# Configuration

> Point the OpenTelemetry Injector at your Collector or backend and control what gets instrumented on a Linux host.

---

LLMS index: [llms.txt](/llms.txt)

---

After [installing](../installation/) the system packages, the
[OpenTelemetry Injector](https://github.com/open-telemetry/opentelemetry-injector)
instruments supported applications and exports telemetry using OTLP to
`localhost` on ports `4317` (gRPC) and `4318` (HTTP) by default. This page
describes how to change where telemetry is sent and how to adjust the injected
configuration.

## Set the export destination

The recommended setup is to run a local
[OpenTelemetry Collector](/docs/collector/) on the host that receives this
telemetry and forwards it to your backend.

To send telemetry somewhere else, the recommended way is to use a configuration
file. You rarely need to write one from scratch: each language package ships a
ready-to-use reference file at `/etc/opentelemetry/<language>/otel-config.yaml`
that wires up the exporter endpoint, headers, and service name through
environment-variable interpolation. Copy or adapt one of these files with your
[declarative configuration](/docs/languages/sdk-configuration/declarative-configuration/),
then activate it by setting `OTEL_CONFIG_FILE` in the injector environment file
at `/etc/opentelemetry/injector/default_env.conf`:

```conf
OTEL_CONFIG_FILE=/etc/opentelemetry/config.yaml
```

> [!NOTE]
>
> For .NET, file-based configuration also requires
> `OTEL_EXPERIMENTAL_FILE_BASED_CONFIGURATION_ENABLED=true`. Without it, the
> configuration file is silently ignored.

Restart your applications for configuration changes to take effect.

## Configure with environment variables

If you prefer not to use a configuration file, you can set standard
OpenTelemetry environment variables directly in the injector environment file at
`/etc/opentelemetry/injector/default_env.conf`. Any variable set there is
applied to every instrumented process. For example, to export directly to an
OTLP endpoint that requires an API key:

```conf
OTEL_EXPORTER_OTLP_ENDPOINT=https://otlp.example.com
OTEL_EXPORTER_OTLP_HEADERS=api-key=REPLACE_ME
```

Because `default_env.conf` uses standard OpenTelemetry environment variables,
you can configure any SDK behavior the same way, such as `OTEL_SERVICE_NAME`,
`OTEL_RESOURCE_ATTRIBUTES`, or the various sampler and exporter settings. See
[SDK environment variables](/docs/languages/sdk-configuration/) for the full
list.

Restart your applications for configuration changes to take effect.

## Run a local Collector

Running a [Collector](/docs/collector/) on the host lets you keep the export
configuration of your applications simple: they send OTLP to `localhost`, and
the Collector handles batching, retries, and routing to one or more backends.
Install and run the Collector separately for now; it is not yet part of the base
`opentelemetry` metapackage.

## Next steps

- Learn more about the [OpenTelemetry Collector](/docs/collector/).
- Review the available
  [SDK environment variables](/docs/languages/sdk-configuration/).