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Making Your Package Match Your Environment

Instead of having to worry and document foo as an exception, just package foo using your distribution's package tools and install it like any other package. There was a time when I felt like this was a pipe dream; having everything in the package manager meant a lot of work to me. But the alternative—being bitten during upgrades because foo was unknown to the package manager—can be a lot of work too. Fortunately, free software has come a long way. Most things you need are in your distribution already, so you can deploy a new version by simply compiling the new version within the constructs of the existing package version's build scripts. In short, fetch the source package from your distribution and build the package on your target system.

For packages not yet in your distribution, GNU's autoconf (which creates those handy "configure" scripts) and a generally improving skill set and standardization among free software developers have gone a long way toward making packaging from scratch a snap. Let's get down the specifics of how you'd package a new version of foo for your system using the Debian package-management tools. For our first example, let's assume that foo- 1.0 is the current version on our system and that the distribution provides for the version of the operating system we're running. There is a foo-2.0 available, but it's for the beta version of the operating system, and when we tried to load it we received all sorts of package-dependency warnings like those listed below:

root@bach:/tmp# dpkg --install foo_2.0-1_i386.deb
(Reading database ... 26613 files and directories currently installed.)
Preparing to replace foo 1.0-1 (using foo_2.0-1_i386.deb) ...
Unpacking replacement foo ...
dpkg: dependency problems prevent configuration of foo:
 foo depends on libc6 (>= 2.1.97); however:
  Version of libc6 on system is 2.1.3-13.
dpkg: error processing foo (--install):
 dependency problems - leaving unconfigured
Errors were encountered while processing:

(Re)building a Package for Your Environment on a Debian System

You need to set up APT (the Advance Package Tool) to pull from the latest available source packages. APT is similar in function to Red Hat's package manager and allows you to pull your binary and source package from a variety of sources. /etc/apt/sources.list controls where APT looks for software. The format is <type> <location> <release> <section(s)>:

# /etc/apt/sources.list
# <type> "deb" means binary packages
deb ftp://ftp.freesoftware.com/pub/linux/debian stable main contrib non-free
deb http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
deb http://security.debian.org/debian-security stable updates/main updates/contrib updates/non-free
# <type> deb-src means source packages
deb-src ftp://ftp.freesoftware.com/pub/linux/debian unstable main contrib non-free
deb-src file:/local-pkgs/debian stable main

In the preceding /etc/apt/sources.list, the bulk of the distribution is pulled from a nearby mirror (ftp.freesoftware.com), while non–U.S. (code that ITAR won't let Americans export) is pulled from a location outside the United States, and security updates come from Debian's security archive. The two deb-src URLs indicate where source packages should be pulled from. Note that the <release> field for source packages is set to unstable so that I can pull from the latest available version. I also have a file URL for the packages I maintain.

Any time APT sources are modified, you have to instruct APT to contact each of the archives listed and pull the current list of packages available from there with this command:

apt-get update

Once that's complete, we're ready to pull the source for foo-2.0 and build it on our system (and against our libraries):

root@bach:/tmp$ apt-get source foo --compile

This command instructs APT to pull the package sources, extract them, and then compile them using dpkg-buildpackage, Debian's main tool for building .debs. In case you're wondering, you don't have to run this command as root—in fact, you probably shouldn't. A tool called fakeroot can be used to trick the package build scripts into thinking that you are root during the build process (so that permissions for the foo binary can be set appropriately). To do this, drop the --compile option and execute these commands after the apt-get source <package>:

tony@bach:/tmp$ cd foo-2.0
tony@bach:/tmp/foo-2.0$ dpkg-buildpackage -rfakeroot -uc -us

The -r will call fakeroot for us, and the -uc and -us switches simply indicate that we're not going to be signing the resulting package with the GPG key of the package maintainer. If all goes well, there will be a newly created foo_2.0-1_i386.deb sitting in /tmp.

Of course, you need to load the appropriate compilers and development libraries to build the binary itself. These are the same things you would need if you were to pull the original ("upstream") source and compile it yourself. To try to make things easier for Debian users, a Build-depends: line in ./foo-2.0/debian/control lists packages required to build the foo package.

Packaging from Scratch

The process just described is great when a source package is available with the version you need, but what about when the source package is outdated, or there's no package foo in your distribution? In that case, you'll need to build a package from scratch, using your distribution's tools. This may sound daunting, but please hear me out before you decide that this is simply too much work. You may be pleasantly surprised, and a little extra time up front builds the package for any number of boxes—and can save you expensive troubleshooting and/or downtime later.

