As per Relevance of the word determine, we have this rfc below:
Network Working Group D. Borman,
Request for Comments: 1408 Cray Research, Inc
January 1993
Telnet Environment
Status of this
This RFC specifies an IAB standards track protocol for the
community, and requests discussion and suggestions for improvements
Please refer to the current edition of the "IAB Official
Standards" for the standardization state and status of this protocol
Distribution of this memo is unlimited
This document specifies a mechanism for passing
information between a telnet client and server. Use of
mechanism enables a telnet user to propagate
information to a remote host when connecting
1. Command Names and
ENVIRON 36
IS 0
SEND 1
INFO 2
VAR 0
VALUE 1
ESC 2
USERVAR 3
2. Command
IAC WILL
The sender of this command is willing to send
variables
IAC WONT
The sender of this command refuses to send environment variables
Telnet Working Group [Page 1]
RFC 1408 Telnet Environment Option January 1993
IAC DO
The sender of this command is willing to receive
variables
IAC DONT
The sender of this command refuses to accept
variables
IAC SB ENVIRON SEND [ type ... [ type ... [ ... ] ] ] IAC
The sender of this command requests that the remote side send
environment variables. The "type" may be either VAR or USERVAR
to indicate either well known or user variable names. Only
side that is DO ENVIRON may initiate a SEND command. If a list
variables is specified, then only those variables should be sent
If no list is specified, then the default environment, of
well known and user defined variables, should be sent. If one
the variables has no name, then all the variables of that
(well known or user defined) in the default environment should
sent
IAC SB ENVIRON IS type ... [ VALUE ... ] [ type ... [ VALUE ... ] [
The sender of this command is sending environment variables.
command is sent in response to a SEND request. Only the side
is WILL ENVIRON may send an IS command. The "type"/VALUE
must be returned in the same order as the SEND request
them, and there must be a response for each "type ..."
requested. The "type" will be VAR or USERVAR.
environment variables may be sent. The characters following
"type" up to the next "type" or VALUE specify the variable name
The characters following a VALUE up to the next "type" specify
value of the variable. If a "type" is not followed by a
(e.g., by another VAR, USERVAR, or IAC SE) then that variable
undefined. If a VALUE is immediately followed by a "type" or IAC
then the variable is defined, but has no value. If an IAC
contained between the IS and the IAC SE, it must be sent as
IAC. If a variable or a value contains a VAR, it must be sent
ESC VAR
If a variable or a value contains a USERVAR, it must be sent
ESC USERVAR. If a variable or a value contains a VALUE, it
be sent as ESC VALUE. If a variable or a value contains an ESC
it must be sent as ESC ESC
Telnet Working Group [Page 2]
RFC 1408 Telnet Environment Option January 1993
IAC SB ENVIRON INFO type ... [ VALUE ... ] [ type ... [ VALUE ... ] [
The sender of this command is sending information about
variables that have changed. It is identical to the IS command
except that the command is INFO instead of IS. Only the side
is WILL ENVIRON may send an INFO command. The INFO command is
to be used to send initial information; the SEND/IS sequence is
be used for that. The INFO command is to be used to
changes in environment variables, and may be
generated
3. Default
The default specification for this option
WONT
DONT
meaning there will not be any exchange of environment information
4.
Many operating systems have startup information and
variables that contain information that should be propagated
remote machines when Telnet connections are established. Rather
create a new Telnet option each time someone comes up with some
information that they need propagated through a Telnet session,
that the Telnet session itself doesn't really need to know about
this generic information option can be used
5. Well Known
USER This variable is used to transmit the user or
name that the client wishes to log into on the
system. The format of the value the USER variable
system dependent, as determined by the remote system
JOB This variable is used to transmit the job ID that
client wishes to use when logging into the remote system
The format of the value the JOB variable is
dependent, as determined by the remote system
ACCT This variable is used to transmit the account ID that
client wishes to use when logging into the remote system
The format of the value the ACCT variable is
dependent, as determined by the remote system
Telnet Working Group [Page 3]
RFC 1408 Telnet Environment Option January 1993
PRINTER This variable is used to identify the default
for printer output. Because there does not
exist a standard way of naming a printer on a network
the format of this variable is currently undefined
SYSTEMTYPE This is used to transmit the type of operating system
the system that sends this variable. It value
identical to the value of the SYSTEM (SYST) command
FTP [2]. The format of the value shall have as
first word one of the system names listed in
current version of the Assigned Numbers document [3].
DISPLAY This variable is used to transmit the X display
of the client. The format for the value of the
variable is
:[.]
