How to create virtual user in vsftpd?

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http://askubuntu.com – My company uses ubuntu server as dedicated server and already it has vsftpd installed and also has some virtual user(done by former system admin). I am new to the system and I have been asked to create a virtual user and give access to specific folder in the server. My questions : I have followed this tutorial to help myself out on this but it asked me to use db_load to convert "user file" to "database file". But this method is not being used to create db file by former sys admin. Then how to update the existing db file after adding new user. The vsftpd version is 2.2.2 and its old. but I (HowTos)