Where Are Application Details Saved

teachernightowl

Where is package details stored if the package is not listed in /var/lib/dpkg/available?

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The Context

On this DPKG module page, it says to use dpkg -p wget to show the information about an installed package.

Here is the output on a newly installed Ubuntu 18.04...

me@me:~$ dpkg -l | grep wget
ii  wget                                       1.19.4-1ubuntu2.2                                amd64        retrieves files from the web
me@me:~$ dpkg -L wget
/.
/etc
/etc/wgetrc
/usr
/usr/bin
/usr/bin/wget
/usr/share
/usr/share/doc
/usr/share/doc/wget
/usr/share/doc/wget/AUTHORS
/usr/share/doc/wget/MAILING-LIST
/usr/share/doc/wget/NEWS.gz
/usr/share/doc/wget/README
/usr/share/doc/wget/changelog.Debian.gz
/usr/share/doc/wget/copyright
/usr/share/info
/usr/share/info/wget.info.gz
/usr/share/man
/usr/share/man/man1
/usr/share/man/man1/wget.1.gz
me@me:~$ dpkg -p wget
dpkg-query: package 'wget' is not available
Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.
me@me:~$ apt-cache show wget
Package: wget
Architecture: amd64
Version: 1.19.4-1ubuntu2.2
Multi-Arch: foreign
Priority: standard
Section: web
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Original-Maintainer: Noël Köthe <noel@debian.org>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 932
...(I trimmed off the rest of the output details to save space)...

When I look in man dpkg, I find this...

-p, --print-avail package-name...
      Display details about package-name, as found in
      /var/lib/dpkg/available. Users of APT-based frontends
      should use apt-cache show package-name instead.

When I search /var/lib/dpkg/available, there is nothing listed for wget. If I run dpkg -p <package> against a package listed in /var/lib/dpkg/available is does return details.

So since the package is obviously installed, I ran apt-cache show wget to find the details and it returned details. So obviously, apt-cache show is pulling from somewhere else.

As a result, I decided to read the manual at man apt-cache. It has this...

show pkg...
   show performs a function similar to dpkg --print-avail; it displays the package records for
   the named packages.

While the action is obviously similar, it is not exactly the same. And I am back at to where I started.

luisviveropena

Hi @teachernightowl ,

I was able to reproduce the behaviour. For some reason, there are many packages on /var/lib/status that are installed, and that are not present in /var/lib/available (and they should). You can confirm that by doing the following:

grep "Package: " available > /tmp/packages_available

grep "Package: " status > /tmp/packages_status

Then compare these files; you will find that there are a lot of packages in /tmp/packages_status that are not in /tmp/packages_available . Why the OS has failed in mantain an updated /var/lib/dpkg/available file? No idea.

Can this be fixed? Yes, totally! I haven't had the need to do this before, this is the first time I see this issue.

So, this can be reconciliated by merging the apt-cache database for available packages with dpkg. This is how it's done:

apt-cache dumpavail | dpkg --merge-avail

So, if you dump the output of apt-cache dumpavail to a file, you will see that "wget" is there (apt-cache dumpavail > apt_packages). Then the output of the first command is passed to dpkg--merge-avail through a pipe.

Then next time you do "dpkg -p wget" it will work (I confirmed it on my Ubuntu LTS 18.04 image).

Note: I found useful information here: https://wiki.debian.org/Teams/Dpkg/FAQ

I hope this helps.

Many regards,
Luis.