2 TELNETD(8) UNIX System Manager's Manual TELNETD(8)
5 t
\bte
\bel
\bln
\bne
\bet
\btd
\bd - DARPA TELNET protocol server
7 S
\bSY
\bYN
\bNO
\bOP
\bPS
\bSI
\bIS
\bS
8 t
\bte
\bel
\bln
\bne
\bet
\btd
\bd [-
\b-B
\bBU
\bUh
\bhk
\bkl
\bln
\bn] [-
\b-D
\bD _
\bd_
\be_
\bb_
\bu_
\bg_
\bm_
\bo_
\bd_
\be] [-
\b-S
\bS _
\bt_
\bo_
\bs] [-
\b-X
\bX _
\ba_
\bu_
\bt_
\bh_
\bt_
\by_
\bp_
\be] [-
\b-a
\ba _
\ba_
\bu_
\bt_
\bh_
\bm_
\bo_
\bd_
\be]
9 [-
\b-r
\br_
\bl_
\bo_
\bw_
\bp_
\bt_
\by_
\b-_
\bh_
\bi_
\bg_
\bh_
\bp_
\bt_
\by] [-
\b-u
\bu _
\bl_
\be_
\bn] [-
\b-d
\bde
\beb
\bbu
\bug
\bg] [-
\b-L
\bL _
\b/_
\bb_
\bi_
\bn_
\b/_
\bl_
\bo_
\bg_
\bi_
\bn] [-
\b-y
\by] [_
\bp_
\bo_
\br_
\bt]
11 D
\bDE
\bES
\bSC
\bCR
\bRI
\bIP
\bPT
\bTI
\bIO
\bON
\bN
12 The t
\bte
\bel
\bln
\bne
\bet
\btd
\bd command is a server which supports the DARPA standard TELNET
13 virtual terminal protocol. T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd is normally invoked by the internet
14 server (see inetd(8)) for requests to connect to the TELNET port as in-
15 dicated by the _
\b/_
\be_
\bt_
\bc_
\b/_
\bs_
\be_
\br_
\bv_
\bi_
\bc_
\be_
\bs file (see services(5)). The -
\b-d
\bde
\beb
\bbu
\bug
\bg option
16 may be used to start up t
\bte
\bel
\bln
\bne
\bet
\btd
\bd manually, instead of through inetd(8).
17 If started up this way, _
\bp_
\bo_
\br_
\bt may be specified to run t
\bte
\bel
\bln
\bne
\bet
\btd
\bd on an alter-
20 The t
\bte
\bel
\bln
\bne
\bet
\btd
\bd command accepts the following options:
22 -
\b-a
\ba _
\ba_
\bu_
\bt_
\bh_
\bm_
\bo_
\bd_
\be This option may be used for specifying what mode should be
23 used for authentication. Note that this option is only use-
24 ful if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd has been compiled with support for the
25 AUTHENTICATION option. There are several valid values for
26 _
\ba_
\bu_
\bt_
\bh_
\bm_
\bo_
\bd_
\be:
28 debug Turns on authentication debugging code.
30 user Only allow connections when the remote user can pro-
31 vide valid authentication information to identify the
32 remote user, and is allowed access to the specified
33 account without providing a password.
35 valid Only allow connections when the remote user can pro-
36 vide valid authentication information to identify the
37 remote user. The login(1) command will provide any
38 additional user verification needed if the remote us-
39 er is not allowed automatic access to the specified
42 other Only allow connections that supply some authentica-
43 tion information. This option is currently not sup-
44 ported by any of the existing authentication mecha-
45 nisms, and is thus the same as specifying -
\b-a
\ba v
\bva
\bal
\bli
\bid
\bd.
47 otp Only allow authenticated connections (as with -
\b-a
\ba
48 u
\bus
\bse
\ber
\br) and also logins with one-time passwords (OTPs).
49 This option will call login with an option so that
50 only OTPs are accepted. The user can of course still
51 type secret information at the prompt.
53 none This is the default state. Authentication informa-
54 tion is not required. If no or insufficient authen-
55 tication information is provided, then the login(1)
56 program will provide the necessary user verification.
