Python Daemon Process Creation Challenge

This challenge requires you to implement a Python script that can run as a daemon process. Daemon processes are background services that run continuously without direct user interaction, making them essential for tasks like monitoring, logging, and scheduled operations. You'll learn to detach a process from the controlling terminal and ensure it runs independently.

Problem Description

Your task is to create a Python script that, when executed, forks itself into a background daemon process. This daemon should continuously write its process ID (PID) to a specified log file at regular intervals. The daemon should also handle potential issues like ensuring it doesn't have a controlling terminal and running in the background.

Key Requirements:

1. Daemonization: The script must successfully fork itself, becoming a daemon process. This involves:
   • Forking the parent process.
   • The parent process should exit immediately.
   • The child process should become a session leader (setsid()).
   • Redirecting standard input, output, and error streams to /dev/null or a log file.
   • Changing the working directory to a safe location (e.g., '/').
   • Ensuring the daemon doesn't acquire a controlling terminal.
2. Logging: The daemon must log its PID to a specified file (e.g., daemon.log) every 5 seconds.
3. Graceful Termination: While not strictly required for this initial implementation, consider how a daemon might be terminated (e.g., via signals). For this challenge, the daemon can run indefinitely until manually stopped.

Expected Behavior:

When the script is run, it should:

• Immediately return control to the terminal.
• Create a daemon.log file (if it doesn't exist).
• Periodically append its PID to daemon.log.

Edge Cases:

• Permissions: Ensure the script has permissions to create and write to the log file.
• Existing Log File: The script should handle the case where daemon.log already exists.

Examples

Example 1: Running the script:

python your_daemon_script.py

After running for 15 seconds, the content of daemon.log would look like:

12345
12345
12345

(Where 12345 is the PID of the daemon process)

Explanation: The script successfully daemonized. The parent process exited, and the child process became a daemon. It then started writing its PID to daemon.log every 5 seconds.

Example 2: If the log file already exists:

touch daemon.log
python your_daemon_script.py

After running for 10 seconds, the content of daemon.log would look like:

<previous content if any>
67890
67890

(Where 67890 is the new PID of the daemon process)

Explanation: The script correctly appends to an existing log file.

Constraints

• The script must be written in Python 3.
• You may use standard Python libraries (e.g., os, sys, time).
• The log file will be named daemon.log and located in the same directory as the script, or a specified path.
• The logging interval is precisely 5 seconds.
• The daemon should run indefinitely until manually terminated.

Notes

• Consider using os.fork() for the initial fork.
• The os.setsid() function is crucial for creating a new session.
• Redirecting standard file descriptors (0, 1, 2) is a key part of daemonization.
• You might want to use try...finally blocks to ensure resources are cleaned up, though for this challenge, indefinite running is acceptable.
• Remember that after os.fork(), both parent and child processes continue execution. You need to ensure the parent exits and the child continues daemonizing.