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RPM Design Goals

The design goals of RPM could best be summed up with the phrase "something for everyone". While the main reason for the existence of RPM was to make it easier for Red Hat to build the several hundred packages that comprised their Linux distribution, it was not the only reason RPM was created. Let's take a look at the various requirements the Red Hat team used in their design of RPM:

Make it easy to get packages on and off the system

As we've seen earlier in this chapter, the act of installing a package can involve many complex steps. Entrusting these steps to a person who may not have the necessary experience is a strategy for failure. So the goal for RPM was to make it as easy as possible for anyone to install packages. The same holds true for removing packages. It is a complex and error-prone operation, and one that RPM should handle for the user.

The other side of this issue is that RPM should give the package builder almost total control in terms of how the package is installed. The reason for this is simple: if the package builders do their homework, their package should install and uninstall properly.

Make it easy to verify a package was installed correctly

Because software problems are a fact of life, the ability to verify the proper installation of a package is vital. If done properly, it should be possible to catch a variety of problems, including things such as missing or modified files.

Make it easy for the package builder

While we're dedicating an entire book to package management, in reality it should be a small portion of the package builder's job. Why? They've got better things to do! If they are the people that are actually creating the software to be packaged, that's where they should be spending the majority of their time.

Even if the package builder isn't actually writing software, they still have better things to do than worry about building packages. For instance, they may be responsible for building many packages. The less time spent on building an individual package translates to more packages that can be built.

Make it start with the original source code

Delving a bit more into the package builder's world, it was deemed important that RPM start with the original, unmodified source code. Why is this so important?

Using the original sources makes it possible to separate the changes required to build the package from any changes implemented to fix bugs, add new features, or anything else. This is a good thing for package builders, since many of them are not the original authors of the programs they package.

This separation makes it easy, months down the road, to know exactly what changes were made in order to get the package to build. This is important when a new version of the packaged software becomes available. Many times it's only necessary to apply the original "package building" changes to the newer software. At worst, the changes provide a starting point to determine what sorts of things might need to be changed in the new version.

Make it work on different computer architectures

One of the tougher things for a package builder to do is to take a program, make it run on more than one type of computer, and distribute packages for each. Because RPM makes it easy to take a program's original source code, add the changes necessary to get it to build, and produce a package for each architecture in one step, it can be pretty handy.