58 off This disables the authentication code. All user ver-
59 ification will happen through the login(1) program.
63 -
\b-D
\bD _
\bd_
\be_
\bb_
\bu_
\bg_
\bm_
\bo_
\bd_
\be
64 This option may be used for debugging purposes. This allows
65 t
\bte
\bel
\bln
\bne
\bet
\btd
\bd to print out debugging information to the connec-
66 tion, allowing the user to see what t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is doing. There
67 are several possible values for _
\bd_
\be_
\bb_
\bu_
\bg_
\bm_
\bo_
\bd_
\be:
69 o
\bop
\bpt
\bti
\bio
\bon
\bns
\bs Prints information about the negotiation of TELNET
72 r
\bre
\bep
\bpo
\bor
\brt
\bt Prints the o
\bop
\bpt
\bti
\bio
\bon
\bns
\bs information, plus some addi-
73 tional information about what processing is going
76 n
\bne
\bet
\btd
\bda
\bat
\bta
\ba Displays the data stream received by t
\bte
\bel
\bln
\bne
\bet
\btd
\bd.
78 p
\bpt
\bty
\byd
\bda
\bat
\bta
\ba Displays data written to the pty.
80 e
\bex
\bxe
\ber
\brc
\bci
\bis
\bse
\be Has not been implemented yet.
82 -
\b-h
\bh Disables the printing of host-specific information before
83 login has been completed.
89 -
\b-n
\bn Disable TCP keep-alives. Normally t
\bte
\bel
\bln
\bne
\bet
\btd
\bd enables the TCP
90 keep-alive mechanism to probe connections that have been
91 idle for some period of time to determine if the client is
92 still there, so that idle connections from machines that
93 have crashed or can no longer be reached may be cleaned up.
95 -
\b-r
\br _
\bl_
\bo_
\bw_
\bp_
\bt_
\by_
\b-_
\bh_
\bi_
\bg_
\bh_
\bp_
\bt_
\by
96 This option is only enabled when t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled for
97 UNICOS. It specifies an inclusive range of pseudo-terminal
98 devices to use. If the system has sysconf variable
99 _SC_CRAY_NPTY configured, the default pty search range is 0
100 to _SC_CRAY_NPTY; otherwise, the default range is 0 to 128.
101 Either _
\bl_
\bo_
\bw_
\bp_
\bt_
\by or _
\bh_
\bi_
\bg_
\bh_
\bp_
\bt_
\by may be omitted to allow changing
102 either end of the search range. If _
\bl_
\bo_
\bw_
\bp_
\bt_
\by is omitted, the -
103 character is still required so that t
\bte
\bel
\bln
\bne
\bet
\btd
\bd can differenti-
104 ate _
\bh_
\bi_
\bg_
\bh_
\bp_
\bt_
\by from _
\bl_
\bo_
\bw_
\bp_
\bt_
\by.
106 -
\b-S
\bS _
\bt_
\bo_
\bs
108 -
\b-u
\bu _
\bl_
\be_
\bn This option is used to specify the size of the field in the
109 utmp structure that holds the remote host name. If the re-
110 solved host name is longer than _
\bl_
\be_
\bn, the dotted decimal val-
111 ue will be used instead. This allows hosts with very long
112 host names that overflow this field to still be uniquely
113 identified. Specifying -
\b-u
\bu0
\b0 indicates that only dotted deci-
114 mal addresses should be put into the _
\bu_
\bt_
\bm_
\bp file.
116 -
\b-U
\bU This option causes t
\bte
\bel
\bln
\bne
\bet
\btd
\bd to refuse connections from ad-
117 dresses that cannot be mapped back into a symbolic name via
118 the gethostbyaddr(3) routine.
120 -
\b-X
\bX _
\ba_
\bu_
\bt_
\bh_
\bt_
\by_
\bp_
\be This option is only valid if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd has been built with
121 support for the authentication option. It disables the use
122 of _
\ba_
\bu_
\bt_
\bh_
\bt_
\by_
\bp_
\be authentication, and can be used to temporarily
123 disable a specific authentication type without having to re-
124 compile t
\bte
\bel
\bln
\bne
\bet
\btd
\bd.
