vsftpd is an FTP server for unix-like systems that is specially built to be efficient and very secure (very secure FTP daemon).
A "daemon" is a program that runs in the background without a graphical interface. In Windows parlance, this would be considered a "service". In the context of FTP and other related Internet technologies, a FTP daemon would be the program "service" that runs in the background (for which the term "server" can refer to the machine that runs such network-facing services or the services themselves).
Secure Shell Protocol
vsftpd, which stands for "Very Secure FTP Daemon"[1], is an FTP server for Unix-like systems, including Linux. It is licensed under the GNU General Public License. It supports IPv6 and SSL.vsftpd supports explicit (since 2.0.0) and implicit (since 2.1.0) FTPS.
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A Secure FTP (File Transfer Protocol) is useful for transferring files from one location to another. i.e. from one server to another. Transferring is secure because the file is encrypted.
Secure file transfering through the Internet.
Ftp is NOT a secure protocol. All usernames and passwords exchanged in setting up an FTP connection are sent in cleartext, data exchanged over and FTP connection is not encryption and the connection is subject to hijacking. A SFTP protocol however, is secure, thus your information is far safer.
Https is a more secure. Http is not necessarily secure at all. FTP is used to connect to a file server while HTTP connects to a web server.
scp is secure copy ftp is file transfer protocol. FTP is a file transfer protocol as send the file inside the network
Usually, if you change the port in a server's configuration file, you will have to stop and restart its daemon or service for the changes to take effect. Changing the FTP port would not stop access, butyou would probably have to specify the port manually on any FTP client.
If you are uploading your files to a remotely-hosted web site, then FTP (or, rather, secure FTP) is a good way of uploading to publish files to maintain your website.