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i am following this link to install ROS2 Crystal on my ubuntu 16.04. I already have ROS Kinetic installed on my machine. During this step . ~/ros2_install/ros2-linux/setup.bash, I get this warning:

[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.

This is asking for RTI DDS installation. How do I make that use some other open source DDS implementation?

Originally posted by Veera Ragav on ROS Answers with karma: 240 on 2019-05-20

Post score: 5


1 Answer 1


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The RMW Implementation used when executing a ROS2 application is chosen according to the value of the following environment variable:


You can set different RMW in the following way:

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export RMW_IMPLEMENTATION=rmw_opensplice_cpp
export RMW_IMPLEMENTATION=rmw_connext_cpp

In any case, by default it will point to Fast-RTPS DDS library (open source and always installed together with ROS2).

Originally posted by alsora with karma: 1322 on 2019-05-20

This answer was ACCEPTED on the original site

Post score: 4

Original comments

Comment by Veera Ragav on 2019-05-20:
My RMW_IMPLEMENTATION was not set. Even after setting it I get the same warning. I tried running the demo talker and listener node which works fine.

Comment by alsora on 2019-05-20:
You can safely ignore the warning as long as you are not setting RMW_IMPLEMENTATION=rmw_connext_cpp. The reason for the warning is that the binaries have been compiled with Connext support, however you do not have the Connext library on your pc, so it's simply saying that you can't use it. If you want to get rid of it, you have to install the Connext library under /opt/rti.com/rti_connext_dds-5.3.1 Follow this: https://index.ros.org/doc/ros2/Installation/Crystal/Linux-Install-Binary/#rti-connext-version-5-3-1-amd64-only

Comment by Veera Ragav on 2019-05-20:
Cool. Thanks.

Comment by William on 2019-05-20:
Also, this is our tutorial for this feature, for reference: https://index.ros.org/doc/ros2/Tutorials/Working-with-multiple-RMW-implementations/


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