def runtime(self, _from='0'):
        """Generate the set of instructions to install the runtime specific
        components from a build in a previous stage.

        # Example

        ```python
        c = charm(...)
        Stage0 += c
        Stage1 += c.runtime()
        ```
        """
        self.rt += comment('Charm++')
        self.rt += copy(_from=_from, src=self.__installdir,
                        dest=self.__installdir)
        if self.ldconfig:
            self.rt += shell(commands=[self.ldcache_step(
                directory=posixpath.join(self.__prefix, 'lib_so'))])
        self.rt += environment(variables=self.environment_step())
        return str(self.rt)
Generate the set of instructions to install the runtime specific
        components from a build in a previous stage.

        # Example

        ```python
        c = charm(...)
        Stage0 += c
        Stage1 += c.runtime()
        ```
        
hpccm/building_blocks/charm.py