In alpha 6 and earlier we were shiping ros2 with Opensplice as the default DDS implementation. libddskernel.so is an opensplice library.
To install it you need to add packages.osrfoundation.org to your sources:
sudo apt-key adv --keyserver ha.pool.sks-keyservers.net --recv-keys D2486D2DD83DB69272AFE98867170598AF249743
sudo bash -c 'echo "deb http://packages.osrfoundation.org/gazebo/ubuntu `lsb_release -cs` main" > /etc/apt/sources.list.d/gazebo-latest.list'
and install libopensplice64:
sudo apt-get install libopensplice64
The installation instructions for alpha6 are available here: https://github.com/ros2/ros2/wiki/Linux-Install-Binary/2610c847225134f0aaf7d24c265298f6775e3abc
Please be aware that many things changed in ROS 2 since alpha 6 (API, features, documentation, supported middleware) so we encourage users to use the latest release. You can run beta2 in a docker container for example.
$ docker run -it ubuntu:xenial
# apt update && apt install dirmngr
# apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 421C365BD9FF1F717815A3895523BAEEB01FA116
# sh -c 'echo "deb http://repo.ros2.org/ubuntu/main xenial main" > /etc/apt/sources.list.d/ros2-latest.list'
# apt update
# apt install ros-r2b2-*
# source /opt/ros/r2b2/setup.bash