Working with Debian binary packages

Posted by Steve on Sun 27 Mar 2005 at 18:11

The Debian distribution is one which is based upon binary packages, which are built from by developers from source, and then uploaded into the archive and mirrors. Obtaining the source code which is used to build packages is very simple - but sometimes you might want to work with the binary packages.

The Debian binary format is very simple, it is nothing more complex than an archive produced using the ar tool containing two files:

data.tar.gz
- This archive is contains the binaries/manpages/whatever which the package is going to install.
control.tar.gz
- This archive contains book-keeping information and information about the package. Along with scripts which run as part of the installation/removal process.

If you have the binary .deb file for a given package you can unpack it's contents in two ways, using ar or using the dpkg command.

The second method is simplest:

skx@mystery:~$ dpkg -x komi_1.03-1_i386.deb tmp
skx@mystery:~$ ls tmp/
usr  var

As you can see we've extracted the contents of the komi package into the directory tmp, which now contains the package.

If you were sufficiently motivated you could "install" binary packages beneath your home directory by unpacking them and setting up your PATH appropriately.

Using ar to unpack the contents is almost as easy, first of all you need to unpack the two .tar.gz files:

skx@mystery:~$ ar -x komi_1.03-1_i386.deb control.tar.gz
skx@mystery:~$ ar -x komi_1.03-1_i386.deb data.tar.gz

Once this has been done you can list the contents of the data file, by running:

skx@mystery:~$ tar -tzvf data.tar.gz
drwxr-xr-x root/root         0 2004-07-12 15:47:05 ./
drwxr-xr-x root/root         0 2004-07-12 15:47:04 ./usr/
drwxr-xr-x root/root         0 2004-07-12 15:47:05 ./usr/games/
-rwxr-xr-x root/root     69464 2004-07-12 15:47:05 ./usr/games/komi
drwxr-xr-x root/root         0 2004-07-12 15:47:04 ./usr/share/
drwxr-xr-x root/root         0 2004-07-12 15:47:03 ./usr/share/games/
.... snip ....

The contents of the control archive are interesting too:

skx@mystery:~$ tar -tzvf control.tar.gz
drwxr-xr-x root/root         0 2004-07-12 15:47:06 ./
-rwxr-xr-x root/root       173 2004-07-12 15:47:05 ./postinst
-rwxr-xr-x root/root       160 2004-07-12 15:47:05 ./postrm
-rw-r--r-- root/root      5472 2004-07-12 15:47:06 ./md5sums
-rw-r--r-- root/root       626 2004-07-12 15:47:06 ./control

Here you can see the some files, postinst is a script which runs post install. postrm is another script which runs post-remove. The control contains information about the package, dependencies etc, and the md5sums contains checksums of all the files in the data.tar.gz file.

If you wished you could make changes to the control file and repack the whole thing - this might be useful if you wish to force the installation of a package by removing a dependency, or performing similar magic.

ar is a pretty simple tool to work with, and is fully described in the fine manpage:

man ar

This article can be found online at the Debian Administration website at the following bookmarkable URL:

http://www.debian-administration.org/articles/116