This is the documentation for CDH 4.6.0.
Documentation for other versions is available at Cloudera Documentation.

Step 10: Set Variables for Secure DataNodes

In order to allow DataNodes to start on a secure Hadoop cluster, you must set the following variables on all DataNodes in /etc/default/hadoop-hdfs-datanode.

export HADOOP_SECURE_DN_USER=hdfs
export HADOOP_SECURE_DN_PID_DIR=/var/lib/hadoop-hdfs
export HADOOP_SECURE_DN_LOG_DIR=/var/log/hadoop-hdfs
export JSVC_HOME=/usr/lib/bigtop-utils/
  Note:
Depending on the version of Linux you are using, you may not have the /usr/lib/bigtop-utils directory on your system. If that is the case, set the JSVC_HOME variable to the /usr/libexec/bigtop-utils directory by using this command:
export JSVC_HOME=/usr/libexec/bigtop-utils