# systemd Talk

First, let's make ourselves a simple python web server with flask:

```python3
from flask import Flask
app = Flask(__name__)
import os

PORT = int(os.getenv('FLASK_PORT', 5000))

@app.route('/')
def hello_world():
    return 'Hello, PuPPy!'

if __name__ == '__main__':
    app.run(port=PORT)

```

Cool! Let's try running it:

```bash
$ python3 main.py
```

Unsurprising.  But, what if we wanted to make sure that this was always running, and was started as soon as the computer turned on? systemd to the rescue!

Let's create a service file at `systemdflaskdemo.service`:

```
[Unit]
Description=A baby fask app

[Service]
ExecStart=/usr/bin/python3 /home/stuart/code/systemd-talk/main.py
Environment=FLASK_PORT=8050
Restart=always

[Install]
WantedBy=default.target
```

This service config file tells systemd when and how to run our process - in this case a web server. After creating this config file, we tell systemd to enable this service for our user:

```bash
$ systemctl --user enable $(pwd)/systemdflaskdemo.service
```

Cool! But it's not running yet, as we can see when checking the status of the service:

```bash
$ systemctl --user status systemdflaskdemo.service
```

Simple enough to fix, let's just start it:

```bash
$ systemctl --user start systemdflaskdemo.service
```

That `WantedBy=default.target` tells systemd that we want the process to start as soon as the user logs in, so we should be covered in the case of a system restart also, if we enable lingering for the current user:

```bash
$ loginctl enable-linger $(whoami)
```

If you ever want to stop the service, that's also easy:

```bash
$ systemctl --user stop systemdflaskdemo.service
```

And, say you want to totally remove the service? Just `disable` it!

```bash
$ systemctl --user disable systemdflaskdemo.service
```

In my experience, `daemon-reload` hasn't always worked for reloading `--user` service configs, but I am still but a systemd noob.  Hope this has helped!