How can I expose JMX of DATANODE in HDFS by using jmx_exporter

Question

I have tried to insert

export HDFS_DATANODE_OPTS="$HDFS_DATANODE_OPTS -javaagent:/usr/local/prometheus/jmx_prometheus_javaagent-0.19.0.jar=hadoop1:30002:/usr/local/prometheus/jmx/prometheus_config.yml"

in hadoop-env.sh, where prometheus_config.yml is an empty file. But 30002 is still closed, why?

I have ever tried to insert

if ! grep -q <<<"$HDFS_DATANODE_OPTS" jmx_prometheus_javaagent; then
export HDFS_DATANODE_OPTS="$HDFS_DATANODE_OPTS -javaagent:/usr/local/prometheus/jmx_prometheus_javaagent-0.19.0.jar=hadoop1:30002:/usr/local/prometheus/jmx/prometheus_config.yml"
fi

but it is still not work!