telnet.1.txt

经典的unix下telnet的c代码

and the
.Ic quit
character is typed, a
.Dv TELNET BRK
sequence (see
.Ic send
.Ic brk
above)
is sent to the remote host.
The initial value for the
.Ic quit
character is taken to be
the terminal's
.Ic quit
character.
.It Ic reprint
If
.Nm
is operating in
.Dv LINEMODE
or ``old line by line'' mode, then this character is taken to
be the terminal's
.Ic reprint
character.
The initial value for the
.Ic reprint
character is taken to be
the terminal's
.Ic reprint
character.
.It Ic rlogin
This is the rlogin escape character.
If set, the normal
.Tn TELNET
escape character is ignored unless it is
preceded by this character at the beginning of a line.
This character, at the beginning of a line, followed by
a "." closes the connection; when followed by a ^Z it
suspends the
.Nm
command.
The initial state is to
disable the
.Ic rlogin
escape character.
.It Ic start
If the
.Dv TELNET TOGGLE-FLOW-CONTROL
option has been enabled,
then this character is taken to
be the terminal's
.Ic start
character.
The initial value for the
.Ic start
character is taken to be
the terminal's
.Ic start
character.
.It Ic stop
If the
.Dv TELNET TOGGLE-FLOW-CONTROL
option has been enabled,
then this character is taken to
be the terminal's
.Ic stop
character.
The initial value for the
.Ic stop
character is taken to be
the terminal's
.Ic stop
character.
.It Ic susp
If
.Nm
is in
.Ic localchars
mode, or
.Dv LINEMODE
is enabled, and the
.Ic suspend
character is typed, a
.Dv TELNET SUSP
sequence (see
.Ic send
.Ic susp
above)
is sent to the remote host.
The initial value for the
.Ic suspend
character is taken to be
the terminal's
.Ic suspend
character.
.It Ic tracefile
This is the file to which the output, caused by
.Ic netdata
or
.Ic option
tracing being
.Dv TRUE ,
will be written.
If it is set to
.Dq Fl ,
then tracing information will be written to standard output (the default).
.It Ic worderase
If
.Nm
is operating in
.Dv LINEMODE
or ``old line by line'' mode, then this character is taken to
be the terminal's
.Ic worderase
character.
The initial value for the
.Ic worderase
character is taken to be
the terminal's
.Ic worderase
character.
.It Ic \&?
Displays the legal
.Ic set
.Pq Ic unset
commands.
.El
.It Ic skey Ar sequence challenge
The
.Ic skey
command computes a response to the S/Key challenge.
See
.Xr skey 1
for more information on the S/Key system.
.It Ic slc Ar state
The
.Ic slc
command (Set Local Characters) is used to set
or change the state of the special
characters when the
.Dv TELNET LINEMODE
option has
been enabled.
Special characters are characters that get mapped to
.Tn TELNET
commands sequences (like
.Ic ip
or
.Ic quit )
or line editing characters (like
.Ic erase
and
.Ic kill ) .
By default, the local special characters are exported.
.Bl -tag -width Fl
.It Ic check
Verify the current settings for the current special characters.
The remote side is requested to send all the current special
character settings, and if there are any discrepancies with
the local side, the local side will switch to the remote value.
.It Ic export
Switch to the local defaults for the special characters.
The local default characters are those of the local terminal at
the time when
.Nm
was started.
.It Ic import
Switch to the remote defaults for the special characters.
The remote default characters are those of the remote system
at the time when the
.Tn TELNET
connection was established.
.It Ic \&?
Prints out help information for the
.Ic slc
command.
.El
.It Ic status
Show the current status of
.Nm telnet .
This includes the peer one is connected to, as well
as the current mode.
.It Ic toggle Ar arguments Op Ar ...
Toggle (between
.Dv TRUE
and
.Dv FALSE )
various flags that control how
.Nm
responds to events.
These flags may be set explicitly to
.Dv TRUE
or
.Dv FALSE
using the
.Ic set
and
.Ic unset
commands listed above.
More than one argument may be specified.
The state of these flags may be interrogated with the
.Ic display
command.
Valid arguments are:
.Bl -tag -width Ar
.It Ic authdebug
Turns on debugging information for the authentication code.
.It Ic autoflush
If
.Ic autoflush
and
.Ic localchars
are both
.Dv TRUE ,
then when the
.Ic ao
or
.Ic quit
characters are recognized (and transformed into
.Tn TELNET
sequences; see
.Ic set
above for details),
.Nm
refuses to display any data on the user's terminal
until the remote system acknowledges (via a
.Dv TELNET TIMING MARK
option)
that it has processed those
.Tn TELNET
sequences.
The initial value for this toggle is
.Dv TRUE
if the terminal user had not
done an "stty noflsh", otherwise
.Dv FALSE
(see
.Xr stty 1 ) .
.It Ic autodecrypt
When the
.Dv TELNET ENCRYPT
option is negotiated, by
default the actual encryption (decryption) of the data
stream does not start automatically.
The
.Ic autoencrypt
.Pq Ic autodecrypt
command states that encryption of the
output (input) stream should be enabled as soon as
possible.
.Pp
.It Ic autologin
If the remote side supports the
.Dv TELNET AUTHENTICATION
option
.Tn TELNET
attempts to use it to perform automatic authentication.
