Advanced Usage of the Debian Packaging System

Debian Policy Packaging Nomenclature dpkg based tools APT utilities Advanced things Brief introduction to source packages S

Advanced Usage of the Debian Packaging System

Richard Darst
With contributions from #debian-nyc

September 15, 2010

Prepared for
New York Linux User’s Group


Contents

Debian Policy

Packaging Nomenclature

dpkg based tools

APT utilities

Advanced things

Brief introduction to source packages

Summary and future reference


Goals of this talk

• Show you what tools are available
• There is not enough time to discuss these tools in detail
• This is not designed to be a tutorial
• Once you know what exists, you can read up on it yourself
easily, and ask us for help.
• man programname
• /usr/share/doc/packagename/
• Things in this presentation which are uncited will usually come
up ﬁrst on an Internet search.


What is a package?

Packages are the fundamental unit of a Debian installation
• Every ﬁle on a system belongs to a package
• ... but some are automatically generated or exceptions
• Packages include ﬁles, but also
• Control information (descriptions, dependencies, versions)
• Installation/removal/upgrade scripts


The Debian Policy

The Debian Policy is rules which packages (and the system in
general) must follow.
• Debian’s quality-control document
• Based on years of experience
• Formed by convention and mailing list discussion
• http://www.debian.org/doc/debian-policy/


Examples of things in policy

• Build interface for packages
• Deﬁnitions of dependency levels
• User interaction (GUI menu interface, defaults, ...)
• Location of ﬁles (POSIX File Hierarchy Standard)
• Installation/removal/upgrade scripts


Policy leads to quality

Policy is considered to be one of the strengths of Debian:
• Makes things uniform, so we can...
• Port to many architectures
• Detect bugs by archive-wide automatic rebuilds
• Consistent user interface
• Have package upgrades that work


Suites

A suite is a section of the Debian archive of packages that go
together.
• Suites for releases:
• Stable - Unchanging released version
• Testing - More stable than unstable, becomes stable upon a
release
• Unstable - New packages go here, use at your own risk
• These suites contain the same packages, but diﬀerent versions
• Specialized suites: security, experimental, volatile, backports


Dependencies

Dependencies indicate the relationship between two packages.
• Depends, Pre-depends, Recommends, Suggests, Enhances,
Breaks, Conﬂicts, Provides, Replaces
• Names are intuitive here
• Usually, “Recommends” of a package are automatically
installed, while “Suggests” are not
• Depends on package manager


Source vs Binary packages

Debian packages come in two main varities: binary and source
• As a user, you always deal with binary packages
• Binary packages are .deb ﬁles: compiled code.
• Source packages are .dsc ﬁle, plus .orig.tar.gz, .diff.gz,
and more: Source code.
• Source packages are not installed directly
• .udeb: installer, .tdeb: translation


dpkg

dpkg is the low-level package manager. Things which it handles
include:
• Ensures dependencies are met
• Installs ﬁles from packages
• Runs scripts for installation/removal/upgrade
• Maintains database of installed packages
dpkg operates on .deb ﬁles. Usually, you won’t download and
install .debs yourself.


APT

APT is the high-level package management system
• Maintains list of all available packages from the archive
• Resolves dependencies
• Downloads and hands install oﬀ to dpkg
• Diﬀerent frontends: aptitude, synaptic
• APT replacements: cupt
APT is what you use for most things you’ll install distributed by
Debian.


debconf
Debian has a configuration management system for basic and
medium customization.
• debconf (as opposed to DebConf, the conference) is the
configuration management system
• Manages the configuration dialogs you see upon
installation/upgrades.
• Maintains database for configuration between upgrades
$ debconf-get-selections
# U p g r a d i n g from GRUB Legacy .
grub grub / migrate _from _legacy note
# Time zone :
# Choices : Adelaide , Brisbane , Broken Hill , Canberra , Currie , Darw
tzdata tzdata / Zones / Australia select
# Do you want system - wide r e a d a b l e home d i r e c t o r i e s ?
adduser adduser / homedir - permission boolean true
# What do you want to do about m o d i f i e d c o n f i g u r a t i o n file ?
# Choices : install the package maintainer ’ s version , keep the loca
ucf ucf / changeprompt select keep _current
# Keymap :
# Choices : Programmer , latin1 , latin1 - no dead keys
console - data console - data / keymap / qwertz / german / standard / keymap


