[daemon函数] #gcc #daemon

daemon.c

// vim: syntax=c
int daemon( int nochdir,  int noclose )
{
   pid_t pid;
   if ( !nochdir && chdir("/") != 0 ) //if nochdir=0,change dir to "/"
       return -1;
   if ( !noclose ) //if noclose is 0
   {
        int fd = open("/dev/null", O_RDWR); 
        if ( fd  <  0 )
            return -1;
	/* Redirect standard input,output,error to /dev/null. */
		dup(fd, 0);
		dup(fd, 1);
		dup(fd, 2);     
		close(fd);
	}
  
   pid = fork();  //Create child process.
   if (pid  <  0)  //fail
      return -1;
   if (pid > 0)
       _exit(0); //Return to the parent process, then the parent process exits, and the child process becomes a real orphan process.

   if ( setsid()  < 0 )   //Create a new session and make the subprocess the root process of the new session
      return -1;
   return 0;
}