Ask a question about daemon

[leetow2003]

Look:

Code: Select all

int main()
{
if(fork())
   exit(0);
  setsid();
  //the second fork
  if(fork())
   exit(0);
  //=========
  int fd=open("/dev/tty",O_RDWR);
  ioctl(fd, TIOCSCTTY, 1);
  while(1)
  {
    sleep(20);
    write(fd,"hello",10);
  }
  //daemon code
}

I am heard if I don't write the second fork,the process can connect
a control terminal,but I find I write the second fork or don't write
the codes,the screen couldn't display the string "hello",Why?
How to correct my codes?

[bluemoon]

put a line feed on the string or flush the output.

[leetow2003]

put a line feed on the string or flush the output.

Could you tell me in detail?Or could you write codes?
Thank you very much.

[bluemoon]

The problem may be caused by the output being buffered.
You may need to open the file with O_SYNC, or flush it with sync().
btw, for text output it's more convenient to use fopen() which come with fflush(fp), while sync() flush all IOs.

could you write codes?

No, sorry.