Hi Suan Hwee Tan,
Thanks for using the Sandbox.
In this version of the Hortonworks Sandbox NFS is not supported. NFS is supported in the full Hortonworks Data Platform Distribution (HDP). They are two different products. The Sandbox is a pre-installed Virtual machine that was built prior to the release of the version of HDP that includes NFS support. To get a hadoop cluster (even pseudo distributed) you will need to download and install the Current version of HDP, not the Sandbox.