This information is identical to the information
using the Telnet X-DISPLAY-LOCATION option. If both
DISPLAY environment variable, and
X-DISPLAY-LOCATION option[4] are received, and
contain conflicting information, the most
received information received should be used
Because it is impossible to anticipate all variables that users
wish to exchange, the USERVAR type is provided to allow users
transmit arbitrary variable/value pairs. The use of an
type allows implementations to distinguish between values derived
the remote host software and values supplied by the user.
implementations will most likely treat both types with an equal
of distrust. The results of a name-space collision between a well
known and a user variable are implementation specific
6. Implementation
WILL and DO are used only at the beginning of the connection
obtain and grant permission for future negotiations
Once the two hosts have exchanged a WILL and a DO, the sender of
DO ENVIRON is free to request that environment variables be sent
Only the sender of the DO may send requests (IAC SB ENVIRON SEND
SE) and only the sender of the WILL may transmit actual
information (via the IAC SB ENVIRON IS ... IAC SE command).
this option may be used at anytime throughout the life of the
connection, the exchange of environment information will
happen at the startup of the connection. This is because
operating systems only have mechanisms for propagating
information at process creation, so the information is needed
the user logs in. In this section, anything that is in quotes
Telnet Working Group [Page 4]
RFC 1408 Telnet Environment Option January 1993
shorthand for a string of ASCII values. For example, "joe" means
three octet sequence (in decimal) 106 111 101.
The receiving host is not required to put all variables that
receives into the environment. For example, if the client
send across USERVAR "TERM" VALUE "xterm" as an environment variable
and the TERMINAL-TYPE [1] option has already been used to
the terminal type, the server may safely ignore the TERM variable
Also, some startup information may be used in other ways;
example, the values for "USER", "ACCT" and "PROJ" values might
used to decide which account to log into, and might never be put
the users environment. In general, if the server has
determined the value of an environment variable by some more
means, or if it does not understand a variable name, it may
the value sent in the ENVIRON option. The server may also prefer
just put all unknown information into the users environment. This
the suggested method of implementation, because it allows the
the most flexibility
The following is an example of use of the option
Host1 Host
IAC DO
IAC WILL
[ Host1 is now free to request environment information ]
IAC SB ENVIRON SEND VAR "USER
VAR "ACCT" VAR USERVAR IAC
[ The server has now explicitly asked for the USER and
variables, the default set of well known environment variables
and the default set of user defined variables. Note that
client includes the USER information twice; once because it
explicitly asked for, and once because it is part of
default environment. ]
IAC SB ENVIRON IS VAR "USER
VALUE "joe" VAR "ACCT"
"kernel" VAR "USER" VALUE "joe
VAR "DISPLAY" VALUE "foo:0.0"
USERVAR "SHELL" VALUE "/bin/csh
IAC
It is legal for a client to respond with an empty environment (
data between the IAC SB and IAC SE) when no well-defined or
variables are currently defined. For example
IAC SB ENVIRON IS IAC
Telnet Working Group [Page 5]
RFC 1408 Telnet Environment Option January 1993
is a valid response to any of the following
IAC SB ENVIRON SEND IAC
IAC SB ENVIRON SEND VAR IAC
IAC SB ENVIRON SEND USERVAR IAC
IAC SB ENVIRON SEND VAR USERVAR IAC
(The last example is equivalent to the first...)
It is expected that any implementation that supports the
ENVIRON option will support all of this specification
7. Security
It is important for an implementor of the ENVIRON option
understand the interaction of setting options and
login/authentication process. Specifically careful analysis should
done to determine which variables are "safe" to set prior to
the client login. An example of a bad choice would be permitting
variable to be changed that allows an intruder to circumvent
compromise the login/authentication program itself
8.
[1] VanBokkelen, J., "Telnet Terminal-Type Option", RFC 1091,
Software, Inc., February 1989.
[2] Postel, J. and J. Reynolds, "File Transfer Protocol (FTP)",
9, RFC 959, USC/Information Sciences Institute, October 1985.
[3] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
USC/Information Sciences Institute, July 1992.
[4] Marcy, G., "Telnet X Display Location Option", RFC 1096,
Mellon University, March 1989.
Security
Security issues are discussed in Section 7.
Telnet Working Group [Page 6]
RFC 1408 Telnet Environment Option January 1993
Author's
David A. Borman,
Cray Research, Inc
655F Lone Oak
Eagan, MN 55123
Phone: (612) 452-6650
EMail: dab@CRAY.
Mailing List: telnet-ietf@CRAY.
Chair's
The working group can be contacted via the current chair
Steve
INTERACTIVE Systems
1901 North Naper
Naperville, IL 60563-8895
Phone: (708) 505-9100 x256
EMail: stevea@isc.
Telnet Working Group [Page 7]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
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