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Where Are Application Details Saved

Posts: 4
edited June 2020 in Cloud Engineer IT Professional Program

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

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...

  1. me@me:~$ dpkg -l | grep wget
  2. ii  wget                                       1.19.4-1ubuntu2.2                                amd64        retrieves files from the web
  3. me@me:~$ dpkg -L wget
  4. /.
  5. /etc
  6. /etc/wgetrc
  7. /usr
  8. /usr/bin
  9. /usr/bin/wget
  10. /usr/share
  11. /usr/share/doc
  12. /usr/share/doc/wget
  13. /usr/share/doc/wget/AUTHORS
  14. /usr/share/doc/wget/MAILING-LIST
  15. /usr/share/doc/wget/NEWS.gz
  16. /usr/share/doc/wget/README
  17. /usr/share/doc/wget/changelog.Debian.gz
  18. /usr/share/doc/wget/copyright
  19. /usr/share/info
  20. /usr/share/info/wget.info.gz
  21. /usr/share/man
  22. /usr/share/man/man1
  23. /usr/share/man/man1/wget.1.gz
  24. me@me:~$ dpkg -p wget
  25. dpkg-query: package 'wget' is not available
  26. Use dpkg --info (= dpkg-deb --info) to examine archive files,
  27. and dpkg --contents (= dpkg-deb --contents) to list their contents.
  28. me@me:~$ apt-cache show wget
  29. Package: wget
  30. Architecture: amd64
  31. Version: 1.19.4-1ubuntu2.2
  32. Multi-Arch: foreign
  33. Priority: standard
  34. Section: web
  35. Origin: Ubuntu
  36. Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
  37. Original-Maintainer: Noël Köthe <noel@debian.org>
  38. Bugs: https://bugs.launchpad.net/ubuntu/+filebug
  39. Installed-Size: 932
  40. ...(I trimmed off the rest of the output details to save space)...

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

  1. -p, --print-avail package-name...
  2.       Display details about package-name, as found in
  3.       /var/lib/dpkg/available. Users of APT-based frontends
  4.       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...

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

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

Comments

  • Posts: 1,276
    edited June 2020

    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.

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