Friday, October 13, 2023

HDFS Commands Reference List With Examples

In this post I have compiled a list of some frequently used HDFS commands along with examples.

Here note that you can either use hadoop fs - <command> or hdfs dfs - <command>. The difference is hadoop fs is generic which works with other file systems too where as hdfs dfs is for HDFS file system. Since we are specifically talking about hdfs here so hdfs dfs synonym is used.

1- If you need HDFS command help
hdfs dfs -help
Gives the list of all the HDFS commands and command description.

To get help about a specific command use that command with help.

As Example: If you want help about rm command

hdfs dfs -help rm

-rm [-f] [-r|-R] [-skipTrash] [-safely] <src> ... :
  Delete all files that match the specified file pattern. Equivalent to the Unix
  command "rm <src>"
                                                                                 
  -f          If the file does not exist, do not display a diagnostic message or 
              modify the exit status to reflect an error.                        
  -[rR]       Recursively deletes directories.                                   
  -skipTrash  option bypasses trash, if enabled, and immediately deletes <src>.  
  -safely     option requires safety confirmation, if enabled, requires          
              confirmation before deleting large directory with more than        
              <hadoop.shell.delete.limit.num.files> files. Delay is expected when
              walking over large directory recursively to count the number of    
              files to be deleted before the confirmation. 
2- Another way to get help for an individual command is to use usage command. It will list all the options that can be used with the given command.
hdfs dfs -usage rm 

Usage: hadoop fs [generic options] -rm [-f] [-r|-R] [-skipTrash] [-safely] <src> ...
3- HDFS command to create a directory
hdfs dfs -mkdir

As example– HDFS command to create test directory inside /user directory.

hdfs dfs -mkdir  /user/test
If you want to create parent directories along the path use -p switch.

As example If you want to create whole directory structure /user/test/abc

hdfs dfs -mkdir -p /user/test/abc

4- To list all the directories and files in the given path

hdfs dfs -ls

As example– HDFS command to list all the files under /user/test

hdfs dfs -ls /user/test
To recursively list all the files and sub directories use -R switch.

For example, HDFS command to recursively list all the files and directories starting from root directory.

hdfs dfs -ls -R /

5- HDFS command to delete a file

hdfs dfs -rm

As example – To delete file display.txt in the directory /user/test

hdfs dfs -rm /user/test/display.txt

To recursively delete a directory and any content under it use -R or -r option.

For example, HDFS command to recursively delete directory /user/test along with all the content under /user/test.

hdfs dfs -rm -R /user/test/

Deleted /user/test

6- HDFS command to delete a directory.

hdfs dfs -rmdir

As example– To delete directory /user/test. Note that rmdir command will delete a directory only if it is empty.

hdfs dfs -rmdir /user/test/

7- To copy file from local file system to HDFS.

hdfs dfs -put

As example– To copy file display.txt from /usr/netjs to /user/process in HDFS.

hdfs dfs -put /usr/netjs/display.txt /user/process

8- To copy file from local file system to HDFS using copyFromLocal command.

As example– To copy file display.txt from /usr/netjs in local file system to /user/process in HDFS.

hdfs dfs -copyFromLocal /usr/netjs/display.txt /user/process

9- To move file from local file system to HDFS. IF you use this command local file is deleted after it’s copied.

As example– HDFS command to move file display.txt from /usr/netjs to /user/process in HDFS.

hdfs dfs -moveFromLocal /usr/netjs/display.txt /user/process

10- HDFS command to copy file from HDFS to local

hdfs dfs -get

As example– If you want to copy file display.txt from /user/process in HDFS to /usr/netjs in local

hdfs dfs -get /user/process/display.txt /usr/netjs/

11- Another way to copy file from HDFS to local is using copyToLocal command.

As example – If you want to copy file display.txt from /user/process in HDFS to /usr/netjs in local

hdfs dfs -copyToLocal /user/process/display.txt /usr/netjs/

12- To copy file from one HDFS location to another HDFS location.

hdfs dfs -cp

As example- If you want to copy display.txt file from /user/process to /user/test with in HDFS.

hdfs dfs -cp /user/process/display.txt /user/test

13- HDFS command to display free space.

hdfs dfs -df

14- To displays sizes of files and directories contained with in the given directory.

hdfs dfs -du

As example- If you want to see the disk usage for /user directory

hdfs dfs -du /user

22  /user/process
22  /user/test
0   /user/test1

15- HDFS command to see the content of the file.

hdfs dfs -cat

As example– To display the content of the file /usr/process/display.txt

hdfs dfs -cat /user/process/display.txt

16- Permanently delete files in checkpoints older than the retention threshold from trash directory, and create new checkpoint.

hdfs dfs -expunge

17- HDFS command to change replication factor of a file.

hdfs dfs -setrep

As example– If you want to change the replication factor of the file /user/process/display.txt to two.

hdfs dfs -setrep 2 /user/process/display.txt

Replication 2 set: /user/process/display.txt

18- HDFS command to run HDFS filesystem checking utility.

hdfs fsck

As example– Running fsck for files under directory /user/process

hdfs fsck /user/process

/user/process/display.txt:  Under replicated BP-1309973318-127.0.1.1-1513945999329:blk_1073741865_1041. Target Replicas is 2 but found 1 live replica(s), 0 decommissioned replica(s), 0 decommissioning replica(s).
Status: HEALTHY
 Total size: 22 B
 Total dirs: 1
 Total files: 1
 Total symlinks:  0
 Total blocks (validated): 1 (avg. block size 22 B)
 Minimally replicated blocks: 1 (100.0 %)
 Over-replicated blocks: 0 (0.0 %)
 Under-replicated blocks: 1 (100.0 %)
 Mis-replicated blocks:  0 (0.0 %)
 Default replication factor: 1
 Average block replication: 1.0
 Corrupt blocks:  0
 Missing replicas:  1 (50.0 %)
 Number of data-nodes:  1
 Number of racks:  1
FSCK ended at Mon Feb 26 13:57:40 IST 2018 in 1 milliseconds

19- If you want to change group association of files.

hdfs dfs -chgrp

As example – Change group of /user/process/display.txt file to sales.

hdfs dfs -chgrp sales /user/process/display.txt

20- To change the permissions of files.

hdfs dfs -chmod

As example- If you want to provide read, write and execute permissions to user and read permission to group and others for file /user/process/display.txt.

hdfs dfs -chmod 744 /user/process/display.txt

That's all for this topic HDFS Commands Reference List With Examples. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Related Topics

  1. What is HDFS
  2. Replica Placement Policy in Hadoop Framework
  3. NameNode, DataNode And Secondary NameNode in HDFS
  4. What is SafeMode in Hadoop
  5. HDFS High Availability

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