# Configuration Settings

An Alluxio cluster can be configured by setting the values of Alluxio [configuration properties](../reference/properties-list) within `${ALLUXIO_HOME}/conf/alluxio-site.properties`.

The two major components to configure are

* [Alluxio servers](#configure-an-alluxio-cluster), consisting of masters and workers
* [Alluxio clients](#configure-applications), which are typically a part of compute applications.

## Configure Applications

Customizing how an application interacts with Alluxio is specific to each application. The following are recommendations for some common applications.

Alluxio properties mostly fall into three categories

* properties prefixed with `alluxio.user` affect Alluxio client operations (e.g. compute applications)
* properties prefixed with `alluxio.master` affect the Alluxio master processes
* properties prefixed with `alluxio.worker` affect the Alluxio worker processes

### Alluxio Shell Commands

Alluxio shell users can put JVM system properties `-Dproperty=value` after the `fs` command and before the subcommand to specify Alluxio user properties from the command line. For example, the following Alluxio shell command sets the write type to `CACHE_THROUGH` when copying files to Alluxio:

```console
$ ./bin/alluxio fs -Dalluxio.user.file.writetype.default=CACHE_THROUGH \
  copyFromLocal README.md /README.md
```

Note that, as a part of Alluxio deployment, the Alluxio shell will also take the configuration in `${ALLUXIO_HOME}/conf/alluxio-site.properties` when it is run from Alluxio installation at `${ALLUXIO_HOME}`.

### Spark

To customize Alluxio client-side properties in Spark applications, Spark users can use pass Alluxio properties as JVM system properties. See examples for [configuring the Spark service](../../compute-integrations/spark#basic-setup) or for [individual Spark jobs](../../compute-integrations/spark#customize-alluxio-user-properties-for-individual-spark-jobs).

### Hadoop MapReduce

See examples to configure Alluxio properties for [the MapReduce service](../../compute-integrations/hadoop-mapreduce#customize-alluxio-user-properties-for-all-mapreduce-jobs) or for [individual MapReduce jobs](../../compute-integrations/hadoop-mapreduce#customize-alluxio-user-properties-for-individual-mapreduce-jobs).

### Hive

Hive can be configured to use customized Alluxio client-side properties for the entire service. See [examples](../../compute-integrations/hive#customize-alluxio-user-properties).

### Presto

Presto can be configured to use customized Alluxio client-side properties for the entire service. See [examples](../../compute-integrations/presto#customize-alluxio-user-properties).

### CDH (Enterprise-only)

CDH can be configured to use customized Alluxio client-side properties for the entire service. See [examples](../compute-integrations/cdh).

### HDP (Enterprise-only)

HDP can be configured to use customized Alluxio client-side properties for the entire service. See [examples](../compute-integrations/hdp).

## Configure an Alluxio Cluster

### `alluxio-site.properties` Files (Recommended)

Alluxio admins can create and edit the properties file `alluxio-site.properties` to configure Alluxio masters or workers. If this file does not exist, it can be created from the template file under `${ALLUXIO_HOME}/conf`:

```console
$ cp conf/alluxio-site.properties.template conf/alluxio-site.properties
```

Make sure that this file is distributed to `${ALLUXIO_HOME}/conf` on every Alluxio master and worker before starting the cluster. Any updates to the server configuration requires a restart of the process.

### Environment Variables

Alluxio supports defining a few frequently used configuration settings through environment variables, including:

