telnet.1.txt

经典的unix下telnet的c代码

.\"	$OpenBSD: telnet.1,v 1.37 2003/12/28 21:53:01 otto Exp $
.\"	$NetBSD: telnet.1,v 1.5 1996/02/28 21:04:12 thorpej Exp $
.\"
.\" Copyright (c) 1983, 1990, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	from: @(#)telnet.1	8.4 (Berkeley) 2/3/94
.\"
.Dd February 3, 1994
.Dt TELNET 1
.Os
.Sh NAME
.Nm telnet
.Nd user interface to the
.Tn TELNET
protocol
.Sh SYNOPSIS
.Nm telnet
.Bk -words
.Op Fl 468EFKLacdfrx
.Op Fl X Ar authtype
.Op Fl b Ar hostalias
.Op Fl e Ar escapechar
.Op Fl k Ar realm
.Op Fl l Ar user
.Op Fl n Ar tracefile
.Oo
.Ar host
.Op Ar port
.Oc
.Ek
.Sh DESCRIPTION
The
.Nm
command
is used to communicate with another host using the
.Tn TELNET
protocol.
If
.Nm
is invoked without the
.Ar host
argument, it enters command mode,
indicated by its prompt
.Pq Nm telnet\&> .
In this mode, it accepts and executes the commands listed below.
If it is invoked with arguments, it performs an
.Ic open
command with those arguments.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl 4
Forces
.Nm
to use IPv4 addresses only.
.It Fl 6
Forces
.Nm
to use IPv6 addresses only.
.It Fl 8
Specifies an 8-bit data path.
This causes an attempt to negotiate the
.Dv TELNET BINARY
option on both input and output.
.It Fl E
Stops any character from being recognized as an escape character.
.It Fl F
If Kerberos authentication is being used, the
.Fl F
option allows the local credentials to be forwarded
to the remote system, including any credentials that
have already been forwarded into the local environment.
.It Fl K
Specifies no automatic login to the remote system.
.It Fl L
Specifies an 8-bit data path on output.
This causes the BINARY option to be negotiated on output.
.It Fl X Ar atype
Disables the
.Ar atype
type of authentication.
.It Fl a
Attempt automatic login.
Currently, this sends the user name via the
.Ev USER
variable
of the
.Ev ENVIRON
option if supported by the remote system.
The name used is that of the current user as returned by
.Xr getlogin 2
if it agrees with the current user ID,
otherwise it is the name associated with the user ID.
.It Fl b Ar hostalias
Uses
.Xr bind 2
on the local socket to bind it to an aliased address (see
.Xr ifconfig 8
and the ``alias'' specifier) or to the address of
another interface than the one naturally chosen by
.Xr connect 2 .
This can be useful when connecting to services which use IP addresses
for authentication and reconfiguration of the server is undesirable (or
impossible).
.It Fl c
Disables the reading of the user's
.Pa \&.telnetrc
file.
(See the
.Ic toggle skiprc
command on this man page.)
.It Fl d
Sets the initial value of the
.Ic debug
toggle to
.Dv TRUE .
.It Fl e Ar escapechar
Sets the initial
.Nm
escape character to
.Ar escapechar .
If
.Ar escapechar
is omitted, then
there will be no escape character.
.It Fl f
If Kerberos authentication is being used, the
.Fl f
option allows the local credentials to be forwarded to the remote system.
.It Fl k Ar realm
If Kerberos authentication is being used, the
.Fl k
option requests that
.Nm
obtain tickets for the remote host in
realm
.Ar realm
instead of the remote host's realm.
.It Fl l Ar user
When connecting to the remote system, if the remote system
understands the
.Ev ENVIRON
option, then
.Ar user
will be sent to the remote system as the value for the variable USER.
This option implies the
.Fl a
option.
This option may also be used with the
.Ic open
command.
.It Fl n Ar tracefile
Opens
.Ar tracefile
for recording trace information.
See the
.Ic set tracefile
command below.
.It Fl r
Specifies a user interface similar to
.Nm rlogin .
In this
mode, the escape character is set to the tilde (~) character,
unless modified by the
.Fl e
option.
.It Fl x
Turn on encryption of the data stream.
When this option is turned on,
.Nm
will exit with an error if authentication cannot be negotiated or if
encryption cannot be turned on.
.It Ar host
Indicates the official name, an alias, or the Internet address
of a remote host.
.It Ar port
Indicates a port number (address of an application).
If a number is not specified, the default
.Nm
port is used.
.El
.Pp
When in rlogin mode, a line of the form ~.\&
disconnects from the
remote host; ~ is the telnet escape character.
Similarly, the line ~^Z suspends the telnet session.
The line ~^] escapes to the normal telnet escape prompt.
.Pp
Once a connection has been opened,
.Nm
will attempt to enable the
.Dv TELNET LINEMODE
option.
If this fails,
.Nm
will revert to one of two input modes:
either ``character at a time''
or ``old line by line''
depending on what the remote system supports.
.Pp
When
.Dv LINEMODE
is enabled, character processing is done on the
local system, under the control of the remote system.
When input
editing or character echoing is to be disabled, the remote system
will relay that information.
The remote system will also relay
changes to any special characters that happen on the remote
system, so that they can take effect on the local system.
.Pp
In ``character at a time'' mode, most
text typed is immediately sent to the remote host for processing.
.Pp
In ``old line by line'' mode, all text is echoed locally,
and (normally) only completed lines are sent to the remote host.
The ``local echo character'' (initially ``^E'') may be used
to turn off and on the local echo
(this would mostly be used to enter passwords
without the password being echoed).
