Usually, I mount some directories to chroot environtment like this:

```
mount -t proc /proc /mnt/chroot/proc
mount --rbind /dev /mnt/chroot/dev
mount --rbind /sys /mnt/chroot/sys
mount --rbind /run /mnt/chroot/run

```

But, after finished, I can't umount those mounted directories and there's a message to get a list of running process that use the dirs which give me a bunch lines of processes list. So, how to properly unmount those directories?