TELNETD(8) BSD System Manager's Manual TELNETD(8)
NNAAMMEE
tteellnneettdd - DARPA TELNET protocol server
SSYYNNOOPPSSIISS
//uussrr//lliibbeexxeecc//tteellnneettdd [--aa _a_u_t_h_m_o_d_e] [--BB] [--DD _d_e_b_u_g_m_o_d_e] [--eeddeebbuugg] [--hh]
[--II_i_n_i_t_i_d] [--ll] [--kk] [--nn] [--rr_l_o_w_p_t_y_-_h_i_g_h_p_t_y] [--ss]
[--SS _t_o_s] [--uu _l_e_n] [--UU] [--XX _a_u_t_h_t_y_p_e] [--ddeebbuugg [_p_o_r_t]]
DDEESSCCRRIIPPTTIIOONN
The tteellnneettdd command is a server which supports the DARPA standard TELNET
virtual terminal protocol. TTeellnneettdd is normally invoked by the internet
server (see inetd(8)) for requests to connect to the TELNET port as in-
dicated by the _/_e_t_c_/_s_e_r_v_i_c_e_s file (see services(5)). The --ddeebbuugg option
may be used to start up tteellnneettdd manually, instead of through inetd(8).
If started up this way, _p_o_r_t may be specified to run tteellnneettdd on an alter-
nate TCP port number.
The tteellnneettdd command accepts the following options:
--aa _a_u_t_h_m_o_d_e This option may be used for specifying what mode should be
used for authentication. Note that this option is only use-
ful if tteellnneettdd has been compiled with support for the
AUTHENTICATION option. There are several valid values for
_a_u_t_h_m_o_d_e_:
debug Turns on authentication debugging code.
user Only allow connections when the remote user can pro-
vide valid authentication information to identify the
remote user, and is allowed access to the specified
account without providing a password.
valid Only allow connections when the remote user can pro-
vide valid authentication information to identify the
remote user. The login(1) command will provide any
additional user verification needed if the remote us-
er is not allowed automatic access to the specified
account.
other Only allow connections that supply some authentica-
tion information. This option is currently not sup-
ported by any of the existing authentication mecha-
nisms, and is thus the same as specifying --aa vvaalliidd.
none This is the default state. Authentication informa-
tion is not required. If no or insufficient authen-
tication information is provided, then the login(1)
program will provide the necessary user verification.
off This disables the authentication code. All user ver-
ification will happen through the login(1) program.
--BB Specifies bftp server mode. In this mode, tteellnneettdd causes
login to start a bftp(1) session rather than the user's nor-
mal shell. In bftp daemon mode normal logins are not sup-
ported, and it must be used on a port other than the normal
TELNET port.
--DD _d_e_b_u_g_m_o_d_e
This option may be used for debugging purposes. This allows
tteellnneettdd to print out debugging information to the connec-
tion, allowing the user to see what tteellnneettdd is doing. There
are several possible values for _d_e_b_u_g_m_o_d_e_:
ooppttiioonnss Prints information about the negotiation of TELNET
options.
rreeppoorrtt Prints the ooppttiioonnss information, plus some addi-
tional information about what processing is going
on.
nneettddaattaa Displays the data stream received by tteellnneettdd..
ppttyyddaattaa Displays data written to the pty.
eexxeerrcciissee Has not been implemented yet.
--ddeebbuugg Enables debugging on each socket created by tteellnneettdd (see
SO_DEBUG in socket(2)).
--eeddeebbuugg If tteellnneettdd has been compiled with support for data encryp-
tion, then the --eeddeebbuugg option may be used to enable encryp-
tion debugging code.
--hh Disables the printing of host-specific information before
login has been completed.
--II _i_n_i_t_i_d This option is only applicable to UNICOS systems prior to
7.0. It specifies the ID from _/_e_t_c_/_i_n_i_t_t_a_b to use when init
starts login sessions. The default ID is fe.
--kk This option is only useful if tteellnneettdd has been compiled with
both linemode and kludge linemode support. If the --kk option
is specified, then if the remote client does not support the
LINEMODE option, then tteellnneettdd will operate in character at a
time mode. It will still support kludge linemode, but will
only go into kludge linemode if the remote client requests
it. (This is done by by the client sending DONT SUPPRESS-
GO-AHEAD and DONT ECHO.) The --kk option is most useful when
there are remote clients that do not support kludge
linemode, but pass the heuristic (if they respond with WILL
TIMING-MARK in response to a DO TIMING-MARK) for kludge
linemode support.
