A relocatable package allows a user to specify where to install the package. For example, if you build a package for Red Hat Linux, the normal directory for binary executable programs is /usr/bin. Other versions of Linux, though, may place executable programs into /opt/bin, for example. If your package forces the use of /usr/bin, then your package won’t work on these other systems.
Cross Reference
Chapter 19 covers using RPM on other versions of Linux.
With a relocatable package, though, you allow the user to redefine the top-level directories for your package, such as changing from /usr/bin to /opt/bin in the previous example. Making relocatable packages is generally considered a good thing, as you make the user’s life easier.
To set up a relocatable package, you need to:
*Set up the prefix directives for the top-level directories
*Define the files under the prefix directories
The Prefix: directive names a top-level directory as a prefix you can relocate to another directory. For example:
Prefix: /usr
This states that all files under /usr can be relocated to other directories by simply mapping /usr to some other directory, such as /opt, on the rpm command line when installing or upgrading the package.
Note
You can define more than one Prefix: directive to list more than one top-level directory.
When you use a Prefix: directive in your spec file, all files in the %files section must be under the directory named with the Prefix: directive. For example, from the jikes compiler package:
Prefix: /usr
...
%files
%defattr(-,root,root)
/usr/bin/jikes
%doc /usr/doc/jikes-%{version}/license.htm
%doc /usr/man/man1/jikes.1*
In this example, all the files are under the /usr directory. All files in the %files section must be located under one of the Prefix: directories. If you have more than one top-level directory, such as /usr and /etc, define more than one Prefix: directive. For example:
Prefix: /usr
Prefix: /etc
Cross Reference
Chapter 4 covers how to install or upgrade packages into different directories using the --relocate and --prefix options.
Not all packages work well as relocatable packages. Some packages have files that simply must go into a certain location and are therefore not relocatable. Some packages have programs that are hard-coded to look for files in a particular location and therefore cannot be relocated elsewhere. Other packages have symbolic links that also may not be relocatable. Furthermore, your package may provide software that is referenced by other packages, in the known directories. Relocating such a package will disable other software packages, packages you may not even know about.
If your packages face any of these problems, chances are that making the package relocatable is not a good idea.
In addition, if you use the %doc directive with local file names, remember that RPM will make a package-specific documentation directory, normally under /usr/doc. For example:
%doc README NEWS
This may defeat your attempts to create a relocatable package, unless you have a Prefix: directive with /usr, because the normal location is under /usr/doc, and all files in the %files section must start with one of the directories named with Prefix: directives.