Hadoop Learning Note: Unable to start namenode and password-free start Hadoop

Preface

Install the hadoop-2.2.0 64-bit version under Linux CentOS, solve two problems: first, resolve namenode cannot start, view log file logs/ Hadoop-root-namenode-itcast.out (your name is not the same as mine, see the Namenode log file on the line), which throws the following exception:
Java.net.BindException:Problem binding to [xxx.xxx.xxx.xxx:9000] Java.net.BindException: Unable to specify the requested address;
The second is SSH password-free login, prompting no permissions:
Permission denied (publickey.gssapi-with-mic) 1, unable to start Namenode

After starting Hadoop, using the JPS command to find that there is no namenode, this is actually etc/core-site.xml file modification is incorrect:

<configuration>
            <!--Specify the communication address of the HDFs boss (Namenode)--
            <property>
                    <name> fs.defaultfs</name>
                    <value>hdfs://0.0.0.0:9000</value>
            </property>
            <!-- Specify the storage path where the Hadoop runtime generates files-
            <property>
                    <name>hadoop.tmp.dir</name>
                    <value>/ cloud/hadoop-2.2.0/tmp</value>
            </property>
        </configuration>

This is the main line:

<value>hdfs://0.0.0.0:9000</value>

This will enable Namenode 2, ssh password-free login

Hadoop has to enter password several times each time, how to use password-free, the steps are as follows:
1, cd ~, go to my home directory
2, CD. ssh/
3, ssh-keygen-t RSA (four return)
After executing this command, two files Id_rsa (private key), id_rsa.pub (public key) will be generated
4. CP Id_rsa.pub Authorized_keys

This is OK, but when testing SSH locahost permission denied (publickey.gssapi-with-mic)

The following modifications need to be made:

Vim  /etc/ssh/sshd_config

Compare the following, if and your non-conformance, change to the following, if you have the line there in front of the #, the # number will be removed (the order may be different from the following)

Permitrootlogin Yes
passwordauthentication Yes
hostkey/etc/ssh/ssh_host_rsa_key
rsaauthentication Yes
pubkeyauthentication Yes
Authorizedkeysfile    . Ssh/authorized_keys

Then restart the sshd service, the CentOS 7 command is as follows:

Systemctl Restart Sshd.service

Next you need to modify the permissions, or you will still be prompted permission denied (Publickey.gssapi-with-mic)

# chmod ~
# chmod ~/.ssh
# chmod 644 ~/.ssh/authorized_keys  //Public key file All rights
# chmod ~/.ssh/id_rsa        all permissions for the//private key file

This is OK, you can start Hadoop normally with password-free.