--ll Specifies line mode. Tries to force clients to use line-
at-a-time mode. If the LINEMODE option is not supported, it
will go into kludge linemode.
--nn Disable TCP keep-alives. Normally tteellnneettdd enables the TCP
keep-alive mechanism to probe connections that have been
idle for some period of time to determine if the client is
still there, so that idle connections from machines that
have crashed or can no longer be reached may be cleaned up.
--rr _l_o_w_p_t_y_-_h_i_g_h_p_t_y
This option is only enabled when tteellnneettdd is compiled for
UNICOS. It specifies an inclusive range of pseudo-terminal
devices to use. If the system has sysconf variable
_SC_CRAY_NPTY configured, the default pty search range is 0
to _SC_CRAY_NPTY; otherwise, the default range is 0 to 128.
Either _l_o_w_p_t_y or _h_i_g_h_p_t_y may be omitted to allow changing
either end of the search range. If _l_o_w_p_t_y is omitted, the -
character is still required so that tteellnneettdd can differenti-
ate _h_i_g_h_p_t_y from _l_o_w_p_t_y.
--ss This option is only enabled if tteellnneettdd is compiled with sup-
port for SecurID cards. It causes the --ss option to be
passed on to login(1), and thus is only useful if login(1)
supports the --ss flag to indicate that only SecurID validated
logins are allowed, and is usually useful for controlling
remote logins from outside of a firewall.
--SS _t_o_s
--uu _l_e_n This option is used to specify the size of the field in the
utmp structure that holds the remote host name. If the re-
solved host name is longer than _l_e_n, the dotted decimal val-
ue will be used instead. This allows hosts with very long
host names that overflow this field to still be uniquely
identified. Specifying --uu00 indicates that only dotted deci-
mal addresses should be put into the _u_t_m_p file.
--UU This option causes tteellnneettdd to refuse connections from ad-
dresses that cannot be mapped back into a symbolic name via
the gethostbyaddr(3) routine.
--XX _a_u_t_h_t_y_p_e This option is only valid if tteellnneettdd has been built with
support for the authentication option. It disables the use
of _a_u_t_h_t_y_p_e authentication, and can be used to temporarily
disable a specific authentication type without having to re-
compile tteellnneettdd.
TTeellnneettdd operates by allocating a pseudo-terminal device (see pty(4)) for
a client, then creating a login process which has the slave side of the
pseudo-terminal as stdin, stdout and stderr. TTeellnneettdd manipulates the mas-
ter side of the pseudo-terminal, implementing the TELNET protocol and
passing characters between the remote client and the login process.
When a TELNET session is started up, tteellnneettdd sends TELNET options to the
client side indicating a willingness to do the following TELNET options,
which are described in more detail below:
DO AUTHENTICATION
WILL ENCRYPT
DO TERMINAL TYPE
DO TSPEED
DO XDISPLOC
DO NEW-ENVIRON
DO ENVIRON
WILL SUPPRESS GO AHEAD
DO ECHO
DO LINEMODE
DO NAWS
WILL STATUS
DO LFLOW
DO TIMING-MARK
The pseudo-terminal allocated to the client is configured to operate in
cooked mode, and with XTABS and CRMOD enabled (see tty(4)).
TTeellnneettdd has support for enabling locally the following TELNET options:
WILL ECHO When the LINEMODE option is enabled, a WILL ECHO or
WONT ECHO will be sent to the client to indicate the
current state of terminal echoing. When terminal echo
is not desired, a WILL ECHO is sent to indicate that
telnetd will take care of echoing any data that needs
to be echoed to the terminal, and then nothing is
echoed. When terminal echo is desired, a WONT ECHO is
sent to indicate that telnetd will not be doing any
terminal echoing, so the client should do any terminal
echoing that is needed.
WILL BINARY Indicates that the client is willing to send a 8 bits
of data, rather than the normal 7 bits of the Network
Virtual Terminal.
WILL SGA Indicates that it will not be sending IAC GA, go
ahead, commands.
WILL STATUS Indicates a willingness to send the client, upon re-
quest, of the current status of all TELNET options.
WILL TIMING-MARK Whenever a DO TIMING-MARK command is received, it is
always responded to with a WILL TIMING-MARK
WILL LOGOUT When a DO LOGOUT is received, a WILL LOGOUT is sent in
response, and the TELNET session is shut down.
