First, open your terminal and enter this: sudo apt-get install nfs-common
A word of caution…
Using apt-get on a v4 firmware MyCloud is asking for trouble, since the MyCloud v4 firmware is built using a non-standard, 64k page size, and loading standard-build Debian packages (as apt-get will) is likely to cause trouble, maybe bricking your device. Hence the work done by users to port common utilities to v4:
http://community.wd.com/t5/WD-My-Cloud/Repository-with-software-worked-on-v4-firmware/td-p/829720
http://community.wd.com/t5/WD-My-Cloud/APP-WebHosting-for-firmware-V4-04-2015/td-p/838660
http://community.wd.com/t5/WD-My-Cloud/APP-Transmission-v2-84-for-firmware-V4-12-2014/td-p/770207
etc.
