This is a known issue of Cassandra - CASSANDRA-13107.
Before Java 9 JVM accepted any integer value for ThreadPriorityPolicy, while 0 and 1 were the only valid values.
ThreadPriorityPolicy=1 allows to raise thread priorities, but only if the process starts with root privileges. When ThreadPriorityPolicy=1, JVM explicitly checks that euid=0:
static int prio_init() {
if (ThreadPriorityPolicy == 1) {
// Only root can raise thread priority. Don't allow ThreadPriorityPolicy=1
// if effective uid is not root. Perhaps, a more elegant way of doing
// this is to test CAP_SYS_NICE capability, but that will require libcap.so
if (geteuid() != 0) {
if (!FLAG_IS_DEFAULT(ThreadPriorityPolicy)) {
warning("-XX:ThreadPriorityPolicy requires root privilege on Linux");
}
ThreadPriorityPolicy = 0;
}
}
Note a bug (or backdoor) in the above code: if you set ThreadPriorityPolicy to something other than 0 or 1, euid check will be skipped, but the application will be still allowed to use priorities above normal. Cassandra uses this backdoor.
As a result of JEP 245 JDK 9 improved command line argument validation, and therefore ThreadPriorityPolicy does not accept values other than 0 or 1 anymore.
How to fix
Edit %CASSANDRA_HOME%/conf/jvm.options file:
- If you run Cassandra under
root on Linux,
replace -XX:ThreadPriorityPolicy=42 with -XX:ThreadPriorityPolicy=1
- Otherwise remove
-XX:ThreadPriorityPolicy=42 line altogether.
