# Runtime Environment & Options

Signal K Server provides the following command line options and environment variables to configure your implementation.

## Command line options

Option | Description
--- | ---
`-s` | Override path to the settings file. (same as `SIGNALK_NODE_SETTINGS` environment variable)
`-c` | Override the path to find server configuration. (same as `SIGNALK_NODE_CONFIG_DIR` environment variable)
`--sample-nmea0183-data` | Starts signalk-server with sample NMEA0183 data.
`--sample-n2k-data` | Starts signalk-server with sample NMEA2000 data.
`--override-timestamps` | Override timestamps in the sample NMEA2000 data with current date and time. Doesn't apply nor makes a difference to NMEA0183 sample data.
`--securityenabled` | Enable security. For a fresh install this makes the Admin UI force the user to create an admin account before he/she can continue further into the UI. See Security for further details.
`--no-plugins` | Start the server without loading any plugins (Node.js or WASM). Useful for debugging, recovering from a misbehaving plugin, or running a stripped-down server. The Admin UI will not show a plugin list while this flag is active.
`--no-webapps` | Start the server without serving any webapps (regular, embeddable, or MFD). The core Admin UI is still served. Useful when running the server purely as a data backend or for diagnosing webapp issues.

## Environment variables

Variable | Description
--- | ---
`PORT` | Override the port for http/ws service (default is 3000).
`SSLPORT` | Override the port for https/wss service. If defined forces ssl as default protocol (default port is 3443).
`PROTOCOL` | Override http/https where the server is accessed via https but the server sees http (e.g. when Heroku handles https termination)
`EXTERNALPORT` | The port used in /signalk response and Bonjour advertisement. Has precedence over configuration file.
`EXTERNALHOST` | The host used in /signalk response and Bonjour advertisement. Has precedence over configuration file.
`EXTERNALSSL` | Indicates that TLS is terminated by an external reverse proxy. Affects mDNS advertisement and discovery protocol selection. Set to `1` or `true` to enable. Has precedence over `proxy_ssl` in the settings file.
`FILEUPLOADSIZELIMIT` | Override the file upload size limit (default is '10mb').
`NMEA0183PORT` | Override the port for the NMEA 0183 over tcp service (default is 10110).
`TCPSTREAMPORT` | Override the port for the Signal K Streaming (deltas) over TCP.
`TCPSTREAMADDRESS` | Override the address the Signal K Stream (deltas) over TCP is listening on.
`DISABLEPLUGINS` | Disable all plugins so that they can not be enabled (default is false).
`DEFAULTENABLEDPLUGINS` | A comma-separated list of plugin ids that are overridden to be enabled by default if no settings exist. Lower preference than `DISABLEPLUGINS`.
`PLUGINS_WITH_UPDATE_DISABLED` | A comma-separated list of plugin that will not be updated.
`SECURITYSTRATEGY` | Override the security strategy module name.
`DISABLE_SECURITY_ACTIVATION` | Prevent security from being activated via the Admin UI or API when the server is running without security. Set to `1` or `true` to enable. Useful for servers that are intentionally running without authentication and should not allow remote security activation (default is false).
`WSCOMPRESSION` | Compress websocket messages (default is false).
`MAXSENDBUFFERSIZE` | The maximum number of bytes allowed in the server's send buffer of a client connection (WebSocket, Signal K TCP, and NMEA TCP). The connection will be terminated if this is exceeded for MAXSENDBUFFERCHECKTIME milliseconds. Guards against slow or dysfunctional clients that can not cope with the message volume (default is 2097152 / 2MB).
`MAXSENDBUFFERCHECKTIME` | How long in milliseconds to wait before terminating a client connection (WebSocket, Signal K TCP, and NMEA TCP) whose send buffer exceeds MAXSENDBUFFERSIZE (default is 30000 / 30s).
`SIGNALK_SERVER_IS_UPDATABLE` | Allows the server to be updated through the GUI even if it is not installed in the standard paths (default is false). If set to true, the server must have been installed with `npm install -g signalk-server`.
`SIGNALK_DISABLE_SERVER_UPDATES` | Disables server updates in the GUI (default is false).
`DEBUG` | A comma-separated list of tags for debugging the specified module (e.g signalk-server*,signalk-provider-tcp). Can now be defined directly in the graphical interface. More help on how to use the debug here: `https://www.npmjs.com/package/debug#wildcards`
`IS_IN_DOCKER` | Used to tell the server it is in Docker and not normally updateable (default is false).
`NPMREGISTRYTIMEOUT` | How long to wait for the registry when retrieving the App Store listing (default is 20s).
`SECRETKEY` | A secret string used to generate an authentication token (the internal default autogenerated is a string of 512 hex chars like 'ef8307a4c7a4bd7...309d947bca3')
`ALLOW_DEVICE_ACCESS_REQUESTS` | Used when a device needs to gain access to a secured Signal K server (default is true) (https://signalk.org/specification/1.4.0/doc/access_requests.html).
`ALLOW_NEW_USER_REGISTRATION` | (default is true).
`ADMINUSER` | Force an account for admin user (username:password format).
`PRESERIALCOMMAND` | Command to run before opening a serial port.
`SIGNALK_NODE_SETTINGS` | Override the path to the settings file.
`SIGNALK_NODE_CONFIG_DIR` | Override the path to find server configuration. Includes all run-time changing content: configuration files, plugins, plugin configuration files, webapps, and so forth.
`SKIP_NODE_VERSION_CHECK` | Skip the Node.js minimum version check. This is not recommended, but allows you to attempt to run the server on unsupported versions of Node. (Added in v2.14.1)
`HTTP_RATE_LIMITS` | Override HTTP rate limits. Provide overrides like `api=1000,loginStatus=1000,login=1000` (optionally `windowMs=600000`). Useful for tests and unusual deployments.
`TRUST_PROXY` | Override the `trustProxy` setting from `settings.json`. Accepts `true`, `false`, an IP address/CIDR string, or an integer hop count. Useful for container and cloud deployments where the setting must be injected via the environment rather than baked into the config file. When set, takes precedence over the value in `settings.json`.

