Troubleshooting

Problem 1: An Error Is Reported When hdfs namenode -format Is Run

Symptom

The error message "Error: JAVA_HOME is not set and could not be found" is displayed when hdfs namenode -format is run.

Possible Causes

The JAVA_HOME environment variable is incorrectly set.

Procedure

Set the JAVA_HOME variable by referring to Configuring the Compilation Environment.

Problem 2: An Error Is Reported When hdfs namenode -format Is Run

Symptom

The error message "Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password)" is displayed when hdfs namenode -format is run.

Possible Causes

The password-free function of the local host is faulty.

Procedure

Run the ssh-keygen -t rsa command to enable password-free function again.

Problem 3: "Could not resolve hostname" Displayed When Hadoop Is Started

Symptom

The error message "ssh: Could not resolve hostname xxx" is displayed when Hadoop is started.

Procedure

You can set the Hadoop environment variable to resolve this problem.

1. Press Ctrl+C to stop the startup.
2. Add the following two lines to ~/.bashrc:
   1. Open the file.

      vi ~/.bashrc

   2. Press i to enter the insert mode and add the following commands to ~/.bashrc:

      export HADOOP_HOME=/usr/local/hadoop
      export HADOOP_COMMON_LIB_NATIVE_DIR=$HADOOP_HOME/lib/native

      

      The setting process is the same as that of the JAVA_HOME variable. In the variable, HADOOP_HOME indicates the Hadoop installation directory.

   3. Press Esc, type :wq!, and press Enter to save the file and exit.
3. Run the following command for the setting to take effect:

   source ~/.bashrc

4. Run the following command to start Hadoop:

   start-dfs.sh