| blob | 95939d9b0d19373b40608348dd645eb3fcaef9b0 |
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7 .TH IN.TELNETD 8 "Oct 29, 2015"
8 .SH NAME
9 in.telnetd, telnetd \- DARPA TELNET protocol server
10 .SH SYNOPSIS
11 .LP
12 .nf
13 \fB/usr/sbin/in.telnetd\fR [\fB-a\fR \fIauthmode\fR] [\fB-EXUh\fR] [\fB-s\fR \fItos\fR]
14 [\fB-S\fR \fIkeytab\fR] [\fB-M\fR \fIrealm\fR]
15 .fi
17 .SH DESCRIPTION
18 .LP
19 \fBin.telnetd\fR is a server that supports the \fBDARPA\fR standard
20 \fBTELNET\fR virtual terminal protocol. \fBin.telnetd\fR is normally invoked in
21 the internet server (see \fBinetd\fR(8)), for requests to connect to the
22 \fBTELNET\fR port as indicated by the \fB/etc/services\fR file (see
23 \fBservices\fR(4)).
24 .sp
25 .LP
26 \fBin.telnetd\fR operates by allocating a pseudo-terminal device for a client,
27 then creating a login process which has the slave side of the pseudo-terminal
28 as its standard input, output, and error. \fBin.telnetd\fR manipulates the
29 master side of the pseudo-terminal, implementing the \fBTELNET\fR protocol and
30 passing characters between the remote client and the login process.
31 .sp
32 .LP
33 When a \fBTELNET\fR session starts up, \fBin.telnetd\fR sends \fBTELNET\fR
34 options to the client side indicating a willingness to do \fIremote\fR
35 \fBecho\fR of characters, and to \fIsuppress\fR \fIgo\fR \fIahead\fR. The
36 pseudo-terminal allocated to the client is configured to operate in "cooked"
37 mode, and with \fBXTABS\fR, \fBICRNL\fR and \fBONLCR\fR enabled. See
38 \fBtermio\fR(7I).
39 .sp
40 .LP
41 \fBin.telnetd\fR is willing to do: \fIecho\fR, \fIbinary\fR, \fIsuppress\fR
42 \fIgo\fR \fIahead\fR, and \fItiming\fR \fImark\fR. \fBin.telnetd\fR is willing
43 to have the remote client do: \fIbinary\fR, \fIterminal\fR \fItype\fR,
44 \fIterminal\fR \fIsize\fR, \fIlogout\fR \fIoption\fR, and \fIsuppress\fR
45 \fIgo\fR \fIahead\fR.
46 .sp
47 .LP
48 \fBin.telnetd\fR also allows environment variables to be passed, provided that
49 the client negotiates this during the initial option negotiation. The
50 \fBDISPLAY\fR environment variable may be sent this way, either by the
51 \fBTELNET\fR general environment passing methods, or by means of the
52 \fBXDISPLOC\fR \fBTELNET\fR option. \fBDISPLAY\fR can be passed in the
53 environment option during the same negotiation where \fBXDISPLOC\fR is used.
54 Note that if you use both methods, use the same value for both. Otherwise, the
55 results may be unpredictable.
56 .sp
57 .LP
58 These options are specified in Internet standards \fIRFC 1096\fR, \fIRFC
59 1408\fR, \fIRFC 1510\fR, \fIRFC 1571\fR, \fIRFC 2941\fR, \fIRFC 2942\fR, \fIRFC
60 2946\fR, and \fIRFC 1572\fR. The following Informational draft is also
61 supported: \fIRFC 2952\fR.
