Help Center > > User Guide> Using an MRS Client> Using the Client of Each Component> Using an HDFS Client

Using an HDFS Client

Updated at: Sep 02, 2021 GMT+08:00

Scenario

This section describes how to use the HDFS client in an O&M scenario or service scenario.

Prerequisites

  • The client has been installed.

    For example, the installation directory is /opt/hadoopclient. The client directory in the following operations is only an example. Change it to the actual installation directory.

  • Service component users are created by the administrator as required. In security mode, machine-machine users need to download the keytab file. A human-machine user needs to change the password upon the first login. (This operation is not required in normal mode.)

Using the HDFS Client

  1. Install a client.

  2. Log in to the node where the client is installed as the client installation user.
  3. Run the following command to go to the client installation directory:

    cd /opt/hadoopclient

  4. Run the following command to configure environment variables:

    source bigdata_env

  5. If the cluster is in security mode, run the following command to authenticate the user. In normal mode, user authentication is not required.

    kinit Component service user

  6. Run the HDFS Shell command. Example:

    hdfs dfs -ls /

Common HDFS Client Commands

The following table lists common HDFS client commands.

For more commands, see https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/CommandsManual.html#User_Commands.

Table 1 Common HDFS client commands

Command

Description

Example

hdfs dfs -mkdir Folder name

Used to create a folder.

hdfs dfs -mkdir /tmp/mydir

hdfs dfs -ls Folder name

Used to view a folder.

hdfs dfs -ls /tmp

hdfs dfs -put Local file on the client node

Used to upload a local file to a specified HDFS path.

hdfs dfs -put /opt/test.txt /tmp

Upload the /opt/tests.txt file on the client node to the /tmp directory of HDFS.

hdfs dfs -get Specified file on HDFS Specified path on the client node

Used to download the HDFS file to the specified local path.

hdfs dfs -get /tmp/test.txt /opt/

Download the /tmp/test.txt file on HDFS to the /opt path on the client node.

hdfs dfs -rm -r -f Specified folder on HDFS

Used to delete a folder.

hdfs dfs -rm -r -f /tmp/mydir

Client-related FAQs

  1. What do I do when the HDFS client exits abnormally and error message "java.lang.OutOfMemoryError" is displayed after the HDFS client command is running?

    This problem occurs because the memory required for running the HDFS client exceeds the preset upper limit (128 MB by default). You can change the memory upper limit of the client by modifying CLIENT_GC_OPTS in <Client installation path>/HDFS/component_env. For example, if you want to set the upper limit to 1 GB, run the following command:

    CLIENT_GC_OPTS="-Xmx1G"

    After the modification, run the following command to make the modification take effect:

    source <Client installation path>//bigdata_env

  2. How can i set the log level when the HDFS client is running?

    By default, the logs generated during the running of the HDFS client are printed to the console. The default log level is INFO. To enable the DEBUG log level for fault locating, run the following command to export an environment variable:

    export HADOOP_ROOT_LOGGER=DEBUG,console

    Then run the HDFS Shell command to generate the DEBUG logs.

    If you want to print INFO logs again, run the following command:

    export HADOOP_ROOT_LOGGER=INFO,console

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