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1 .\" Copyright (c) 1995
2 .\" Bill Paul <wpaul@ctr.columbia.edu>. All rights reserved.
3 .\"
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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9 .\" 2. Redistributions in binary form must reproduce the above copyright
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12 .\" 3. All advertising materials mentioning features or use of this software
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14 .\" This product includes software developed by Bill Paul.
15 .\" 4. Neither the name of the author nor the names of any co-contributors
16 .\" may be used to endorse or promote products derived from this software
17 .\" without specific prior written permission.
18 .\"
19 .\" THIS SOFTWARE IS PROVIDED BY Bill Paul AND CONTRIBUTORS ``AS IS'' AND
20 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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31 .\" $FreeBSD: src/usr.sbin/ypserv/ypserv.8,v 1.22.2.8 2002/12/29 16:35:44 schweikh Exp $
32 .\" $DragonFly: src/usr.sbin/ypserv/ypserv.8,v 1.7 2007/07/30 22:11:34 swildner Exp $
33 .\"
34 .Dd February 4, 1995
35 .Dt YPSERV 8
36 .Os
37 .Sh NAME
38 .Nm ypserv
39 .Nd NIS database server
40 .Sh SYNOPSIS
41 .Nm
42 .Op Fl n
43 .Op Fl d
44 .Op Fl p Ar path
45 .Sh DESCRIPTION
46 .Tn NIS
47 is an RPC-based service designed to allow a number of
48 .Ux Ns -based
49 machines to share a common set of configuration files.
50 Rather than
51 requiring a system administrator to update several copies of files
52 such as
53 .Pa /etc/hosts ,
54 .Pa /etc/passwd
55 and
56 .Pa /etc/group ,
57 which tend to require frequent changes in most environments,
58 .Tn NIS
59 allows groups of computers to share one set of data which can be
60 updated from a single location.
61 .Pp
62 The
63 .Nm
64 program is the server that distributes
65 .Tn NIS
66 databases to client systems within an
67 .Tn NIS
68 .Em domain .
69 Each client in an
70 .Tn NIS
71 domain must have its domainname set to
72 one of the domains served by
73 .Nm
74 using the
75 .Xr domainname 1
76 command.
77 The clients must also run
78 .Xr ypbind 8
79 in order to attach to a particular server, since it is possible to
80 have several servers within a single
81 .Tn NIS
82 domain.
83 .Pp
84 The databases distributed by
85 .Nm
86 are stored in
87 .Pa /var/yp/[domainname]
88 where
89 .Pa domainname
90 is the name of the domain being served.
91 There can be several
92 such directories with different domainnames, and you need only one
93 .Nm
94 daemon to handle them all.
95 .Pp
96 The databases, or
97 .Pa maps
98 as they are often called,
99 are created by
100 .Pa /var/yp/Makefile
101 using several system files as source.
102 The database files are in
103 .Xr db 3
104 format to help speed retrieval when there are many records involved.
105 In
106 .Dx ,
107 the maps are always readable and writable only by root for security
108 reasons.
109 Technically this is only necessary for the password
110 maps, but since the data in the other maps can be found in
111 other world-readable files anyway, it doesn't hurt and it's considered
112 good general practice.
113 .Pp
114 The
115 .Nm
116 program is started by
117 .Pa /etc/rc.network
118 if it has been enabled in
119 .Pa /etc/rc.conf .
120 .Sh SPECIAL FEATURES
121 There are some problems associated with distributing a
122 .Dx
123 password
124 database via
125 .Tn NIS Ns :
126 .Dx
127 normally only stores encrypted passwords
128 in
129 .Pa /etc/master.passwd ,
130 which is readable and writable only by root.
131 By turning this file
132 into an
133 .Tn NIS
134 map, this security feature would be completely defeated.
135 .Pp
136 To make up for this, the
137 .Dx
138 version of
139 .Nm
140 handles the
141 .Pa master.passwd.byname
142 and
143 .Pa master.passwd.byuid
144 maps in a special way.
145 When the server receives a request to access
146 either of these two maps, it will check the TCP port from which the
147 request originated and return an error if the port number is greater
148 than 1023.
149 Since only the superuser is allowed to bind to TCP ports
150 with values less than 1024, the server can use this test to determine
151 whether or not the access request came from a privileged user.