62 .sp
63 .LP
64 The banner printed by \fBin.telnetd\fR is configurable. The default is (more or
65 less) equivalent to `\fBuname\fR \fB-sr\fR` and will be used if no banner is
66 set in \fB/etc/default/telnetd\fR. To set the banner, add a line of the form
67 .sp
68 .in +2
69 .nf
70 BANNER="..."
71 .fi
72 .in -2
74 .sp
75 .LP
76 to \fB/etc/default/telnetd\fR. Nonempty banner strings are fed to shells for
77 evaluation. The default banner may be obtained by
78 .sp
79 .in +2
80 .nf
81 BANNER="\e\er\e\en\e\er\e\en`uname -s` `uname -r`\e\er\e\en\e\er\e\en"
82 .fi
83 .in -2
85 .sp
86 .LP
87 and no banner will be printed if \fB/etc/default/telnetd\fR contains
88 .sp
89 .in +2
90 .nf
91 BANNER=""
92 .fi
93 .in -2
95 .SH OPTIONS
96 .LP
97 The following options are supported:
98 .sp
99 .ne 2
100 .na
101 \fB\fB-a\fR \fIauthmode\fR\fR
102 .ad
103 .RS 15n
104 This option may be used for specifying what mode should be used for
105 authentication. There are several valid values for \fIauthmode\fR:
106 .sp
107 .ne 2
108 .na
109 \fB\fBvalid\fR\fR
110 .ad
111 .RS 9n
112 Only allows connections when the remote user can provide valid authentication
113 information to identify the remote user, and is allowed access to the specified
114 account without providing a password.
115 .RE
117 .sp
118 .ne 2
119 .na
120 \fB\fBuser\fR\fR
121 .ad
122 .RS 9n
123 Only allows connections when the remote user can provide valid authentication
124 information to identify the remote user. The \fBlogin\fR(1) command will
125 provide any additional user verification needed if the remote user is not
126 allowed automatic access to the specified account.
127 .RE
129 .sp
130 .ne 2
131 .na
132 \fB\fBnone\fR\fR
133 .ad
134 .RS 9n
135 This is the default state. Authentication information is not required. If no or
136 insufficient authentication information is provided, then the \fBlogin\fR(1)
137 program provides the necessary user verification.
138 .RE
140 .sp
141 .ne 2
142 .na
143 \fB\fBoff\fR\fR
144 .ad
145 .RS 9n
146 This disables the authentication code. All user verification happens through
147 the \fBlogin\fR(1) program.
148 .RE
150 .RE
152 .sp
153 .ne 2
154 .na
155 \fB\fB-E\fR\fR
156 .ad
157 .RS 15n
158 Disables encryption support negotiation.
159 .RE
161 .sp
162 .ne 2
163 .na
164 \fB\fB-h\fR\fR
165 .ad
166 .RS 15n
167 Disables displaying host specific information before login has been completed.
168 .RE
170 .sp
171 .ne 2
172 .na
173 \fB\fB-M\fR \fIrealm\fR\fR
174 .ad
175 .RS 15n
176 Uses the indicated Kerberos V5 realm. By default, the daemon will determine its
177 realm from the settings in the \fBkrb5.conf\fR(4) file.
178 .RE
180 .sp
181 .ne 2
182 .na
183 \fB\fB-s\fR \fItos\fR\fR
184 .ad
185 .RS 15n
186 Sets the \fBIP\fR \fBTOS\fR option.
187 .RE
189 .sp
190 .ne 2
191 .na
192 \fB\fB-S\fR \fIkeytab\fR\fR
193 .ad
194 .RS 15n
195 Sets the \fBKRB5\fR keytab file to use. The\fB/etc/krb5/krb5.keytab\fR file is
196 used by default.
197 .RE
199 .sp
200 .ne 2
201 .na
202 \fB\fB-U\fR\fR
203 .ad
204 .RS 15n
205 Refuses connections that cannot be mapped to a name through the
206 \fBgetnameinfo\fR(3SOCKET) function.
207 .RE
209 .sp
210 .ne 2
211 .na
212 \fB\fB-X\fR\fR
213 .ad
214 .RS 15n
215 Disables Kerberos V5 authentication support negotiation.
216 .RE
218 .SH USAGE
219 .LP
220 \fBtelnetd\fR and \fBin.telnetd\fR are IPv6-enabled. See \fBip6\fR(7P).
