Cassandra and Java 9 - ThreadPriorityPolicy=42 is outside the allowed range

I had exactly the same issue: Can't start Cassandra (Single-Node Cluster on CentOS7)

If it is an option for you, using Java 8, instead of 9, is the simplest way to solve the issue.

Setting the following env variables solved the problem in MAC export JAVA8_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home