Sending signals to C programs

For simple and easy IPC to the C program we can use signals. https://www.man7.org/linux/man-pages/man7/signal.7.html

Only two user defined signals are available (SIGUSR1 and SIGUSR2) but you can hijack other ones even though this is really not advisable.

// signal.c
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

void handle_signal(int signal) {
    printf("Signal received: %d\n", signal);
}

int main() {
    signal(SIGUSR1, handle_signal); // is equal to 10
    signal(SIGUSR2, handle_signal); // is equal to 12

    while(1) {
        sleep(1);
    }

    return 0;
}

Compile with gcc -o signal signal.c and run the program with ./signal and then from another terminal send the signal to the program with kill -10 $(pidof signal) which should print out Signal received: 10.