Version numbers
Version numbers are important since they indicate upgrades and
preferred versions. Simple case:
10.16.2 - 1
upstream version debian revision

Epoch fixes problematic upstream version changes:
1 : 10.16.2 - 1
epoch upstream version debian revision

Extra modifier for stable updates, backports, other situations:
2 : 3.2.5 -4 lenny11
epoch upstream version extra modifier
debian revision


dpkg based tools

For working and learning about installed packages or .deb files,
use dpkg and its related tools.
• dpkg installs files and runs scripts
• Package naming convention:

python-numpy 1.3.0-4 amd64 .deb
vers. num. architecture
package name

• dpkg state directories: /var/lib/dpkg/
• /var/lib/dpkg/status
•
/var/lib/dpkg/info/packagename.{postinst,prerm,md5sums,conffiles,..
• /var/lib/dpkg/available
• /var/lib/dpkg/


dpkg state

dpkg maintains a database of state of installed and partly installed
packages.
• A package can be: not-installed, installed, config-files,
unpacked, half-installed, and some more.
• dpkg --remove → leave config files
• dpkg --purge → remove config files, too
• The other states are various combinations of installation
scripts partially run
• man dpkg


Examining .deb files

If you have downloaded a .deb yourself, you can learn some about
it before installing.
• To extract a .deb: dpkg-deb -x
• dpkg (really dpkg-deb) can look inside .deb files and tell you
about them.
• List files with in a package:
$ dpkg -c python-numpy 1.3.0-4 amd64.deb
drwxr - xr - x root / root 0 2009 -11 -19 02:19 ./
drwxr - xr - x root / root 0 2009 -11 -19 02:19 ./ usr /
drwxr - xr - x root / root 0 2009 -11 -19 02:19 ./ usr / bin /
- rwxr - xr - x root / root 675 2009 -11 -19 02:19 ./ usr / bin / f2py2 .4
- rwxr - xr - x root / root 675 2009 -11 -19 02:19 ./ usr / bin / f2py2 .5
drwxr - xr - x root / root 0 2009 -11 -19 02:19 ./ usr / share /
drwxr - xr - x root / root 0 2009 -11 -19 02:19 ./ usr / share / man /
...


Examining .deb ﬁles

• List control information:

$ dpkg -I python-numpy 1.3.0-4 amd64.deb
new debian package , version 2.0.
size 1818486 bytes : control archive = 11769 bytes .
1274 bytes , 22 lines control
30246 bytes , 363 lines md5sums
349 bytes , 11 lines * postinst # !/ bin / sh
280 bytes , 10 lines * preinst # !/ bin / sh
1219 bytes , 47 lines * prerm # !/ bin / sh
Package : python - numpy
Version : 1:1.3.0 -4
Architecture : amd64
Maintainer : Debian Python Modules Team
< python - modules - team@lists . alioth . debian . org >
Installed - Size : 7640
...


Querying installed packages

Once a package is installed, a diﬀerent set of commands is
necessary to examine them.
• dpkg -s shows control information for a package
• dpkg -l lists packages and states
$ dpkg -l ’bash*’
Desired = Unknown / Install / Remove / Purge / Hold
| Status = Not / Inst / Cfg - files / Unpacked / Failed - cfg / Half - inst / trig - aWa
|/ Err ?=( none )/ Hold / Reinst - required / X = both - problems ( Status , Err : u
||/ Name Version Description
+++ -============== -============== -================================
ii bash 3.2 -4 The GNU Bourne Again SHell
ii bash - completio 20080705 programmable completion for the
un bash - doc < none > ( no description available )


