NOP Protocol Commands
Many computer protocols, 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 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
- FTP
- SMTP
- X11
- POP3
- NNTP
- finger
- IMAP4
- BitTorrent
- Character encoding: the null control character
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 ftpd daemon of MINIX responds to NOOP with the message:
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