Wojtek.Pilorz wrote:
On Sun, 15 Apr 2007, Akemi Yagi wrote:
Date: Sun, 15 Apr 2007 06:37:18 -0700
From: Akemi Yagi <amyagi@xxxxxxxxx>
Reply-To: CentOS mailing list <centos@xxxxxxxxxx>
To: CentOS mailing list <centos@xxxxxxxxxx>
Subject: Re: Scripts to generate exact copy of
CentOS-5.0-i386-bin-DVD.iso from CD images
On 4/14/07, Wojtek.Pilorz <wpilorz@xxxxxx> wrote:
I am enclosing scripts and config files to generate exact copy
of CentOS 5.0 i386 installation DVD image, that is
CentOS-5.0-i386-bin-DVD.iso
if you have CD images for i386.
I have 2 questions:
(1) There is one thing that is puzzling to me. You present an
alternative method that makes use of the existing
CentOS-5.0-i386-bin-DVD.iso file. In this case (if you already have
it), what is the purpose of running the scripts?
You prepare a DVD containing CD images and include scripts to generate DVD
image - so on one media you have, in a sense, both. Other than that, perhaps
not much reason.
(2) The scripts are specific for CentOS 5.0 as you described. What
The method I use is general. The scripts should be made more general,
indeed. That would require a bit of planning.
would it take to make them more generic?
Is there any way to achieve
the same without having to extract info from the original DVD?
Actually I did not have DVD image file. I had CD images on local fast mirror
which I could easily download.
I downloaded header of DVD image (part containing all directories definition)
and compared file length and timestamps.
With CentOS 5.0 it was easy - there were less than 50 files differing, most
of them needed to be downloaded (specific parts of DVD image).
The file resulting from the tree had SHA1 and MD5 checksums as advertised on
CentOS mirrors, so I could use it further in the process.
[
In case it did not match, I would use sha1 values for image segments from
bittorrent definition file to find out, where are the differences.
I have scripts that help me with that, but the process is not easy, unless
one is fluent with perl or similar tool.
]
Once I have destination DVD image, the process is quite straighforward, it
amounts to finding what files should be placed where in the image. To find out
I run the script which compares SHA1 values for 2K-aligned 2K chunks of
destination image with SHA1 values of 2K chunks for files supposed to be in the
image.
If anyone is interested in the tools I use, I can post then (all mine, all GPL).
Akemi
Best regards,
Wojtek
Wojtek
Debian's been using a similar system for years. Their current tool is
called Jigdo-file, and requires special action by the CD/DVD authors. So
far as I know, Debian is the only project using Jigdo, though I do know
at least one Linux magazine has used it.
The Debian special action is to create two files, a .jigdo file and a
.template. Together, they provide a similar function to the .bittorrent
files so many authors do create.
Jigdo uses the two files and some input from the user to download the
files from one or more (hopefully, local) sites and reconstruct the images.
It doesn't directly use an existing ISO image, but it can use its
contents if it's mounted.
Jigdo has some advantages:
1. I can choose a local download site, my side of the Internet
connexion, where components of the required image can be found.
2. I can choose more, friendly to my IAP, download sites to get further
packages to fill in for where the most local falls short.
In contrast, bittorrent chooses its own download sites, and my IAP pays
over and over for the same downloads, even if he has a local copy.
3. It uses standard download protocols, http and ftp, that uses ports
most commonly open in firewalls and is practical for everyone.
In contrast, bittorrent requires special firewall rules and one can't
(and shouldn't) give everyone bittorrent access, even if they have http
and ftp access to the Internet.
Your use of the so-popular bittorrent images is a big advantage for your
idea. Whether your use of existing ISO images is an advantage depends,
but it's valuable that you can.
Do you think you could discuss the matter with Richard Atterer, the
Jigdo guru at Debian? Find whether Would it be possible to combine the
approaches, so that jigdo-lite (the downloader part) could use the
bittorrent image? If the two approaches could be combined into the one
tool, it would be wonderful.
It would also ensure your new tool doesn't get lost.
You can find jigdo-file from here:
http://packages.debian.org/stable/utils/jigdo-file
--
Cheers
John
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