Transcript Live Cd’s - Brigham Young University–Idaho

Live CDs
By: Lawrence Wellman
What is a Live CD
• A Live CD is a computer operating system that is
executed upon boot, without installation to a hard
disk drive.
• The concept of a Live CD can be applied across
many mediums: Floppy, CD, DVD, USB, all which
can be used to boot from, without installing on your
hard drive.
Reasons to use a Live CD
• Testing a new version or flavor of Linux
• Determine compatibility of a particular
hardware configuration.
• System repair and restoration (Rescue
Windows)
• Network security testing
• A fall back when a hard drive fails
• Password Recovery
Creating a Linux Live multiboot DVD
• Pointers:
– You will need aprox 10 GB free
– Use a virtual machine to test DVDs (makes
mistakes much cheaper)
First Obtain Your Desired Live CDs
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*Backtrack
*nUbuntu
Slax
Knoppix
*Helix
Fedora
F.I.R.E
*Insert
Operator
*Ophcrack
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Kanotix
PCLinuxOS
Damn Small Linux
Puppy Linux
Gentoo
Kaella
Morphix
Sabayon
Clusterix
www.frozentech.com/content/livecd.php
Create the folder structure
dvdroot
– isolinux
– A folder for each distro (BT, ubuntu)
Mount the iso’s
mount –o loop /home/mouse/Desktop/bt2final.iso /home/mouse/Desktop/backtrack/
• Note: It is generally best to work through the whole
process with one distro and then add distros as you get
the previous version working.
• Caution: If you are doing more than 8 iso’s at one time
you will need to increase your number of loopbacks.
• Add a folder in dvdroot for each distro. We
will then copy all the main file system
images for each live distro.
• Note: It will make life easier if you can
keep the same name as on the iso
although generally not possible.
Now we need to setup our DVD
• In the isolinux folder we need the following files. (Which
will be pulled from one of the live CDs and modified to
meet our needs)
We will take these files unaltered:
– isolinux.bin - boot loader for no-emulation boot
– isolinux.boot - required for isolinux
We will edit these files
– boot.msg - contains a message displayed on boot
– isolinux.cfg - configuration file
– vmlinuz (from each distro) - is the name of the Linux kernel
executable
– .gz file (from each distro) - contains info of where to find linux files
vmlinuz file from each distro
• Vmlinuz is a compressed bootable Linux
kernel
• We need the vmlinuz from each distro we
will rename each to have an extentions(no
more than 3 characters)
• ex. vmlinuz.bt – for Backtrack
vmlinuz.nu – for nUbuntu
.gz file from each distro
• If you renamed the folder in dvdroot that
contains the file system image we will
need to open and modify the linuxrc file. If
not you can copy the initrd.gz file over and
rename it to keep name different and
make it easer to recognize make sure not
to exceed 8 characters.
Editing the initrd.gz file
• Commands needed to open and modify linuxrc
– gunzip initrd.gz
– mkdir /testmount
– mount -o loop initrd /testmount/
• Now go to the /testmount folder there should be a file probably
linuxrc that will declare the dir to be the name of the folder that we
changed, which will need to be changed to the new name. (ex.
KNOPPIX_DIR = ‘KNOPIX’ change to KNOPPIX_DIR = ‘helix’)
• Then recreate gz file
– umount /testmount
– gzip initrd
isolinux.cfg
• Basic Commands:
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# - Comment
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DEFAULT – Specifies what will be boot after boot timeout or if user just hist
ENTER
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TIMEOUT {x} – sets timeout in 1/10 sec
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DISPLAY {filename} – Displays text contained with in file (boot.msg)
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LABEL {label name} – Explains boot options for {label name} (aka if the user
types {label name} it will boot with options declared after declaration)
– KERNEL – kernel to use when {label name} is typed
– APPEND – declares additional parameters to the kernel declaration
• Note: Things work best if you copy the label
out of the isolinux.cfg file each distro.
Example isolinux.cfg
boot.msg
• Contains an introduction message displayed
on boot.
Now to create the iso
sudo mkisofs -r -ldots -J -V “Multiboot DVD” -b
isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot boot -load-size 4 -boot-info-table -x lost+found -o
/multiboot.iso .
A little explanation of mkisofs
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sudo Allows us to excute the
command as root
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mkisofs create a hybrid
ISO9660/JOLIET/HFS filesystem
-c isolinux/boot.cat Specifies the path
and filename of the boot catalog to be
used when making a bootable cd.
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-r uses naming conventions for
compatibility and makes all files
publicly readable
-no-emul-boot Specifies that it is not a
image of a floppy
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-ldots *Allow ISO9960 filenames to
begin with a period.
-boot-load-size 4 Specifies the
number of “virtual” sectors to load in
no-emulation mode.
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-boot-info-table Specifies that a 56byte table with info of the CD-ROM
layout will be patched in at offset 8 in
the boot file
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-x lost+found exclude path from being
written to CDROM
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-o /multiboot.iso names the new .iso
image file
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. Specifies the path to the source for
the image
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-J uses Joliet naming records, for
Windows compatibility
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-V “Multiboot DVD” provides a volume
ID, this is the disk name that shows
up in Window’s Explorer
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-b isolinux/isolinux.bin Specifies the
path and filename of the boot image
to be used when making a bootable
cd.
Finished or So We Hope
• Now we have the iso boot it in a virtual
machine to make sure all works as
expected.
– If not trouble shoot.
• Burn iso to DVD using favorite burning
program.
Some Problems you may run into
• Some distros (Mandriva) codes the name of the
cd into initrd which you will need to change with
a hex editor. Others like Fedora declare the
cdlabel in the isolinux.cfg
• Every distro and live CD is setup a little
differently, so if your having trouble finding the
boot files, boot the live CD in a virtual machine
and watch as it boots to see what files it
requires, or consult google.
References & Further Reading
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Wiki
linux.about.com
members.chello.at/bobby100/ILpart1.htm
pcquest.ciol.com/content/enterprise/2005/
105070101.asp
• Linux.com
• http://linuxgazette.net/issue85/sipos.html
• http://www.linuxjournal.com/article/7246