telnet.1

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.\" Copyright (c) 1983, 1990 The Regents of the University of California.
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.\"
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.\" specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\"     @(#)telnet.1	6.13 (Berkeley) 7/28/90
.\"
.Dd July 28, 1990
.Dt TELNET 1
.Os BSD 4.2
.Sh NAME
.Nm telnet
.Nd User interface to the 
.Li TELNET
protocol
.Sh SYNOPSIS
.Nm telnet
.Op Fl 8
.Op Fl E
.Op Fl K
.Op Fl L
.Op Fl X Ar atype
.Op Fl a
.Op Fl c
.Op Fl d
.Op Fl e Ar escapechar
.Op Fl k Ar realm
.Op Fl l Ar user
.Op Fl n Ar tracefile
.Op Fl r
.Op Fl x
.Ob
.Ar host
.Op port
.Oe
.Sh DESCRIPTION
The
.Nm telnet
command
is used to communicate with another host using the 
.Li TELNET
protocol.
If
.Nm telnet
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
Options:
.Tw Fl
.Tp Fl 8
Use an eight bit data path.  This will cause
an attempt to negotiate the BINARY option on both
input and output.
.Tp Fl E
The
.Fl E
option stops any character from being recognized as an escape character.
.Tp Fl K
Do not attempt to do automatic login to the
remote system.
.Tp Fl L
Use an eight bit data path on output.
This causes the BINARY option to be negotiated
on output.
.Tp Cx Fl X
.Cx \&\ \&
.Ar atype
.Cx
Disable the
.Ar atype
type of authentication.
.Tp Fl a
Attempt automatic login.
Currently, this sends the user name via the USER variable
of the 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.
.Tp Fl c
The
.Fl c
flag disables the reading of the users 
.Pa \&.telnetrc.
(See the
.Ic toggle
.Ic skiprc
command below.)
.Tp Fl d
Sets the initial value of the
.Ic debug
toggle to
.Li TRUE
.Tp Cx Fl e
.Cx \&\ \&
.Ar escape char
.Cx
Sets the initial
.Nm
.B telnet
escape character to
.Ar escape char.
If
.Ar escape char
is ommitted, then
there will be no escape character.
.Tp Cx Fl k
.Cx \&\ \&
.Ar realm
.Cx
If Kerberos authentication is being used, the
.Fl k
option requests that
.Nm telnet
obtain tickets for the remote host in realm
.Ar realm
instead of the remote host's
realm as determined by
.Xr krb_realmofhost 3  .
.Tp Cx Fl l
.Cx \&\ \&
.Ar user
.Cx
When connecting to the remote system, if the remote system
understands the 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.
.Tp Cx Fl n
.Cx \&\ \&
.Ar tracefile
.Cx
Opens
.Ar tracefile
for recording trace information.
See the
.Ic set tracefile
command below.
.Tp Fl r
Use a user interface similar to
.Xr rlogin 1  .
In this mode, the escape character is set to the tilde (``~'')
character, unless modified by the
.Fl e
flag.
.Tp Fl x
Turn on encryption of the data stream, if possible.
.Tp Ar host
Indicates the official name, an alias, or the Internet address
of a remote host.
.Tp Ar port
Indicates a port number (address of an application) or name.  If a number is
not specified, the default
.Nm telnet
port is used.
Port names are mapped to port numbers via the
/etc/services
file.
Normally when a port number is specified,
.Nm telnet
will not send out any initial
.Li TELNET
option negotiation.
If the port number/name is preceded by
a minus sign, then
the initial
.Li TELNET
option negotiation will be sent.
.Tp
.Pp
When in
.Nm rlogin
mode, a line of the form ``~.'' disconnects from the remote host,
where ``~'' is the
.Nm
escape character.
Similarly, the line ``~^Z'' will suspend the
.Nm telnet
session.
The line ``~^]'' will escape to the normal
.Nm telnet
escape prompt.
.Pp
Once a connection has been opened,
.Nm telnet
will attempt to enable the
.Li TELNET LINEMODE
option.
If this fails, then
.Nm telnet
will revert to one of two input modes:
either \*(Lqcharacter at a time\*(Rq
or \*(Lqold line by line\*(Rq
depending on what the remote system supports.
.Pp
When 
.Li 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 \*(Lqcharacter at a time\*(Rq mode, most
text typed is immediately sent to the remote host for processing.
.Pp
In \*(Lqold line by line\*(Rq mode, all text is echoed locally,
and (normally) only completed lines are sent to the remote host.
The \*(Lqlocal echo character\*(Rq (initially \*(Lq^E\*(Rq) 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 
.Li LINEMODE
option is enabled, or if the
.Ic localchars
toggle is TRUE (the default for \*(Lqold line by line\*(Lq; see below),
the user's
.Ic quit  ,
.Ic intr ,
and
.Ic flush
characters are trapped locally, and sent as
.Li TELNET
protocol sequences to the remote side.
