Good morning folks, I discovered "common/application_instance.py" and the class in it. I was wondering what it does. In my current state of investigation I would describe it as a "PID file and flock manager". I've never used PID files or flock in my own projects but I do understand the basics. I also found a good explanation [1] why PID and flock is used in combination. My problem is to understand that technology in the context of Back In Time. In which situation does Back In Time need it. Maybe someone else understand that better? Maybe I will dive deeper into the code and document my findings in the modules docstring. I want to understand in which situations PID and flock is used by BIT and why. Kind Christian [1] -- <https://unix.stackexchange.com/a/12816/136851>