Trap signal - helpful to debug

trap_signal.c

/*
  gcc trap_signal.c -o trap_signal
  start:
 ./trap_signal $(pidof trap_signal)
 tail -f /tmp/log.txt
*/
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <stdbool.h>

bool terminate = false;
int trap_signal = 0;

void sig_handler(int sig)
{
    trap_signal = sig;
    terminate = true;
}

int main(int argc, char *argv[])
{   

    if (signal(SIGUSR1, sig_handler) == SIG_ERR) printf("\ncan't catch SIGUSR1\n");
    if (signal(SIGTERM, sig_handler) == SIG_ERR) printf("\ncan't catch SIGTERM\n");
    if (signal(SIGHUP, sig_handler)  == SIG_ERR) printf("\ncan't catch SIGHUP\n");
    if (signal(SIGINT, sig_handler)  == SIG_ERR) printf("\ncan't catch SIGINT\n");

    int count;
    if (argc > 1)
    { 
      for (count = 1; count < argc; count++)
        { 
          printf("pid = %i\n", atoi(argv[count]) );
          kill( atoi(argv[count]),SIGTERM);
        }
    }

    pid_t process_id = 0;
    pid_t sid = 0;
    process_id = fork();
    if (process_id < 0) {
        printf("fork failed!\n");
        exit(1);
    }
    if (process_id > 0) {
        printf("process_id of child process %d \n", process_id);
        exit(0);
    }
    umask(0);
    sid = setsid();
    if (sid < 0) {
        exit(1);
    }
    chdir("/tmp");
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);

    while (!terminate) {
        sleep(1);
    }

    FILE *fp = NULL;
    fp = fopen("log.txt", "a");
    fprintf(fp, "received %i terminated...exiting\n", trap_signal);
    fflush(fp);
    fclose(fp);
    return (0);
}