========================================
 APT and DPKG - Debian Packages Unwrapped
 ========================================
              Tim Booth - tbooth@ed.ac.uk
 Presented not in PowerPoint on  20160218
    bitbucket.org/snippets/timbooth/bKRXL

0) APT/DPKG both provide suites of tools
    apt                 apt-cdrom           apt-get               apt-sortpkgs
    apt-add-repository  apt-config          apt-extracttemplates  apt-key
    apt-cache           apt-ftparchive      apt-mark              apturl-gtk

    dpkg
    dpkg-architecture        dpkg-gensymbols          dpkg-scanpackages
    dpkg-buildflags          dpkg-log-summary         dpkg-scansources
    dpkg-buildpackage        dpkg-maintscript-helper  dpkg-shlibdeps
    dpkg-checkbuilddeps      dpkg-mergechangelogs     dpkg-source
    dpkg-deb                 dpkg-name                dpkg-split
    dpkg-distaddfile         dpkg-parsechangelog      dpkg-statoverride
    dpkg-divert              dpkg-preconfigure        dpkg-trigger
    dpkg-genchanges          dpkg-query               dpkg-vendor
    dpkg-gencontrol          dpkg-reconfigure

    ...or, if you like:
    synaptic    gdebi   update-manager


1) Everything (in Debian) is packages.

$ dpkg-query -Wf $'${Essential}\t${Package}\t\t\t${Version}\n' | grep '^yes'
yes base-files          7.2ubuntu11
yes base-passwd         3.5.38
yes bash            4.3-14ubuntu1
yes bsdutils            1:2.26.2-6ubuntu3
yes coreutils           8.23-4ubuntu2
yes dash            0.5.7-4ubuntu2
yes debianutils         4.5.1
yes diffutils           1:3.3-1
yes dpkg            1.18.2ubuntu5.1
yes e2fsprogs           1.42.12-1ubuntu2
yes findutils           4.4.2-9build1
yes grep            2.21-2
yes gzip            1.6-4ubuntu1
yes hostname            3.15ubuntu2
yes init            1.23ubuntu3
yes libc-bin            2.21-0ubuntu4.1
yes login           1:4.1.5.1-1.1ubuntu7
yes mount           2.26.2-6ubuntu3
yes ncurses-base            5.9+20150516-2ubuntu1
yes ncurses-bin         5.9+20150516-2ubuntu1
yes perl-base           5.20.2-6ubuntu0.1
yes sed         4.2.2-6.1
yes tar         1.27.1-2
yes util-linux          2.26.2-6ubuntu3

Also, the kernel, but that's not considered "essential":

$ dpkg-query -l | grep linux-image-
ii  linux-image-4.2.0-27-generic         4.2.0-27.32    amd64
 Linux kernel image for version 4.2.0 on 64 bit x86 SMP
ii  linux-image-extra-4.2.0-27-generic   4.2.0-27.32    amd64
 Linux kernel extra modules for version 4.2.0 on 64 bit x86 SMP
ii  linux-image-generic                  4.2.0.27.30    amd64
 Generic Linux kernel image


2) Basic usage - find, install, remove

$ sudo apt-get install sl
$ sl
$ sudo apt-get remove sl


3) The package manager believes in consistency

$ apt-get download stacks-web
$ sudo dpkg -i stacks-web_1.34-1_all.deb

...fails due to missing deps :-(
...and now your system is inconsistent!

$ sudo apt-get -f install

...satisfies deps and makes it all good :-)

4) Removing a package does not lose your custom settings -
   for that you need to purge it.

$ sudo apt-get remove stacks-web
$ dpkg -s stacks-web
Package: stacks-web
Status: deinstall ok config-files
...
$ dpkg -L stacks-web
/etc
/etc/stacks
/etc/stacks/constants.php
/etc/apache2
/etc/apache2/conf-available
/etc/apache2/conf-available/stacks-web.conf

$ sudo apt-get purge stacks-web
$ dpkg -L stacks-web
dpkg-query: package 'stacks-web' is not installed

(NB - for the example in 2, sl doesn't have any config, so remove == purge)


4) DO NOT FIGHT THE PACKAGE MANAGER!

dpkg has a --force-all option.  It is occasionally useful for removing a
package that refuses to die:

$ sudo dpkg --force-all -P stubborn-orrid-package

But don't try to force install anything.  It won't work.


5) Do not mess with files that belong to the package manager

$ dpkg -L cups
...
$ dpkg -s cups
...

You can edit /etc/cups/snmp.conf because it's in Conffiles.  Leave the
rest alone.  Updates will clobber them.

If you do need to edit a package-owned file, dpkg-divert is your friend:

$ cd /usr/share/X11/xkb/symbols
$ dpkg -S `pwd`/gb

#Note the counterintuitive order of old and new names
$ sudo dpkg-divert --local --divert `pwd`/gb.distrib --rename `pwd`/gb

Now, /usr/share/X11/xkb/symbols/gb is yours to tinker with.


6) How to install a .deb package on a .rpm system or vice-versa

Don't

..."But I heard about this tool called Alien!"

Don't bother

7) How to install two versions of a package at once

You can't

8) How to install a package to a different location

You can't

9) How to have multiple package sources for APT

This is not only possible but encouraged.

(This specific example only works on Ubuntu!)
# apt-get install software properties-common
# apt-add-repository ppa:bugs-launchpad-net-falkensweb/cool-retro-term
# apt-get update
# apt-get install cool-retro-term

$ cool-retro-term

In general, edit /etc/apt/sources.list as you like.

While we're at it, you can also poke around in /var/lib/dpkg.

10) When you have multiple sources, apt-cache policy is useful

$ apt-cache policy openssh-server

11) How to install two versions of a package at once?
    How to install a package to a different location?

I though we covered this.  You can't!

Oh, alright then, you can unpack a package manually...

$ wget some_package_you_found.deb
$ mkdir -p some_package/DEBIAN
$ dpkg -x some_package_you_found.deb some_package
$ dpkg -e some_package_you_found.deb some_package/DEBIAN

For some packages, you will be able to run them from the unpacked
folder.  You can also tinker with the contents and then:

$ fakeroot dpkg -b . ..

12) APT can help you if you're building a package from source.

Say you want to build a specific version of R.  You unpack the .tar.gz,
try running ./configure and it reports a bunch of missing libraries.

$ dpkg -S /usr/bin/R
r-base-core: /usr/bin/R
$ sudo apt-get build-dep r-base-core

This will install everything APT thinks is needed to build R.

13) Where do .deb packages come from?

Mumble mumble...something about a stork...ask your father...


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