.Pp
If the
.Dv LINEMODE
option is enabled, or if the
.Ic localchars
toggle is
.Dv TRUE
(the default for ``old line by line''; see below),
the user's
.Ic quit ,
.Ic intr ,
and
.Ic flush
characters are trapped locally, and sent as
.Tn TELNET
protocol sequences to the remote side.
If
.Dv LINEMODE
has ever been enabled, then the user's
.Ic susp
and
.Ic eof
are also sent as
.Tn TELNET
protocol sequences,
and
.Ic quit
is sent as a
.Dv TELNET ABORT
instead of
.Dv BREAK .
There are options (see
.Ic toggle
.Ic autoflush
and
.Ic toggle
.Ic autosynch
below)
which cause this action to flush subsequent output to the terminal
(until the remote host acknowledges the
.Tn TELNET
sequence) and flush previous terminal input
(in the case of
.Ic quit
and
.Ic intr ) .
.Pp
While connected to a remote host,
.Nm
command mode may be entered by typing the
.Nm
``escape character'' (initially ``^]'').
When in command mode, the normal terminal editing conventions are available.
Note that the escape character will return to the command mode of the initial
invocation of
.Nm
that has the controlling terminal.
Use the
.Cm send escape
command to switch to command mode in subsequent
.Nm
processes on remote hosts.
.Pp
The following
.Nm
commands are available.
Only enough of each command to uniquely identify it need be typed
(this is also true for arguments to the
.Ic mode ,
.Ic set ,
.Ic toggle ,
.Ic unset ,
.Ic slc ,
.Ic environ ,
and
.Ic display
commands).
.Bl -tag -width "mode type"
.It Ic auth Ar argument Op Ar ...
The
.Ic auth
command manipulates the information sent through the
.Dv TELNET AUTHENTICATE
option.
Valid arguments for the
.Ic auth
command are as follows:
.Bl -tag -width "disable type"
.It Ic disable Ar type
Disables the specified
.Ar type
of authentication.
To obtain a list of available types, use the
.Ic auth disable ?\&
command.
.It Ic enable Ar type
Enables the specified
.Ar type
of authentication.
To obtain a list of available types, use the
.Ic auth enable ?\&
command.
.It Ic status
Lists the current status of the various types of
authentication.
.El
.It Ic close
Close a
.Tn TELNET
session and return to command mode.
.It Ic display Ar argument Op Ar ...
Displays all, or some, of the
.Ic set
and
.Ic toggle
values (see below).
.It Ic encrypt Ar argument Op Ar ...
The
.Ic encrypt
command manipulates the information sent through the
.Dv TELNET ENCRYPT
option that's available when Kerberos is used.
.Pp
Valid arguments for the encrypt command are as follows:
.Bl -tag -width Ar
.It Ic disable Ar type Ic [input|output]
Disables the specified
.Ar type
of encryption.
If you omit
.Ic input
and
.Ic output ,
both input and output
are disabled.
To obtain a list of available types, use the
.Ic encrypt disable ?\&
command.
.It Ic enable Ar type Ic [input|output]
Enables the specified
.Ar type
of encryption.
If you omit
.Ic input
and
.Ic output ,
both input and output are
enabled.
To obtain a list of available types, use the
.Ic encrypt enable ?\&
command.
.It Ic input
This is the same as the
.Ic encrypt start input
command.
.It Ic -input
This is the same as the
.Ic encrypt stop input
command.
.It Ic output
This is the same as the
.Ic encrypt start output
command.
.It Ic -output
This is the same as the
.Ic encrypt stop output
command.
.It Ic start Ic [input|output]
Attempts to start encryption.
If you omit
.Ic input
and
.Ic output ,
both input and output are enabled.
To obtain a list of available types, use the
.Ic encrypt enable ?\&
command.
.It Ic status
Lists the current status of encryption.
.It Ic stop Ic [input|output]
Stops encryption.
If you omit
.Ic input
and
.Ic output ,
encryption is on both input and output.
.It Ic type Ar type
Sets the default type of encryption to be used
with later
.Ic encrypt start
or
.Ic encrypt stop
commands.
.El
.It Ic environ Ar arguments Op Ar ...
The
.Ic environ
command is used to manipulate the
variables that may be sent through the
.Dv TELNET ENVIRON
option.
The initial set of variables is taken from the users
environment, with only the
.Ev DISPLAY
and
.Ev PRINTER
variables being exported by default.
The
.Ev USER
variable is also exported if the
.Fl a
or
.Fl l
options are used.
.br
Valid arguments for the
.Ic environ
command are:
.Bl -tag -width Fl
.It Ic define Ar variable value
Define the variable
.Ar variable
to have a value of
.Ar value .
Any variables defined by this command are automatically exported.
The
.Ar value
may be enclosed in single or double quotes so
that tabs and spaces may be included.
.It Ic undefine Ar variable
Remove
.Ar variable
from the list of environment variables.
.It Ic export Ar variable
Mark the variable
.Ar variable
to be exported to the remote side.
.It Ic unexport Ar variable
Mark the variable
.Ar variable
to not be exported unless
explicitly asked for by the remote side.
.It Ic list
List the current set of environment variables.
Those marked with a
.Cm *
will be sent automatically,
other variables will only be sent if explicitly requested.
.It Ic \&?
Prints out help information for the
.Ic environ
command.
.El
.It Ic logout
Sends the
.Dv TELNET LOGOUT
option to the remote side.
This command is similar to a
.Ic close