126 -
\b-L
\bL _
\bp_
\ba_
\bt_
\bh_
\bn_
\ba_
\bm_
\be Specify pathname to an alternative login program.
128 -
\b-y
\by Makes t
\bte
\bel
\bln
\bne
\bet
\btd
\bd not warn when a user is trying to login with a
132 T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd operates by allocating a pseudo-terminal device (see pty(4)) for
133 a client, then creating a login process which has the slave side of the
134 pseudo-terminal as stdin, stdout and stderr. T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd manipulates the mas-
135 ter side of the pseudo-terminal, implementing the TELNET protocol and
136 passing characters between the remote client and the login process.
138 When a TELNET session is started up, t
\bte
\bel
\bln
\bne
\bet
\btd
\bd sends TELNET options to the
139 client side indicating a willingness to do the following TELNET options,
140 which are described in more detail below:
149 WILL SUPPRESS GO AHEAD
157 The pseudo-terminal allocated to the client is configured to operate in
158 ``cooked'' mode, and with XTABS and CRMOD enabled (see tty(4)).
160 T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd has support for enabling locally the following TELNET options:
162 WILL ECHO When the LINEMODE option is enabled, a WILL ECHO or
163 WONT ECHO will be sent to the client to indicate the
164 current state of terminal echoing. When terminal echo
165 is not desired, a WILL ECHO is sent to indicate that
166 telnetd will take care of echoing any data that needs
167 to be echoed to the terminal, and then nothing is
168 echoed. When terminal echo is desired, a WONT ECHO is
169 sent to indicate that telnetd will not be doing any
170 terminal echoing, so the client should do any terminal
171 echoing that is needed.
173 WILL BINARY Indicates that the client is willing to send a 8 bits
174 of data, rather than the normal 7 bits of the Network
177 WILL SGA Indicates that it will not be sending IAC GA, go
180 WILL STATUS Indicates a willingness to send the client, upon re-
181 quest, of the current status of all TELNET options.
183 WILL TIMING-MARK Whenever a DO TIMING-MARK command is received, it is
184 always responded to with a WILL TIMING-MARK
186 WILL LOGOUT When a DO LOGOUT is received, a WILL LOGOUT is sent in
187 response, and the TELNET session is shut down.
189 WILL ENCRYPT Only sent if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled with support for data
190 encryption, and indicates a willingness to decrypt the
193 T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd has support for enabling remotely the following TELNET options:
195 DO BINARY Sent to indicate that telnetd is willing to receive an
200 DO LFLOW Requests that the client handle flow control charac-
203 DO ECHO This is not really supported, but is sent to identify
204 a 4.2BSD telnet(1) client, which will improperly re-
205 spond with WILL ECHO. If a WILL ECHO is received, a
206 DONT ECHO will be sent in response.
208 DO TERMINAL-TYPE Indicates a desire to be able to request the name of
209 the type of terminal that is attached to the client
210 side of the connection.
212 DO SGA Indicates that it does not need to receive IAC GA, the
215 DO NAWS Requests that the client inform the server when the
216 window (display) size changes.
218 DO TERMINAL-SPEED Indicates a desire to be able to request information
219 about the speed of the serial line to which the client
222 DO XDISPLOC Indicates a desire to be able to request the name of
223 the X windows display that is associated with the tel-
226 DO NEW-ENVIRON Indicates a desire to be able to request environment
227 variable information, as described in RFC 1572.
229 DO ENVIRON Indicates a desire to be able to request environment
230 variable information, as described in RFC 1408.
232 DO LINEMODE Only sent if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled with support for
233 linemode, and requests that the client do line by line
236 DO TIMING-MARK Only sent if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled with support for both
237 linemode and kludge linemode, and the client responded
238 with WONT LINEMODE. If the client responds with WILL
239 TM, the it is assumed that the client supports kludge
240 linemode. Note that the [-
\b-k
\bk] option can be used to
243 DO AUTHENTICATION Only sent if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled with support for au-
244 thentication, and indicates a willingness to receive
245 authentication information for automatic login.
