Editing NOP (code) (section)

== NOP protocol commands ==
Many [[protocol (computing)|computer protocol]]s, such as [[telnet]], include a NOP command that a client can issue to request a response from the server without requesting any other actions. Such a command can be used to [[Keepalive|ensure the connection is still alive]] or that the server is responsive. A NOOP command is part of the following protocols (''this is a partial list''):
* [[telnet]]
* [[File Transfer Protocol|FTP]]
* [[Simple Mail Transfer Protocol|SMTP]]
* [[X Window core protocol|X11]]
* [[Post Office Protocol|POP3]]
* [[Network News Transfer Protocol|NNTP]]
* [[Finger protocol|finger]]
* [[Internet Message Access Protocol|IMAP4]]
* [[BitTorrent (protocol)|BitTorrent]]

Note that unlike the other protocols listed, the IMAP4 NOOP command has a specific purpose—it allows the server to send any pending notifications to the client.

While most [[telnet]] or [[FTP]] servers respond to a NOOP command with "OK" or "+OK", some programmers have added quirky responses to the client. For example, the <code>ftpd</code> daemon of [[MINIX]] responds to NOOP with the message:<ref name="minix_ftpd">{{cite web|url=http://www.cise.ufl.edu/~cop4600/cgi-bin/lxr/http/source.cgi/commands/ftpd/ftpd.c#L139|title=ftpd.c|access-date=2016-06-19}}</ref>
 [[List of FTP server return codes|200]] NOOP to you too!