这里是引用文字
hadoop@ubuntu:~/Desktop/myfiles/hadoop-2.8.5/sbin$ ./start-dfs.sh
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.apache.hadoop.security.authentication.util.KerberosUtil (file:/home/hadoop/Desktop/myfiles/hadoop-2.8.5/share/hadoop/common/lib/hadoop-auth-2.8.5.jar) to method sun.security.krb5.Config.getInstance()
WARNING: Please consider reporting this to the maintainers of org.apache.hadoop.security.authentication.util.KerberosUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
18/10/16 20:02:48 WARN hdfs.DFSUtilClient: Namenode for null remains unresolved for ID null. Check your hdfs-site.xml file to ensure namenodes are configured properly.
Starting namenodes on [hadoop]
hadoop: ssh: Could not resolve hostname hadoop: Name or service not known
ubuntu: starting datanode, logging to /home/hadoop/Desktop/myfiles/hadoop-2.8.5/logs/hadoop-hadoop-datanode-ubuntu.out
ubuntu: WARNING: An illegal reflective access operation has occurred
ubuntu: WARNING: Illegal reflective access by org.apache.hadoop.security.authentication.util.KerberosUtil (file:/home/hadoop/Desktop/myfiles/hadoop-2.8.5/share/hadoop/common/lib/hadoop-auth-2.8.5.jar) to method sun.security.krb5.Config.getInstance()
ubuntu: WARNING: Please consider reporting this to the maintainers of org.apache.hadoop.security.authentication.util.KerberosUtil
ubuntu: WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
ubuntu: WARNING: All illegal access operations will be denied in a future release
Starting secondary namenodes [0.0.0.0]
0.0.0.0: starting secondarynamenode, logging to /home/hadoop/Desktop/myfiles/hadoop-2.8.5/logs/hadoop-hadoop-secondarynamenode-ubuntu.out
0.0.0.0: WARNING: An illegal reflective access operation has occurred
0.0.0.0: WARNING: Illegal reflective access by org.apache.hadoop.security.authentication.util.KerberosUtil (file:/home/hadoop/Desktop/myfiles/hadoop-2.8.5/share/hadoop/common/lib/hadoop-auth-2.8.5.jar) to method sun.security.krb5.Config.getInstance()
0.0.0.0: WARNING: Please consider reporting this to the maintainers of org.apache.hadoop.security.authentication.util.KerberosUtil
0.0.0.0: WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
0.0.0.0: WARNING: All illegal access operations will be denied in a future release
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.apache.hadoop.security.authentication.util.KerberosUtil (file:/home/hadoop/Desktop/myfiles/hadoop-2.8.5/share/hadoop/common/lib/hadoop-auth-2.8.5.jar) to method sun.security.krb5.Config.getInstance()
WARNING: Please consider reporting this to the maintainers of org.apache.hadoop.security.authentication.util.KerberosUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

请问这是什么原因呢