Let's assume that we need qux, and our distribution doesn't currently ship with qux, nor can we find qux binary packages by browsing around the Web. We've retrieved the upstream tarball, qux_1.2.tgz, and we should extract it into a directory named qux-1.2 (a well-mannered tarball will do this for us anyway, so check the contents of the tarball with tar tzvf qux_1.2.tgz before you go to any trouble). Now, on a Debian system, change directories to qux-1.2 and invoke this command:

tony@bach:/tmp/qux/qux-1.2$ dh_make -s -etmancill@debian.org

Take a look at the build: and install: targets in debian/rules (it's a Makefile) to make sure that they do reasonable things, that is, the things that you would do from a command line to build the package yourself. About the only trick is that you want files (binaries, man pages—whatever comprises the package) to end up under debian/tmp/, as this represents the root of what will be copied over when the package is installed. Also add a comment or two to debian/changelog to indicate anything special about this release (this is also where you'll indicate the version number of the package). Once you're satisfied, use the dpkg-buildpackage command as shown previously to build your .deb.

Now, let's not beat around the bush—building packages can be complex. Often the packaging is involved because of how the software interacts with other packages and subsystems on the box. (Does it need to update inetd.conf and restart inetd? Is it a daemon that needs to be started on bootup? Do configuration files need to be converted from formats used by older versions of the package?) But the process is conceptually simple, and the difficult part is learning the arbitrary nuances of the package-building tools. So it's not much different from UNIX itself… The key is to take the time to read the documentation and not be intimidated by your first attempt. By building your own packages, you gain ultimate control over what's installed in your environment, including configuration files precustomized for your environment, site-specific documentation in the man pages, and binaries compiled with optimizations for your processor.

Now, after you build a slew of local packages, you need some easy way to distribute them. If you have to run around and install them by hand, you might as well just compile them by hand on every box! (Not really, since you'd be missing the point of having the software under the packaging system.) The sample /etc/apt/sources.list presented earlier should give you an idea; simply create your own local mirror and add the appropriate URL to all of your production systems' sources.list files. This provides an excellent way to control what's loaded into your environment, by giving you the opportunity to create local versions of packages that are either newer versions than those that ship with the distribution, or preconfigured for your environment. Keeping all your local packages in one central repository also helps you keep versions consistent across your environment.

As justification for building your own packages, I covered one type of dependency problem—the case where the binary is compiled against a newer library version than what you have installed. I should discuss a couple other dependency issues that can be resolved by rolling your own packages:

  • Dependencies on a particular kernel revision. Some system tools are sensitive to the kernel version on your system, and may break after a kernel upgrade. This is because the program may access /proc/kcore and/or need to access kernel data structures directly. (lsof is an example.) These programs use the header files in /usr/src/linux/include to determine the appropriate data structures to use to represent certain kernel memory objects, so a new kernel can mean new data structures. In most cases, the program merely needs to be compiled on a system running the same version of the kernel as the target environment.

  • Dependencies on newer versions of supporting libraries. Libraries evolve to include new functionality, and a developer may require that you run at least version X.Y to run foo-2.0. An example would be a dependency upon a particular version of GTK. (GTK is a GUI toolkit; see http://www.gtk.org.) Now you not only need to build a new foo package, but you have to upgrade libfoo as well. You might want to go ahead and build packages for both, but take note. Other packages that depend on libfoo may not be happy with the new library version, so you could end up recompiling for everything that depends on libfoo. This was probably not your intention, and really could result in a lot of work. In this situation, you may want to build a foo package that contains binaries statically linked against the newer version of libfoo. Note that this alternative may not be suitable for binaries that are being spawned very rapidly, such as a CGI program on a Web server, as process creation can be more expensive for statically linked binaries.

Having all of your system software under control is a Good Thing. It may take a bit more effort up front, but this effort is the difference between a point-in-time solution (quickly installing foo by hand and having to deal with issues down the road) and a solution that will survive future system changes. Installing all software via the package manager helps create consistency across installation and troubleshooting procedures, and it makes version inventory a snap. Furthermore, getting acquainted with your distribution's package tool will help you understand issues you may encounter during upgrades or with other third-party packages. For the more community-minded, you can share your packages with others and the Open Source community at large.

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