• echo

...> echo [accept|refuse]

Display or set the flag controlling the Telnet's client response to a remote WILL ECHO offer from the server during initialization. Sessions already established are unaffected. The Telnet presentation protocol specifies that in the absence of a negotiated agreement to the contrary, neither end echoes data received from the other. Default is "accept". When communicating from keyboard to keyboard the standard local echo mode is used, so the setting of this parameter has no effect.

• NOTE: This command is not intended to "echo text to the console" -- See the remark command. If this command is used in place of the remark command, the command output will appear on the "error" device.

If 'accept' mode is in effect, an incoming WILL ECHO offer is answered with a DO ECHO response. In this mode:

• local echoing and editing is turned off
• each key stroke is sent immediately (subject to the Nagle tinygram algorithm in TCP).

If 'refuse' mode is in effect, an incoming WILL ECHO offer is answered with a DONT ECHO response. In this mode:

• a Telnet client session echoes keyboard input locally and nothing is actually sent until a CR is typed.
• Local line editing is also performed:
  • backspace deletes the last character typed
  • control-U deletes the entire line.

Many multi-user and timesharing systems (e.g. UNIX & Linux) prefer to do their own echoing of typed input (This makes screen editors work right, among other things). Such systems send a Telnet WILL ECHO offer immediately upon receiving an incoming Telnet connection request.

While accept mode is just fine across an Ethernet, it is clearly inefficient and painful across slow paths like packet radio channels.

• (NOTE: Berkeley Unix has a bug in that it will still echo input even after the client has refused the WILL ECHO offer. To get around this problem, enter the 'stty - echo' command to the shell once you have logged in).