Ubuntu, can not start react-native: Could not find tools.jar

Solved it by installing openjdk again:

sudo apt-get install openjdk-8-jdk

In Ubuntu

sudo apt-get install openjdk-8-jdk-headless

Check to make sure the Java compiler is available. I don't normally develop in Java, so, while there's Java stuff running, I haven't ever specifically compiled a Java project. Run:

javac -version

If you get the same thing I received, well... you know the issue. I installed the latest Oracle JDK (shiver), and I have react-native up and running now. I ran into some other issues with environment variables, which were solved by:

unset $JAVA_HOME
source ~/.profile

Note: the .profile script had my SDK env vars in it.

Hope this helps!