In my Ubuntu application, I wanted to perform certain finalization for my application before the system is being shutdown. For that, I need to identify the shutdown event in my application.

From what I have read online, there are mainly two major solutions, that are being suggested.

using the 'PrepareForShutdown' dbus signal.
trapping the SIGTERM signal that is send to the running applications prior to shutdown.
However, I have tried both the ways and they don't seem to work for me. The handler that I m registering for 'PrepareForShutdown' never gets invoked.

For method 2, I have observed that my application does not receive SIGTERM signal, instead it receives some other signal a moment before being terminated using SIGKILL.

Can someone help me out, what should I be using to identify the shutdown correctly? I do not intend to read it from certain OS files, please provide an event based solution.

You can hook into systemd shutdown sequence: https://www.freedesktop.org/software...st/bootup.html (at the end).

My application can be launched in multiple ways, and the above suggested way will be effective only If my application is launched as systemd service. I need a more generic solution to this.

exactly what do you want? Either you can catch the signal (like sigterm), or hook the shutdown sequence (and send a signal to your app). But sigkill cannot be catched at all, there is no way to do that.
The normal shutdown process allows the processes to exit, probably your app cannot manage it very well. What*kind of process is it? (shell, python, java?). How was it started at all?

Incorrect, service can be used only for stopping or it could be a unit started before=shutdown.service