Control whether users are allowed to switch to the upper directory in vsftp

The specific situations are as follows:

1. When chroot_list_enable=yes and chroot_local_user=yes, users listed in the /etc/vsftpd/chroot_list file can switch to the upper-level directory; users not listed in the file cannot switch to the upper-level directory of the site root directory.
2. When chroot_list_enable=yes and chroot_local_user=no, users listed in the /etc/vsftpd/chroot_list file cannot be switched to the parent directory of the site root directory; users not listed in the file can switch to the parent directory.
3. When chroot_list_enable=no and chroot_local_user=yes, all users cannot switch to the upper-level directory.
4. When chroot_list_enable=no, chroot_local_user=no, all users can switch to the upper directory.
5. When the user is not allowed to switch to the upper-level directory, the root directory "/" of the ftp site after logging in is the home directory of the ftp account, that is, the /var/ftp directory of the file system. 

Note: To view the effect for local users, you need to set local_root=/var/ftp first