[LINUX] Note to daemonize python

I want to make something written in python a daemon

I always wanted to run a program written in python on Sakura's VPS. In addition, it is easy because it can be operated with systemctl. The method is the following pakuri. Try to make your own command into a service using Systemd


--Sakura's VPS

How to



#!/usr/bin/env python
import time
import os
import sys

def main_unit():#Write the time every 10 seconds
	while True:
		filepath = '/opt/pydmon.log'
		log_file = open(filepath,'a')

def daemonize():
	pid = os.fork()#Fork the process here
	if pid > 0:#For parent process(pid is the process ID of the child process)
		pid_file = open('/var/run/python_daemon.pid','w')
	if pid == 0:#For child processes

if __name__ == '__main__':
	while True:

Let's specify Shebang.

Add #! / Usr / bin / env python or #! / Usr / bin / python to the beginning. #! / usr / bin / env python seems to preferentially use python at the beginning of $ PATH. On the other hand, #! / Usr / bin / python seems to directly specify python under / usr / bin /. Inconvenience may occur if the version is different.

I was familiar with Stack overflow, so if you are interested, please refer to it. Why do people write #!/usr/bin/env python on the first line of a Python script?

About daemonize ()

Forking the process, the parent process writes the child process ID returned in the variable pid to the pid file and disappears. The child process, on the other hand, runs main_unit () every 10 seconds in an infinite loop.

After saving, give execute permission.

sudo chmod 755 /opt/python_daemon.py You should now have execute permission.

Create a unit definition file





Daemon definition file. If ExecStart and PID File match, I think it's okay to copy and paste.

Start the daemon

sudo systemctl daemon-reload sudo systemctl start pythondaemon.service

After reloading the daemon, the newly created pythondaemon.service will be recognized. Then start it with start.


$ sudo systemctl status pythondaemon.service

● pythondaemon.service - PythonDaemon
   Loaded: loaded (/usr/lib/systemd/system/pythondaemon.service; disabled; vendor preset: disabled)
   Active: active (running)since month 2017-09-11 00:35:12 JST; 10s ago
  Process: 4633 ExecStart=/opt/python_daemon.py (code=exited, status=0/SUCCESS)
 Main PID: 4634 (python)
   CGroup: /system.slice/pythondaemon.service
           └─4634 python /opt/python_daemon.py

It moved!

pydmon.log looks like this

$ cat pydmon.log 
Mon Sep 11 00:35:12 2017
Mon Sep 11 00:35:22 2017
Mon Sep 11 00:35:32 2017
Mon Sep 11 00:35:42 2017
Mon Sep 11 00:35:52 2017
Mon Sep 11 00:36:02 2017
Mon Sep 11 00:36:12 2017
Mon Sep 11 00:36:22 2017
Mon Sep 11 00:36:32 2017
Mon Sep 11 00:36:42 2017
Mon Sep 11 00:36:52 2017
Mon Sep 11 00:37:02 2017


It was fun and impressed because it can be managed with systemctl

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