| Environment Variable                  | Description                                                                                                                                                                                                       |
| ------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `ALLUXIO_CONF_DIR`                    | The path to the alluxio configuration directory.                                                                                                                                                                  |
| `ALLUXIO_LOGS_DIR`                    | The path to the directory that stores Alluxio server logs                                                                                                                                                         |
| `ALLUXIO_USER_LOGS_DIR`               | The path to the directory that stores Alluxio user logs                                                                                                                                                           |
| `ALLUXIO_MASTER_HOSTNAME`             | hostname of the Alluxio master. Defaults to localhost                                                                                                                                                             |
| `ALLUXIO_MASTER_MOUNT_TABLE_ROOT_UFS` | The under storage system addess. Defaults to `${ALLUXIO_HOME}`/underFSStorage which is a local file system.                                                                                                       |
| `ALLUXIO_RAM_FOLDER`                  | The directory where a worker stores its in-memory data. Defaults to `/mnt/ramdisk`                                                                                                                                |
| `ALLUXIO_JAVA_OPTS`                   | Java VM options for the Alluxio master, worker, and shell commands. Note that, by default `ALLUXIO_JAVA_OPTS` is included in `ALLUXIO_MASTER_JAVA_OPTS`, `ALLUXIO_WORKER_JAVA_OPTS`, and `ALLUXIO_USER_JAVA_OPTS` |
| `ALLUXIO_MASTER_JAVA_OPTS`            | Additional Java VM options for Alluxio master configuration.                                                                                                                                                      |
| `ALLUXIO_WORKER_JAVA_OPTS`            | Additional Java VM options for Alluxio worker configuration.                                                                                                                                                      |
| `ALLUXIO_USER_JAVA_OPTS`              | Additional Java VM options for Alluxio shell command configuration.                                                                                                                                               |
| `ALLUXIO_CLASSPATH`                   | Additional classpath entries for Alluxio processes. Empty by default.                                                                                                                                             |
| `ALLUXIO_LOGSERVER_HOSTNAME`          | Hostname of the log server. Empty by default.                                                                                                                                                                     |
| `ALLUXIO_LOGSERVER_PORT`              | The port number of the log server. Defaults to `45600`                                                                                                                                                            |
| `ALLUXIO_LOGSERVER_LOGS_DIR`          | The path to the local directory where the Alluxio log server stores logs received from the Alluxio servers                                                                                                        |

For example, to setup the following:

* an Alluxio master at `localhost`
* the root mount point as an HDFS cluster with a namenode also running at `localhost`
* enable Java remote debugging at port 7001 run the following commands before startingthe master process:

```console
$ export ALLUXIO_MASTER_HOSTNAME="localhost"
$ export ALLUXIO_MASTER_MOUNT_TABLE_ROOT_UFS="hdfs://localhost:9000"
$ export ALLUXIO_MASTER_JAVA_OPTS=\
"$ALLUXIO_JAVA_OPTS -agentlib:jdwp=transport=dt_socket,server=y, suspend=n,address=7001"
```

Users can either set these variables through the shell or in `conf/alluxio-env.sh`. If this file does not exist yet, create one by copying the template:

```console
$ cp conf/alluxio-env.sh.template conf/alluxio-env.sh
```

### Cluster Defaults

> Since version 1.8, each Alluxio client or worker can initialize its configuration with the cluster-wide configuration values retrieved from Alluxio masters.

When different client applications (Alluxio Shell CLI, Spark jobs, MapReduce jobs) or Alluxio workers connect to an Alluxio master, they will initialize their own Alluxio configuration properties with the default values supplied by the masters based on the master-side `${ALLUXIO_HOME}/conf/alluxio-site.properties` files. As a result, cluster admins can set default client-side settings (e.g., `alluxio.user.*`), or network transport settings (e.g., `alluxio.security.authentication.type`) in `${ALLUXIO_HOME}/conf/alluxio-site.properties` on all the masters, which will be distributed and become cluster-wide default values when clients and workers connect.

For example, the property `alluxio.user.file.writetype.default` defaults to `MUST_CACHE`, which only writes to Alluxio space.

In an Alluxio cluster where data persistence is preferred and all jobs need to write to both the UFS and Alluxio, the administrator can add `alluxio.user.file.writetype.default=CACHE_THROUGH` in each master's `alluxio-site.properties` file. After restarting the cluster, all jobs will automatically set `alluxio.user.file.writetype.default` to `CACHE_THROUGH`.

Clients can ignore or overwrite the cluster-wide default values by following the approaches described in [Configure Applications](#configure-applications) to overwrite the same properties.

> Note that, before version 1.8, `${ALLUXIO_HOME}/conf/alluxio-site.properties` file is only loaded by Alluxio server processes and will be ignored by applications interacting with Alluxio service through Alluxio client, unless `${ALLUXIO_HOME}/conf` is on applications' classpath.

### Path Defaults

Since version 2.0, Alluxio administrators can set default client-side configurations for specific Alluxio filesystem paths. Filesystem client operations have options which are derived from client side configuration properties. Only client-side configuration properties can be set as as path defaults.

