linux deamon

http://blog.csdn.net/u013485792/article/details/51507685

http://blog.csdn.net/hepeng597/article/details/9816751

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

void init_daemon(void)
{
    int pid1, pid2;
    int i;
    pid1 = fork();
    if( pid1 < 0 ){
        fprintf( stderr, "fork failed, process exit
" );
        exit(1);//fork失败，退出
    }else if(pid1){
        fprintf( stderr, "Child process created, pid = %d
", pid1 );
        fprintf( stderr, "parent process exit
" );
        exit(0);//是父进程，结束父进程
    }

    //是第一子进程，后台继续执行
    if(setsid() == -1){//第一子进程成为新的会话组长和进程组长
        printf("setsid failed
");
        exit(-1);
    }

    //并与控制终端分离
    pid2 = fork();
    if( pid2 < 0 ){
        fprintf( stderr, "fork failed, process exit
" );
        exit(1);//fork失败，退出
    }else if(pid2){
        fprintf( stderr, "Child process created, pid = %d, " 
            "create in %d
", pid2, pid1 );
        fprintf( stderr, "process %d exit.
", pid1 );
        exit(0);//是第一子进程，结束第一子进程
    }

    //是第二子进程，继续
    //第二子进程不再是会话组长
    for(i=0;i< NOFILE;++i)//关闭打开的文件描述符
        close(i);

    chdir("/tmp");//改变工作目录到/tmp
    umask(0);
    //umask(S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);//重设文件创建掩码 mask = arg & 0777

    return;
}


int main()
{
    FILE *fp;
    time_t t;
    init_daemon();//初始化为Daemon

    while(1){//每隔一分钟向test.log报告运行状态        
        fp = fopen("test.log", "a");
        if( fp >= 0 ){
            t = time(NULL);
            fprintf( fp, "I'm here at %s
", asctime(localtime(&t)) );
            fclose(fp);
        }

        sleep(60);//睡眠一分钟
    }

    return 0;
}