`BACKPRESSURE_ENTER`

Backpressure threshold in bytes to enter backpressure mode (default is 524288 / 512KB). Applies to WebSocket, Signal K TCP, NMEA TCP, and TCP client connections. When a connection's send buffer exceeds this, the server switches to accumulating only latest values per path (for delta connections), dropping messages (for NMEA connections), or skipping outbound writes (for TCP client connections).

`BACKPRESSURE_EXIT` | Backpressure threshold in bytes to exit backpressure mode (default is 1024 / 1KB). When the buffer drains below this, accumulated values are flushed. Applies to WebSocket and Signal K TCP connections. Primarily for testing.
`EVENT_EMITTER_MAX_LISTENERS` | Maximum number of delta event listeners (default is 50). Increase if you see MaxListenersExceededWarning when connecting many WebSocket clients.
`MAX_WS_CONNECTIONS_PER_IP` | Maximum number of concurrent WebSocket connections allowed from a single IP address (default is 30). Connections beyond the limit are rejected during the HTTP upgrade with HTTP 429 Too Many Requests.
`SIGNALK_ADMIN_UI` | Select the Admin UI version. Set to `react19` to use the React 19 Admin UI. If not set, the legacy Admin UI is used.

## Settings file options

The following options can be set in `settings.json` or via the server settings API.

Option | Description
--- | ---

`wsPingInterval`

Interval in milliseconds for native WebSocket ping/pong heartbeat (default is 30000). The server sends a WebSocket ping frame to each connected client at this interval. Clients that do not respond with a pong are considered dead and disconnected. This prevents stale connections from accumulating when clients drop without a close frame (e.g. WiFi disconnects). Set to `false` to disable.