After transferring the files between ftp_client and ftp_server, the vsftpd.log file is still empty
check the ownership of the file. If it is root, change it to the user. Try opening it again in editor, it will display its contents.
Already this has been answered, there is some mistake in the config file which is being neglected.
may be you haven’t set the log file directory in config file
set the path for storing the log file data to your directory log file
Now I can see the content of the log file