# 🔧 Creating and Understanding a systemd Service File on Raspberry Pi

A **systemd service file** is used in Linux (including Raspberry Pi OS) to define how a service (like a Python script or web server) should be started, stopped, restarted, and managed.

Here’s the **basic structure** of a `.service` file:

```ini
[Unit]
Description=Your Service Description
After=network.target

[Service]
ExecStart=/usr/bin/python3 /path/to/your/script.py
WorkingDirectory=/path/to/your/
StandardOutput=inherit
StandardError=inherit
Restart=always
User=pi

[Install]
WantedBy=multi-user.target
```

---

### 🔍 Section Breakdown

#### `[Unit]`

* `Description=`: Human-readable description of the service.
    
* `After=`: Specifies service start order. Commonly set to [`network.target`](http://network.target) if the service depends on networking.
    

#### `[Service]`

* `ExecStart=`: The full command to run your service. Use full paths!
    
* `WorkingDirectory=`: Directory where the script will be run.
    
* `StandardOutput=` and `StandardError=`: Where logs are directed. `inherit` passes it to the system journal.
    
* `Restart=`: Automatically restart the service if it crashes. Use `always` or `on-failure`.
    
* `User=`: Specifies the user under which the service will run (commonly `pi` on Raspberry Pi).
    

#### `[Install]`

* `WantedBy=`[`multi-user.target`](http://multi-user.target): Tells systemd to start the service at boot in the typical multi-user (non-graphical) mode.
    

---

### Example: Blink LED Python Script Service

Let's say you have a script: `/home/pi/`[`blink.py`](http://blink.py)

```ini
[Unit]
Description=Blink LED on Raspberry Pi
After=network.target

[Service]
ExecStart=/usr/bin/python3 /home/pi/blink.py
WorkingDirectory=/home/pi/
StandardOutput=inherit
StandardError=inherit
Restart=always
User=pi

[Install]
WantedBy=multi-user.target
```

Save this file as `/etc/systemd/system/blink.service`

---

### To Use It:

```bash
sudo systemctl daemon-reload           # Reload systemd manager configuration
sudo systemctl enable blink.service    # Enable on boot
sudo systemctl start blink.service     # Start the service
sudo systemctl status blink.service    # Check its status
```

To create a **Linux systemd service file** that runs your [`blink.py`](http://blink.py) Python script on a Raspberry Pi (e.g., at boot), follow these steps:

---

### ✅ 1. **Sample** [`blink.py`](http://blink.py) script

Make sure your script is executable and working:

```python
# blink.py
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)

try:
    while True:
        GPIO.output(17, GPIO.HIGH)
        time.sleep(1)
        GPIO.output(17, GPIO.LOW)
        time.sleep(1)
except KeyboardInterrupt:
    pass
finally:
    GPIO.cleanup()
```

Save this file at `/home/pi/`[`blink.py`](http://blink.py) (or wherever you'd like).

---

### ✅ 2. **Make it executable**

```bash
chmod +x /home/pi/blink.py
```

---

### ✅ 3. **Create a systemd service file**

Create a new service file:

```bash
sudo nano /etc/systemd/system/blink.service
```

Paste the following content:

```ini
[Unit]
Description=Blink LED using Python script
After=multi-user.target

[Service]
ExecStart=/usr/bin/python3 /home/pi/blink.py
WorkingDirectory=/home/pi
StandardOutput=inherit
StandardError=inherit
Restart=always
User=pi

[Install]
WantedBy=multi-user.target
```

> **Note:** If you're using a virtual environment, replace `/usr/bin/python3` with the path to your virtual environment's Python binary.

---

### ✅ 4. **Enable and start the service**

```bash

sudo systemctl daemon-reload
sudo systemctl enable blink.service
sudo systemctl start blink.service
```

---

### ✅ 5. **Check status**

```bash
sudo systemctl status blink.service
```

---

### ✅ 6. **Logs (optional)**

If your script prints something or crashes:

```bash
journalctl -u blink.service -f
```

---

To **disable** or **stop** your `blink.service` on Raspberry Pi (or any Linux system using `systemd`):

---

### 🛑 To **stop** the service (immediately):

```bash
sudo systemctl stop blink.service
```

> This halts the running service but **does not prevent it from starting at boot**.

---

### 🚫 To **disable** the service (prevent it from starting at boot):

```bash
sudo systemctl disable blink.service
```

> You can combine both:

```bash
sudo systemctl stop blink.service
sudo systemctl disable blink.service
```

---

### ✅ To **re-enable** later:

```bash
sudo systemctl enable blink.service
sudo systemctl start blink.service
```