532 lines
13 KiB
Groff
532 lines
13 KiB
Groff
.\" Copyright (c) 1983, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)telnetd.8 8.4 (Berkeley) 6/1/94
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.\"
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.Dd June 1, 1994
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.Dt TELNETD 8
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.Os BSD 4.2
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.Sh NAME
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.Nm telnetd
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.Nd DARPA
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.Tn TELNET
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protocol server
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.Sh SYNOPSIS
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.Nm telnetd
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.Op Fl BUhkln
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.Op Fl D Ar debugmode
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.Op Fl S Ar tos
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.Op Fl X Ar authtype
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.Op Fl a Ar authmode
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.Op Fl r Ns Ar lowpty-highpty
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.Op Fl u Ar len
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.Op Fl debug
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.Op Fl L Ar /bin/login
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.Op Ar port
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.Sh DESCRIPTION
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The
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.Nm telnetd
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command is a server which supports the
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.Tn DARPA
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standard
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.Tn TELNET
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virtual terminal protocol.
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.Nm Telnetd
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is normally invoked by the internet server (see
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.Xr inetd 8 )
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for requests to connect to the
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.Tn TELNET
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port as indicated by the
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.Pa /etc/services
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file (see
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.Xr services 5 ) .
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The
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.Fl debug
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option may be used to start up
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.Nm telnetd
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manually, instead of through
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.Xr inetd 8 .
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If started up this way,
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.Ar port
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may be specified to run
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.Nm telnetd
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on an alternate
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.Tn TCP
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port number.
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.Pp
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The
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.Nm telnetd
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command accepts the following options:
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.Bl -tag -width "-a authmode"
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.It Fl a Ar authmode
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This option may be used for specifying what mode should
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be used for authentication.
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Note that this option is only useful if
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.Nm telnetd
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has been compiled with support for the
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.Dv AUTHENTICATION
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option.
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There are several valid values for
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.Ar authmode :
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.Bl -tag -width debug
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.It debug
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Turns on authentication debugging code.
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.It user
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Only allow connections when the remote user
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can provide valid authentication information
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to identify the remote user,
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and is allowed access to the specified account
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without providing a password.
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.It valid
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Only allow connections when the remote user
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can provide valid authentication information
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to identify the remote user.
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The
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.Xr login 1
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command will provide any additional user verification
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needed if the remote user is not allowed automatic
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access to the specified account.
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.It other
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Only allow connections that supply some authentication information.
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This option is currently not supported
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by any of the existing authentication mechanisms,
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and is thus the same as specifying
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.Fl a
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.Cm valid .
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.It otp
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Only allow authenticated connections (as with
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.Fl a
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.Cm user )
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and also logins with one-time passwords (OTPs). This option will call
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login with an option so that only OTPs are accepted. The user can of
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course still type secret information at the prompt.
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.It none
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This is the default state.
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Authentication information is not required.
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If no or insufficient authentication information
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is provided, then the
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.Xr login 1
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program will provide the necessary user
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verification.
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.It off
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This disables the authentication code.
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All user verification will happen through the
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.Xr login 1
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program.
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.El
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.It Fl B
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Ignored.
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.It Fl D Ar debugmode
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This option may be used for debugging purposes.
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This allows
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.Nm telnetd
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to print out debugging information
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to the connection, allowing the user to see what
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.Nm telnetd
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is doing.
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There are several possible values for
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.Ar debugmode :
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.Bl -tag -width exercise
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.It Cm options
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Prints information about the negotiation of
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.Tn TELNET
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options.
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.It Cm report
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Prints the
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.Cm options
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information, plus some additional information
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about what processing is going on.
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.It Cm netdata
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Displays the data stream received by
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.Nm telnetd .
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.It Cm ptydata
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Displays data written to the pty.
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.It Cm exercise
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Has not been implemented yet.
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.El
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.It Fl h
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Disables the printing of host-specific information before
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login has been completed.
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.It Fl k
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.It Fl l
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Ignored.
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.It Fl n
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Disable
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.Dv TCP
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keep-alives. Normally
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.Nm telnetd
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enables the
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.Tn TCP
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keep-alive mechanism to probe connections that
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have been idle for some period of time to determine
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if the client is still there, so that idle connections
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from machines that have crashed or can no longer
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be reached may be cleaned up.
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.It Fl r Ar lowpty-highpty
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This option is only enabled when
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.Nm telnetd
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is compiled for
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.Dv UNICOS .
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It specifies an inclusive range of pseudo-terminal devices to
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use. If the system has sysconf variable
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.Dv _SC_CRAY_NPTY
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configured, the default pty search range is 0 to
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.Dv _SC_CRAY_NPTY ;
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otherwise, the default range is 0 to 128. Either
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.Ar lowpty
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or
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.Ar highpty
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may be omitted to allow changing
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either end of the search range. If
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.Ar lowpty
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is omitted, the - character is still required so that
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.Nm telnetd
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can differentiate
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.Ar highpty
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from
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.Ar lowpty .
