To only allow specified users using FTP

Edit /etc/vsftpd/vsftpd.conf. Add towards the bottom of the file:

userlist_deny=NO
userlist_enable=YES
userlist_file=/etc/vsftpd/vsftpd.allowed_users

Create vsftpd.allowed_users

#To allow just some users to login:
#Code:
#userlist_deny=NO
#userlist_enable=YES
#userlist_file=/etc/vsftpd.allowed_users
#
#In the file /etc/vsftpd.allowed_users add the username of the users that can login.
#The not allowed users will get an error that they can't login before they type their password.
jforces

Restart VSFTPD

$ service vsftpd restart