
echo 'Ubuntu 9.10 "Karmic Koala Remix" - i386 (20090429)' > info
echo "http//ubuntu-rescue-remix.org" > release_notes_url
cd ../..


Calculate MD5


sudo -s
(cd image && find . -type f -print0 | xargs -0 md5sum | grep -v "\./md5sum.txt" > md5sum.txt)
exit

This calculates the md5sum of everything in the image folder,
except the file named md5sum.txt.

Create ISO Image for a LiveCd

Create iso from the image directory using the command-line
cd image
sudo mkisofs -r -V "$IMAGE_NAME" -cache-inodes -J -l -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o ../ubuntu-remix.iso .
cd ..

The boot.cat file will be automatically created. You may test
your image through virtualbox-ose instead of rebooting your real system if you
wish.

Make a bootable Usb image

The USB-Creator works properly with the iso image that has been
created so long as the hidden ".disk" folder and its contents are present. If
you prefer to do it "by hand", you can put your live system onto a USB drive
yourself. Follow these six steps to do so. You can use these steps to put an
existing
LiveCd
onto a
Usb bootable device.

FAT16 file-system (Windows)

1. Prepare your work area:
mkdir ../liveusb ../liveusb/mnt
cd ../liveusb
touch loop

2. Create a loop device with a fat16 file-system. Use whatever
size you need to fit your image; in this case it's a 200Mb sparse file. A sparse
file is a file that is bigger than the actual number of bytes it takes up on the
disk.
dd if=/dev/zero of=loop bs=1 count=1 seek=200M
mkdosfs -F 16 -n rescue loop

3. Two options here;
3a Mount the Cd-Rom iso image and your new file-system:
mkdir tmp
sudo mount -o loop ../rescue-remix-804Alpha.iso tmp
sudo mount -o loop loop mnt

3b Just use the "image" folder instead of mounting the iso
image. This is useful if you don't want to make anything other than a Usb image
from scratch (You don't have to make a Cd iso image if you don't need it)
ln -s ../image tmp
sudo mount -o loop loop mnt

4. Copy the files
sudo cp -a tmp/* mnt/

5. Change the location of the boot-loader and its configuration
file and make it bootable (For fat16 file-system (default))
cd mnt
sudo mv isolinux/* .
sudo rmdir isolinux/
sudo mv isolinux.bin syslinux.bin
sudo mv isolinux.cfg syslinux.cfg
cd ..
sudo umount mnt
sudo umount tmp
syslinux loop

6. Pack it up
gzip -c loop > remixusb.gz

To install onto a usb drive. Insert the drive and identify it's
mount-point, for example /dev/sdc. Ensure that the device has a partition table
on it and run
zcat remixusb.gz | sudo tee /dev/sdc1 >/dev/null


Ext2 file-system (proper Linux)

An ext2 file-system is useful in that it can hold larger files
and the boot-loader can support relative symlinks. Follow the same steps as
above, but substitute the instructions in steps 2 & 5
2. Create an ext2 file-system instead of FAT16, obviously.
dd if=/dev/zero of=loop bs=1 count=1 seek=200M
mkfs.ext2 -L rescue -m 0 loop

5. It needs to be made bootable *before* unmounting.
cd mnt
sudo mkdir boot
sudo mv isolinux boot/extlinux
sudo mv boot/extlinux/isolinux.cfg boot/extlinux/extlinux.conf
sudo extlinux --install boot/extlinux/
cd ..
sudo umount mnt
sudo umount tmp


Partitioning your Usb device

A persistent home can be included within a file instead of a
partition. If you want to use a whole partition, do the following.
The Usb image can be installed to any
partition
on the
device. Just make sure that partition is the only one that is marked as
bootable. You can partition your Usb storage device to contain the
LiveUsb

image as well as a storage partition. You can use the storage partition to:
- keep a small amount of recovered files.
- create a persistent home.
- or you can use it as swap space.
To partition your device, see
HowtoPartition
.
If the storage partition is located after the LiveUsb image
partition then Windows wont be able to see it. This is not a problem since you
can create the storage partition first and put the live image at the end of the
drive. Just make the LiveUsb image partition the only partition flagged as
bootable.
When the drive boots the bootable partition will be used and
you are good to go. The
LiveUsb
image's partition
won't be seen by Windows.

Troubleshooting

If the device does not boot, you may need to install an MBR
onto the device.
sudo apt-get install mbr
sudo install-mbr /dev/sdc

and try again.

Persistent Data

Create an ext2, ext3 or ext4 partition named "casper-rw" as a
separate partition and append the word "persistent" to your "append" line
configuration and all your session data will be stored there. You will be able
to keep your changes between boots.
LABEL live
  menu label ^Start or install Ubuntu
  kernel /casper/vmlinuz
  append  file=/cdrom/preseed/ubuntu.seed boot=casper persistent initrd=/casper/initrd.gz quiet splash --
               
               
               
               

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