hi Surya
i am new to Hadoop as well
you will need to understand that HADOOP is not a database firstly.
Java is used to process data in the nodes thus the more you know the better you will be at processing data.
to answer your question:
depends
if you are starting and you do not have a requirement that needs to be delivered by tomorrow
you will need the basic Java – and learn everything together!
as for Linux – if you are coming from a Windows only background
please install Linux on your laptop and start hacking.
there is nothing better to learn Linux than breaking and fixing a system.
Good Luck with your learning