HDFS command line interface in Hadoop - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to list files in the HDFS root directory.

Hadoop

hdfs dfs -ls [1]

Drag options to blanks, or click blank then click option'

A/tmp

B/data

C/

D/user

Attempts:

3 left

💡 Hint

Common Mistakes

Using a subdirectory like /user instead of root.

Forgetting the leading slash.

The root directory in HDFS is represented by '/'. Using hdfs dfs -ls / lists files and directories at the root.

2fill in blank

medium

Complete the code to copy a local file named 'data.txt' to the HDFS directory '/user/hadoop/'.

Hadoop

hdfs dfs -[1] data.txt /user/hadoop/

Drag options to blanks, or click blank then click option'

Acat

Bput

Cget

Dls

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'put'.

Using 'cat' which only displays file content.

The put command uploads a local file to HDFS. So hdfs dfs -put data.txt /user/hadoop/ copies the file to HDFS.

3fill in blank

hard

Fix the error in the command to remove the directory '/user/hadoop/temp' and all its contents.

Hadoop

hdfs dfs -rm [1] /user/hadoop/temp

Drag options to blanks, or click blank then click option'

A-r

B-f

C-d

D-R

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-r' (lowercase) instead of '-R'.

Forgetting the recursive flag and getting an error.

The -rm command needs the -R option (recursive) to delete directories with contents. So hdfs dfs -rm -R /user/hadoop/temp works.

4fill in blank

hard

Fill both blanks to display the first 10 lines of the HDFS file '/user/hadoop/log.txt'.

Hadoop

hdfs dfs -[1] /user/hadoop/log.txt | head -[2]

Drag options to blanks, or click blank then click option'

Acat

Btail

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tail' instead of 'cat' which shows last lines.

Using 'head -5' which shows only 5 lines.

The cat command outputs the file content. Piping it to head -10 shows the first 10 lines.

5fill in blank

hard

Fill all three blanks to create a directory '/user/hadoop/newdir' and then move the file 'data.csv' into it.

Hadoop

hdfs dfs -[1] /user/hadoop/newdir
hdfs dfs -[2] [3] /user/hadoop/newdir/

Drag options to blanks, or click blank then click option'

Amkdir

Bmv

Cdata.csv

Dcp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cp' instead of 'mv' which copies instead of moving.

Forgetting to create the directory before moving the file.

First, create the directory with mkdir. Then move the file using mv. The source file is 'data.csv'.

Practice

1. What does the HDFS command hdfs dfs -ls /user/hadoop do?

easy

A. Uploads local files to /user/hadoop in HDFS

B. Deletes the directory /user/hadoop from HDFS

C. Lists all files and directories in the HDFS path /user/hadoop

D. Displays the content of files in /user/hadoop

Solution

1. Step 1: Understand the command structure

   The command hdfs dfs -ls is used to list files and directories in HDFS.

2. Step 2: Analyze the given path

   The path /user/hadoop specifies the directory to list.

3. Final Answer:

   Lists all files and directories in the HDFS path /user/hadoop -> Option C

4. Quick Check:

   hdfs dfs -ls lists files [OK]

Hint: Remember: '-ls' always lists files in given HDFS path [OK]

Common Mistakes:

• Confusing '-ls' with '-rm' which deletes files
• Thinking '-ls' uploads files
• Assuming it shows file content

2. Which of the following is the correct syntax to upload a local file data.txt to HDFS directory /user/hadoop?

easy

A. hdfs dfs -put /user/hadoop data.txt

B. hdfs dfs -copyFromLocal /user/hadoop data.txt

C. hdfs dfs -get data.txt /user/hadoop

D. hdfs dfs -put data.txt /user/hadoop

Solution

1. Step 1: Identify the correct command for uploading

   -put uploads local files to HDFS, and the syntax is hdfs dfs -put <local_path> <hdfs_path>.

2. Step 2: Match the syntax with options

   hdfs dfs -put data.txt /user/hadoop correctly places data.txt as local file and /user/hadoop as HDFS destination.

3. Final Answer:

   hdfs dfs -put data.txt /user/hadoop -> Option D

4. Quick Check:

   -put local_file hdfs_path is correct [OK]

Hint: Remember: local file first, then HDFS path in '-put' [OK]

Common Mistakes:

• Swapping local and HDFS paths
• Using '-get' which downloads files
• Using '-copyFromLocal' with wrong argument order

3. What will be the output of the command hdfs dfs -cat /user/hadoop/sample.txt if the file contains:

Hello Hadoop
Welcome to HDFS

medium

A. Lists the file details of sample.txt

B. Prints the content of sample.txt to the console

C. Deletes sample.txt from HDFS

D. Uploads sample.txt to HDFS

Solution

1. Step 1: Understand the '-cat' command

   hdfs dfs -cat prints the content of a file in HDFS to the console.

2. Step 2: Analyze the file content

   The file sample.txt contains two lines: 'Hello Hadoop' and 'Welcome to HDFS'.

3. Final Answer:

   Prints the content of sample.txt to the console -> Option B

4. Quick Check:

   -cat shows file content [OK]

Hint: Use '-cat' to display file content in HDFS [OK]

Common Mistakes:

• Confusing '-cat' with '-ls' which lists files
• Thinking it deletes files
• Assuming it uploads files

4. You run the command hdfs dfs -rm /user/hadoop/data.csv but get an error saying file not found. What is the most likely cause?

medium

A. The file /user/hadoop/data.csv does not exist in HDFS

B. You used the wrong command; '-rm' cannot delete files

C. You need to use '-put' to delete files

D. The HDFS service is down

Solution

1. Step 1: Understand the error message

   The error 'file not found' means the specified file does not exist at the given path.

2. Step 2: Check command correctness

   -rm is the correct command to delete files in HDFS, so the error is not due to wrong command.

3. Final Answer:

   The file /user/hadoop/data.csv does not exist in HDFS -> Option A

4. Quick Check:

   File missing causes 'file not found' error [OK]

Hint: Check file existence before deleting with '-rm' [OK]

Common Mistakes:

• Assuming '-rm' is wrong command
• Trying to delete with '-put'
• Ignoring file path correctness

5. You want to copy all files from local directory /local/data/ to HDFS directory /user/hadoop/data/ and then verify the files are uploaded. Which sequence of commands is correct?

hard

A. hdfs dfs -put /local/data/* /user/hadoop/data/ then hdfs dfs -ls /user/hadoop/data/

B. hdfs dfs -get /local/data/* /user/hadoop/data/ then hdfs dfs -cat /user/hadoop/data/

C. hdfs dfs -rm /local/data/* then hdfs dfs -ls /user/hadoop/data/

D. hdfs dfs -copyToLocal /local/data/* /user/hadoop/data/ then hdfs dfs -rm /user/hadoop/data/

Solution

1. Step 1: Choose the correct upload command

   -put uploads local files to HDFS. Using /local/data/* uploads all files from local directory.

2. Step 2: Verify files in HDFS

   hdfs dfs -ls /user/hadoop/data/ lists files in the HDFS directory to confirm upload.

3. Final Answer:

   hdfs dfs -put /local/data/* /user/hadoop/data/ then hdfs dfs -ls /user/hadoop/data/ -> Option A

4. Quick Check:

   Upload with '-put' then list with '-ls' [OK]

Hint: Upload with '-put' then check with '-ls' [OK]

Common Mistakes:

• Using '-get' which downloads files
• Deleting local files before upload
• Using '-copyToLocal' which copies from HDFS to local