kfiresmith/demonstrate-pidfile-management.sh

#!/usr/bin/env python3

import os
import sys
import atexit

# Obtain the name of the script dynamically so that we can re-use this code block on any script
script_fullname = os.path.basename(__file__)
# Trim off the file extension if one is present
script_trimmedname = os.path.splitext(script_fullname)[0]

# /run is superior to /tmp, but we can't write a lock file there if we aren't root.
# We want to maintain the option of using this code block in scripts not run by root,
# so we fall back to using good old /tmp
lock_dir = "/run" if os.access("/run", os.W_OK) else "/tmp"
lock_file = os.path.join(lock_dir, f"{script_trimmedname}.lock")

def cleanup():
    """Remove the lock file on exit."""
    if os.path.exists(lock_file):
        os.remove(lock_file)

# Register the cleanup function to run on script exit
atexit.register(cleanup)

# Check if the lock file exists. If it already exists, we just exit to prevent
# creating a cron pileup by re-running the running script over itself.
if os.path.exists(lock_file):
    print("Script is already running. Exiting.")
    sys.exit(1)

# If we've made it this far, write the current PID to the lock file.
with open(lock_file, 'w') as f:
    f.write(str(os.getpid()))

# Do stuff below

# Exit (cleanup will be handled by atexit)
sys.exit(0)