WILL ENCRYPT Only sent if tteellnneettdd is compiled with support for data
encryption, and indicates a willingness to decrypt the
data stream.
TTeellnneettdd has support for enabling remotely the following TELNET options:
DO BINARY Sent to indicate that telnetd is willing to receive an
8 bit data stream.
DO LFLOW Requests that the client handle flow control charac-
ters remotely.
DO ECHO This is not really supported, but is sent to identify
a 4.2BSD telnet(1) client, which will improperly re-
spond with WILL ECHO. If a WILL ECHO is received, a
DONT ECHO will be sent in response.
DO TERMINAL-TYPE Indicates a desire to be able to request the name of
the type of terminal that is attached to the client
side of the connection.
DO SGA Indicates that it does not need to receive IAC GA, the
go ahead command.
DO NAWS Requests that the client inform the server when the
window (display) size changes.
DO TERMINAL-SPEED Indicates a desire to be able to request information
about the speed of the serial line to which the client
is attached.
DO XDISPLOC Indicates a desire to be able to request the name of
the X windows display that is associated with the tel-
net client.
DO NEW-ENVIRON Indicates a desire to be able to request environment
variable information, as described in RFC 1572.
DO ENVIRON Indicates a desire to be able to request environment
variable information, as described in RFC 1408.
DO LINEMODE Only sent if tteellnneettdd is compiled with support for
linemode, and requests that the client do line by line
processing.
DO TIMING-MARK Only sent if tteellnneettdd is compiled with support for both
linemode and kludge linemode, and the client responded
with WONT LINEMODE. If the client responds with WILL
TM, the it is assumed that the client supports kludge
linemode. Note that the [--kk] option can be used to
disable this.
DO AUTHENTICATION Only sent if tteellnneettdd is compiled with support for au-
thentication, and indicates a willingness to receive
authentication information for automatic login.
DO ENCRYPT Only sent if tteellnneettdd is compiled with support for data
encryption, and indicates a willingness to decrypt the
data stream.
EENNVVIIRROONNMMEENNTT
FFIILLEESS
_/_e_t_c_/_s_e_r_v_i_c_e_s
_/_e_t_c_/_i_n_i_t_t_a_b (UNICOS systems only)
_/_e_t_c_/_i_p_t_o_s (if supported)
_/_u_s_r_/_u_c_b_/_b_f_t_p (if supported)
SSEEEE AALLSSOO
telnet(1), login(1), bftp(1) (if supported)
SSTTAANNDDAARRDDSS
RRFFCC--885544 TELNET PROTOCOL SPECIFICATION
RRFFCC--885555 TELNET OPTION SPECIFICATIONS
RRFFCC--885566 TELNET BINARY TRANSMISSION
RRFFCC--885577 TELNET ECHO OPTION
RRFFCC--885588 TELNET SUPPRESS GO AHEAD OPTION
RRFFCC--885599 TELNET STATUS OPTION
RRFFCC--886600 TELNET TIMING MARK OPTION
RRFFCC--886611 TELNET EXTENDED OPTIONS - LIST OPTION
RRFFCC--888855 TELNET END OF RECORD OPTION
RRFFCC--11007733 Telnet Window Size Option
RRFFCC--11007799 Telnet Terminal Speed Option
RRFFCC--11009911 Telnet Terminal-Type Option
RRFFCC--11009966 Telnet X Display Location Option
RRFFCC--11112233 Requirements for Internet Hosts -- Application and Support
RRFFCC--11118844 Telnet Linemode Option
RRFFCC--11337722 Telnet Remote Flow Control Option
RRFFCC--11441166 Telnet Authentication Option
RRFFCC--11441111 Telnet Authentication: Kerberos Version 4
RRFFCC--11441122 Telnet Authentication: SPX
RRFFCC--11557711 Telnet Environment Option Interoperability Issues
RRFFCC--11557722 Telnet Environment Option
BBUUGGSS
Some TELNET commands are only partially implemented.
Because of bugs in the original 4.2 BSD telnet(1), tteellnneettdd performs some
dubious protocol exchanges to try to discover if the remote client is, in
fact, a 4.2 BSD telnet(1).
Binary mode has no common interpretation except between similar operating
systems (Unix in this case).
The terminal type name received from the remote client is converted to
lower case.
TTeellnneettdd never sends TELNET IAC GA (go ahead) commands.
4.2 Berkeley Distribution February 3, 1994 5