---
description: Describes parameters used to configure Grafana Loki.
menuTitle: Configuration parameters
title: Grafana Loki configuration parameters
weight: 500
---

# Grafana Loki configuration parameters

{{ .GeneratedFileWarning }}

Grafana Loki is configured in a YAML file (usually referred to as `loki.yaml` )
which contains information on the Loki server and its individual components,
depending on which mode Loki is launched in.

Configuration examples can be found in the [Configuration Examples]({{ `{{< relref "./examples/" >}}` }}) document.

## Printing Loki config at runtime

If you pass Loki the flag `-print-config-stderr` or `-log-config-reverse-order`, (or `-print-config-stderr=true`)
Loki will dump the entire config object it has created from the built-in defaults combined first with
overrides from config file, and second by overrides from flags.

The result is the value for every config object in the Loki config struct, which is very large...

Many values will not be relevant to your install such as storage configs which you are not using and which you did not define,
this is expected as every option has a default value if it is being used or not.

This config is what Loki will use to run, it can be invaluable for debugging issues related to configuration and
is especially useful in making sure your config files and flags are being read and loaded properly.

`-print-config-stderr` is nice when running Loki directly e.g. `./loki ` as you can get a quick output of the entire Loki config.

`-log-config-reverse-order` is the flag we run Loki with in all our environments, the config entries are reversed so
that the order of configs reads correctly top to bottom when viewed in Grafana's Explore.

## Reload at runtime

Promtail can reload its configuration at runtime. If the new configuration
is not well-formed, the changes will not be applied.
A configuration reload is triggered by sending a `SIGHUP` to the Promtail process or
sending a HTTP POST request to the `/reload` endpoint (when the `--server.enable-runtime-reload` flag is enabled).

## Configuration file reference

To specify which configuration file to load, pass the `-config.file` flag at the
command line. The value can be a list of comma separated paths, then the first
file that exists will be used.
If no `-config.file` argument is specified, Loki will look up the `config.yaml` in the
current working directory and the `config/` subdirectory and try to use that.

The file is written in [YAML
format](https://en.wikipedia.org/wiki/YAML), defined by the scheme below.
Brackets indicate that a parameter is optional. For non-list parameters the
value is set to the specified default.

### Use environment variables in the configuration

> **Note:** This feature is only available in Loki 2.1+.

You can use environment variable references in the configuration file to set values that need to be configurable during deployment.
To do this, pass `-config.expand-env=true` and use:

```
${VAR}
```

Where VAR is the name of the environment variable.

Each variable reference is replaced at startup by the value of the environment variable.
The replacement is case-sensitive and occurs before the YAML file is parsed.
References to undefined variables are replaced by empty strings unless you specify a default value or custom error text.

To specify a default value, use:

```
${VAR:-default_value}
```

Where default_value is the value to use if the environment variable is undefined.

Pass the `-config.expand-env` flag at the command line to enable this way of setting configs.

### Generic placeholders

- `<boolean>` : a boolean that can take the values `true` or `false`
- `<int>` : any integer matching the regular expression `[1-9]+[0-9]*`
- `<duration>` : a duration matching the regular expression `[0-9]+(ns|us|µs|ms|[smh])`
- `<labelname>` : a string matching the regular expression `[a-zA-Z_][a-zA-Z0-9_]*`
- `<labelvalue>` : a string of unicode characters
- `<filename>` : a valid path relative to current working directory or an absolute path.
- `<host>` : a valid string consisting of a hostname or IP followed by an optional port number
- `<string>` : a string
- `<secret>` : a string that represents a secret, such as a password

### Supported contents and default values of `loki.yaml`

{{ .ConfigFile }}