1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
613 lines
15 KiB
Groff
613 lines
15 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 8.3 (Berkeley) 3/1/94
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.\" $FreeBSD$
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.\"
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.Dd March 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 /usr/libexec/telnetd
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.Op Fl BUhlkns
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.Op Fl D Ar debugmode
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.Op Fl I Ns Ar initid
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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 edebug
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.Op Fl P Ar loginprog
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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 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 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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Specifies bftp server mode. In this mode,
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.Nm telnetd
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causes login to start a
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.Xr bftp 1
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session rather than the user's
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normal shell. In bftp daemon mode normal
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logins are not supported, and it must be used
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on a port other than the normal
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.Tn TELNET
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port.
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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 debug
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Enables debugging on each socket created by
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.Nm telnetd
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(see
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.Dv SO_DEBUG
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in
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.Xr socket 2 ) .
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.It Fl edebug
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If
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.Nm telnetd
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has been compiled with support for data encryption, then the
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.Fl edebug
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option may be used to enable encryption debugging code.
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.It Fl P Ar loginprog
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Specifies an alternate
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.Xr login 1
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command to run to complete the login. The alternate command must
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understand the same command arguments as the standard login.
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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 I Ar initid
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This option is only applicable to
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.Tn UNICOS
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systems prior to 7.0.
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It specifies the
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.Dv ID
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from
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.Pa /etc/inittab
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to use when init starts login sessions. The default
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.Dv ID
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is
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.Dv fe.
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.It Fl k
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This option is only useful if
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.Nm telnetd
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has been compiled with both linemode and kludge linemode
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support. If the
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.Fl k
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option is specified, then if the remote client does not
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support the
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.Dv LINEMODE
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option, then
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.Nm telnetd
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will operate in character at a time mode.
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It will still support kludge linemode, but will only
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go into kludge linemode if the remote client requests
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it.
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(This is done by the client sending
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.Dv DONT SUPPRESS-GO-AHEAD
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and
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.Dv DONT ECHO . )
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The
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.Fl k
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option is most useful when there are remote clients
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that do not support kludge linemode, but pass the heuristic
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(if they respond with
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.Dv WILL TIMING-MARK
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in response to a
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.Dv DO TIMING-MARK)
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for kludge linemode support.
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.It Fl l
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Specifies line mode. Tries to force clients to use line-
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at-a-time mode.
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If the
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.Dv LINEMODE
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option is not supported, it will go
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into kludge linemode.
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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
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This option is only enabled if
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.Nm telnetd
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is compiled with support for
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.Tn SecurID
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cards.
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It causes the
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.Fl s
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option to be passed on to
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.Xr login 1 ,
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and thus is only useful if
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.Xr login 1
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supports the
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.Fl s
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flag to indicate that only
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.Tn SecurID
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validated logins are allowed, and is
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usually useful for controlling remote logins
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from outside of a firewall.
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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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.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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.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 \*(lqcooked\*(rq 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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.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 Window System 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
|
|
option can be used to disable this.
|
|
.It "DO AUTHENTICATION"
|
|
Only sent if
|
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.Nm telnetd
|
|
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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.Sh ENVIRONMENT
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.Sh FILES
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.Pa /etc/services
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|
.br
|
|
.Pa /etc/inittab
|
|
(UNICOS systems only)
|
|
.br
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|
.Pa /etc/iptos
|
|
(if supported)
|
|
.br
|
|
.Pa /usr/ucb/bftp
|
|
(if supported)
|
|
.Sh "SEE ALSO"
|
|
.Xr bftp 1 ,
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|
.Xr login 1 ,
|
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.Xr telnet 1
|
|
(if supported)
|
|
.Sh STANDARDS
|
|
.Bl -tag -compact -width RFC-1572
|
|
.It Cm RFC-854
|
|
.Tn TELNET
|
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PROTOCOL SPECIFICATION
|
|
.It Cm RFC-855
|
|
TELNET OPTION SPECIFICATIONS
|
|
.It Cm RFC-856
|
|
TELNET BINARY TRANSMISSION
|
|
.It Cm RFC-857
|
|
TELNET ECHO OPTION
|
|
.It Cm RFC-858
|
|
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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.Sh BUGS
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Some
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.Tn TELNET
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commands are only partially implemented.
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.Pp
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Because of bugs in the original 4.2 BSD
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.Xr telnet 1 ,
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.Nm telnetd
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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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