AutoPackage – Introduction to the Next Generation Linux Packaging

If you’ve used Linux for more than ten minutes, you’ve almost certainly come across the nightmare that is package management. You know what I mean – dependancy hell has become legendary and it’s no exagguration to say that one of the most offputting aspects of Linux for a new user is the lack of InstallShield type 3 click installs. This article looks at how we ended up in the quagmire of RPM and dependancy hell, and then moves on to talk about a possible solution in the form of autopackage. It takes a high level overview of how autopackage works and what it’s capable of. If you want more technical details, check out the website. Finally, this article assumes only that you’re interested, not that you have any Linux experience.

First off, I’m not going to assume you’ve used Linux before, so I’ll start with a few definitions:

  • RPM: The Redhat package manager. Despite the name, it’s
    used by many Linux distributions and is probably the most popular
    package manager statistically speaking today. Unfortunately,
    RPM has many faults, perhaps the most important being that it was
    never designed for internet based distribution of software for Linux
    in general. What this means is that it’s optimized for transferring
    large amounts of software to an OS from a CD or Redhat update
    site. Because of the lack of flexibility in the RPM file format,
    various distros have tweaked it and so forked the format – if you
    want to install an RPM you’d better be sure it’s designed for your
    distro. Only the very simplest of packages can be realistically
    distributed in this way by third parties. To make matters worse
    RedHat often gratuitously break backwards compatability.
  • Dependancy hell: Due to the non commercial nature of
    Linux, packages often have lots of dependancies. These are other
    packages that must be installed before that package can be
    installed, we say one depends on the other. All operating
    systems have dependancies, but Linux software has far more than
    most. Dependancy hell arises when you want to install a package, but
    your system doesn’t have the required dependancies present. Raw RPM
    cannot fix this itself – you must manually track down and install
    those packages. Just pray that there are no sub-dependancies as
    well!
  • APT: Advanced Packaging Tools, originally built for
    Debian and later ported to RPM, apt can automatically resolve
    dependancies. Installing software with apt is easy, even easier than
    on Windows – you just type in the name of the software you want, for
    instance with apt-get install gimp. Unfortunately, apt
    requires centralised repositories to be maintained for every distro
    (and often, every subversion), and as such often the software you
    want is simply not available in the repositories, or it is present,
    but its dependancies are not. Although Debian has many thousands of
    packages in its repositories, the manpower required to keep them all
    up to date means the latest versions of the packages are often only
    available in Debian some time after they have been
    released. emerge is a similar idea, but tied to Gentoo.
  • RPM Hell: another type of unpleasantness that is caused
    by the type of package managers in use today on Linux. If the
    software you want to install isn’t available as a package for your
    distro then all is not lost, you can just compile it from the source
    (which unless you use a ports based distro a la Gentoo has its own
    set of problems). Unfortunately, you just entered the twilight zone:
    RPM (and also the debian system) assume that you use them to install
    everything on your computer. Because often packages are not
    available of course this doesn’t happen, but then RPM is not aware
    of the presence of those packages and will refuse to install other
    packages that depend on them without manual overrides. Hacks around
    this problem exist (see checkinstall) but they only partially solve
    the problem

Having witnessed several of my friends try Linux only to give up in
disgust after spending several hours attempting to do something as
trivial as upgrade Mozilla, I resolved to do something about the
problem. So, what issues do we face, and how to other operating
systems fix these issues?

The first one is that RPM doesn’t posseses enough flexibility to
deal with the myriad little differences between distributions. An RPM
is basically made up of a list of files and a set of pre and post
install scripts. The list of files is always relative to root, so if
your distro does not use the exact same filing system layout as the
one it was built for, the RPM will not install correctly. Another
example of distro differences would be the “install-info” script,
which is responsible for integrating TeXinfo manuals into the system:
Debian has its own version which is incompatible with the Free
Software Foundation version used in most other forms of Linux.

Another issue, perhaps one of the biggest, is that there are no
standard mechanisms for naming packages. Because of that, an RPM
designed for one system will know dependancies by different names to
that of another. The difference between package “python-dev” and
“python-devel” may be small, but it’s enough to break
compatability.

Finally, you have differences in the compiled binaries
themselves. A KDE application compiled for Redhat 7.3 will not install
on Redhat 8 as they use different versions of gcc, and the binaries
produced by these compilers are not compatible. RPM has no way of
dealing with this other than to force people to have 2 different
packages for the 2 different versions.

A bit of a mess isn’t it? If you’re a Windows or Mac user you’re
probably feeling a bit smug right now, but actually there’s no reason
to be. Windows and MacOS both have ways of dealing with these issues,
and neither of them are particularly elegant. On Windows, we are all
familiar with the name InstallShield. The standard mechanism for
installing software onto Windows has for many years been to create an
installer executable that the user runs and then extracts the program
from itself and performs any needed setup. The installer checks
dependancies (usually different versions of MS dlls) and often
contains copies of them just in case they aren’t present. Finally it
integrates the program with the environment (often too well!) by
creating menu entries, app associations and so on.

Why does this system suck? Well, from the point of view of the
user, it doesn’t, the experience is simple, fast and effective. Behind
the scenes however, things are rather ugly. For starters, modern
installers are complex beasts – InstallShield is actually a complete
scripting language and all the code necessary to interpret these
scripts, create the user front ends etc are shipped with the Windows
app in every single case. This is pretty wasteful, and the need to
ship all the DLLs an app might require just in case they are not
present on the system also adds a lot of overhead.

