Understanding Debian Packages

Fri Jun 25 05:57:50 2004 Understanding Deb Packages

Posted by Drag
Search Keys: debian packages rpm deb package dpkg
Referencing: /Words/2004_06_25.html

I wouldn't exactly call RPMS and Deb packages complicated.

RPM's are simply a cpio archive.

Debs I know a bit more about.

Debs are a "ar" archive, with 2 tarballs inside them and debian-binary text file to identify which generation of deb file it is (I am supposing).

One tarball is the control.tar.gz file, and that contains 4 text files. "conffiles" show a list what config files the program uses (they usually get left after a uninstall unless you use the --purge flag), "control" contains the "meat" of the control of the package.

When you update against a online repository you download a text file that contains all the inputs from the confiles. It tells dpkg how to handle the file.

This is the containts of the conf file for "3ddesktop":

Package: 3ddesktop
Version: 0.2.4-1
Section: utils
Priority: optional
Architecture: i386
Depends: libc6 (>= 2.3.1-1), libgcc1 (>= 1:3.2.1-1), libglut3, libimlib2, libstdc++5 (>= 1:3.2.1-1), libttf2, xlibmesa3 | libgl1, xlibs (>> 4.1.0)
Installed-Size: 400
Maintainer: Marcelo E. Magallon 
Description: "Three-dimensional" desktop switcher
 3D-Desktop is an OpenGL program for switching virtual desktops in
 a seamless 3-dimensional manner.  The current desktop is mapped into a
 fullscreen 3D environment where you may choose other screens.  Several
 different visualization modes are available.  A window manager
 compatible with the GNOME pager standard is required.
 .
 The transition from working desktop to fullscreen 3D environment is
 seamless: when the pager activates you see your current desktop appear
 to zoom out to a point in space where you can see your other virtual
 desktops allowing you to select another.
 .
 The program is rather memory-hungry and it is CPU intensive, but it's
 accessible from the command line, which makes it perfect for show
 floors and impressing your non-UN*X-using friends.

It's all pretty self explanatory. This is all the information dkpg needs to handle your package correctly. A simple text file.

The 3rd text file in control.tar.gz has the md5sums of the files that will actually get installed on your OS, so to check and make sure nothing is corrupted before it gets copied into your file system.

The 4th file contains postinst and prerm bash scripts for any little thing that you have to do to the OS besides copying the files to make them work after you install the package, or before you remove the package.

Both the script file and the md5sum file are optional.

Data.tar.gz is a traditional unix tarball that contains the files you need going to install.

So you see it's not very complicated at all.

The complicated part comes into action when you need to have package maintainers that are disicplined enough to be able to cooridinate the efforts of thousands of maintainers and developers in order to make sure that every one of the 100,000+ packages aviable for debian's OS is kept in working order.

Debian maintains 3 active versions of it's OSes, Stable, Testing, Unstable. It officially supports 10 different ports (x86, 68k(motorola), Sun sparc, Alpha, PowerPC, HP PA-RISC, IA-64, S/390.) with 2 more being developed. Also has 3 non-linux versions GNU/Hurd, GNU/FreeBSD, GNU/NetBSD.

Of course x86 GNU/Linux is the best supported. Also PowerPC is pretty good,too.

Deb package files are very simple thing to mess around with, but are very powerful. They are easy enough that you can easily create your own versions for casual use or for administrating a network of machines so that you can easily install custom programs or configs on them.

For more details check out the http://tldp.org/HOWTO/Debian-Binary-Package-Building-HOWTO/ site for a howto.

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