checkMD5sums checks the files against a file MD5.checkMD5sums(package, dir)checkMD5sums returns a logical, NA if there is no
  MD5 file to be checked.MD5 which is created is in a format which can be
  checked by md5sum -c MD5 if a suitable command-line version
  of md5sum is available.  (For Windows, one is supplied in
  the bundle at https://cran.r-project.org/bin/windows/Rtools.) If dir is missing, an installed package of name package
  is searched for. The private function tools:::.installMD5sums is used to create
  MD5 files in the Windows build.md5sum