(If you have questions/comments about this answer, please add a comment. Or, if you have sufficient rep, you can ping me in chat.)
Directly installing binary packages from a newer version of Debian - not the answer.
Suppose you are running some version of a Debian-based distribution. You want a more recent version of a package than is available to you. The first thing that every beginner tries to do it to install the binary package directly on your version of Debian. This may or not work, depending on what version you are running, and how much newer the package is. In general, this procedure will not work well.
Consider for example the case where one is trying to install a binary package from testing/unstable directly on stable. This will most likely not go well, unless testing/unstable happen to very close to stable at that moment. The reason has to do with the nature of a Linux-based binary distribution like Debian. Such operating systems depend heavily on shared libraries, and these dependencies are often very tightly version-dependent; often much more so than necessary. Debian currently does not have a good way of making version dependencies "tight" - a shorthand way of saying that the version dependency is exactly as restrictive as necessary.
What does this mean for the user? Suppose for example that you are trying to install say
slrn from Debian unstable to Debian stable. What would this look like?
# apt-get install slrn/unstable
Reading package lists... Done
Building dependency tree
Reading state information... Done
Selected version '1.0.1-10' (Debian:testing [amd64]) for 'slrn'
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
slrn : Depends: libc6 (>= 2.15) but 2.13-38+deb7u1 is to be installed
E: Unable to correct problems, you have held broken packages.
Despite the error produced by
apt, there are no broken packages here. So, what went wrong? The problem is that the version of
libc6 that the unstable
slrn was compiled against is different (and has a higher version number) than the one available on Debian stable. (
libc6 is the GNU C library. The C library is central to any Unix-like operating system, and GNU C library is the version that Linux-based operating systems generally use.)
Therefore the unstable
slrn requires a higher numbered version of
libc6 than is available for stable. Note that because a package has been compiled against a higher version of library does not necessarily require a higher version of that library, but it is often the case.
apt-get install slrn/unstable
means: use the unstable
slrn but for all other packages only use the versions from stable. To be more precise, it uses priority numbers. See
man apt_preferences for details.
One can also do
apt-get install -t unstable slrn
This is much more likely to work, but you generally don't want to do it. Why?
This means: temporarily treat all packages in unstable on an equal footing with the packages in stable. Therefore this will pull in the unstable
slrn's dependencies from unstable if they are of a higher version number, and they generally will be. This will generally include the GNU C library for reasons already explained. Now, this approach will generally "succeed", in that the dependencies will be satisfied by definition (unstable's
slrn has dependencies which are satisfied in unstable), but you end up with a mixture of packages that suddenly are being forced to run with versions of libraries different from what they were built for. This will probably not end well.
The answer is... BACKPORTS!
So, what is the correct way to do this? It is to rebuild the Debian sources of more recent versions on your system, popularly known as "backporting".
Consider the following cases:
There are semiofficial/official sources of additional packages available for that version of Debian.
The first place to look is Debian Backports, which is the official site for Debian backports.
Another place to look at is the various PPAs by Ubuntu maintainers. You can do a search for "packagename PPA".
There are no more recent versions of the package available for that version of the OS, but there are more recent versions available for more recent versions/releases of the OS. This is the standard case for backporting.
Backporting means that you rebuild the Debian sources from a later version of Debian on the version you are running. This procedure may be easy or involved and difficult depending on the package. Here is an outline of how to do this.
A Brief Backporting Tutorial for Beginners
For concreteness I will assume you are running the current Debian stable, currently wheezy. I'll use the package
slrn as an example.
First, note that all the Debian packaging files live in the
debian/ subdirectory of the source directory.
The first step is to check whether a more recent version is available. You can do this using
apt-cache policy slrn
50 http://debian.lcs.mit.edu/debian/ testing/main amd64 Packages
50 http://debian.lcs.mit.edu/debian/ unstable/main amd64 Packages
*** 1.0.0~pre18-1.3 0
500 http://debian.lcs.mit.edu/debian/ wheezy/main amd64 Packages
500 http://debian.lcs.mit.edu/debian/ squeeze/main amd64 Packages
We would like to backport
NB: Make sure that the
deb-src lines for the source version you want to download appears in your
/etc/apt/sources.list. For example, if you want to download the unstable version of
slrn, you need the
deb-src line for unstable, or it won't work. Note that you don't need the corresponding
deb lines to download the sources, though
apt-cache policy uses that information, so if you don't have the corresponding
deb lines, then
apt-cache policy won't show you the relevant version(s). If you do have the
deb lines, don't forget to pin the newer versions using an entry in
/etc/apt/preferences or similar. An entry in
/etc/apt/preferences like this (for unstable) will work, for example.
Pin: release a=unstable
If you add lines in
/etc/apt/sources.list, don't forget to run
apt-get update afterwards.
Download the sources for
slrn. A good place is
apt-get source slrn=1.0.1-10
Change the version number slightly, so as to distinguish your backport from the upstream version. Run
dch -i, which will automatically add an entry to the
debian/changelog file. Then change the entry to look something like this, for example.
slrn (1.0.1-10.username) UNRELEASED; urgency=low
* Backport to wheezy.
-- User <user@domain> Sun, 02 Feb 2014 23:54:13 +0530
Attempt to build the sources. If the packages required for the build are not available, then the attempt will fail. Change directory into the source directory. Use
debuild from the
debuild -uc -us
If the build dependencies are satisfied, then the sources will build and produce some debs at the level above the source directory; in this case
Suppose the build dependencies are not satisfied. Then you need to try to install the build dependencies. This may or may not work, as the dependencies may not be available for your version, or if available, may not be available in the right version.
NB: It is unfortunately not uncommon for Debian packages to require versions of build dependencies that are higher than necessary. There is no automated way in Debian to check this, and often package maintainers don't care as long as it works on the corresponding version/release. Therefore, take a skeptical attitude to dependency versions, and use common sense. For example, widely used packages like Python and the GNU tools will not depend on very specific versions of their dependencies, regardless what the Debian packager lists.
In any case, you can try to install them doing
apt-get build-dep slrn=1.0.1-10
If this succeeds, then try building the package again (STEP 2). If it fails, then further work is needed. Note that
debuild looks at the Build Dependencies in the
debian/control file, and you can change these if necessary. So let us talk about that now. Here are the Build Dependencies for slrn.
Build-Depends: debhelper (>=9), libslang2-dev, libuu-dev,
exim4 | mail-transport-agent, libgnutls-openssl-dev, po-debconf, autoconf,
libcanlock2-dev, autotools-dev, dpkg-dev (>= 1.16.0), chrpath, dh-autoreconf, inn2-inews
An alternative to using
apt-get build-dep is to install these manually, by doing
apt-get install debhelper libslang2-dev ...
If you start changing these values in the control file, then you should switch to a manual installation, as then
apt-get build-dep will no longer be doing the right thing.
There are no packaged versions of more recent versions of the software available. Options available are to package the more recent version.
In many cases, one can reuse the packaging from earlier versions of the software in conjunction with newer sources. This approach can run into problems, notably patches that applied to earlier versions of the software may not apply here, so one may need to resync them with the sources. The 3.0 (quilt) source format which is now becoming standard uses quilt, and patches are located in the
However, a detailed discussion of these issues is out of scope for this post.