Killing forked child kills parent?

Question

I am into this weird behaviour where I have my main program and a forked child. They are piped like this(the numbers are file descriptors):

 ___parent___
|            |                     ____child_____
| 0 stdin    |                    |              |
| 1 pipe1[1]----------.           |  1 stdout    |
| 2 pipe2[1]----------.\          |  2 stderr    |
|____________|         \`----------> 3 pipe1[0]  | 
                        `----------> 5 pipe2[0]  |
                                  |______________|

So parent gets input from stdin but redirects stdout and stderr to two pipes. The child has closed its stdin and uses the read ends of the pipes instead.

Then I have a function to just kill the child:

void killChild(){
  printf("Killing %d\n", (int)childID);
  fflush(stdout);
  kill(childID, SIGKILL);
  waitpid(childID, NULL, 0);   // getting rid of the zombie
}

The child gets succesfully killed but the problem is that the parent itself gets killed as well. I checked the PID of the child and it's correct.

So why does the parent die?

Does the parent attempt to write to stdout or stderr after killing the child? If so, it dies because of the SIGPIPE. Are you changing handling of SIGCHLD? — William Pursell

rob mayoff rob mayoff · Accepted Answer · 2011-11-22T13:32:25

Any attempt by the parent to write to its fd 1 or fd 2 after the child exits will result in the kernel sending SIGPIPE to the parent. The default behavior for SIGPIPE is process termination. That's probably what's happening.

Killing forked child kills parent?

2 Answers