createrepo
Initializes an RPM repository in the given directory, including all XML and SQLite files.
TLDR
Initialize a basic repository in a directory
$ createrepo [path/to/directory]
Initialize a repository, exclude test RPMs and display verbose logs
$ createrepo -v -x [test_*.rpm] [path/to/directory]
Initialize a repository, using SHA1 as the checksum algorithm, and ignoring symbolic links
$ createrepo -S -s [sha1] [path/to/directory]