Using a build root

The build root is very similar to Root: (which is now legacy). By using Buildroot: in your spec file you are indicating that your package can be built (installed into and packaged from) a user-definable directory. This helps package building by normal users.

The Spec File

Simply use

  Buildroot: <dir>

in your spec file. The actual buildroot used by RPM during the build will be available to you (and your %prep, %build, and %install sections) as the environment variable RPM_BUILD_ROOT. You must make sure that the files for the package are installed into the proper buildroot. As with Root:, the files listed in the %files section should not contain the buildroot. For example, the following hypothetical spec file:

  Name: foo
  ...
  Root: /tmp
  
  %prep
  ...
  
  %build
  ...
  
  %install
  install -m755 fooprog /tmp/usr/bin/fooprog
  
  %files
  /usr/bin/fooprog

would be changed to:

  Name: foo
  ...
  BuildRoot: /tmp
  
  %prep
  ...
  
  %build
  ...
  
  %install
  install -m755 fooprog $RPM_BUILD_ROOT/usr/bin/fooprog
  
  %files
  /usr/bin/fooprog

Building With a Build Root

RPM will use the buildroot listed in the spec file as the default buildroot. There are two ways to override this. First, you can have “buildroot:

" in your rpmrc. Second, you can override the default, and any entry in an rpmrc by using "--buildroot " on the RPM command line.

Caveats using Build Roots

Care should be taken when using buildroots that the install directory is owned by the correct package. For example the file

	/usr/lib/perl5/site_perl/MD5.pm

is installed by the package perl-MD5. If we were to use a buildroot and specified

	%files  
	/usr/lib/perl5/site_perl

we would end up with the directory /usr/lib/perl5/site_perl being owned by the library package. This directory is in fact used by ALL perl libraries and should be owned by the package for perl not any of its libraries. It is important that the %files command specifies all the known directories explicitly. So this would be preferable:

	/usr/lib/perl5/site_perl/*

Since we only want the files and directories that the package perl-MD5 installed into /usr/lib/perl5/site_perl/ to be owned by the package. The directory /usr/lib/perl5/site_perl/ is created when perl is installed.

If we were to use the bad %files line shown above, then when the MD5 package is removed, RPM will try to remove each of the perl-MD5 files and then try to remove the dir itself. If there’s still files in the site_perl directory (e.g. from other packages) then the Unix rmdir(2) will fail and you will get a non-zero return code from RPM. If the rmdir succeeds then you will no longer have a site_perl directory on your machine even though this directory was created when Perl was installed.

The other common problem is that two packages could install two files with the the same name into the same directory. This would lead to other collision problems when removing the file. Care should be taken by the packager to ensure that all packages install unique files. Explicit use of %files can help make the packager aware of potential problems before they happen. When you try to install a package which contains file names already used by other packages on the system then RPM will warn you of the problem and give a fatal error. This error can be overridden with –force and the installed file will be replaced by the new file and when the new package is removed the file will be removed as well.