Re: An INCOMPLETE solution - was [Re: Where is data stored when Synaptic scans DVDs?]
On Sun 26 Mar 2017 at 11:31:57 (+0000), Curt wrote:
> On 2017-03-25, David Wright <deblis@lionunicorn.co.uk> wrote:
> > On Sat 25 Mar 2017 at 10:50:50 (+0000), Curt wrote:
> >> Actually, srcpkgcache.bin includes the information contained in the files
> >> in /var/lib/apt/lists; that is, all the info you obtain from the internet
> >> via your deb and deb-src lines -- this information changes only on
> >> apt-get update.
> >>
> >> pkgcache.bin caches the information in srcpkgcache.bin + the information
> >> extracted from the apt and dpkg status files. This info changes on every
> >> install/remove done by apt or directly by dpkg.
> >>
> >> The above scandalously pilfered from David Kalnischkies here:
> >>
> >> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=566275
> >
> > Thanks for the useful reference. Whether it ties in to what apt-cdrom
> > does, I don't know and have no way of testing.
>
> It ties in to the context that you snipped; i.e. "the two .bin files in
> /var/cache/apt" and how you found it "tricky to check what's actually
> in them."
>
> Well, maybe it is tricky to "check" but not to know what's in those two
> files (if we can depend on the other David), a distinction that may not
> be of much use or significance.
>
> >> You can run 'strings' on pkgcache.bin BTW.
> >>
> >> curty@einstein:/var/cache/apt$ strings pkgcache.bin | less
[...]
> >> It doesn't appear that tricky.
> >
> > What doesn't?
> >
> > Getting a ¼million-line output file is straightforward, but
> > have you tried to interpret it? What do you think it shows?
> >
>
> Package names, versions, 'Description-md5' as far as I can tell is what
> is "actually" and obviously contained in the file, verifiable with very
> little effort via 'strings',
Yes, one might expect items like this in a file maintained by apt!
You can also see from the head of the file that the most of the
"versions" are not the versions of the packages but are actually
constraints, ie dependencies/replacements/breakages etc. all just
jumbled up.
Within this jumble, I think it would be difficult to unambiguously
locate information that was specific to apt-cdrom or synaptic, were
either of these to add information not covered by your reference.
$ ls -l /var/cache/apt/srcpkgcache.bin
... 22531192 Mar 27 21:00 /var/cache/apt/srcpkgcache.bin
$ strings /var/cache/apt/srcpkgcache.bin | wc -c
3655511
$
so the output of strings amounts to about 16% which means that
84% could be "hiding" other information from our eyes.
I've never looked at (let alone examined) these files after scanning
CDs with synaptic (assuming these same filenames are used), so I have
no idea whether they contain the same information as apt-get update
writes, or more. And as for what man apt-cdrom means by
"correcting for several possible mis-burns", I have no idea.
> beyond that I ain't gonna go because I have
> other things to do. Sorry I'm writing the story of my life and there are
> many many chapters.
I'm sorry too. And for causing a disturbance.
Cheers,
David.
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