221 .SH SECURITY
222 .LP
223 \fBin.telnetd\fR can authenticate using Kerberos V5 authentication,
224 \fBpam\fR(3PAM), or both. By default, the telnet server will accept valid
225 Kerberos V5 authentication credentials from a \fBtelnet\fR client that supports
226 Kerberos. \fBin.telnetd\fR can also support an encrypted session from such a
227 client if the client requests it.
228 .sp
229 .LP
230 The \fBtelnet\fR protocol only uses single DES for session
231 protection\(emclients request service tickets with single DES session keys. The
232 KDC must know that host service principals that offer the \fBtelnet\fR service
233 support single DES, which, in practice, means that such principals must have
234 single DES keys in the KDC database.
235 .sp
236 .LP
237 In order for Kerberos authentication to work, a \fBhost/\fR\fI<FQDN>\fR
238 Kerberos principal must exist for each Fully Qualified Domain Name associated
239 with the \fBtelnetd\fR server. Each of these \fBhost/\fR\fI<FQDN>\fR principals
240 must have a \fBkeytab\fR entry in the \fB/etc/krb5/krb5.keytab\fR file on the
241 \fBtelnetd\fR server. An example principal might be:
242 .sp
243 .LP
244 \fBhost/bigmachine.eng.example.com\fR
245 .sp
246 .LP
247 See \fBkadmin\fR(8) for instructions on adding a principal to a
248 \fBkrb5.keytab\fR file. See \fI\fR for a discussion of Kerberos
249 authentication.
250 .sp
251 .LP
252 \fBin.telnetd\fR uses \fBpam\fR(3PAM) for authentication, account management,
253 session management, and password management. The \fBPAM\fR configuration
254 policy, listed through \fB/etc/pam.conf\fR, specifies the modules to be used
255 for \fBin.telnetd\fR. Here is a partial \fBpam.conf\fR file with entries for
256 the \fBtelnet\fR command using the UNIX authentication, account management,
257 session management, and password management modules.
258 .sp
259 .in +2
260 .nf
261 telnet auth requisite pam_authtok_get.so.1
262 telnet auth required pam_dhkeys.so.1
263 telnet auth required pam_unix_auth.so.1
265 telnet account requisite pam_roles.so.1
266 telnet account required pam_projects.so.1
267 telnet account required pam_unix_account.so.1
269 telnet session required pam_unix_session.so.1
271 telnet password required pam_dhkeys.so.1
272 telnet password requisite pam_authtok_get.so.1
273 telnet password requisite pam_authtok_check.so.1
274 telnet password required pam_authtok_store.so.1
275 .fi
276 .in -2
278 .sp
279 .LP
280 If there are no entries for the \fBtelnet\fR service, then the entries for the
281 "other" service will be used. If multiple authentication modules are listed,
282 then the user may be prompted for multiple passwords.
283 .sp
284 .LP
285 For a Kerberized telnet service, the correct \fBPAM\fR service name is
286 \fBktelnet\fR.
287 .SH FILES
288 .ne 2
289 .na
290 \fB\fB/etc/default/telnetd\fR\fR
291 .ad
292 .RS 24n
294 .RE
296 .SH SEE ALSO
297 .LP
298 \fBlogin\fR(1), \fBsvcs\fR(1), \fBtelnet\fR(1),
299 \fBinetadm\fR(8), \fBinetd\fR(8), \fBkadmin\fR(8), \fBsvcadm\fR(8),
300 \fBpam\fR(3PAM), \fBgetnameinfo\fR(3SOCKET), \fBissue\fR(4),
301 \fBkrb5.conf\fR(4), \fBpam.conf\fR(4), \fBservices\fR(4), \fBattributes\fR(5),
302 \fBpam_authtok_check\fR(5), \fBpam_authtok_get\fR(5),
303 \fBpam_authtok_store\fR(5), \fBpam_dhkeys\fR(5), \fBpam_passwd_auth\fR(5),
304 \fBpam_unix_account\fR(5), \fBpam_unix_auth\fR(5), \fBpam_unix_session\fR(5),
305 \fBsmf\fR(5), \fBip6\fR(7P), \fBtermio\fR(7I)
