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Re: Where is data stored when Synaptic scans DVDs?

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?)

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.

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).

> >  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
> >else.

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