Is there any Gnu/Linux distribution that provides by default an Hadoop installation?
Not sure of a stand-alone Linux distribution but you can get a VM with pre-installed Hadoop here:
There is no GNO or linux distribution with hadoop.
What can be done is to use a pre-configured sandboxes from cloudera and hortonworks.
Second, what would be even more good if u set-up a standalone on your local. Although this is pretty tiring may be , as it might take a lot of your time. But from my experience it gives a better understanding of the ecosystem.
There are several tutorials available to to that. just search bogotobogo on google. I liked this tutorial.
Also once hadoop deployment is done successfully, do try your hands on Spark. Its fun and great learning once you see its processing power.
All the best!!
There is no "distribution" per se but you can give the ambari project a try. It's an apache project that is a set of automated scripts and related plumbing to install and monitor a Hadoop installation. You even get a web based gui with it that you can use to monitor your install and restart:stop services etc. It'll even let you do a clustered install. Try it.