rpmbuild(8) is a command to build a RPM file (binary software package.) Usually rpmbuild's build process is running with only one CPU. But it is possible to run with more than one CPU. To run with more than one CPU, edit ~/.rpmmacros and add: 

%__make         /usr/bin/make -j 6

Specify -j 6 if you have a hexa-core CPU. Specify -j 4 if dual-core. Clearer advices that just only -j make to create as many threads as it feels like.

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See also