How to pause until signal and not have C print?

Question

I'm guessing I need to call some function in my signal handler and I have no idea what it is

My program wants to sleep until it receives some kind of signal. So naturally I used pause(). Now it ran just fine when I sent my app SIGUSR1 however I get a print out of User defined signal 1 which is not what I want because I plan to send many signals and it will make the console unreadable. I tried handling the signal by writing signal(SIGUSR1, mySignalHandler); but now pause() no longer resumes after I receive the signal. Is there some kind of function I need to call from mySignalHandler?

Answer 1

The default behavior when a program receive a USR1 signal is to terminate (see https://www.man7.org/linux/man-pages/man7/signal.7.html, standard signal).

An empty signal handle will just do what you want: no message will be displayed.

#include <unistd.h>
#include <stdio.h>
#include <signal.h>

static int s_got = 0;

void handler(int s) 
{
    ++s_got;
}

int main(void)
{
    signal(SIGUSR1, handler);
    while(1) {
        pause();
        printf("resumed %d\n", s_got);
    }
    return 0;
}

:~/so/pause$ gcc -Wall main.c
:~/so/pause$ ./a.out &
[1] 2286
:~/so/pause$ pkill -USR1 a.out
resumed 1
:~/so/pause$ pkill -USR1 a.out
resumed 2
:~/so/pause$ pkill -USR1 a.out
resumed 3
:~/so/pause$ pkill -USR1 a.out
resumed 4
:~/so/pause$ pkill -USR1 a.out
resumed 5
:~/so/pause$