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The NetBeans 8.1 installer makes a bad default choice for the Java runtime to use on Ubuntu, and doesn't check if the selected Java runtime is a JDK. When I installed NetBeans on my Ubuntu 15.04s system, with Java 6 and 7 OpenJDK installed and Java 6, 7 and 8 Oracle JDKs, it by default selected "/usr" as the Java runtime for NetBeans, Glassfish and Tomcat. I'm guessing it's because there is a /usr/bin/javac, but of course there is *no* /usr/lib/tools.jar, which it apparently fails to check for.