daemon进程

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>

#define ERROR(flag)                 if(flag)                        {                                    printf("%d: ",__LINE__);        fflush(stdout);                    perror("error");                exit(errno);                }

int init_daemon()
{
    pid_t pid = fork();
    ERROR(pid == -1);
    if(pid > 0)
        exit(0);
    printf("pid = %d\n",getpid());
//--------------------------------------------------------
    int ret = setsid();
    ERROR(ret == -1);

//下面的创建新进程后,父退子留是system V的建议, 以保证不是会话的首进程, 防止取得控制终端
    pid = fork();
    ERROR(pid == -1);
    if(pid > 0)
        exit(0);
//--------------------------------------------------------
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
//--------------------------------------------------------
    chdir("/");
//--------------------------------------------------------
    umask(0);
//--------------------------------------------------------
    signal(SIGCHLD,SIG_IGN);
}

int main(int argc, char *argv[])
{
    time_t now;
    
    init_daemon();

    while(1)
    {
        int fd = open("daemon.log",O_WRONLY | O_CREAT | O_APPEND, 0600);
        time(&now);
        char *s = ctime(&now);
        write(fd,s,strlen(s));
        sleep(2);
        close(fd);
    }

#if 0
    syslog(LOG_USER | LOG_INFO,"test daemon, pid = %d\n",getpid());
    while(1)
    {
        sleep(3);
        time(&now);
        syslog(LOG_USER | LOG_INFO,"hello now is: %s\n",ctime(&now));
    }
#endif
    return 0;
}