If the
.Dv AUTHENTICATION
option is not supported, the user's login
name is propagated through the
.Dv TELNET ENVIRON
option.
This command is the same as specifying
.Ar a
option on the
.Ic open
command.
.It Ic autosynch
If
.Ic autosynch
and
.Ic localchars
are both
.Dv TRUE ,
then when either the
.Ic intr
or
.Ic quit
character is typed (see
.Ic set
above for descriptions of the
.Ic intr
and
.Ic quit
characters), the resulting
.Tn TELNET
sequence sent is followed by the
.Dv TELNET SYNCH
sequence.
This procedure
.Em should
cause the remote system to begin throwing away all previously
typed input until both of the
.Tn TELNET
sequences have been read and acted upon.
The initial value of this toggle is
.Dv FALSE .
.It Ic binary
Enable or disable the
.Dv TELNET BINARY
option on both input and output.
.It Ic inbinary
Enable or disable the
.Dv TELNET BINARY
option on input.
.It Ic outbinary
Enable or disable the
.Dv TELNET BINARY
option on output.
.It Ic crlf
If this is
.Dv TRUE ,
then carriage returns will be sent as
.Li <CR><LF> .
If this is
.Dv FALSE ,
then carriage returns will be sent as
.Li <CR><NUL> .
The initial value for this toggle is
.Dv FALSE .
.It Ic crmod
Toggle carriage return mode.
When this mode is enabled, most carriage return characters received from
the remote host will be mapped into a carriage return followed by
a line feed.
This mode does not affect those characters typed by the user, only
those received from the remote host.
This mode is not very useful unless the remote host
only sends carriage return, but never line feeds.
The initial value for this toggle is
.Dv FALSE .
.It Ic debug
Toggles socket level debugging (useful only to the superuser).
The initial value for this toggle is
.Dv FALSE .
.It Ic encdebug
Turns on debugging information for the encryption code.
.It Ic localchars
If this is
.Dv TRUE ,
then the
.Ic flush ,
.Ic interrupt ,
.Ic quit ,
.Ic erase ,
and
.Ic kill
characters (see
.Ic set
above) are recognized locally, and transformed into (hopefully) appropriate
.Tn TELNET
control sequences
(respectively
.Ic ao ,
.Ic ip ,
.Ic brk ,
.Ic ec ,
and
.Ic el ;
see
.Ic send
above).
The initial value for this toggle is
.Dv TRUE
in ``old line by line'' mode,
and
.Dv FALSE
in ``character at a time'' mode.
When the
.Dv LINEMODE
option is enabled, the value of
.Ic localchars
is ignored, and assumed to always be
.Dv TRUE .
If
.Dv LINEMODE
has ever been enabled, then
.Ic quit
is sent as
.Ic abort ,
and
.Ic eof
and
.Ic suspend
are sent as
.Ic eof
and
.Ic susp
(see
.Ic send
above).
.It Ic netdata
Toggles the display of all network data (in hexadecimal format).
The initial value for this toggle is
.Dv FALSE .
.It Ic options
Toggles the display of some internal
.Nm
protocol processing (having to do with
.Tn TELNET
options).
The initial value for this toggle is
.Dv FALSE .
.It Ic prettydump
When the
.Ic netdata
toggle is enabled, if
.Ic prettydump
is enabled the output from the
.Ic netdata
command will be formatted in a more user readable format.
Spaces are put between each character in the output, and the
beginning of any
.Tn TELNET
escape sequence is preceded by a '*' to aid in locating them.
.It Ic skiprc
When the skiprc toggle is
.Dv TRUE ,
.Tn TELNET
skips the reading of the
.Pa \&.telnetrc
file in the user's home
directory when connections are opened.
The initial value for this toggle is
.Dv FALSE .
.It Ic termdata
Toggles the display of all terminal data (in hexadecimal format).
The initial value for this toggle is
.Dv FALSE .
.It Ic verbose_encrypt
When the
.Ic verbose_encrypt
toggle is
.Dv TRUE ,
.Nm
prints out a message each time encryption is enabled or
disabled.
The initial value for this toggle is
.Dv FALSE .
.It Ic \&?
Displays the legal
.Ic toggle
commands.
.El
.It Ic z
Suspend
.Nm telnet .
This command only works when the user is using the
.Xr csh 1 .
.It Ic \&! Op Ar command
Execute a single command in a subshell on the local
system.
If
.Ar command
is omitted, then an interactive
subshell is invoked.
.It Ic \&? Op Ar command
Get help.
With no arguments,
.Nm
prints a help summary.
If a command is specified,
.Nm
will print the help information for just that command.
.El
.Sh ENVIRONMENT
.Nm
uses at least the
.Ev HOME ,
.Ev SHELL ,
.Ev DISPLAY ,
and
.Ev TERM
environment variables.
Other environment variables may be propagated
to the other side via the
.Dv TELNET ENVIRON
option.
.Sh FILES
.Bl -tag -width ~/.telnetrc -compact
.It Pa ~/.telnetrc
user customized telnet startup values
.El
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Sh NOTES
On some remote systems, echo has to be turned off manually when in
``old line by line'' mode.
.Pp
In ``old line by line'' mode or
.Dv LINEMODE
the terminal's
.Ic eof
character is only recognized (and sent to the remote system)
when it is the first character on a line.
.Pp
Source routing is not supported yet for IPv6.