List files within a package
You can list the files in an installed package with dpkg -l
• I often use this to get a hint about how to use a package after
I install it
• Will not list files that were automatically generated from the
package’s scripts
$ dpkg -L bash
/.
/ bin
/ bin / bash
/ etc
/ etc / skel
/ etc / skel /. bashrc
/ etc / skel /. profile
/ etc / skel /. bash_logout
/ etc / bash . bashrc
/ usr
/ usr / share
/ usr / share / doc
/ usr / share / doc / bash
/ usr / share / doc / bash / CHANGES . gz


Backup package selections

dpkg --get-selections lists installed packages.
• Back up package installation states
• Could be used to transfer selections to another computer
• This does not backup the “automatic/manual” database.
$ dpkg –get-selections
a2ps install
acl install
acpi install
acpi - support - base install
acpid install
acx100 - source install
adduser install
alsa - base install

• Use with dpkg --set-selections


Which package owns a file?

If you are looking at a file and want to know what package put it
there, use dpkg -S
• These commands only search currently installed packages
• Next section gives a better way to search for files
• Will miss automatically generated files
$ dpkg -S /etc/bash completion
bash - completion : / etc / ba s h_ co mp l et io n

$ dpkg -S /etc/debian version
base - files : / etc / de bian_ver sion


Other places to look for information on installed packages
After installing a package, a common question is “How do I use
it?”
• It is usually worth it to take a bit of time to learn the Debian
way of using a package, instead of rolling your own
conﬁguration.
• List ﬁles in it: dpkg -l packagename
• Per-package documentation:
/usr/share/doc/packagename/
• /usr/share/doc/packagename/NEWS.Debian.gz - Major
changes you should be aware of
• /usr/share/doc/packagename/changelog.gz - upstream
changelog
• /usr/share/doc/packagename/changelog.Debian.gz -
Debian changelog
• /etc/defaults/packagename - Sometimes useful for
daemon-like packages


APT: Advanced Packaging Tool

APT is the companion to dpkg
• APT is a higher level than dpkg
• APT handles dependencies and downloading
• Conﬁgure mirrors and suites in /etc/apt/sources.list
• Stores it’s state in /var/cache/apt/
• dpkg deals with what is installed, APT deals with what can be
installed
APT is a set of libraries with diﬀerent frontends.


Frontends to APT

There are diﬀerent frontends to APT , and they can have slightly
behaviors:
• apt-cache, apt-get
• aptitude
• Smarter at resolving dependencies
• Installs recommends by default (aptitude
--without-recommends to change)
• The currently recommended distribution upgrade program
• synaptic, KPackage, apt-rpm, and many more...


APT cache utilities

The ﬁrst thing APT can do is search available packages
• Run apt-get update to refresh the list of what is available.
• Use apt-cache to search for packages and show packages
$ apt-cache search calculator
abakus - calculator for KDE
allegro - examples - example programs and demo tools for the Allegro
apcalc - common - Arbitrary precision calculator ( common files )
apcalc - dev - Library for arbitrary precision arithmetic
...

$ apt-cache show abakus
Package : abakus
Priority : optional
Section : kde
Installed - Size : 728
...


APT dependency handling
APT handles dependencies intelligently (downloading them), while
dpkg just fails if dependencies are not met.
• To ﬁnd related programs, look at dependencies and reverse
dependencies - you may ﬁnd something that will help you
• I always just do this from the aptitude user interface
$ apt-cache depends units
units
Depends : libc6
Depends : libncurses5
Depends : libreadline6
| Depends : dpkg
Depends : install - info

$ apt-cache rdepends units
units
Reverse Depends :
octave - miscellaneous
ibid


apt-file

You can do archive-wide searches of files within packages.
• dpkg -S only finds currently installed files
• apt-file searches all the archive (using Contents.gz) for
files
$ aptitude install apt-file
$ apt-file update
$ apt-file search bin/host
apt - file search bin / host
bind9 - host : / usr / bin / host
coreutils : / usr / bin / hostid
host : / usr / bin / host
hostap - utils : / usr / sbin / h o s t a p _ c r y p t _ c o n f
hostap - utils : / usr / sbin / hostap_diag
...


