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It's common in the world of free software to study source code or even make corrections to buggy code. Building from source may also be useful if you want to enable features that are disabled in the official package, or disable some which is enabled. To do this, you would need to download the source of the program. The APT system provides an easy way to obtain source code to the many programs contained in the distribution, including all the files needed to create a .deb for the program.
Another common use of Debian sources is to adapt a more recent version of a program, from the unstable distribution, for example, for use with the stable distribution. Compiling a package against stable will generate .debs with dependencies adjusted to match the packages available in this distribution.
To accomplish this, the deb-src entry in your /etc/apt/sources.list should be pointed at unstable. It should also be enabled (uncommented). See section The /etc/apt/sources.list file, Section 3.1.
Aptitude, the Debian Package Manager is mainly targeted at binary packages. To
use source packages we'll need to use apt-get
instead. To
download a source package, you would use the following command:
$ apt-get source packagename
This will download three files: a .orig.tar.gz, a .dsc and a .diff.gz. In the case of debian-native packages, the last of these is not downloaded and the first usually won't have "orig" in the name.
The .dsc file is used by dpkg-source for unpacking the source package into the directory packagename-version. Within each downloaded source package there is a debian/ directory that contains the files needed for creating the .deb package.
To auto-build the package when it's been downloaded, just add -b to the command line, like this:
$ apt-get -b source packagename
If you decide not to create the .deb at the time of the download, you can create it later by running the following command from within the directory that was created for the package after downloading:
$ dpkg-buildpackage -rfakeroot -uc -b
Notice that to build most packages you'll need at least the following packages:
devscripts
, dpkg-dev
, debhelper
,
fakeroot
, take a look at Installing and reinstalling packages,
Section 4.4 and install them before proceeding. Most packages will also
depend on compilation tools, so it may be useful to install the
build-essential
package as well. Other packages may be needed,
take a look at Packages needed for compiling a source
package, Section 5.2 for more information.
To install the package built by the commands above one must use the package
manager directly. Take a look at Installing manually downloaded or
locally created debian packages, Section 4.5. A useful tool is provided by
the devscripts
package: debi
. If you run
debi
from inside the source package directory it will look for the
.changes file at the parent directory to discover what are the
binary packages the package produces and will run dpkg
to install
all of them. While this is not very useful if your source package produces
conflicting packages, it might be in most circunstances. Of course you need
root powers in order to perform this.
There's a difference between apt-get
's source method
and its other methods. The source method can be used by normal
users, without needing special root powers. The files are downloaded to the
directory from which the apt-get source package command was
called.
Normally, specific headers and shared libraries need to be present in order for a source package to be compiled. All source packages have a field in their control files called 'Build-Depends:' that indicates which additional packages are needed for the package to be built from source. Some basic packages are also needed, check Downloading source packages, Section 5.1 before continuing.
APT has a simple way of downloading these packages. Just run apt-get build-dep package, where `package' is the name of the package you're going to build. For example:
# apt-get build-dep gmc Reading Package Lists... Done Building Dependency Tree... Done The following NEW packages will be installed: comerr-dev e2fslibs-dev gdk-imlib-dev imlib-progs libgnome-dev libgnorba-dev libgpmg1-dev 0 packages upgraded, 7 newly installed, 0 to remove and 1 not upgraded. Need to get 1069kB of archives. After unpacking 3514kB will be used. Do you want to continue? [Y/n]
The packages that will be installed are the packages needed in order for
gmc
to be built correctly. It's important to note that this
command doesn't download the source package of the program to be compiled. You
will therefore need to run apt-get source separately to get it.
If all you want is checking what packages are needed to build a given package,
there's a showpkg method for apt-cache
command (see
Getting information about packages., Chapter 6,
which will show, among other informations, the Build-Depends line
that lists those packages.
# apt-cache showsrc package
If you want to build a package for debuging purposes to, for example, report a bug -- or fix one, you can use simple environment variables that are supported by most Debian packages.
To build a package which contains unstriped binaries[6] all you need to do is prefix it with DEB_BUILD_OPTIONS=nostrip. Optimizations can also make debuging harder, so you can disable them by adding the noopt string to the DEB_BUILD_OPTIONS variable too. Example:
$ DEB_BUILD_OPTIONS="nostrip noopt" dpkg-buildpackage -rfakeroot -uc -b
If what you want is to customize the way the package is built you'll have to go
about editing the debian/rules
file. This means: inside the main
directory created when the source package is extracted there will be a
debian directory, which contains many files. One of them is
special: the rules
file.
