# Global Variables Sling utilizes the following global environment variables to further configure the load behavior. You can simply define them in your environment, the `env.yaml` file or the `env` section in a task or replication.

Variable Name	Description
`SLING_HOME_DIR`	The sling home directory, which contains `env.yaml`. Will use default if not provided.
`SLING_LOADED_AT_COLUMN`	Whether to add an audit timestamp column named `_sling_loaded_at` in target object. Accepts values `true`, `false`, `unix` (for epoch integer values) or `timestamp`. `true` defaults to `unix`.
`SLING_SYNCED_AT_COLUMN`	Whether to add sync tracking columns `_sling_synced_at` (timestamp) and `_sling_synced_op` (operation type) in target object. The `_sling_synced_op` column tracks the last operation: `I` = Insert, `U` = Update, `D` = Delete (soft delete). This is useful when streaming from staging to multiple destinations to track when records were last touched. To enable, set to `true`. When enabled, `_sling_synced_at` replaces `_sling_deleted_at` for soft deletes.
`SLING_STREAM_URL_COLUMN`	If source is file, whether to add a column `_sling_stream_url` with the source file path / url in target object. To enable, set to `true`.
`SLING_TIMEOUT`	The maximum number of minutes the sling replication should run. Once reached, it will kill the process. To enable, set a number (`SLING_TIMEOUT=10.5`)
`SLING_RECURSIVE_LIMIT`	The number limit of file names to pull, when listing from cloud file systems such as S3, GCP and Azure Storage.
`SLING_ROW_ID_COLUMN`	Whether to add a column named `_sling_row_id` in the target object, which will have a random UUIDv7 value. This will be unique. To enable, set to `true`.
`SLING_ROW_NUM_COLUMN`	If source is file, whether to add a column named `_sling_row_num` in the target object, which will be the row number of the stream (incremented by record processed). To enable, set to `true`.
`SLING_EXEC_ID_COLUMN`	Whether to add a column named `_sling_exec_id` in the target object, which will have the run / execution string (a random UUIDv7 value). This will be unique per run. To enable, set to `true`.
`SLING_STATE`	The location to read/write information such as incremental values. Proper input format is `CONN_NAME/key`. For example: `POSTGRES/sling_state.state_table` , `AWS_S3/my/folder` or `MY_SFTP/my/folder`.
`SLING_ALLOW_EMPTY`	This is useful to create tables / files using the stream columns structure, even if there is no data. To enable, set to `true`.
`SLING_DIRECT_INSERT`	Tells sling to insert directly into the final table (not create a temp table before). To enable, set to `true`.
`SLING_THREADS`	sets the maximum number of concurrent stream runs. Accepts an integer value, default is `1`.
`SLING_RETRIES`	sets the maximum number of retries for a failed stream run. Accepts an integer value, default is `0`.
`SLING_KEEP_TEMP`	Tells sling to keep any temporary files or tables created in the load process. To enable, set to `true`
`SLING_ENV_YAML`	Provide the body of the `env.yaml` file as an environment variable.
`SLING_DISABLE_TELEMETRY`	this disables any anonymous usage reporting. These are used to improve sling. To disable, set this to `true`.
`SLING_SHOW_PROGRESS`	Whether the progress of the stream should be displayed (`true` or `false`).
`SLING_LOGGING`	How sling formats the log lines. Accepts values `JSON`, `NO_COLOR` or `CONSOLE` (default).
`SLING_LOG_DIR`	Directory for automatic date-based debug log files. When set, Sling creates a `sling_debug_YYYY_MM_DD.log` file in the specified directory and automatically cleans up old log files, keeping the latest 15. Supports `~` for home directory (e.g., `~/.sling/logs`).
`SLING_SAMPLE_SIZE`	The number of records to process in order to infer column types (especially for file sources). Default is `900`.
`SLING_DUCKDB_COMPUTE`	Whether to use DuckDB for writing to parquet files and partitioned parquet/CSV files. DuckDB provides optimized performance for these formats. To disable DuckDB compute, set to `false`. Default is `true`.
`SLING_OTEL_ENDPOINT`	The OpenTelemetry HTTP endpoint URL to export logs to (e.g., `http://otel.host.ip:4318/v1/logs`). When set, Sling will send structured logs to the specified OTLP endpoint with execution attributes including `project_id`, `job_id`, and `exec_id` if configured. Requires CLI Pro.
`SLING_PROXY`	Route database connections through a SOCKS5 proxy. Accepts a SOCKS5 URL (e.g., `socks5://user:pass@host:1080`). To proxy a specific connection instead, set `proxy_url` in its `env.yaml` connection entry. Useful for reaching databases behind VPNs or private networks (e.g., Tailscale). Available in v1.5.9+

--- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.slingdata.io/sling-cli/variables.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.