[CentOS] Scripts to generate exact copy of CentOS-5.0-i386-bin-DVD.iso from CD images

Sun Apr 15 23:15:49 UTC 2007
John Summerfield <debian at herakles.homelinux.org>

Wojtek.Pilorz wrote:
> On Sun, 15 Apr 2007, Akemi Yagi wrote:
> 
>> Date: Sun, 15 Apr 2007 06:37:18 -0700
>> From: Akemi Yagi <amyagi at gmail.com>
>> Reply-To: CentOS mailing list <centos at centos.org>
>> To: CentOS mailing list <centos at centos.org>
>> Subject: Re: [CentOS] Scripts to generate exact copy of
>>     CentOS-5.0-i386-bin-DVD.iso from CD images
>>
>> On 4/14/07, Wojtek.Pilorz <wpilorz at bdk.pl> 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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