How to safely exit my program before KEY_POWER shutdown?

[njsss]

The gpio-shutdown overlay shuts down the system, but how can I monitor this KEY_POWER event and safely shuts down my own program (save import files) before the system shutdown?

[thagrol]

Given that AIUI all the overlay does is send a KEY_POWER event you'd do it the same way you'd trap a clean shutdown by any other means: trap a few signals and act on them.

The exact way you do that depends on which language your programme is written in.

[njsss]

Given that AIUI all the overlay does is send a KEY_POWER event you'd do it the same way you'd trap a clean shutdown by any other means: trap a few signals and act on them.

The exact way you do that depends on which language your programme is written in.

Does it mean I won't be able to act upon the KEY_POWER event? If so can I register a system event and act on it, so I don't have to constantly monitor the gpio pin. I use c++ but has limited knowledge about Linux.

[thagrol]

Given that AIUI all the overlay does is send a KEY_POWER event you'd do it the same way you'd trap a clean shutdown by any other means: trap a few signals and act on them.

The exact way you do that depends on which language your programme is written in.

Does it mean I won't be able to act upon the KEY_POWER event? If so can I register a system event and act on it, so I don't have to constantly monitor the gpio pin. I use c++ but has limited knowledge about Linux.

Can't help you with C++, I don't know it. My understanding is that when the switch is pressed the kernel sees a KEY_POWER event which triggers the normal shutdown process. You shouldn't need to monitor the gpio yourself, just have your programme trap and respond to a SIGTERM (I think it's SIGTERM, google will probably know).

[DougieLawson]

Normal shutdown sends SIGTERM to every process. If the process doesn't end normally then 90s later it sends SIGKILL.

You can trap SIGTERM with a C++ signal handler. You can't trap SIGKILL.

https://www.tutorialspoint.com/cplusplu ... ndling.htm gives you an example of trapping signals.

[ghans]

You need to write a signal handler for your program. SIGTERM is the one you should take care of first.

ghans

[njsss]

I tried to implement a simple test in both c++ and python, but couldn't trap SIGTERM. Shutdown happens immediately either by pull the shutdown-pin down or just type "sudo shutdown now".