# Environment variables

s1bursts reads credentials and SNAP settings from environment variables. Set them in your shell, or keep them in a `.env` file:


    .env


``` bash
CDSE_USERNAME=your-account-name
CDSE_PASSWORD=your-password
SNAP_MAX_RAM_GB=16
```


s1bursts does not read `.env` by itself. Run your script with `uv run --env-file .env script.py`, or call `dotenv.load_dotenv()` from [python-dotenv](https://pypi.org/project/python-dotenv/) at its start.

> **Warning: Warning**
>
> Keep `.env` out of version control, since it holds your password.


# CDSE credentials

Downloads need a [CDSE account](https://dataspace.copernicus.eu/), but searching needs none. The S3 keys are optional and enable a second download route, which [takes over](finding-and-downloading.md#when-the-burst-service-fails) when CDSE's burst service fails:

| Variable | Purpose |
|----|----|
| `CDSE_USERNAME`, `CDSE_PASSWORD` | CDSE account, used by the burst service |
| `CDSE_S3_ACCESS_KEY_ID`, `CDSE_S3_SECRET_ACCESS_KEY` | CDSE S3 keys, from the [S3 key manager](https://eodata-s3keysmanager.dataspace.copernicus.eu/) |
| `CDSE_S3_PROFILE` | Instead of the two keys: a profile in `~/.aws/credentials` that holds them |


# SNAP

SNAP needs plenty of memory. `SNAP_MAX_RAM_GB` is the total budget shared by all parallel SNAP processes. s1bursts reserves 3 GB of it for overhead and splits the rest between the processes, so the default of 8 GB gives one process 5 GB. That is enough for backscatter and coherence. Raise the budget when you run several processes in parallel:

| Variable | Purpose | Default |
|----|----|----|
| `SNAP_BIN` | The SNAP installation's `bin` directory | `gpt` on `PATH` |
| `SNAP_MAX_WORKERS` | SNAP processes run in parallel | 1 |
| `SNAP_MAX_RAM_GB` | Memory budget across those processes, in GB | 8 |
| `SNAP_THREADS_PER_JOB` | Threads per SNAP process | CPU count divided by workers |
| `SNAP_CACHE_RATIO` | Share of each process's memory used as tile cache | 0.7 |
| `SNAP_TIMEOUT` | Seconds one SNAP process may run before it is stopped and its burst recorded as failed, or `none` for no limit | 3600 |
| `SNAP_AUXDATA_PATH` | Cache for orbit files and DEM tiles | `~/.snap/auxdata` |
| `SNAP_DEM_CACHE` | Cache for [prepared external DEMs](external-dems.md) | `~/.s1bursts/dem` |

[SNAPConfig](../reference/snap_client.SNAPConfig.md#s1bursts.snap_client.SNAPConfig) sets the same values in code and takes precedence over the environment. See [Processing with SNAP](processing.md#run-several-jobs-at-once).


# Temporary files

SNAP writes large uncompressed files while it works, in the folder that `TMPDIR` names. Point `TMPDIR` at a local disk with several GB free, since on many systems the default `/tmp` is held in memory.