Trying to kill a spawned process ends ups with a defunct process

Question

Scenario: I'm developing a daemon monitoring application which starts and stops daemons on by request (TCP-IP). To achieve that, after forking, I'm calling setsid() in order to "detach" the new process from the parent (the monitoring process).

When I try to kill one of the processes the monitoring application created it ends up defuncted.

Here's my code:

int retval;
char* arg_list[] = {
  NULL      /* The argument list must end with a NULL.  */
};
retval = fork();
if (retval == 0)
{
    umask(0);
    setsid();
    execv(LBSDPATH, arg_list);
    exit(0);
}

As I understand, defunct/zombie process means that the parent haven't joined with the process yet. don't setsid() solve it ?

alk · Accepted Answer · 2013-05-28T12:37:51.683

3

The parent needs to call wait() or waitpid() to have the child process be "freed" out of the defunct/zombie state.

This could be done in a parent's thread, as well as in a parent's signal handler servering the SIGCHLD signal received upon a child's death.

Update

Refering the need to have a child reparented to init to let it live as a damon as stated in a comment by Mellowcandle:

Just fork() twice. That is: the first fork()ed process just fork()s off another one.

Let the secondly fork()ed process do the exec*(), and let the first fork()ed process end.

When then first fork()ed process ends, its child (the secondly fork()ed process and with it it successor: the exec*()'ed one) is inherited by init which then handles the SIGCHLD/the death of this child.

edited May 28 '13 at 12:37

answered May 27 '13 at 11:48

alk

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I know that, but I want the process that I spawn to work independently, like a daemon. – stdcall May 27 '13 at 11:57
1

@Mellowcandle: Then `fork()` twice. Let the secondly `fork()`ed process do the `exec*()`, and the first `fork()`ed process end. When then first `fork()`ed process dies, its children (the secondly `fork()`ed process and with it the `exec*()`'ed one) are inherited by `init` which then handles the `SIGCHLD`/the death of the child. – alk May 27 '13 at 12:02
I don't think that I explained myself right, please see my edit to the qustion. – stdcall May 27 '13 at 13:57
1

I recommend that you read http://stackoverflow.com/questions/881388 , and when you've read the whole thing, and think you understand it, read it a second time just to make sure. I'm pretty sure you'll find your answer in there. – This isn't my real name May 27 '13 at 15:52
@mellowcandle: Please see *Elchonon Edelson*'s comment above. – alk May 27 '13 at 17:12
@alk Thanks, it solved my problem, if you write this as the answer I will accept the answer ! – stdcall May 28 '13 at 12:29

Trying to kill a spawned process ends ups with a defunct process

1 Answers1