What are you trying to accomplish:
Execute a thread dump to troubleshoot an unresponsive druid process.
Workaround or Solution:
Run the command as the linux user that is running the process. For instance,
ps -f | grep java
[root@localhost ~]# ps -ef | grep java
root 2341 2318 0 14:41 ? 00:00:19 java -server -Xms128m -Xmx128m -Duser.timezone=UTC -cp /tmp/imply-2.7.8/bin/../dist/zk/lib/*:/tmp/imply-2.7.8/bin/../dist/zk/*:/tmp/imply-2.7.8/conf-quickstart/zk org.apache.zookeeper.server.quorum.QuorumPeerMain /tmp/imply-2.7.8/conf-quickstart/zk/zoo.cfg
Based on this output, you can see that the root user is running the process. Hence, in order to run the jstack command, you will need to be logged in as this user.
Executing the command with a linux user that isn't the same as the user running the druid process.