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.It Fl S Ar tos
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.It Fl u Ar len
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This option is used to specify the size of the field
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in the
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.Dv utmp
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structure that holds the remote host name.
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If the resolved host name is longer than
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.Ar len ,
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the dotted decimal value will be used instead.
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This allows hosts with very long host names that
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overflow this field to still be uniquely identified.
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Specifying
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.Fl u0
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indicates that only dotted decimal addresses
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should be put into the
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.Pa utmp
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file.
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.ne 1i
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.It Fl U
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This option causes
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.Nm telnetd
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to refuse connections from addresses that
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cannot be mapped back into a symbolic name
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via the
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.Xr gethostbyaddr 3
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routine.
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.It Fl X Ar authtype
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This option is only valid if
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.Nm telnetd
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has been built with support for the authentication option.
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It disables the use of
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.Ar authtype
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authentication, and
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can be used to temporarily disable
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a specific authentication type without having to recompile
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.Nm telnetd .
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.It Fl L pathname
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Specify pathname to an alternative login program.
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.El
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.Pp
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.Nm Telnetd
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operates by allocating a pseudo-terminal device (see
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.Xr pty 4 )
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for a client, then creating a login process which has
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the slave side of the pseudo-terminal as
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.Dv stdin ,
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.Dv stdout
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and
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.Dv stderr .
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.Nm Telnetd
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manipulates the master side of the pseudo-terminal,
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implementing the
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.Tn TELNET
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protocol and passing characters
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between the remote client and the login process.
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.Pp
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When a
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.Tn TELNET
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session is started up,
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.Nm telnetd
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sends
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.Tn TELNET
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options to the client side indicating
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a willingness to do the
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following
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.Tn TELNET
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options, which are described in more detail below:
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.Bd -literal -offset indent
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DO AUTHENTICATION
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WILL ENCRYPT
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DO TERMINAL TYPE
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DO TSPEED
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DO XDISPLOC
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DO NEW-ENVIRON
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DO ENVIRON
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WILL SUPPRESS GO AHEAD
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DO ECHO
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DO LINEMODE
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DO NAWS
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WILL STATUS
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DO LFLOW
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DO TIMING-MARK
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.Ed
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.Pp
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The pseudo-terminal allocated to the client is configured
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to operate in
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.Dq cooked
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mode, and with
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.Dv XTABS and
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.Dv CRMOD
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enabled (see
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.Xr tty 4 ) .
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.Pp
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.Nm Telnetd
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has support for enabling locally the following
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.Tn TELNET
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options:
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.Bl -tag -width "DO AUTHENTICATION"
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.It "WILL ECHO"
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When the
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.Dv LINEMODE
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option is enabled, a
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.Dv WILL ECHO
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or
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.Dv WONT ECHO
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will be sent to the client to indicate the
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current state of terminal echoing.
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When terminal echo is not desired, a
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.Dv WILL ECHO
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is sent to indicate that
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.Tn telnetd
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will take care of echoing any data that needs to be
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echoed to the terminal, and then nothing is echoed.
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When terminal echo is desired, a
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.Dv WONT ECHO
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is sent to indicate that
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.Tn telnetd
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will not be doing any terminal echoing, so the
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client should do any terminal echoing that is needed.
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.It "WILL BINARY"
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Indicates that the client is willing to send a
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8 bits of data, rather than the normal 7 bits
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of the Network Virtual Terminal.
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.It "WILL SGA"
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Indicates that it will not be sending
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.Dv IAC GA ,
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go ahead, commands.
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.It "WILL STATUS"
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Indicates a willingness to send the client, upon
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request, of the current status of all
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.Tn TELNET
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options.
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.It "WILL TIMING-MARK"
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Whenever a
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.Dv DO TIMING-MARK
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command is received, it is always responded
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to with a
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.Dv WILL TIMING-MARK
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.ne 1i
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.It "WILL LOGOUT"
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When a
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.Dv DO LOGOUT
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is received, a
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.Dv WILL LOGOUT
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is sent in response, and the
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.Tn TELNET
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session is shut down.
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.It "WILL ENCRYPT"
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Only sent if
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.Nm telnetd
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is compiled with support for data encryption, and
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indicates a willingness to decrypt
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the data stream.
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.El
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.Pp
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.Nm Telnetd
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has support for enabling remotely the following
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.Tn TELNET
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options:
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.Bl -tag -width "DO AUTHENTICATION"
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.It "DO BINARY"
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Sent to indicate that
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.Tn telnetd
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is willing to receive an 8 bit data stream.
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.It "DO LFLOW"
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Requests that the client handle flow control
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characters remotely.
