During Linux system development, sometimes your program might crash or be stopped. To keep it running continuously, adding the program to the service list is a very good practice. Here is an explanation of how to add your own program to system services in Linux, taking CentOS7 as an example.

Steps:

  1. Build a simple Flask web program with Python
  2. Add it to system services
  3. Start the service and detailed explanation of parameters

Build a simple Flask web program with Python

This step can be any program you want to add to system services. The example here is a simple Flask web app that only outputs “Hello, World!”

yum install python-pip -y  
pip install --upgrade pip  
pip install flask

Create a simple Flask program under root user directory, first:

## Location /root/hello.py  
from flask import Flask  
app = Flask(__name__)  

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

Test run:

export FLASK_APP=hello.py  
flask run

You should see it running successfully:
flask_app

Test with wget:
wget_test

Add to system services

First, write a script to run the hello program. Flask needs environment variables so it’s a bit more complicated, others are easier. The script hello.sh is as follows:

cd /root  
export FLASK_APP=hello.py  
flask run

Create a systemd service file, for example named flask_app:

touch /etc/systemd/system/flask_app.service

Write the following content into it:

[Unit]  
Description=flask_app service  
After=network.target  
StartLimitIntervalSec=0  

[Service]  
Type=simple  
Restart=always  
RestartSec=1  
User=www  
ExecStart=/usr/bin/bash /root/hello.sh  

[Install]  
WantedBy=multi-user.target

Start service and explanation of parameters

Start the service:

systemctl start flask_app  
## or service flask_app start
  • Description: system service description
  • After: runs after specified target, here after network is up
  • StartLimitIntervalSec: time interval for restart limit, here runs once network is up
  • Restart: whether to restart after stopping
  • RestartSec: wait time before restarting after stopping
  • User: specify which user runs the program
  • ExecStart: the command to run the service program, full path required

Just copy the install section as is…

Summary:

This article solves a common problem: how to add your own program as a system service, and how to achieve automatic restart when the program stops, to ensure the program runs stably in the background.