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signal_pro won't fire if you kill the parent, and when you kill the child posix_getpid will return the PID of the current process (which is the parent).
What do you think it should do?

Oh, wait, I misread that.

> kill parent id,not output
> kill child id,is output:parent id
I think you have that backwards. Are you sure you were killing the right processes?

Here's a test script I just wrote: https://pastebin.com/vwGiFYGT
It all seems to be working correctly for me.

pcntl_fork() && exit;


$parent = posix_getpid();

if ($child = pcntl_fork()) {
	echo "parent: parent is " . posix_getpid() . "\n";
	echo "parent: child is {$child}\n";
	echo "parent running\n";
} else {
	echo "child running\n";
	sleep(1000);
	//child processes not register signal
	exit;//child processes stop here
}

//only parent run this code...

pcntl_signal(SIGTERM, function() use ($child) {
	echo $child ? "parent sigterm\n" : "child sigterm\n";
});

declare(ticks = 1){
	while (true){
		//on term kill parent processes ,no response
		//but i kill child processes,parent processes receive a term signal,why?
		$pid=pcntl_wait($status);
		if($pid==-1)break;
	}
}
// [root@rabbitmq-node02 gs]# php -v
// PHP 7.1.3 (cli) (built: Mar 21 2017 10:38:32) ( NTS )
// Copyright (c) 1997-2017 The PHP Group
// Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies
// with Zend OPcache v7.1.3, Copyright (c) 1999-2017, by Zend Technologies
// [root@rabbitmq-node02 gs]# php tt.php
// parent: parent is 77506
// parent: child is 77507
// parent running
// child running
// [root@rabbitmq-node02 gs]# kill 77506 // kill parent processes,No output
// [root@rabbitmq-node02 gs]# kill 77507 //kill child  processes,parent processes receive a term signal,why,child not register signal function
// [root@rabbitmq-node02 gs]# parent sigterm

PHP CODE:
<?php
pcntl_fork() && exit;


$parent = posix_getpid();

if ($child = pcntl_fork()) {
	echo "parent: parent is " . posix_getpid() . "\n";
	echo "parent: child is {$child}\n";
	echo "parent running\n";
} else {
	echo "child running\n";
	sleep(1000);
	//child processes not register signal
	exit;//child processes stop here
}

//only parent run this code...

pcntl_signal(SIGTERM, function() use ($child) {
	echo $child ? "parent sigterm\n" : "child sigterm\n";
});

declare(ticks = 1){
	while (true){
		//on term kill parent processes ,no response
		//but i kill child processes,parent processes receive a term signal,why?
		$pid=pcntl_wait($status);
		if($pid==-1)break;
	}
}
?>
// test history...
// [root@rabbitmq-node02 gs]# php -v
// PHP 7.1.3 (cli) (built: Mar 21 2017 10:38:32) ( NTS )
// Copyright (c) 1997-2017 The PHP Group
// Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies
// with Zend OPcache v7.1.3, Copyright (c) 1999-2017, by Zend Technologies
// [root@rabbitmq-node02 gs]# php tt.php
// parent: parent is 77506
// parent: child is 77507
// parent running
// child running
// [root@rabbitmq-node02 gs]# kill 77506 // kill parent processes,No output
// [root@rabbitmq-node02 gs]# kill 77507 //kill child  processes,parent processes receive a term signal,why,child not register signal function
// [root@rabbitmq-node02 gs]# parent sigterm

You're misunderstanding what is happening. Change the child's sleep to 10 seconds, run, kill the parent, and DON'T kill the child. Just wait.

Why the child process exit before parent process on receiving the signal?

i try c code,is normal:
```c

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
void signal_test(int signal_num){
    printf("%d",getpid());
   fflush(stdout);
}

int main(){
    if(!fork()){
                sleep(100);
                return EXIT_SUCCESS;
    }

        signal(SIGTERM,signal_test);

        int t,c;
        while(1){
                c=wait(t);
                if(c==-1)break;
        }
    return EXIT_SUCCESS;
}

```
on term:
[root@rabbitmq-node02 gs]# gcc t.c -o t
[root@rabbitmq-node02 gs]# ./t &
[1] 77776
[root@rabbitmq-node02 gs]# kill 77776  //kill parent processes is output..
77776[root@rabbitmq-node02 gs]#

//why php is child all exit,The signal function begins to execute

i try c code,is work:
```c

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
void signal_test(int signal_num){
    printf("%d",getpid());
   fflush(stdout);
}

int main(){
    if(!fork()){//child 
                sleep(100);
                return EXIT_SUCCESS;
    }
//on parent process register signal function
        signal(SIGTERM,signal_test);

        int t,c;
        while(1){
                c=wait(t);
                if(c==-1)break;
        }
    return EXIT_SUCCESS;
}

```
on term:
[root@rabbitmq-node02 gs]# gcc t.c -o t
[root@rabbitmq-node02 gs]# ./t &
[1] 77776
[root@rabbitmq-node02 gs]# kill 77776  //kill parent processes is output..
77776[root@rabbitmq-node02 gs]#

//why php is child all exit,The signal function begins to execute

may be not a bug...