306 .sp
307 .LP
308 \fI\fR
309 .sp
310 .LP
311 Alexander, S. \fIRFC 1572, TELNET Environment Option\fR. Network Information
312 Center, SRI International, Menlo Park, Calif., January 1994.
313 .sp
314 .LP
315 Borman, Dave. \fIRFC 1408, TELNET Environment Option\fR. Network Information
316 Center, SRI International, Menlo Park, Calif., January 1993.
317 .sp
318 .LP
319 Borman, Dave. \fIRFC 1571, TELNET Environment Option Interoperability
320 Issues\fR. Network Information Center, SRI International, Menlo Park, Calif.,
321 January 1994.
322 .sp
323 .LP
324 Crispin, Mark. \fIRFC 727, TELNET Logout Option\fR. Network Information Center,
325 SRI International, Menlo Park, Calif., April 1977.
326 .sp
327 .LP
328 Marcy, G. \fIRFC 1096, TELNET X Display Location Option\fR. Network Information
329 Center, SRI International, Menlo Park, Calif., March 1989.
330 .sp
331 .LP
332 Postel, Jon, and Joyce Reynolds. \fIRFC 854, TELNET Protocol Specification\fR.
333 Network Information Center, SRI International, Menlo Park, Calif., May 1983.
334 .sp
335 .LP
336 Waitzman, D. \fIRFC 1073, TELNET Window Size Option\fR. Network Information
337 Center, SRI International, Menlo Park, Calif., October 1988.
338 .sp
339 .LP
340 Kohl, J., Neuman, C., \fIThe Kerberos Network Authentication Service (V5), RFC
341 1510\fR. September 1993.
342 .sp
343 .LP
344 Ts'o, T. and J. Altman, \fITelnet Authentication Option, RFC 2941\fR. September
345 2000.
346 .sp
347 .LP
348 Ts'o, T., \fITelnet Authentication: Kerberos Version 5, RFC 2942\fR. September
349 2000.
350 .sp
351 .LP
352 Ts'o, T., \fITelnet Data Encryption Option, RFC 2946\fR. September 2000.
353 .sp
354 .LP
355 Ts'o, T., \fITelnet Encryption: DES 64 bit Cipher Feedback, RFC 2952\fR.
356 September 2000.
357 .SH NOTES
358 .LP
359 Some \fBTELNET\fR commands are only partially implemented.
360 .sp
361 .LP
362 Binary mode has no common interpretation except between similar operating
363 systems.
364 .sp
365 .LP
366 The terminal type name received from the remote client is converted to lower
367 case.
368 .sp
369 .LP
370 The \fIpacket\fR interface to the pseudo-terminal should be used for more
371 intelligent flushing of input and output queues.
372 .sp
373 .LP
374 \fBin.telnetd\fR never sends \fBTELNET\fR \fIgo\fR \fIahead\fR commands.
375 .sp
376 .LP
377 The \fBpam_unix\fR(5) module is no longer supported.. Similar functionality is
378 provided by \fBpam_authtok_check\fR(5), \fBpam_authtok_get\fR(5),
379 \fBpam_authtok_store\fR(5), \fBpam_dhkeys\fR(5), \fBpam_passwd_auth\fR(5),
380 \fBpam_unix_account\fR(5), \fBpam_unix_auth\fR(5), and
381 \fBpam_unix_session\fR(5).
382 .sp
383 .LP
384 The \fBin.telnetd\fR service is managed by the service management facility,
385 \fBsmf\fR(5), under the service identifier:
386 .sp
387 .in +2
388 .nf
389 svc:/network/telnet
390 .fi
391 .in -2
392 .sp
394 .sp
395 .LP
396 Administrative actions on this service, such as enabling, disabling, or
397 requesting restart, can be performed using \fBsvcadm\fR(8). Responsibility for
398 initiating and restarting this service is delegated to \fBinetd\fR(8). Use
399 \fBinetadm\fR(8) to make configuration changes and to view configuration
400 information for this service. The service's status can be queried using the
401 \fBsvcs\fR(1) command.