telnet.1

这是关于远程登陆TELNET 的源代码 已经测试过的。

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.\"	from: @(#)telnet.1	6.16 (Berkeley) 7/27/91
.\"	$Id: telnet.1,v 1.15 2000/07/30 23:57:08 dholland Exp $
.\"
.Dd August 15, 1999
.Dt TELNET 1
.Os "Linux NetKit (0.17)"
.Sh NAME
.Nm telnet
.Nd user interface to the 
.Tn TELNET
protocol
.Sh SYNOPSIS
.Nm telnet
.Op Fl 8ELadr
.Op Fl S Ar tos
.Op Fl e Ar escapechar
.Op Fl l Ar user
.Op Fl n Ar tracefile
.Oo
.Ar host
.Op Ar port
.Oc
.Sh DESCRIPTION
The
.Nm telnet
command
is used for interactive communication with another host using the 
.Tn TELNET
protocol. It begins in command mode, where it prints a telnet prompt 
("telnet\&> "). If
.Nm telnet
is invoked with a
.Ar host
argument, it performs an
.Ic open
command implicitly; see the description below.
.Pp
Options:
.Bl -tag -width indent
.It Fl 8
Request 8-bit operation. This causes an attempt to negotiate the
.Dv TELNET BINARY
option for both input and output. By default telnet is not 8-bit
clean. 
.It Fl E
Disables the escape character functionality; that is, sets the escape
character to ``no character''.
.It Fl L
Specifies an 8-bit data path on output.  This causes the 
.Dv TELNET BINARY 
option to be negotiated on just output.
.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 username is retrieved
via
.Xr getlogin 3 .
.It Fl d
Sets the initial value of the
.Ic debug
toggle to
.Dv TRUE.
.It Fl r
Emulate 
.Xr rlogin 1 .
In this mode, the default escape character is a tilde. Also, the
interpretation of the escape character is changed: an escape character
followed by a dot causes
.Nm telnet 
to disconnect from the remote host. A ^Z instead of a dot suspends
.Nm telnet ,
and a ^] (the default
.Nm telnet
escape character) generates a normal telnet prompt. These codes are
accepted only at the beginning of a line. 
.It Fl S Ar tos
Sets the IP type-of-service (TOS) option for the telnet
connection to the value
.Ar tos .
.It Fl e Ar escapechar
Sets the escape character to
.Ar escapechar.
If no character is supplied, no escape character will be used.
Entering the escape character while connected causes telnet to drop to
command mode.
.It Fl l Ar user
Specify 
.Ar user
as the user to log in as on the remote system. This is accomplished by
sending the specified name as the 
.Dv USER
environment variable, so it requires that the remote system support the
.Ev TELNET ENVIRON
option. This option implies the
.Fl a
option, and 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 Ar host
Specifies a host to contact over the network.
.It Ar port
Specifies a port number or service name to contact. If not specified,
the 
.Nm telnet
port (23) is used.
.El
.Pp
Protocol:
.Pp
Once a connection has been opened,
.Nm telnet
will attempt to enable the
.Dv 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 
.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 \*(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 
.Dv LINEMODE
option is enabled, or if the
.Ic localchars
toggle is
.Dv 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
.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
Commands:
.Pp
The following
.Nm telnet
commands are available. Unique prefixes are understood as abbreviations.
.Pp
.Bl -tag -width "mode type"
.It Ic auth Ar argument ... 
The
.Ic auth
command controls the
.Dv TELNET AUTHENTICATE
protocol option.  If 
.Nm telnet
was compiled without authentication, the 
.Ic auth
command will not be supported. 
Valid arguments are as follows:
.Bl -tag -width "disable type"
.It Ic disable Ar type
Disable the specified type of authentication.  To
obtain a list of available types, use the
.Ic auth disable \&?
command.
.It Ic enable Ar type
Enable the specified type of authentication.  To
obtain a list of available types, use the
.Ic auth enable \&?
command.
.It Ic status
List the current status of the various types of
authentication.
.El
.Pp
Note that the current version of 
.Nm telnet
does not support authentication.
.It Ic close
Close the connection to the remote host, if any, and return to command
mode.
.It Ic display Ar argument ... 
Display all, or some, of the
.Ic set
and
.Ic toggle
values (see below).
.It Ic encrypt Ar argument ...
The encrypt command controls the
.Dv TELNET ENCRYPT
protocol option. If 
.Nm telnet
was compiled without encryption, the
.Ic encrypt
command will not be supported. 