152 Any requests made by non-privileged users are therefore rejected.
153 .Pp
154 Furthermore, the
155 .Xr getpwent 3
156 routines in the
157 .Dx
158 standard C library will only attempt to retrieve
159 data from the
160 .Pa master.passwd.byname
161 and
162 .Pa master.passwd.byuid
163 maps for the superuser: if a normal user calls any of these functions,
164 the standard
165 .Pa passwd.byname
166 and
167 .Pa passwd.byuid
168 maps will be accessed instead.
169 The latter two maps are constructed by
170 .Pa /var/yp/Makefile
171 by parsing the
172 .Pa master.passwd
173 file and stripping out the password fields, and are therefore
174 safe to pass on to unprivileged users.
175 In this way, the shadow password
176 aspect of the protected
177 .Pa master.passwd
178 database is maintained through
179 .Tn NIS .
180 .Sh NOTES
181 .Ss Setting Up Master and Slave Servers
182 .Xr ypinit 8
183 is a convenient script that will help setup master and slave
184 .Tn NIS
185 servers.
186 .Ss Limitations
187 There are two problems inherent with password shadowing in
188 .Tn NIS
189 that users should
190 be aware of:
191 .Bl -enum -offset indent
192 .It
193 The
194 .Sq TCP port less than 1024
195 test is trivial to defeat for users with
196 unrestricted access to machines on your network (even those machines
197 which do not run
198 .Ux Ns -based
199 operating systems).
200 .It
201 If you plan to use a
202 .Dx
203 system to serve
204 .No non- Ns Dx Ns / Ns Fx
205 clients that
206 have no support for password shadowing (which is most of them), you
207 will have to disable the password shadowing entirely by uncommenting the
208 .Em UNSECURE=True
209 entry in
210 .Pa /var/yp/Makefile .
211 This will cause the standard
212 .Pa passwd.byname
213 and
214 .Pa passwd.byuid
215 maps to be generated with valid encrypted password fields, which is
216 necessary in order for
217 .No non- Ns Dx Ns / Ns Fx
218 clients to perform user
219 authentication through
220 .Tn NIS .
221 .El
222 .Ss Security
223 In general, any remote user can issue an RPC to
224 .Nm
225 and retrieve the contents of your
226 .Tn NIS
227 maps, provided the remote user
228 knows your domain name.
229 To prevent such unauthorized transactions,
230 .Nm
231 supports a feature called
232 .Pa securenets
233 which can be used to restrict access to a given set of hosts.
234 At startup,
235 .Nm
236 will attempt to load the securenets information from a file
237 called
238 .Pa /var/yp/securenets .
239 (Note that this path varies depending on the path specified with
240 the
241 .Fl p
242 option, which is explained below.)
243 This file contains entries
244 that consist of a network specification and a network mask separated
245 by white space.
246 Lines starting with
247 .Dq \&#
248 are considered to be comments.
249 A
250 sample securenets file might look like this:
251 .Bd -unfilled -offset indent
252 # allow connections from local host -- mandatory
253 127.0.0.1 255.255.255.255
254 # allow connections from any host
255 # on the 192.168.128.0 network
256 192.168.128.0 255.255.255.0
257 # allow connections from any host
258 # between 10.0.0.0 to 10.0.15.255
259 10.0.0.0 255.255.240.0
260 .Ed
261 .Pp
262 If
263 .Nm
264 receives a request from an address that matches one of these rules,
265 it will process the request normally.
266 If the address fails to match
267 a rule, the request will be ignored and a warning message will be
268 logged.
269 If the
270 .Pa /var/yp/securenets
271 file does not exist,
272 .Nm
273 will allow connections from any host.
274 .Pp
275 The
276 .Nm
277 program also has support for Wietse Venema's
278 .Em tcpwrapper
279 package, though it is not compiled in by default since
280 the
281 .Em tcpwrapper
282 package is not distributed with
283 .Dx .
284 However, if you have
285 .Pa libwrap.a
286 and
287 .In tcpd.h ,
288 you can easily recompile
289 .Nm
290 with them.
291 This allows the administrator to use the tcpwrapper
292 configuration files
293 .Pa ( /etc/hosts.allow
294 and
295 .Pa /etc/hosts.deny )
296 for access control instead of
297 .Pa /var/yp/securenets .
298 .Pp
299 Note: while both of these access control mechanisms provide some
300 security, they, like the privileged port test, are both vulnerable
301 to
302 .Dq IP spoofing
303 attacks.
304 .Ss NIS v1 compatibility
305 This version of
306 .Nm
307 has some support for serving
308 .Tn NIS
309 v1 clients.
