Will install CD and Live CD be merged in the future?

[John Richard Moser]

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Matt Zimmerman wrote:
> On Sun, Mar 19, 2006 at 09:33:31PM +0100, Jaap Haitsma wrote:
>> Since the Live CD now also contains an installer I was wondering if one
>> of the future plans is to merge the Live CD and the Install CD to one
>> CD. The boot menu then would be the same as the one of the current
>> Install CD plus one extra item which would launch the Live session.
>>
>> So is this on the roadmap?
> 
> There are two questions here:
> 
> - Will I be able to install Ubuntu using the live CD?
> 
>   Answer: Yes, absolutely!  This is a new feature in Dapper, allowing the
>   standard desktop environment to be installed from the live CD using a
>   friendly graphical installer application.  Please help to test it!
> 
> - Will both the traditional (text-mode, flexible) installer and the live
>   environment be available on the same disc?
> 
>   Answer: Not on a CD, since there isn't enough space for both.  However,
>   both are available on the DVD.
> 

There isn't enough space for both given the current implementation of
dpkg.  A few less-than-trivial hacks could make it happen, though.

Basically, what would be needed would be to teach dpkg to recognize two
types of files in a deb:

 - Files
   Files with their data, as today.
 - Meta-files
   Lists of SHA1SUM, PERMISSIONS, USER, GROUP, and SIZE coupled with an
   actual install path.  This path would be used to copy the file
   assuming it is 'already installed' in a system rooted at a given
   path.  In this way, the file data can be stored in the LiveCD file
   system.

The dpkg hacks would require a new command line switch, and a new
structure in the control info in the package.  This new structure would
be completely optional; new packages would not contain it until
specially processed with a tool to strip them based on an image of a
live system.

Assuming approximately 1300 packages and 150M free on the CD, each
package could be 120KB.  This would be mainly control info and
configuration files.  Not all packages are installed on the LiveCD, of
course, so there may be some fuzzing; then again, some "live debs" may
be as small as 20-50KB.

The advantage of this design is that the LiveCD and the InstallCD don't
have to be separate any more, ever.  They work as normal CDs, they share
the same media, they don't take up double the space on the mirrors or
massive amounts of bandwidth, and they are shipped on one CD on shipit.

The disadvantage of this design is that somebody has to implement a new
feature into dpkg and teach apt to use it.

Once implemented, dpkg is backwards compatible with old debs; and new
debs are backwards compatible with old dpkg.  "Live debs" will not work
on old dpkg of course.

It is also trivial to distill packages into "live debs," as the process
would mainly require processing the debs that would go on the CD against
the tree used to build the LiveCD squashfs.  This would involve
unpacking each deb; locating its files in the tree; comparing them;
removing byte-for-byte identical files; generating appropriate
replacement control information; repackaging the debs as new "Live
debs"; and signing the new "live debs."  Of course, all of this can be
automated in a completely hands-off script and integrated with the
Live/Install CD build process, taking the complexity out of the hands of
the developers.

When Ubuntu gets a graphical installer, Live/Install CDs would be able
to use this installer straight from the Live environment.  With some
less-than-trivial work, it may even be possible to simulate a full,
working system from the get-go before the system is installed; and then
transfer all user files into the new system.  This would facilitate an
"instant installation," where the system appears to be ready and usable
about 1 minute after the CD touches the drive.

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