daemonize is complicated ...

import sys
import os
import time

# 1. first fork
if os.fork() > 0:
    print("Kill the parent")
    sys.exit(0)

# 2. new session
print("setsid")
os.setsid()

# 3. second fork
if os.fork() > 0:
    print("Kill the parent")
    sys.exit(0)

# 4. umask
print("umask 0")
os.umask(0)


print(f"Hello from child: {os.getpid()}")

# 5. change working directory
print("chdir /")
os.chdir("/")

print("GAG the child process!!!")

# 6. flush stdin/stdout/stderr
sys.stdin.flush()
sys.stdout.flush()
sys.stderr.flush()

# 7. copy filedescriptor of dev_null to sys.stdin
#    dev_null is closed, but 0 stays open and points to os.devnull
with open(os.devnull, "rb", 0) as dev_null:
    os.dup2(dev_null.fileno(), sys.stdin.fileno())


with open(os.devnull, "ab", 0) as dev_null:
    os.dup2(dev_null.fileno(), sys.stdout.fileno())
    os.dup2(dev_null.fileno(), sys.stderr.fileno())


time.sleep(20)