You need to run it without using sudo. Try adding this run_as_launching_user=YES to your config file and then run ./vsftpd …
There are multiple ways to solve the issue, one of them being setting up the correct ownership for the concerned files. You can read about Ownership and Permissions in Linux here.
Now my QBox server is running from root but still I am getting
ftp 0.0.0.0 8081 Connected to 0.0.0.0. 220 (vsFTPd 3.0.3) Name (0.0.0.0:crio-user): root 331 Please specify the password. Password: 421 Service not available, remote server has closed connection Login failed. No control connection for command: Success
Are you entering the correct credentials for the user? The user name should be crio-user and the password will be your workspace password. Make sure you have set up the config file correctly.