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This article mainly introduces what are the basic operations of Hadoop. It is very detailed and has a certain reference value. Friends who are interested must finish it!

Let's start with a rough description of the difference between "hadoop fs" and "hadoop dfs": fs is a relatively abstract level. In a distributed environment, fs is dfs, but in a local environment, fs is local file system, and dfs is not available.

1. List the HDFS files:

Hadoop fs-ls

A)-if nothing is followed by ls, list the contents under the "/ user/ username /" directory of HDFS

B) if you want to list the contents of a folder,-ls is followed by the path to the folder, such as listing the contents of the input:

Hadoop fs-ls input

2. Create a folder in HDFS:

Name of the hadoop fs-mkdir folder

For example:

Hadoop fs-mkdir input

3. Delete files or folders in HDFS

Hadoop fs-rmr folder name or file name

4. Upload files to HDFS:

Hadoop fs-put ~ / file test

Upload the file file from this machine to HDFS and rename it to test.

If you want to upload to a folder, change test to the address of the folder. At this point, the name of the uploaded file will not change, such as the local file.

Upload the file test1.txt,test2.txt,test3.txt in test to input in HDFS:

Hadoop fs-put ~ / test/test*.txt input

5. View a file under HDFS:

Hadoop fs-cat file path

For example, view the contents of the test file in input:

Hadoop fs-cat input/test

6. Copy the files in HDFS to the local system:

Filename in hadoop fs-get HDFS filename local storage address in local system

For example: copy the output file in HDFS to the local system Documents folder

Hadoop fs-get output / home/kevin/Documents/

7. Enter / exit safe mode

Sometimes, operations such as creating and deleting files cannot be carried out on the file system when hadoop is started. At this time, the state of the file system is called safe mode, and you can search the Internet for its use. the author will not repeat it here (because the author is a beginner, there are not many things on HDFS and there are not many nodes, so the author generally turns on Hadoop, regardless of whether it is in safe mode or not. Enter the command to exit safe mode first.

Hadoop dfsadmin-safemode enterhadoop dfsadmin-safemode leave above are all the contents of this article entitled "what are the basic Operations in Hadoop". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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