Why or how does killing the parent process clean the zombie child processes in linux?

Consider this example - #include #include #include int main() { pid_t pid = fork(); if (pid > 0) { printf("Child pid is %d\n", (int)pid); sleep(10); system("ps -ef | grep defunct | grep -v grep"); } return 0; } In this example, the child process remains a zombie until the parent process terminates. How did this zombie process get cleaned up without being reaped by any process ? $ ./a.out Child pid is 32029 32029 32028 0 05:40 pts/0 00:00:00 [a.out] $ ps -p 32029 PID TTY TIME CMD