# System packages

Cortex looks for a file named `dependencies.sh` in the top level Cortex project directory (i.e. the directory which contains `cortex.yaml`). For example:

```
./my-classifier/
├── cortex.yaml
├── predictor.py
├── ...
└── dependencies.sh
```

`dependencies.sh` is executed with `bash` shell during the initialization of each replica (before installing Python packages in `requirements.txt` or `conda-packages.txt`). Typical use cases include installing required system packages to be used in your Predictor, building Python packages from source, etc. If initialization time is a concern, see [Docker images](/0.29/workloads/dependencies/images.md) for how to build and use custom Docker images.

Here is an example `dependencies.sh`, which installs the `tree` utility:

```bash
apt-get update && apt-get install -y tree
```

The `tree` utility can now be called inside your `predictor.py`:

```python
# predictor.py
import subprocess

class PythonPredictor:
    def __init__(self, config):
        subprocess.run(["tree"])
    ...
```

If you need to upgrade the Python Runtime version on your image, you can do so in your `dependencies.sh` file:

```bash
# upgrade python runtime version
conda update -n base -c defaults conda
conda install -n env python=3.8.5

# re-install cortex core dependencies
/usr/local/cortex/install-core-dependencies.sh
```


---

# 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.cortexlabs.com/0.29/workloads/dependencies/system-packages.md?ask=<question>
```

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.