How To Run A Python Script As A Service On CentOS?

Using Systemd

Systemd manages services for Linux operating systems. It controls what programs run when a Linux system starts. To use Systemd for running Python scripts as services:

1. Create a service file in /etc/systemd/system/.
2. Define service parameters, including the Python script path.
3. Set service file permissions.
4. Reload the Systemd daemon.
5. Enable and start the service.

[Unit]
Description=My Python Script Service
After=network.target

[Service]
ExecStart=/usr/bin/python3 /path/to/your/script.py
Restart=always
User=yourusername

[Install]
WantedBy=multi-user.target

Using Supervisor

Supervisor is a system that helps you monitor and control processes on UNIX-like operating systems. It's useful for managing long-running Python scripts. To use Supervisor:

1. Install Supervisor with the package manager.
2. Create a configuration file for your Python script in Supervisor's configuration directory.
3. Define program parameters, including the command to run your script.
4. Update Supervisor to recognize the new configuration.
5. Start the program using Supervisor's control commands.

autorestart=true

Both methods offer reliable ways to run Python scripts as services. Systemd integrates well with modern Linux systems, while Supervisor provides specific process management features.

Writing the Service File

To create a Systemd service for your Python script, you need to write a service file. This file defines how the service runs and behaves. The service file has a structure with different sections:

1. [Unit]: Contains metadata and dependencies.
2. [Service]: Defines the service behavior and execution.
3. [Install]: Specifies how to install the service.

When configuring the service file, focus on two key parameters:

• ExecStart: This specifies the command to start your Python script. Use the full path to both the Python interpreter and your script.
• WorkingDirectory: This sets the working directory for your script. It's important if your script uses relative file paths.

Example service file structure:

[Unit]
Description=My Python Script Service
After=network.target

[Service]
ExecStart=/usr/bin/python3 /path/to/your/script.py
WorkingDirectory=/path/to/script/directory
Restart=always
User=yourusername

[Install]
WantedBy=multi-user.target

Replace the placeholders with your specific paths and username.

Environment=PYTHONPATH=/path/to/your/python/modules

Enabling and Starting the Service

After creating the service file, you need to enable and start it. Use these commands:

1. Reload the Systemd daemon to recognize the new service file:

   sudo systemctl daemon-reload

2. Enable the service to start on boot:

   sudo systemctl enable your_service_name.service

3. Start the service:

   sudo systemctl start your_service_name.service

4. Check the service status:

   sudo systemctl status your_service_name.service

This status command will show if the service is running or if there are any issues. If you see "Active: active (running)", your Python script is now running as a service.

Installing Supervisor

To install Supervisor on CentOS:

1. Update your system packages:

   sudo yum update

2. Install EPEL repository if not installed:

   sudo yum install epel-release

3. Install Supervisor:

   sudo yum install supervisor

4. Start the Supervisor service:

   sudo systemctl start supervisord

5. Enable Supervisor to start on boot:

   sudo systemctl enable supervisord

To check the installation, view the Supervisor status:

sudo systemctl status supervisord

This command should show that Supervisor is active and running.

supervisord --version

Configuring Supervisor

To configure Supervisor for your Python script:

1. Create a new configuration file in the Supervisor configuration directory:

   sudo nano /etc/supervisord.d/your_script_name.ini

2. Add this content to the file:

   [program:your_script_name]
   command=/usr/bin/python3 /path/to/your/script.py
   directory=/path/to/script/directory
   user=your_username
   autostart=true
   autorestart=true
   stderr_logfile=/var/log/your_script_name.err.log
   stdout_logfile=/var/log/your_script_name.out.log

   Replace the placeholders with your paths and username.

3. Save the file and exit the editor.

4. Reload Supervisor to apply the new configuration:

   sudo supervisorctl reread
   sudo supervisorctl update

5. Start your program:

   sudo supervisorctl start your_script_name

These steps will set up Supervisor to manage your Python script as a service, keeping it running and restarting it if it stops.

Monitoring Service Status

To check your Python service health, use these commands:

For Systemd:

sudo systemctl status your_service_name

For Supervisor:

sudo supervisorctl status your_program_name

These commands show if your service is running, stopped, or has issues.

To view logs and fix problems:

For Systemd:

sudo journalctl -u your_service_name

For Supervisor:

sudo tail -f /var/log/your_program_name.out.log
sudo tail -f /var/log/your_program_name.err.log

These commands show the latest log entries, helping you find and fix issues.

sudo journalctl -u your_service_name --since "2023-05-01" --until "2023-05-02"

Stopping and Restarting Services

To control your Python service, use these commands:

For Systemd:

• Stop: sudo systemctl stop your_service_name
• Start: sudo systemctl start your_service_name
• Restart: sudo systemctl restart your_service_name

For Supervisor:

• Stop: sudo supervisorctl stop your_program_name
• Start: sudo supervisorctl start your_program_name
• Restart: sudo supervisorctl restart your_program_name

To automate restarts:

For Systemd, add this line to your service file:

Restart=always

For Supervisor, add this line to your program configuration:

autorestart=true

These settings make your service restart automatically if it stops unexpectedly.