killing parent process doesn't kill child

I have a question. Studying processes management I observed a strange behavior, on a CentOS 7. I know that killing a parent process, the child processes are killed also. But not in the following case. I ran the command dd, just for example: [root@server2 ~]# dd if=/dev/zero of=/dev/null & 1756 [root@server2 ~]# ps fax | grep -B2 dd 1737 pts/2 S 0:00 \_ su - 1741 pts/2 S 0:00 \_ -bash 1756 pts/2 R 1:18 \_ dd if=/dev/zero of=/dev/null After that I tried to kill (with SIGKILL signal) the parent process, that is the bash, but this action doesn't kill the dd process: [root@server2 ~]# kill -9 1741 Killed [user@server2 ~]# The shell terminates but as you can see in the top command output, the dd process is still working: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1756 root 20 0 107948 612 512 R 99.9 0.1 10:06.98 dd Do you have any idea about it please?