2. Backing up critical HDFS metadata

Back up the following critical data before attempting an upgrade. On the node that hosts the NameNode, open the Hadoop Command line shortcut that opens a command window in the Hadoop directory. Run the following commands:

Open the command prompt using the Hadoop user account and go to the HDFS home directory:
```
runas /user:hdfs "cmd /K cd %HDFS_HOME%"
```
Run the fsck command to fix any file system errors.
```
hdfs fsck / -files -blocks -locations > dfs-old-fsck-1.log
```
The console output is printed to the dfs-old-fsck-1.log file.
Capture the complete namespace directory tree of the file system:
```
hdfs fs -lsr / > dfs-old-lsr-1.log
```

Create a list of DataNodes in the cluster:

hdfs dfsadmin -report > dfs-old-report-1.log

Capture output from fsck command:

hdfs fsck / -block -locations -files > fsck-old-report-1.log

	Note
	Verify there are no missing or corrupted files/replicas in the `fsck` command output.

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