You need to do two things:
- Delete the main hadoop storage directory from every node. This directory is defined by the hadoop. tmp. dir property in your hdfs-site. xml.
- Reformat the namenode:
Simply follow this path; from the Ambari Dashboard, click HDFS -> Configs -> Advanced -> Advanced core-site. Then set the 'fs. trash. interval' to 0 to disable.
Use the hdfs dfs -ls command to list files in Hadoop archives. Run the hdfs dfs -ls command by specifying the archive directory location. Note that the modified parent argument causes the files to be archived relative to /user/ .
bin/hdfs dfs -mkdir /geeks => '/' means absolute path bin/hdfs dfs -mkdir geeks2 => Relative path -> the folder will be created relative to the home directory. touchz: It creates an empty file. copyFromLocal (or) put: To copy files/folders from local file system to hdfs store. This is the most important command.
HDFS is a distributed file system that handles large data sets running on commodity hardware. It is used to scale a single Apache Hadoop cluster to hundreds (and even thousands) of nodes. HDFS is one of the major components of Apache Hadoop, the others being MapReduce and YARN.
List directories (and their subdirectories) with hadoop command line
- Probably not valid for every user but it might work: > hadoop fs -lsr path | cut -d' ' -f1,19 | grep '^d.*$' "$@" | cut -d' ' -f2. – Ivan Fernandez.
- A better solution: > hadoop fs -lsr $inputPath | awk '{ print $1,$8 }' | grep '^d.*$' – Ivan Fernandez.
How to Remove Directories (Folders)
- To remove an empty directory, use either rmdir or rm -d followed by the directory name: rm -d dirname rmdir dirname.
- To remove non-empty directories and all the files within them, use the rm command with the -r (recursive) option: rm -r dirname.
Access the HDFS using its web UI. Open your Browser and type localhost:50070 You can see the web UI of HDFS move to utilities tab which is on the right side and click on Browse the File system, you can see the list of files which are in your HDFS.
The hadoop fs -ls command allows you to view the files and directories in your HDFS filesystem, much as the ls command works on Linux / OS X / *nix. A user's home directory in HDFS is located at /user/userName. For example, my home directory is /user/akbar.
Remove storage directories using Cloudera Manager
- Stop the cluster.
- Go to the HDFS service.
- Click the Configuration tab.
- Select Scope > DataNode.
- Remove the current directories and add new ones to the DataNode Data Directory property.
- Enter a Reason for change, and then click Save Changes to commit the changes.
The following syntax is used to drop a partition: ALTER TABLE table_name DROP [IF EXISTS] PARTITION partition_spec, PARTITION partition_spec,; The following query is used to drop a partition: hive> ALTER TABLE employee DROP [IF EXISTS] > PARTITION (year='1203'); Let's say you have a large table with a state column
You can look for the following stanza in /etc/hadoop/conf/hdfs-site.xml (this KVP can also be found in Ambari; Services > HDFS > Configs > Advanced > Advanced hdfs-site > dfs.
Hadoop includes various shell-like commands that directly interact with HDFS and other file systems that Hadoop supports. The command bin/hdfs dfs -help lists the commands supported by Hadoop shell. These commands support most of the normal files system operations like copying files, changing file permissions, etc.
To answer your query, deleting a file doesn't delete the file contents and its blocks from the datanodes.
Q 20 - When using HDFS, what occurs when a file is deleted from the command line? A - It is permanently deleted if trash is enabled.
To write a file in HDFS, a client needs to interact with master i.e. namenode (master). Now namenode provides the address of the datanodes (slaves) on which client will start writing the data. Client directly writes data on the datanodes, now datanode will create data write pipeline.
The reasons for the large size of blocks are: To minimize the cost of seek: For the large size blocks, time taken to transfer the data from disk can be longer as compared to the time taken to start the block. This results in the transfer of multiple blocks at the disk transfer rate.
You can copy a directory from one node to another node in Hadoop. You need to use distcp command as shown below.
In other words, the minimum amount of data that HDFS can read or write is called a Block. The default block size is 64MB, but it can be increased as per the need to change in HDFS configuration.
By default, HDFS block size is 128MB which you can change as per your requirement. All HDFS blocks are the same size except the last block, which can be either the same size or smaller. Hadoop framework break files into 128 MB blocks and then stores into the Hadoop file system.
2 Answers
- Correct Answer: Data Node Failure.
- HDFS unavailability is totally independent of the Jobtracker. If at least the NameNode is up, HDFS is nominally usable.
- If you are interested to learn Hadoop, you can check out this Hadoop Training program by Intellipaat.
- Also, watch this video for more information:
The goals of HDFS are handling the hardware failure and recovery, handling datasets effectively, and provide high network bandwidth for data movement.