This file is usually a Makefile that has targets to configure, build, install
and create the package. For example, if I want to have the
luola
[7] built
without sound I can, after downloading and extracting its source edit the
debian/rules
file that looks like this:
[...] configure: configure-stamp configure-stamp: dh_testdir # Add here commands to configure the package. ./configure $(confflags) \ --prefix=/usr \ --mandir=share/man \ --infodir=share/info \ --datadir=share/games \ --bindir=games \ --enable-sound # --enable-sdl-gfx touch configure-stamp [...]
See the --enable-sound switch? If I remove it or replace it with --disable-sound and then rebuild the package using the technique described on Downloading source packages, Section 5.1 I'll have a luola package that is built with no sound.
If you really want to work with source packages on a daily basis I would
suggest reading the Debian New Maintainers
Guide
and the Debian Policy
,
mainly. Other documentation available from the Debian Developers Corner
may be
useful too.
Sometimes, people want to use a specific version of a program available only on source code, with no Debian package. But the packaging system can be a trouble when doing this. Suppose you want to compile a new version of your email server. All is fine, but many packages in Debian depend on an MTA (Mail Transfer Agent). Since you installed something you compiled by yourself, the packaging system doesn't know about it.
That's where equivs
enters the scene. To use it, install the
package with that name. Equivs creates an empty package that fullfills
dependencies, making the package system believe that the dependencies are
satisfied.
Before we begin, it is good to remind you that there are safer ways of compiling a program which is already packaged for Debian with different options, and that one should not use equivs to replace dependencies if she doesn't know what she is doing. See Downloading source packages, Section 5.1 for more information.
Let's continue with the MTA example, you just installed your new compiled
postfix
and goes on for installing mutt
. Suddenly
you discover that mutt
wants to install another MTA. But you
already have yours.
Go to some directory (/tmp
, for example) and run:
# equivs-control name
Replace name for the name of the control file you want to create. The file will be created as the following:
Section: misc Priority: optional Standards-Version: 3.5.10 Package: <enter package name; defaults to equivs-dummy> Version: <enter version here; defaults to 1.0> Maintainer: Your Name <yourname@foo.com> Pre-Depends: <packages> Depends: <packages> Recommends: <packages> Suggests: <package> Provides: <(virtual)package> Architecture: all Copyright: <copyright file; defaults to GPL2> Changelog: <changelog file; defaults to a generic changelog> Readme: <README.Debian file; defaults to a generic one> Extra-Files: <additional files for the doc directory, commaseperated> Description: <short description; defaults to some wise words> long description and info . second paragraph
We just need modify this to do what we want. Have a look at the field's format and at their descriptions, there's no need to explain each one here, let's look at an example instead:
Section: misc Priority: optional Standards-Version: 3.0.1 Package: mta-local Conflicts: mail-transport-agent Replaces: mail-transport-agent Provides: mail-transport-agent
Yes, that's all. mutt
depends on
mail-transport-agent
, that is a virtual package provided by all
MTAs, mta-local "registers" itself as an mail-transport-agent using
the Provides field.
The Conflicts and Replaces fields are needed, too, so
that APT
and dpkg
will understand they should remove
the currently installed MTA package in favour of the new one you're installing.
Now you only need to build the package:
# equivs-build name dh_testdir touch build-stamp dh_testdir dh_testroot dh_clean -k # Add here commands to install the package into debian/tmp. touch install-stamp dh_testdir dh_testroot dh_installdocs dh_installchangelogs dh_compress dh_fixperms dh_installdeb dh_gencontrol dh_md5sums dh_builddeb dpkg-deb: building package `name' in `../name_1.0_all.deb'. The package has been created. Attention, the package has been created in the current directory,
And install the resulting .deb. See Installing manually downloaded or locally created debian packages, Section 4.5.
As one can see, there are several uses for equivs
. One can even
create a my-favorites package, which depends on the programs you
usually installs, for example. Just free your imagination, although being
carefull.
It is important to note that there are example control files in
/usr/share/doc/equivs/examples
. Check them out.
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APT HOWTO
2.0.2 - October 2006kov@debian.org