HDFS command line interface in Hadoop - Step-by-Step Execution

Concept Flow - HDFS command line interface

Start HDFS CLI

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Enter Command

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Parse Command

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Execute Command on HDFS

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Return Output or Error

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Prompt for Next Command or Exit

The HDFS CLI starts, waits for user commands, parses and executes them on HDFS, then shows results or errors, and repeats.

Execution Sample

Hadoop

hdfs dfs -ls /user/hadoop
hdfs dfs -mkdir /user/hadoop/newdir
hdfs dfs -put localfile.txt /user/hadoop/newdir
hdfs dfs -cat /user/hadoop/newdir/localfile.txt

These commands list files, create a directory, upload a file, and display file contents in HDFS.

Execution Table

Step	Command	Action	Result	Output
1	hdfs dfs -ls /user/hadoop	List directory contents	Success	Found files: file1.txt, file2.txt
2	hdfs dfs -mkdir /user/hadoop/newdir	Create directory	Success	Directory /user/hadoop/newdir created
3	hdfs dfs -put localfile.txt /user/hadoop/newdir	Upload local file to HDFS	Success	File localfile.txt uploaded
4	hdfs dfs -cat /user/hadoop/newdir/localfile.txt	Display file contents	Success	Hello Hadoop!
5	hdfs dfs -rm /user/hadoop/newdir/localfile.txt	Remove file	Success	File deleted
6	hdfs dfs -ls /user/hadoop/newdir	List directory contents	Success	No files found
7	exit	Exit CLI	End	Session terminated

💡 User typed 'exit' to end the HDFS CLI session

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
/user/hadoop directory contents	file1.txt, file2.txt	file1.txt, file2.txt	file1.txt, file2.txt, newdir/	file1.txt, file2.txt, newdir/	file1.txt, file2.txt, newdir/	file1.txt, file2.txt, newdir/	file1.txt, file2.txt, newdir/	file1.txt, file2.txt, newdir/
/user/hadoop/newdir contents	N/A	N/A	empty	localfile.txt	localfile.txt	empty	empty	empty
localfile.txt in HDFS	N/A	N/A	N/A	exists	exists	deleted	deleted	deleted

Key Moments - 3 Insights

Why does 'hdfs dfs -ls' show 'newdir/' after creating the directory?

Because after step 2, the directory 'newdir' is created inside /user/hadoop, so listing shows it as a folder with a trailing slash (see execution_table step 2).

What happens if you try to 'cat' a file that does not exist?

The command will return an error saying file not found. In our trace, step 4 succeeds because the file exists, but if missing, it would show an error instead.

Why does the directory become empty after deleting the file?

Because after step 5, the only file in 'newdir' is removed, so listing the directory in step 6 shows no files (see execution_table steps 5 and 6).

Visual Quiz - 3 Questions

Look at the execution table, what files are listed in /user/hadoop after step 2?

A file1.txt, file2.txt

B newdir/ only

C file1.txt, file2.txt, newdir/

D No files

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step is the file 'localfile.txt' deleted from HDFS?

A Step 4

B Step 5

C Step 3

D Step 6

💡 Hint

Look for the 'Remove file' action in the execution_table.

If you run 'hdfs dfs -ls /user/hadoop/newdir' after step 5, what will you see?

A No files found

B Error: Directory not found

C localfile.txt

D newdir/

💡 Hint

Check the output of step 6 in the execution_table.

Concept Snapshot

HDFS CLI lets you interact with Hadoop files.
Use 'hdfs dfs -ls <path>' to list files.
Use 'hdfs dfs -mkdir <dir>' to create directories.
Use 'hdfs dfs -put <local> <hdfs>' to upload files.
Use 'hdfs dfs -cat <file>' to view contents.
Use 'hdfs dfs -rm <file>' to delete files.

Full Transcript

The HDFS command line interface (CLI) starts and waits for user commands. When you type a command like 'hdfs dfs -ls /user/hadoop', it lists files in that directory. Creating a directory with 'hdfs dfs -mkdir' adds a new folder visible in listings. Uploading files with 'hdfs dfs -put' copies local files to HDFS. Viewing file contents uses 'hdfs dfs -cat'. Deleting files removes them from HDFS. The CLI shows success or error messages after each command. You can exit the CLI by typing 'exit'. This trace showed commands listing files, creating directories, uploading, viewing, and deleting files step-by-step.