9 Answers
- bin/hadoop fs -get /hdfs/source/path /localfs/destination/path.
- bin/hadoop fs -copyToLocal /hdfs/source/path /localfs/destination/path.
- Point your web browser to HDFS WEBUI( namenode_machine:50070 ), browse to the file you intend to copy, scroll down the page and click on download the file.
2 Answers
- move csv file to hadoop sanbox (/home/username) using winscp or cyberduck.
- use -put command to move file from local location to hdfs. hdfs dfs -put /home/username/file.csv /user/data/file.csv.
You
enter the Sqoop import command on the command line of your cluster to import data into HDFS.
Specify the data to import in the command.
- Import an entire table.
- Import a subset of the columns.
- Import data using a free-form query.
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.
Hi@akhtar, You can create an empty file in Hadoop. In Linux, we use touch command.
The following arguments are available with hadoop ls command: Usage: hadoop fs -ls [-d] [-h] [-R] [-t] [-S] [-r] [-u] <args> Options: -d: Directories are listed as plain files. -h: Format file sizes in a human-readable fashion (eg 64.0m instead of 67108864). -R: Recursively list subdirectories encountered.
You can use the cp command in Hadoop. This command is similar to the Linux cp command, and it is used for copying files from one directory to another directory within the HDFS file system.
You can copy the data from hdfs to the local filesystem by following two ways:
- bin/hadoop fs -get /hdfs/source/path /localfs/destination/path.
- bin/hadoop fs -copyToLocal /hdfs/source/path /localfs/destination/path.
To be simple, hadoop fs is more “generic†command that allows you to interact with multiple file systems including Hadoop, whereas hdfs dfs is the command that is specific to HDFS. Note that hdfs dfs and hadoop fs commands become synonymous if the filing system which is used is HDFS.
Description
- Get all the *.zip files in an hdfs dir.
- One-by-one: copy zip to a temp dir (on filesystem)
- Unzip.
- Copy all the extracted files to the dir of the zip file.
- Cleanup.
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.
To list out the databases in Hive warehouse, enter the command 'show databases'. The database creates in a default location of the Hive warehouse. In Cloudera, Hive database store in a /user/hive/warehouse. Copy the input data to HDFS from local by using the copy From Local command.
​Creating Directories on HDFS
- Create the Hive user home directory on HDFS. Login as $HDFS_USER and run the following command: hdfs dfs -mkdir -p /user/$HIVE_USER hdfs dfs -chown $HIVE_USER:$HDFS_USER /user/$HIVE_USER.
- Create the warehouse directory on HDFS.
- Create the Hive scratch directory on HDFS.
There is no cd (change directory) command in hdfs file system. You can only list the directories and use them for reaching the next directory. You have to navigate manually by providing the complete path using the ls command.
Commands: ls: This command is used to list all the files. Use lsr for recursive approach.
- SSH onto your EMR cluster ssh hadoop@emrClusterIpAddress -i yourPrivateKey.ppk.
- List the contents of that directory we just created which should now have a new log file from the run we just did.
- Now to view the file run hdfs dfs -cat /eventLogging/application_1557435401803_0106.
-Put and -copyFromLocal is almost same command but a bit difference between both of them. -put command can copy single and multiple sources from local file system to destination file system. copyFromLocal is similar to put command, but the source is restricted to a local file reference.
Copying files between local and hdfsWe can use the hdfs dfs -copyFromLocal <path_on_local> <path_on_hdfs> or hdfs dfs -put <path_on_local> <path_on_hdfs> to copy files locally to hdfs. Something interesting when you list the contents of the directory.
DataNodes are the slave nodes in HDFS. The actual data is stored on DataNodes. A functional filesystem has more than one DataNode, with data replicated across them. The NameNode also initiates replication of blocks on the DataNodes as and when necessary.
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.
Using Impala and Hive LLAP
| Impala | Hive LLAP |
|---|
| Good choice for Business Intelligence tools that allow users to quickly change queries | Good choice for Dashboards that are pre-defined and not customizable by the viewer |
Data Replication. HDFS is designed to reliably store very large files across machines in a large cluster. It stores each file as a sequence of blocks; all blocks in a file except the last block are the same size. The blocks of a file are replicated for fault tolerance.
Hadoop HDFS ls Command Description:The Hadoop fs shell command ls displays a list of the contents of a directory specified in the path provided by the user.
Below are three options:
- Remove the file on localmachine with rm command and use copyToLocal/get .
- Rename your local file to new name so that you can have the file with same name as on cluster. use mv command for that and use get/copyTolocal command.
- Rename the file there on the cluster itself and use copytolocal.
