3. RPM packages

The major part of the Red Hat distribution consists of a set of RPM (Redhat Package Manager) files. An RPM package typically contains binary executables, along with relevant configuration files and documentation. The rpm program is a powerful package manager, which can be used to install, query, verify, update, erase and build software packages in the RPM format. Rpm convieniently maintains a database of all the software packages it has installed, so information on the installed software is available at any time.

The binary RPM files in the distribution have been built on a system running the distribution itself. This is important, because most of the programs in the packages rely on shared libraries. From RedHat version 5.0, the new version 2 of the GNU standard C library (which is 64-bit clean) has been used. This version of the library is commonly referred to as glibc or in Linux: libc 6. All executables in the distribution have been linked against this library. If you attempt to install binary files from a different distribution, chances are that they will not work, unless you install the libc5 package for backwards compability. There are also incompatibilities between the various version of the Redhat Package Manager itself which will make the installation of some packages fail even on machines they are supposed to (and they would probably) run on.

The names of the RPM packages contain the suffix .arch.rpm, where arch is the architecture, usually having the value i386 for Intel platform binaries. The packages you install must match the versions of the shared libraries available on the machine. The rpm program is usually quite good at ensuring that this is indeed the case, however, there are ways around this check, and you should be sure that you know what you are doing if you force installation of packages this way. However, using the RedHat installation boot disk, it is ensured that the correct set of RPM packages are installed on the machine.

If you discover a RPM package that was not installed on your system during the installation process, don't despair. At any time, you may (as root) install RPM packages, for example:

# rpm --install WindowMaker-0.18-1b.i386.rpm

You can even install directly from the Internet, if you know the URL of a RPM package:

# rpm --install ftp://rufus.w3.org/redhat-contrib/noarch/mirror-2.9-2.noarch.rpm

If you want to update (or install if it's not present on the machine) a RPM package, use the command:

# rpm --update WindowMaker-0.18-1b.i386.rpm

If you want to update a RPM package only if a previous version is already installed on the machine use the command:

# rpm --freshen WindowMaker-0.18-1b.i386.rpm

Another version of the RPM packages contains the original sources used to build the binaries. These packages have the suffix .src.rpm and are situated in the SRPMS directory. These packages compose the last two CDs and part of the third one out of the five which compose the 8.0 (or 7.3) release. For 6.2 (and previous, not too old, versions), things change a bit because there is only one installation CD not comprising the SRPMS packages, which you can burn on a different disc, if you want.

To obtain more informations on the Redhat package manager, I suggest you to read the man pages and the fairly detailed book maximum rpm.

In the next section, I will introduce a C program which will be used in various scripts throughout the rest of the howto. It just returns, given two versions of the same RPM package, which one is newer. This program is based on the code used in the Redhat Package Manager (release 4.1) and is used when the --freshen option is given.