How to detect whether system is going to standby in Linux using C

Question

I want to know how I can detect whether the system is going to a standby mode in Linux using C. I found a message called WM_POWERBROADCAST in windows for that purpose, which sends this message before going to the sleep mode.

Is there any alternatives in C, for Linux?

I heard that DBus can be used for same purpose, could somebody explain it more?

Answer 1

Finally I found a solution.

We can use the pm utility for that.

If you put any shell script in /etc/pm/sleep.d folder it will be executed automatically just before the system going to sleep and after the system is resumed.

The content will be like

#!/bin/bash
case $1 in
suspend)
    #suspending to RAM
    /home/harikrishnan/Desktop/sleepd Sleeping
    ;;
resume)
    #resume from suspend
    sleep 3
    /home/harikrishnan/Desktop/sleepd Woken
    ;;
esac

here it will execute the /home/harikrishnan/Desktop/sleepd program with the arguments

Answer 2

AFAIK there's no such signal in Linux, but you can try

a) acpid daemon hooks, if its present, acpid configs are usually in /etc/acpi
b) DBus daemon hooks, again if its presend on a system
c) reading acpid sources to see how it gets the signals
d) writing your own kernel module