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Re: Where is data stored when Synaptic scans DVDs?

On 03/17/2017 10:43 PM, David Wright wrote:
On Fri 17 Mar 2017 at 15:29:58 (-0500), Richard Owlett wrote:
On 03/17/2017 11:15 AM, songbird wrote:
Richard Owlett wrote:
As I have limited bandwidth, I install from DVDs.
Also I frequently experiment with various options by doing a fresh
install to a different partition.
It is annoying to keep re-scanning a set of 13 DVDs.
Where is the information stored?
/etc/apt/sources.list is obvious, but where is the data about contents
of each DVD stored?

 man apt-get

It implies *BUT DOES _NOT_ STATE* the all the requested data is in
the /var/lib/apt directory.

(Three levels of emphasis?)

Sorry, but I was having a generally bad day ;}

IIRC the command to scan is apt-cdrom. Are DVDs handled any
differently? Anyway,   man apt-cdrom   says:

    "APT uses a CD-ROM ID to track which disc is currently in the drive
     and maintains a database of these IDs in /var/lib/apt/cdroms.list"

I don't think the apt suite has much choice about where to put this
information; the FHS mandates it in §5.8.1.

But I don't think /var/lib is designed to be shared between systems,
and so I think you may need to delve into the intricacies of how
the information is stored if you're going to share it in any way.

Between FHS and man apt-cdrom references and included links I've just bookmarked 13 pages for further study. They give answers to some questions I haven't been able to articulate. There are hints of how-to {and how-NOT-to} accomplish some of my goals.

I assume you can find out which files are involved just by scanning a
disc and looking at the file timestamps. I would also assume that one
disc≡one file rather like the Packages files, but have nothing to
check this out with. If it's that simple, it then just comes down to
how the files link with the contents of cdroms.list. Looking at the
latter, I would imagine they use the GUID in there for the
lists/<filename>. I'm not sure about the -2 suffix I see in there.

I hadn't thought of looking at apt-get when I posted, even though I
had just chased down some differences on how synaptic and apt-get
differed in how they logged some trans action. mea culpa ;>

 and as i've previously said, you can copy the
dvds to spinning rust or a SSD and avoid all
future needs to reload from them again...

Yes but <smile>
in my peculiar situation it is better to know on which DVD something
resides than to spend ~1000 times more storage space to duplicate
the data.

I thought you had copied your DVDs back in 2015. I remember only
because you incorrectly shouted that you'd used the past tense when
you wrote "I have copied…". No, it was also because I objected to
the word "VIOLATES" (also shouted).

That has gone thru several variations, some mutually inconsistent. That's one of my reasons to work from the DVDs themselves.

 and futhermore, if you are doing partitions
you can do some minimal install to get the base
system going, then do a partition copy of that
and you'll not have to redo the previous steps
again to recover if you want to try something

I presume it's those "previous steps" that interest you,
in continuance of your research into preseeding installations.