Other APT package states
APT has more states that dpkg . dpkg just looks at installed or
not, but APT has more
• Some APT frontends (aptitude was ﬁrst, apt-get has it now,
too) maintain a database of manually installed vs
automatically installed as dependencies.
• If you uninstall a package, its dependencies are automatically
uninstalled, too.
• This is why I used to recommend always using aptitude. Use
“m”/“M” to adjust auto-ﬂag.
• aptitude vs apt-get databases here
• Hold - APT will never upgrade this package to a newer
version.
• Recommends vs suggests
• Recommends are usually automatically installed, suggests are
usually not.


Pinning
Pinning indicates package preferences:
• If you mixed suites (Stable and Testing, backports), pinning
can tell APT to prefer certain
• suites
• repositories
• versions
• and more
• man apt preferences
• Example (Use testing and unstable, but prefer testing):
Package : *
Pin : release a = testing
Pin - Priority : 900

Package : *
Pin : release a = unstable
Pin - Priority : 800


Diversions and overrides
You can tell dpkg to preserve certain custom modifications.
• You want to change a file in a package, but have it not get
overridden when you upgrade the package the next time
• Diversion: Tell dpkg to install a file in a different location, so
that your can replace it and not be squashed on upgrades
• dpkg-divert
• Stat-override: tell dpkg to keep file permissions/owner at
some value
• dpkg-statoverride
• These are used by packaging scripts, too. Try listing
$ dpkg-divert –divert /etc/dnsmasq.conf.dpkg –rename
/etc/dnsmasq.conf
Adding ’ local diversion of / etc / dnsmasq . conf to / etc / dnsmasq . conf .

$ dpkg-statoverride –add richard richard 0755
/etc/bash.bashrc $ dpkg-divert –list $ dpkg-statoverride
–list


equivs
equivs lets you easily make meta-packages.
• Sample uses:
• Meta-package to pull in programs you use often
• Fix broken dependency problem (your package Provides:
something)
• Let dpkg know about your local version
• Can include dependencies, scripts, and ﬁles
• equivs-control and equivs-build
$ less rkd-standard-system
...
Package : rkd - standard - system
Version : 1.0
Maintainer : Richard Darst < rkd@zgib . net >
Depends : less ,
screen ,
python2 .5 ,
bash - completion ,
openssh - server ,
openssh - client
...


The alternatives system
Debian has many choices, and the alternatives system allows the
user to choose among them.
• Sometimes different packages can provide equivalent utilities.
• Alternates system selects among them
• /usr/bin/vim links to /etc/alternates/vim/ links to
/usr/bin/vim.tiny
• Different packages install alternates with different priorities
• Select among them with update-alternatives. Handles
things like man page links also.
• GUI interface in package galternatives
• You have to install the relevant packages first!
$ sudo update-alternatives –list vim
/ usr / bin / vim . basic
/ usr / bin / vim . basic
/ usr / bin / vim . nox

$ sudo update-alternatives –config vim


dpkg-repack

dpkg-repack undoes an installation in emergency situations.
• Convert installed files back to the package it came from
• includes control info, scripts, and files
• Inherits changes that have been made to the files
• Kind of a hack, use a native package if possible
• rpm, deb, tgz, pkg


alien

You can convert between package formats with alien
• Is not safe since diﬀerent OSs have diﬀerent conventions (e.g.
Debian Policy vs Red Hat Policy)
• But for small unobtrusive things it’s probably safe enough.
• Do not use for major system utilities


auto-apt

auto-apt traces a program to figure out what packages it needs.
• Run a program in auto-apt environment and it will trap
system calls for missing files
• Can automatically install packages providing the missing files


Debtags
To help people ﬁnd what they are looking for, the Debtags system
was developed
• Free-form tags for packages
• http://debtags.alioth.debian.org/ssearch.html -
package search, enhanced by debtags
• http://debtags.alioth.debian.org/cloud/ - interactive
tag cloud
• You can help tag packages online, too!