.Pp
Valid arguments are as follows:
.Bl -tag -width Ar
.It Ic disable Ar type Ic [input|output]
Disable the specified type of encryption.  If you do not specify input
or output, encryption of both is disabled.  To obtain a list of
available types, use ``encrypt disable \&?''.
.It Ic enable Ar type Ic [input|output]
Enable the specified type of encryption.  If you do not specify input
or output, encryption of both is enabled.  To obtain a list of
available types, use ``encrypt enable \&?''.
.It Ic input
This is the same as ``encrypt start input''.
.It Ic -input
This is the same as ``encrypt stop input''.
.It Ic output
This is the same as ``encrypt start output''.
.It Ic -output
This is the same as ``encrypt stop output''.
.It Ic start Ic [input|output]
Attempt to begin encrypting.  If you do not specify input or output, 
encryption of both input and output is started. 
.It Ic status
Display the current status of the encryption module.
.It Ic stop Ic [input|output]
Stop encrypting.  If you do not specify input or output, encryption of
both is stopped.
.It Ic type Ar type
Sets the default type of encryption to be used with later ``encrypt start''
or ``encrypt stop'' commands.
.El
.Pp
Note that the current version of 
.Nm telnet
does not support encryption.
.It Ic environ Ar arguments... 
The
.Ic environ
command is used to propagate environment variables across the 
.Nm telnet
link using the
.Dv TELNET ENVIRON
protocol option.
All variables exported from the shell are defined, but only the 
.Ev DISPLAY
and
.Ev PRINTER
variables are marked to be sent by default.  The
.Ev USER
variable is marked to be sent if the
.Fl a
or 
.Fl l
command-line options were used.
.Pp
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 marked for
propagation (``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 any existing definition of
.Ar variable .
.It Ic export Ar variable 
Mark the specified variable for propagation to the remote host.
.It Ic unexport Ar variable 
Do not mark the specified variable for propagation to the remote
host. The remote host may still ask explicitly for variables that are
not exported.
.It Ic list
List the current set of environment variables.
Those marked with a
.Cm *
will be propagated to the remote host. The remote host may still ask
explicitly for the rest.
.It Ic \&?
Prints out help information for the
.Ic environ
command.
.El
.It Ic logout
Send the
.Dv TELNET LOGOUT
protocol option to the remote host.
This command is similar to a
.Ic close
command. If the remote host does not support the
.Dv LOGOUT
option, nothing happens.  But if it does, this command should cause it
to close the connection.  If the remote side also supports the concept
of suspending a user's session for later reattachment, the logout
command indicates that the session should be terminated immediately.
.It Ic mode Ar type 
.Ar Type
is one of several options, depending on the state of the session.
.Tn Telnet
asks the remote host to go into the requested mode. If the remote host
says it can, that mode takes effect.
.Bl -tag -width Ar
.It Ic character
Disable the
.Dv TELNET LINEMODE
option, or, if the remote side does not understand the
.Dv LINEMODE
option, then enter \*(Lqcharacter at a time\*(Lq mode.
.It Ic line
Enable the
.Dv TELNET LINEMODE
option, or, if the remote side does not understand the
.Dv LINEMODE
option, then attempt to enter \*(Lqold-line-by-line\*(Lq mode.
.It Ic isig Pq Ic \-isig 
Attempt to enable (disable) the 
.Dv TRAPSIG
mode of the 
.Dv LINEMODE
option.
This requires that the 
.Dv LINEMODE
option be enabled.
.It Ic edit Pq Ic \-edit 
Attempt to enable (disable) the 
.Dv EDIT
mode of the 
.Dv LINEMODE
option.
This requires that the 
.Dv LINEMODE
option be enabled.
.It Ic softtabs Pq Ic \-softtabs 
Attempt to enable (disable) the 
.Dv SOFT_TAB
mode of the 
.Dv LINEMODE
option.
This requires that the 
.Dv LINEMODE
option be enabled.
.It Ic litecho Pq Ic \-litecho 
Attempt to enable (disable) the 
.Dv LIT_ECHO
mode of the 
.Dv LINEMODE
option.
This requires that the 
.Dv LINEMODE
option be enabled.
.It Ic \&?
Prints out help information for the
.Ic mode
command.