If 
.Li LINEMODE
has ever been enabled, then the user's
.Ic susp
and
.Ic eof
are also sent as
.Li TELNET
protocol sequences,
and
.Ic quit
is sent as a 
.Li TELNET ABORT
instead of 
.Li 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
.Li TELNET
sequence) and flush previous terminal input
(in the case of
.Ic quit
and
.Ic intr  ) .
.Pp
While connected to a remote host,
.Nm telnet
command mode may be entered by typing the
.Nm telnet
\*(Lqescape character\*(Rq (initially \*(Lq^
\*(Rq).
When in command mode, the normal terminal editing conventions are available.
.Pp
The following
.Nm telnet
commands are available.
Only enough of each command to uniquely identify it need be typed
(this is also true for most of the arguments to the
commands).
.Pp
.Tw Ic
.\" ######## BEGIN the "auth" command
.Tp Cx Ic auth
.Cx \&\ \&
.Ar arguments...
.Cx
The
.Ic auth
command is used to manipulate the
the information that my be sent through the
.Li TELNET AUTHENTICATE
option.
.br
Valid arguments for the \fBauth\fP command are:
.Tw Fl
.Tp Cx Ic disable
.Cx \&\ \&
.Ar type
.Cx
Disable the specified
.Ar type
of authentication.
A list of available types can be gotten by
doing an
.Ic auth
.Ic disable
.Ic ?
command.
.Tp Cx Ic enable
.Cx \&\ \&
.Ar type
.Cx
Enable the specified
.Ar type
of authentication.
A list of available types can be gotten by
doing an
.Ic auth
.Ic enable
.Ic ?
command.
.Tp Ic status
List the current status of the various
types of authentication.
.Tp
.\" ######## END the "auth" command
.\"
.\" ######## BEGIN the "close" command
.Tp Ic close
Close a
.Li TELNET
session and return to command mode.
.\" ######## END the "close" command
.\"
.\" ######## BEGIN the "display" command
.Tp Cx Ic display
.Cx \&\ \&
.Ar argument ...
.Cx
Displays all, or some, of the
.Ic set
and
.Ic toggle
values (see below).
.\" ######## END the "display" command
.\"
.\" ######## BEGIN the "encrypt" command
.Tp Cx Ic encrypt
.Cx \&\ \&
.Ar arguments...
.Cx
The
.Ic encrypt
command is used to manipulate the
the information that my be sent through the
.Li TELNET ENCRYPT
option.
.br
Valid arguments for the \fBencrypt\fP command are:
.Tw Fl
.Tp Cx Ic disable
.Cx \&\ \&
.Ar type
.Op input|output
.Cx
Disable the specified
.Ar type
of encryption.
If the
.Op input
or
.Op output
is not specified, both input and output will be disabled.
A list of available types can be gotten by
doing an
.Ic encrypt
.Ic disable
.Ic ?
command.
.Tp Cx Ic enable
.Cx \&\ \&
.Ar type
.Op input|output
.Cx
Enable the specified
.Ar type
of encryption.
If
.Op input
or
.Op output
is not specified, both input and output will be enabled.
A list of available types can be gotten by
doing an
.Ic encrypt
.Ic enable
.Ic ?
command.
.Tp Cx Ic type
.Cx \&\ \&
.Ar type
.Cx
Set the default type of encryption to be used with later
.Ic encrypt start
or
.Ic encrypt stop
commands.
.Tp Cx Ic start
.Op input|output
.Cx
Attempt to start encryption.
If
.Op input
or
.Op output
is not specified, encryption of both input and output will be attempted.
The
.Ic encrypt type
command must have been used to set the encryption type.
.Tp Cx Ic stop
.Op input|output
.Cx
Stop encryption.
If
.Op input
or
.Op output
is not specified, encryption will be stopped on both input and output.
.Tp Ic input
This is the same as the
.Ic encrypt start input
command.
.Tp Ic -input
This is the same as the
.Ic encrypt stop input
command.
.Tp Ic output
This is the same as the
.Ic encrypt start output
command.
.Tp Ic -output
This is the same as the
.Ic encrypt stop output
command.
.Tp Ic status
List the current status of encryption.
.Tp
.\" ######## END the "encrypt" command
.\"
.\" ######## BEGIN the "environ" command
.Tp Cx Ic environ
.Cx \&\ \&
.Ar arguments...
.Cx
The
.Ic environ
command is used to manipulate the
the variables that my be sent through the
.Li 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 \fBenviron\fP command are:
.Tw Fl
.Tp Cx Ic define
.Cx \&\ \&
.Ar variable value
.Cx
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