Kernel help: make-kpkg and module-assistant

There are tools which help create packages of kernel images and
modules.
• make-kpkg automates building and packaging kernels when
you get the source from elsewhere
• module-assistant automates building module packages
• The packagename-source packages use this
• packagename-dkms (“Dynamic Kernel Module Support”)
packages are another system for automatically compiling
modules.
$ aptitude install lustre-source –without-recommends
$ module-assistant auto-install lustre


reportbug and reportbug-ng
If people help report bugs, Debian’s quality goes up.
• http://bugs.debian.org
• There isn’t a web interface to report bugs
• reportbug and reportbug-ng make reporting easy, though.
Gathers all information and submits.
$ reportbug –email=MYEMAIL@zgib.net python-lzma
Which of the following packages is the bug in ?
Just press ENTER to exit reportbug .

1 python - lzma Python bindings for liblzma

2 python - lzma - dbg python - lzma debug symbols
Select one of these packages : 1
Please enter the version of the package this report applies to ( bl
>
Will send report to Debian ( per lsb_release ).
Querying Debian BTS for reports on python - lzma ( source )...
1 bug report found :

Outstanding bugs -- Minor bugs ; Unclassified (1 bug )
1) # 594943 python - lzma has d u p l i c a t e d c h a n g e l o g . gz
Please briefly describe your problem ( max . 100 characters allowed ;


Useful web services

Over the years Debian has developed a lot of useful but
undermarketed web services.
• backports.debian.org - Find newer versions of packages
for stable
• snapshot.debian.org - Archive of every single debian
package on the mirrors ever
• bugs.debian.org - Search bug reports for a package
• packages.debian.org - Web interface to some of these
tools


Source package layout

Source packages contain buildable source code, and can be
retrieved from the APT system.
• debian/ directory should contain all Debian information
• debian/rules - build instructions (a Makeﬁle)
• debian/control - Meta-information
• debian/changelog - Version number and changes
• dpkg-source packs and unpacks source trees
• dpkg-buildpackage builds binary packages
• dpkg-deb packs and unpacks binary packages
• Getting the source to any package
• Make sure a deb-src line is in your /etc/apt/sources.list
• apt-get source packagename
• apt-get build-dep packagename


Useful devscripts

devscripts contains a lot of useful tools for packagers and
developers.
• rmadison queries versions of packages in all suites
• debdiff intelligently diﬀs source or binary packages
• aptitude install devscripts --without-recommends
• Has a lot of recommends
$ rmadison bash
bash | 3.2 -4 | stable | source , alpha , amd64 , ar
bash | 4.1 -3 | testing | source , amd64 , armel , hp
bash | 4.1 -3 | unstable | source , alpha , amd64 , ar


Fast package rebuliding

The consistent build interface means it is easy to rebuild packages:
$ apt-get source bash
$ sudo apt-get build-dep bash
$ cd bash-VERSION/
$ debuild


There is much, much more

• We’ve gone over some basic utilities here
• This list is biased towards what I know - there so much that I
am missing
• Debian-NYC has workshops which go into more detail about
the development side of things
• http://wiki.debian.org/DebianNYC


More resources

User resources:
• http://www.debian.org/doc/manuals/reference/ -
Debian user guide, highly recommended
• http://www.debian.org/doc/manuals/refcard/
refcard.en.pdf - Debian reference card
Development resources:
• http://www.debian.org/doc/developers-reference/ -
Developer’s reference, useful for creating packages
• http://www.debian.org/doc/debian-policy/ - Debian
policy document
• http://www.debian.org/doc/maint-guide/ - New
Maintainer’s guide, ﬁrst steps to making a package


The end

Thank you


Presentation permissions
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Copyright (c) Richard Darst, 2010
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