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.It "DO ECHO"
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This is not really supported, but is sent to identify a 4.2BSD
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.Xr telnet 1
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client, which will improperly respond with
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.Dv WILL ECHO .
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If a
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.Dv WILL ECHO
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is received, a
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.Dv DONT ECHO
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will be sent in response.
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.It "DO TERMINAL-TYPE"
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Indicates a desire to be able to request the
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name of the type of terminal that is attached
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to the client side of the connection.
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.It "DO SGA"
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Indicates that it does not need to receive
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.Dv IAC GA ,
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the go ahead command.
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.It "DO NAWS"
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Requests that the client inform the server when
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the window (display) size changes.
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.It "DO TERMINAL-SPEED"
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Indicates a desire to be able to request information
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about the speed of the serial line to which
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the client is attached.
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.It "DO XDISPLOC"
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Indicates a desire to be able to request the name
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of the X windows display that is associated with
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the telnet client.
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.It "DO NEW-ENVIRON"
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Indicates a desire to be able to request environment
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variable information, as described in RFC 1572.
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.It "DO ENVIRON"
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Indicates a desire to be able to request environment
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variable information, as described in RFC 1408.
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.It "DO LINEMODE"
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Only sent if
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.Nm telnetd
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is compiled with support for linemode, and
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requests that the client do line by line processing.
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.It "DO TIMING-MARK"
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Only sent if
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.Nm telnetd
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is compiled with support for both linemode and
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kludge linemode, and the client responded with
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.Dv WONT LINEMODE .
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If the client responds with
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.Dv WILL TM ,
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the it is assumed that the client supports
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kludge linemode.
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Note that the
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.Op Fl k
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option can be used to disable this.
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.It "DO AUTHENTICATION"
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Only sent if
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.Nm telnetd
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is compiled with support for authentication, and
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indicates a willingness to receive authentication
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information for automatic login.
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.It "DO ENCRYPT"
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Only sent if
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.Nm telnetd
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is compiled with support for data encryption, and
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indicates a willingness to decrypt
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the data stream.
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.El
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.Sh ENVIRONMENT
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.Sh FILES
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.Pa /etc/services
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.br
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.Pa /etc/inittab
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(UNICOS systems only)
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.br
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.Pa /etc/iptos
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(if supported)
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.br
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.Sh "SEE ALSO"
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.Xr telnet 1 ,
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.Xr login 1
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.Sh STANDARDS
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.Bl -tag -compact -width RFC-1572
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.It Cm RFC-854
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.Tn TELNET
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PROTOCOL SPECIFICATION
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.It Cm RFC-855
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TELNET OPTION SPECIFICATIONS
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.It Cm RFC-856
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TELNET BINARY TRANSMISSION
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.It Cm RFC-857
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TELNET ECHO OPTION
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.It Cm RFC-858
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TELNET SUPPRESS GO AHEAD OPTION
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.It Cm RFC-859
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TELNET STATUS OPTION
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.It Cm RFC-860
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TELNET TIMING MARK OPTION
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.It Cm RFC-861
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TELNET EXTENDED OPTIONS - LIST OPTION
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.It Cm RFC-885
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TELNET END OF RECORD OPTION
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.It Cm RFC-1073
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Telnet Window Size Option
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.It Cm RFC-1079
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Telnet Terminal Speed Option
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.It Cm RFC-1091
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Telnet Terminal-Type Option
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.It Cm RFC-1096
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Telnet X Display Location Option
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.It Cm RFC-1123
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Requirements for Internet Hosts -- Application and Support
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.It Cm RFC-1184
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Telnet Linemode Option
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.It Cm RFC-1372
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Telnet Remote Flow Control Option
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.It Cm RFC-1416
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Telnet Authentication Option
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.It Cm RFC-1411
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Telnet Authentication: Kerberos Version 4
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.It Cm RFC-1412
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Telnet Authentication: SPX
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.It Cm RFC-1571
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Telnet Environment Option Interoperability Issues
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.It Cm RFC-1572
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Telnet Environment Option
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.El
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.Sh BUGS
|
|
Some
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.Tn TELNET
|
|
commands are only partially implemented.
|
|
.Pp
|
|
Because of bugs in the original 4.2 BSD
|
|
.Xr telnet 1 ,
|
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.Nm telnetd
|
|
performs some dubious protocol exchanges to try to discover if the remote
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client is, in fact, a 4.2 BSD
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.Xr telnet 1 .
|
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.Pp
|
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Binary mode
|
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has no common interpretation except between similar operating systems
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(Unix in this case).
|
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.Pp
|
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The terminal type name received from the remote client is converted to
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lower case.
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.Pp
|
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.Nm Telnetd
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never sends
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.Tn TELNET
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.Dv IAC GA
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(go ahead) commands.
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