Hey there, fellow Hadoop beginner! Let's work through that "page doesn't exist" error when trying to access localhost:9870—this is a super common hiccup when getting started, so don't worry, we'll fix it together.

Here are the most likely fixes, ordered from easiest to check:

1. Verify Hadoop Services Are Running #

The localhost:9870 URL is for the NameNode Web UI, which only works if the Hadoop HDFS services are up and running.

• Open your terminal and run this command to check active Hadoop processes:

  jps
  

  You should see at least NameNode, DataNode, and ResourceManager in the output. If these are missing, start the services:

  start-dfs.sh  # Starts HDFS services (NameNode/DataNode)
  start-yarn.sh # Starts YARN services (ResourceManager/NodeManager)
  

  Note: Some older Hadoop setups use start-all.sh, but it's deprecated in newer versions—stick to the two separate commands above.

2. Double-Check Hadoop Configuration Files #

Incorrect configs are the #1 culprit here. You'll need to verify two key files in your Hadoop installation directory (usually $HADOOP_HOME/etc/hadoop/):

core-site.xml #

Open it with a text editor (e.g., nano $HADOOP_HOME/etc/hadoop/core-site.xml) and make sure it has this property:

<property>
  <name>fs.defaultFS</name>
  <value>hdfs://localhost:9000</value>
</property>

hdfs-site.xml #

Check this file for the NameNode HTTP address property:

<property>
  <name>dfs.namenode.http-address</name>
  <value>localhost:9870</value>
</property>

After making any changes, restart all Hadoop services to apply them.

3. Check Ubuntu Firewall Settings #

Ubuntu's default firewall (ufw) might be blocking port 9870.

• First, test if disabling the firewall fixes the issue:

  sudo ufw disable
  

  If you can access localhost:9870 now, re-enable the firewall and add a rule to allow the port:

  sudo ufw allow 9870/tcp
  sudo ufw enable
  

4. Ensure Port 9870 Isn't Occupied by Another Process #

Sometimes another app might be using port 9870. Check with this command:

ss -tulpn | grep 9870

If you see a process listed here, you can either:

• Kill that process (use sudo kill <PID> where <PID> is the process ID), or
• Update the dfs.namenode.http-address property in hdfs-site.xml to use a different port (e.g., 9871), then restart Hadoop.

5. Rule Out Browser Issues #

• Double-check you typed the URL correctly: it's http://localhost:9870 (not 9070 or another typo).
• Try accessing it in a private/incognito window to bypass cached pages.

If none of these steps work, feel free to share the output of jps and your config files—we can dig deeper!

内容的提问来源于stack exchange，提问作者Kevin Su