ROS2 installation connext cmake module error

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I am trying to insall ros2-eloquent on ubuntu Linux Bionic Beaver on Virtual box.

When sourcing setup.bash, the following error message appears.

Error message [connext_cmake_module] Warning: The location at which Connext was found when the workspace was built [[/opt/rti.com/rti_connext_dds-5.3.1]] does not point to a valid directory, and the NDDSHOME environment variable has not been set. Support for Connext will not be available.

Environment setup

yanagi@yanagi-VirtualBox:~/ros2-eloquent$ . ~/ros2-eloquent/ros2-linux/setup.bash

Environment Install ubuntu Linux Bionic Beaver Desktop image.