HDFS Error: org.apache.hadoop.security.AccessControlException: Permission denied

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class TestHDFS {
    public static void main(String[] args) throws Exception{
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://master:8020");
        FileSystem fs = FileSystem.get(conf);

        //If it exists, it will overwrite the previous directory
        boolean success = fs.mkdirs(new Path("/xiaol"));
        System.out.println(success);
    }
}

Exception in thread “main” org.apache.hadoop.security.AccessControlException: Permission denied: user=xiaol, access=WRITE, inode=”/xiaol”:root:supergroup:drwxr-xr-x

Solution

1. Modify the configuration file

In the HDFS configuration file, change dfs.permissions.enabled to false

2. Change HDFS root permission

hadoop fs -chmod 777 /

3. Add access user

Hadoop will perform permission authentication when accessing HDFS. The process of obtaining the user name is as follows:

Read Hadoop_USER_Name system environment variable. If it is not empty, take it as username. If it is empty

Read Hadoop_ SER_Name is a Java environment variable. If it is empty

Get username from the instance of com.sun.security.auth.ntuserprincipal or com.sun.security.auth.unixprincipal.

If all the above attempts fail, an exception loginexception (“can’t find user name”) will be thrown

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.util.Properties;

public class TestHDFS {
    public static void main(String[] args) throws Exception{
        Properties properties = System.getProperties();
        properties.setProperty("HADOOP_USER_NAME", "root");

        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://master:8020");
        FileSystem fs = FileSystem.get(conf);

        //If it exists, it will overwrite the previous directory
        boolean success = fs.mkdirs(new Path("/xiaol"));
        System.out.println(success);
    }
}

This is actually a vulnerability. If the user uses the user name of root or other directories, he can perform any operation on the corresponding directories, so it is still very dangerous.