1. Edit /etc/vsftpd.conf as follow.
chroot_local_user=NO chroot_list_enable=YES chroot_list_file=/etc/vsftpd.chroot_list
2. Create the /etc/vsftpd.chroot_list and enter the usernames which you want to jail.
userA userB userC ...
3. By default, the chroot folder has to be non-writable. The simplest way is to change the user home folder permission but this is not a perfect solution. If you are looking for a better solution. please refer to this.
chmod a-w /home/<username>
4. Restart the vsftpd.
5. Connect to the server using any FTP client, the jailed FTP account should work.