For example, the `createFile` operation has an option to specify write type. By default, the write type is the value of the configuration key `alluxio.user.file.writetype.default`. The administrator can set default value of `alluxio.user.file.write.type.default` to `MUST_CACHE` for all paths with prefix `/tmp` by running:

```console
$ bin/alluxio fsadmin pathConf add --property alluxio.user.file.writetype.default=MUST_CACHE /tmp`
```

After executing this command any create operations on paths with prefix `/tmp` will use the `MUST_CACHE` write type by default unless the application configuration overrides the cluster defaults.

Path defaults will be automatically propagated to long running clients if they are updated. If the administrator updates path defaults using

```console
$ bin/alluxio fsadmin pathConf add --property alluxio.user.file.writetype.default=THROUGH /tmp
```

afterwards, all write operations that occur on a path with the prefix `/tmp` prefix will use the `THROUGH` write type by default.

See [`fsadmin pathConf`](../admin-cli#pathconf) on how to show, add, update, and remove path defaults.

## Configuration Sources

Alluxio properties can be configured from multiple sources. A property's final value is determined by the following priority list, from highest priority to lowest:

1. [JVM system properties (i.e., `-Dproperty=key`)](http://docs.oracle.com/javase/jndi/tutorial/beyond/env/source.html#SYS)
2. [Environment variables](#environment-variables)
3. [Property files](#alluxio-siteproperties-files-recommended): When an Alluxio cluster starts, each server process including master and worker searches for `alluxio-site.properties` within the following directories in the given order, stopping when a match is found: `${CLASSPATH}`, `${HOME}/.alluxio/`, `/etc/alluxio/`, and `${ALLUXIO_HOME}/conf`
4. [Path default values](#path-defaults)
5. [Cluster default values](#cluster-defaults): An Alluxio client may initialize its configuration based on the cluster-wide default configuration served by the masters.

If no user-specified configuration is found for a property, Alluxio will fall back to its [default property value](../reference/properties-list).

To check the value of a specific configuration property and the source of its value, users can run the following command:

```console
$ ./bin/alluxio getConf alluxio.worker.rpc.port
29998
$ ./bin/alluxio getConf --source alluxio.worker.rpc.port
DEFAULT
```

To list all of the configuration properties with sources:

```console
$ ./bin/alluxio getConf --source
alluxio.conf.dir=/Users/bob/alluxio/conf (SYSTEM_PROPERTY)
alluxio.debug=false (DEFAULT)
...
```

Users can also specify the `--master` option to list all of the cluster-wide configuration properties served by the masters. Note that with the `--master` option, `getConf` will query the master which requires the master process to be running. Otherwise, without `--master` option, this command only checks the local configuration.

```console
$ ./bin/alluxio getConf --master --source
alluxio.conf.dir=/Users/bob/alluxio/conf (SYSTEM_PROPERTY)
alluxio.debug=false (DEFAULT)
...
```

## Java 11 Configuration

Alluxio now supports Java 11. To run alluxio on Java 11, configure the `JAVA_HOME` environment variable to point to a Java 11 installation directory. If you only want to use Java 11 for Alluxio, you can set the `JAVA_HOME` environment variable in the `alluxio-env.sh` file. Setting the `JAVA_HOME` in `alluxio-env.sh`will not affect the Java version which may be used by other application running in the same environment.

## Server Configuration Checker

The server-side configuration checker helps discover configuration errors and warnings. Suspected configuration errors are reported through the web UI, `fsadmin doctor` CLI, and master logs.

The web UI shows the result of the server configuration check.

<figure><img src="https://1793983847-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGeffGGmwrYFLzhXkLOLn%2Fuploads%2Fgit-blob-558a17551ce619bdbbe2c945b9282fd1c2edfb5e%2Fscreenshot_configuration_checker_webui.png?alt=media" alt=""><figcaption></figcaption></figure>

Users can also run the `fsadmin doctor` command to get the same results.

```console
$ ./bin/alluxio fsadmin doctor configuration
```

Configuration warnings can also be found in the master logs.

<figure><img src="https://1793983847-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGeffGGmwrYFLzhXkLOLn%2Fuploads%2Fgit-blob-9bcfbd2ad0e23bac75f466f113e9d955d3ae7d1e%2Fscreenshot_configuration_checker_masterlogs.png?alt=media" alt=""><figcaption></figcaption></figure>