.El
.It Xo
.Ic open Ar host
.Oo Op Fl l
.Ar user
.Oc Ns Oo Fl
.Ar port Oc
.Xc
Open a connection to the named host.  If no port number is specified,
.Nm telnet
will attempt to contact a
.Tn telnet
daemon at the standard port (23).
The host specification may be a host name or IP address.
The
.Fl l
option may be used to specify a user name to be passed to the remote
system, like the
.Fl l
command-line option.
.Pp
When connecting to ports other than the 
.Nm telnet
port,
.Nm telnet
does not attempt 
.Tn telnet
protocol negotiations. This makes it possible to connect to services
that do not support the
.Tn telnet
protocol without making a mess. Protocol negotiation can be forced by
placing a dash before the port number.
.Pp
After establishing a connection, any commands associated with the
remote host in the user's
.Pa .telnetrc
file are executed.
.Pp
The format of the .telnetrc file is as follows: Lines beginning with a
#, and blank lines, are ignored.  The rest of the file should consist
of hostnames and sequences of
.Nm telnet
commands to use with that host. Commands should be one per line,
indented by whitespace; lines beginning without whitespace are
interpreted as hostnames. Upon connecting to a particular host, the
commands associated with that host are executed.
.It Ic quit
Close any open session and exit
.Nm telnet .
An end of file condition on input, when in command mode, will trigger
this operation as well.
.It Ic send Ar arguments 
Send one or more special 
.Tn telnet
protocol character sequences to the remote host.  The following are
the codes which may be specified (more than one may be used in one
command):
.Pp
.Bl -tag -width escape
.It Ic abort
Sends the
.Dv TELNET ABORT
(Abort Processes) sequence.
.It Ic ao
Sends the
.Dv TELNET AO
(Abort Output) sequence, which should cause the remote system to flush
all output
.Em from
the remote system
.Em to
the user's terminal.
.It Ic ayt
Sends the
.Dv TELNET AYT
(Are You There?) sequence, to which the remote system may or may not
choose to respond.
.It Ic brk
Sends the
.Dv TELNET BRK
(Break) sequence, which may have significance to the remote
system.
.It Ic ec
Sends the
.Dv TELNET EC
(Erase Character)
sequence, which should cause the remote system to erase the last character
entered.
.It Ic el
Sends the
.Dv TELNET EL
(Erase Line)
sequence, which should cause the remote system to erase the line currently
being entered.
.It Ic eof
Sends the
.Dv TELNET EOF
(End Of File)
sequence.
.It Ic eor
Sends the
.Dv TELNET EOR
(End of Record)
sequence.
.It Ic escape
Sends the current
.Nm telnet
escape character.
.It Ic ga
Sends the
.Dv TELNET GA
(Go Ahead)
sequence, which likely has no significance to the remote system.
.It Ic getstatus
If the remote side supports the
.Dv TELNET STATUS
command,
.Ic getstatus
will send the subnegotiation to request that the server send
its current option status.
.It Ic ip
Sends the
.Dv TELNET IP
(Interrupt Process) sequence, which should cause the remote
system to abort the currently running process.
.It Ic nop
Sends the
.Dv TELNET NOP
(No Operation)
sequence.
.It Ic susp
Sends the
.Dv TELNET SUSP
(Suspend Process)
sequence.
.It Ic synch
Sends the
.Dv TELNET SYNCH
sequence.
This sequence causes the remote system to discard all previously typed
(but not yet read) input.
This sequence is sent as
.Tn TCP
urgent
data (and may not work if the remote system is a
.Bx 4.2
system -- if
it doesn't work, a lower case \*(Lqr\*(Rq may be echoed on the terminal).
.It Ic do Ar cmd
.It Ic dont Ar cmd
.It Ic will Ar cmd
.It Ic wont Ar cmd
Sends the
.Dv TELNET DO
.Ar cmd
sequence.
.Ar cmd
can be either a decimal number between 0 and 255,
or a symbolic name for a specific
.Dv TELNET
command.
.Ar cmd
can also be either
.Ic help
or
.Ic \&?
to print out help information, including
a list of known symbolic names.
.It Ic \&?
Prints out help information for the
.Ic send
command.
.El
.It Ic set Ar argument value 
.It Ic unset Ar argument value 
The
.Ic set
command will set any one of a number of
.Nm telnet
variables to a specific value or to
.Dv TRUE .
The special value
.Ic off
turns off the function associated with
the variable. This is equivalent to using the
.Ic unset
command.
The
.Ic unset
command will disable or set to