HDFS command line interface in Hadoop - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HDFS command?

Given the HDFS command hdfs dfs -ls /user/hadoop, what will it display?

Hadoop

hdfs dfs -ls /user/hadoop

A Lists all files and directories inside /user/hadoop with details like permissions, owner, size, and modification date.

B Deletes the directory /user/hadoop and all its contents.

C Creates a new directory named /user/hadoop.

D Displays the content of the file /user/hadoop.

💡 Hint

The command uses '-ls' which is similar to the Unix 'ls' command but for HDFS.

The 'hdfs dfs -ls' command lists files and directories in the specified HDFS path with detailed information.

❓ data_output

intermediate

What is the result of this HDFS command?

What will be the result of running hdfs dfs -mkdir /user/hadoop/newdir if the directory already exists?

Hadoop

hdfs dfs -mkdir /user/hadoop/newdir

A The command silently ignores and does nothing.

B The directory is overwritten with a new empty directory.

C The command creates a new directory inside /user/hadoop/newdir.

D An error message indicating the directory already exists.

💡 Hint

Think about what happens when you try to create a directory that already exists in HDFS.

The 'hdfs dfs -mkdir' command fails with an error if the directory already exists.

🔧 Debug

advanced

Identify the error in this HDFS command

What error will this command produce? hdfs dfs -put localfile.txt /user/hadoop/ when localfile.txt does not exist locally.

Hadoop

hdfs dfs -put localfile.txt /user/hadoop/

A Permission denied error on HDFS directory.

B FileNotFoundException: localfile.txt (No such file or directory)

C Command runs successfully and uploads an empty file.

D Syntax error due to missing arguments.

💡 Hint

The command tries to upload a file that does not exist locally.

The 'hdfs dfs -put' command fails with a FileNotFoundException if the local file does not exist.

🧠 Conceptual

advanced

What does the HDFS command hdfs dfs -du -h /user/hadoop show?

Choose the correct description of the output of hdfs dfs -du -h /user/hadoop.

A Displays the disk usage of files and directories in /user/hadoop in human-readable format.

B Displays the content of all files in /user/hadoop.

C Deletes all files in /user/hadoop and shows confirmation.

D Shows the replication factor of files in /user/hadoop.

💡 Hint

The '-du' option is similar to Unix 'du' command but for HDFS.

The 'hdfs dfs -du -h' command shows disk usage of files/directories with sizes in human-readable units.

🚀 Application

expert

Which command sequence correctly copies a local directory to HDFS and verifies the copy?

You want to copy a local directory data/ to HDFS path /user/hadoop/data/ and then list the contents to verify. Which sequence of commands is correct?

A hdfs dfs -put data /user/hadoop/data && hdfs dfs -ls /user/hadoop/data

B hdfs dfs -copyFromLocal data /user/hadoop/data && hdfs dfs -cat /user/hadoop/data

C hdfs dfs -mkdir /user/hadoop/data && hdfs dfs -put data /user/hadoop/data && hdfs dfs -ls /user/hadoop/data

D hdfs dfs -get data /user/hadoop/data && hdfs dfs -ls /user/hadoop/data

💡 Hint

Remember that the target directory must exist before copying if you want to keep the directory structure.

First create the target directory, then copy the local directory into it, then list contents to verify.