247 DO ENCRYPT Only sent if t
\bte
\bel
\bln
\bne
\bet
\btd
\bd is compiled with support for data
248 encryption, and indicates a willingness to decrypt the
253 /etc/inittab (UNICOS systems only)
254 /etc/iptos (if supported)
256 S
\bSE
\bEE
\bE A
\bAL
\bLS
\bSO
\bO
259 S
\bST
\bTA
\bAN
\bND
\bDA
\bAR
\bRD
\bDS
\bS
260 R
\bRF
\bFC
\bC-
\b-8
\b85
\b54
\b4 TELNET PROTOCOL SPECIFICATION
261 R
\bRF
\bFC
\bC-
\b-8
\b85
\b55
\b5 TELNET OPTION SPECIFICATIONS
264 R
\bRF
\bFC
\bC-
\b-8
\b85
\b56
\b6 TELNET BINARY TRANSMISSION
265 R
\bRF
\bFC
\bC-
\b-8
\b85
\b57
\b7 TELNET ECHO OPTION
266 R
\bRF
\bFC
\bC-
\b-8
\b85
\b58
\b8 TELNET SUPPRESS GO AHEAD OPTION
267 R
\bRF
\bFC
\bC-
\b-8
\b85
\b59
\b9 TELNET STATUS OPTION
268 R
\bRF
\bFC
\bC-
\b-8
\b86
\b60
\b0 TELNET TIMING MARK OPTION
269 R
\bRF
\bFC
\bC-
\b-8
\b86
\b61
\b1 TELNET EXTENDED OPTIONS - LIST OPTION
270 R
\bRF
\bFC
\bC-
\b-8
\b88
\b85
\b5 TELNET END OF RECORD OPTION
271 R
\bRF
\bFC
\bC-
\b-1
\b10
\b07
\b73
\b3 Telnet Window Size Option
272 R
\bRF
\bFC
\bC-
\b-1
\b10
\b07
\b79
\b9 Telnet Terminal Speed Option
273 R
\bRF
\bFC
\bC-
\b-1
\b10
\b09
\b91
\b1 Telnet Terminal-Type Option
274 R
\bRF
\bFC
\bC-
\b-1
\b10
\b09
\b96
\b6 Telnet X Display Location Option
275 R
\bRF
\bFC
\bC-
\b-1
\b11
\b12
\b23
\b3 Requirements for Internet Hosts -- Application and Support
276 R
\bRF
\bFC
\bC-
\b-1
\b11
\b18
\b84
\b4 Telnet Linemode Option
277 R
\bRF
\bFC
\bC-
\b-1
\b13
\b37
\b72
\b2 Telnet Remote Flow Control Option
278 R
\bRF
\bFC
\bC-
\b-1
\b14
\b41
\b16
\b6 Telnet Authentication Option
279 R
\bRF
\bFC
\bC-
\b-1
\b14
\b41
\b11
\b1 Telnet Authentication: Kerberos Version 4
280 R
\bRF
\bFC
\bC-
\b-1
\b14
\b41
\b12
\b2 Telnet Authentication: SPX
281 R
\bRF
\bFC
\bC-
\b-1
\b15
\b57
\b71
\b1 Telnet Environment Option Interoperability Issues
282 R
\bRF
\bFC
\bC-
\b-1
\b15
\b57
\b72
\b2 Telnet Environment Option
285 Some TELNET commands are only partially implemented.
287 Because of bugs in the original 4.2 BSD telnet(1), t
\bte
\bel
\bln
\bne
\bet
\btd
\bd performs some
288 dubious protocol exchanges to try to discover if the remote client is, in
289 fact, a 4.2 BSD telnet(1).
291 Binary mode has no common interpretation except between similar operating
292 systems (Unix in this case).
294 The terminal type name received from the remote client is converted to
297 T
\bTe
\bel
\bln
\bne
\bet
\btd
\bd never sends TELNET IAC GA (go ahead) commands.
299 4.2 Berkeley Distribution June 1, 1994 5