Installer executables bring with them their own set of
problems. The user interface is often inconsistent, and they are extremely
hard to automate. I once spent a week at a company in which all I did
was travel to every computer and put in the IE6 upgrade CD for each
one. There was almost no good way of transparently deploying
applications. Although products do exist that automate this on
Windows, they usually work by watching what the installer does then
“rebuilding” the installation from scratch which can lead to all kinds
of nasty issues. The current system was never really designed as such,
in the absence of any solution provided by Microsoft companies sprung
up to fill the gap. Windows is now moving to an appfolders style
system whereby dependancies can be sideloaded in an attempt to avoid
dependancies also.

Does the Mac fare any better? Unfortunately not. MacOS X has (in theory) totally eschewed installers in favour of App Folders, which are specially marked directories, the idea being that you simply drag and drop the app into the Applications directory. To uninstall, just drag it to the wastebasket. This is good UI, but bad everything else. By eliminating (un)install logic, it becomes extremely hard to check for dependancies, to provide system components, to clean up configuration changes, other application metadata and so on. Although technically apps can have dependancies via bundles, the lack of OS side install logic means that in practice it’s not possible to install these bundles into the OS if required – the user must do it for the app. As such, apps can only rely on funtionality that was known to ship with the operating system. That suits Apples goal of selling more copies of OS X, but is rather limiting for the user. By trying to hide the problems dependancies pose all together, it creates bigger problems further down the line. As such, some Mac apps ship with install apps anyway which rather defeats the point. Note that my beef with appfolders are more to do with the way they have been implemented in NeXTStep – you can use autopackage to install apps into an appfolders style arrangement (for instance i test with
/apps/packagename) and one day there may well be a VFS plugin that lets you view installed packages as folders/directories. I think it is highly unlikely that you’ll ever be able to just drag app directories off a CD onto the system however.

So does Linux have the right idea? Yes, it does. Operating systems
are just that – systems, systems that are made up of multiple
components. In the absence of centralised control and the use of
parallel development, properly managing dependancies and system
differences is a must. The problem is that we don’t do it very
well. So how can we improve?

I think the answer lies in autopackage, a project I started work on
over 6 months ago in response to these issues. It uses a variety of
ideas and approaches to solve the problems posed by Linux package
management.

  • Distribution neutral: unlike many package managers, autopackage
    was not developed by a distribution project. As such, it is
    completely distribution neutral both in technical design and
    political stance. You can build an autopackage once, and it will (in
    theory πŸ™‚ install on any distro, assuming it’s not totally off this
    planet.
  • Designed for flexibility: In a similar vein to
    InstallShield a .package file is script based rather than table
    based. The install scripts, backed up by a large number of provided
    library funtions, are easily capable of dealing with the multitude
    of differences between distributions.
  • Net based: RPM was designed to manage everything a distro comes
    with, from the kernel to the Solitaire games. In contrast,
    autopackage is designed for net based distribution of software. It’s
    not designed to install new kernels, or to be used exclusively by a
    distro (maybe one day it would be capable of this too, but it’s not
    a design priority). As a part of the project we will be constructing
    the autopackage network, a network of resolution servers that
    work like DNS to convert root names (see below) into URLs for where
    the packages can be downloaded. By turning our back on the idea of
    apt-style massively centralised repositories, we hope to allow the
    network to scale. If a programmer creates a piece of software, they
    don’t have to wait for somebody from the network to create a package
    and upload it for them, they can create it themselves and then
    register their own node of the network from which they can plug in
    any packages they may create
  • Global names: from the start, autopackage was designed to allow
    packages to have multiple names. All packages must have a root name,
    to which other names can map to. A root name looks something like
    this: “@gnome.org/gedit/2.2”. As you can see, rather than creating a
    new naming authority, it leverages off the DNS system. As most
    projects these days have a website, they can easily be assigned a
    root name. Other, more human friendly names include short names,
    which are rpm style (for instance “gimp”, “gnome2” or “xchat-text”),
    and display names, which describe in the users native language
    briefly what the application is, ie “Evolution Mail
    Client”.
  • Database independant dependancy management: the approach
    autopackage takes to dependancies is similar to the configure
    scripts we all use, in that it checks the system directly for the
    presence of the dependancy, ie for libraries it will check the
    systems linker cache. I won’t go into the exact details of this
    system, you can find out more information from the website.
  • Front end independance: right now we have only a terminal front
    end, and very pretty it is too. As we work towards 0.3, we’ll be
    developing a graphical front end based on GTK. We’ll also be adding
    a front end that records your choices and can then play them back,
    allowing seamless automation of installs. By insulating packages
    from the details of how they interact with the user, packages are
    simpler to build and we can get much better integration with the
    users host environment. The best is chosen automatically, so if you
    install the package from the command line it’ll use the terminal
    front end, and if you install it from Nautilus or Konqueror (visual
    file managers) it’ll use the graphical front end.
  • Automatic and easy: installing a .package file is simply a
    matter of running it. If you’ve never used autopackage before, the
    needed files will be downloaded and setup for you. Packages have
    minimal bloat because of this, so far it runs to about 11kb.

So is this just fantasy, a pipe dream? Not at all thankfully, a few
days ago we released 0.2 which can build, install, verify, query and
uninstall packages in a distro-neutral fashion. We’re a long way from
having a complete solution to the problem, but let’s hope that in a
few years the days of RPM hell will be long forgotten.

About the Author:
I’m Mike Hearn, an 18 year old from England who has been using Linux for about a year. By day I work for what was Ministry of Defence research, and by night I hack on free software (when i’m not out with friends ;). I also help run the theoretic.com website and am a chronic daydreamer πŸ™‚

102 Comments

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