I am running this as root:
# wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-4.0.1.tar.gz
--2015-11-17 20:31:46-- http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-4.0.1.tar.gz
Resolving prdownloads.sourceforge.net... failed: Name or service not known.
wget: unable to resolve host address “prdownloads.sourceforge.net”
ping
it? What doesdig prdownloads.sourceforge.net
yield?