守护进程Linux

mydaemon.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
//#include <syslog.h>
   static  FILE* fp = NULL;
#define FNAME "/tmp/out"
static void daemon_exit(int signo)
{
        fclose(fp);
        //closelog();
        exit(0);
}
static int daemonize(void)
{
    pid_t pid = fork();
    if( pid < 0)
    {
        return -1;
    }
    if(pid >0)
    {
        printf("parent exit\n");
        exit(0);
    }
    else{

        printf("this is son \n");
       int fd = open("/dev/null",O_RDWR);
        if( fd < 0)
         {
             perror("open()");
             return -1;
         }
        int ret =    dup2(fd,0);
        if( ret == -1)
        {
            perror("dup2");
         }  
         ret =    dup2(fd,1);
        if( ret == -1)
        {
            perror("dup2");
        }
       ret =    dup2(fd,2);
        if( ret == -1)
        {
            perror("dup2");
}
         if( fd > 2)
            close(fd);
    pid_t spid =     setsid();
    printf("sessionid:%d\n",spid);
        chdir("/");
     //   umask(0);
    }
    return 0;
}
int main( int argc,char** argv)
{
//      signal(SIGINT,daemon_exit)
//      signal(SIGQUIT,daemon_exit);
//      signal(SIGTERM,daemon_exit);

        struct sigaction sa;
        sa.sa_handler = daemon_exit;
        sigemptyset(&sa.sa_mask);
        sigaddset(&sa.sa_mask,SIGQUIT);
        sigaddset(&sa.sa_mask,SIGTERM);  
        sigaddset(&sa.sa_mask,SIGINT);
        sa.sa_flags = 0;
        sigaction(SIGINT,&sa,NULL); 
        sigaction(SIGQUIT,&sa,NULL);  
        sigaction(SIGTERM,&sa,NULL);  

    if(daemonize()){
       exit(1); 
    }
    fp = fopen(FNAME,"w");
    if( fp == NULL)
    {
        perror("fopen()");
        exit(0);
    }
    
    for(int i = 0 ; ;i++)
    {
        sleep(1);
        fprintf(fp,"%d\n",i);
        fflush(fp);
    }
    exit(0);
}