310 The
311 .Dx
312 .Tn NIS
313 implementation only uses the
314 .Tn NIS
315 v2 protocol, however other implementations
316 include support for the v1 protocol for backwards compatibility
317 with older systems.
318 The
319 .Xr ypbind 8
320 daemons supplied with these systems will try to establish a binding
321 to an
322 .Tn NIS
323 v1 server even though they may never actually need it (and they may
324 persist in broadcasting in search of one even after they receive a
325 response from a v2 server). Note that while
326 support for normal client calls is provided, this version of
327 .Nm
328 does not handle v1 map transfer requests; consequently, it cannot
329 be used as a master or slave in conjunction with older
330 .Tn NIS
331 servers that
332 only support the v1 protocol.
333 Fortunately, there probably aren't any
334 such servers still in use today.
335 .Ss NIS servers that are also NIS clients
336 Care must be taken when running
337 .Nm
338 in a multi-server domain where the server machines are also
339 .Tn NIS
340 clients.
341 It is generally a good idea to force the servers to
342 bind to themselves rather than allowing them to broadcast bind
343 requests and possibly become bound to each other: strange failure
344 modes can result if one server goes down and
345 others are dependent upon on it.
346 (Eventually all the clients will
347 time out and attempt to bind to other servers, but the delay
348 involved can be considerable and the failure mode is still present
349 since the servers might bind to each other all over again).
350 .Pp
351 Refer to the
352 .Xr ypbind 8
353 man page for details on how to force it to bind to a particular
354 server.
355 .Sh OPTIONS
356 The following options are supported by
357 .Nm :
358 .Bl -tag -width flag
359 .It Fl n
360 This option affects the way
361 .Nm
362 handles yp_match requests for the
363 .Pa hosts.byname
364 and
365 .Pa hosts.byaddress
366 maps.
367 By default, if
368 .Nm
369 can't find an entry for a given host in its hosts maps, it will
370 return an error and perform no further processing.
371 With the
372 .Fl n
373 flag,
374 .Nm
375 will go one step further: rather than giving up immediately, it
376 will try to resolve the hostname or address using a DNS nameserver
377 query.
378 If the query is successful,
379 .Nm
380 will construct a fake database record and return it to the client,
381 thereby making it seem as though the client's yp_match request
382 succeeded.
383 .Pp
384 This feature is provided for compatibility with SunOS 4.1.x,
385 which has brain-damaged resolver functions in its standard C
386 library that depend on
387 .Tn NIS
388 for hostname and address resolution.
389 The
390 .Dx
391 resolver can be configured to do DNS
392 queries directly, therefore it is not necessary to enable this
393 option when serving only
394 .Dx
395 .Tn NIS
396 clients.
397 .It Fl d
398 Cause the server to run in debugging mode.
399 Normally,
400 .Nm
401 reports only unusual errors (access violations, file access failures)
402 using the
403 .Xr syslog 3
404 facility.
405 In debug mode, the server does not background
406 itself and prints extra status messages to stderr for each
407 request that it receives.
408 Also, while running in debug mode,
409 .Nm
410 will not spawn any additional subprocesses as it normally does
411 when handling yp_all requests or doing DNS lookups.
412 (These actions
413 often take a fair amount of time to complete and are therefore handled
414 in subprocesses, allowing the parent server process to go on handling
415 other requests.)
416 This makes it easier to trace the server with
417 a debugging tool.
418 .It Fl p Ar path
419 Normally,
420 .Nm
421 assumes that all
422 .Tn NIS
423 maps are stored under
424 .Pa /var/yp .
425 The
426 .Fl p
427 flag may be used to specify an alternate
428 .Tn NIS
429 root path, allowing
430 the system administrator to move the map files to a different place
431 within the filesystem.
432 .El
433 .Sh FILES
434 .Bl -tag -width Pa -compact
435 .It Pa /var/yp/[domainname]/[maps]
436 the
437 .Tn NIS
438 maps
439 .It Pa /etc/host.conf
440 resolver configuration file
441 .It Pa /var/yp/securenets
442 host access control file
443 .El
444 .Sh SEE ALSO
445 .Xr ypcat 1 ,
446 .Xr db 3 ,
447 .Xr rpc.yppasswdd 8 ,
448 .Xr yp 8 ,
449 .Xr ypbind 8 ,
450 .Xr ypinit 8 ,
451 .Xr yppush 8 ,
452 .Xr ypxfr 8
453 .Sh HISTORY
454 This version of
455 .Nm
456 first appeared in
457 .Fx 2.2 .
458 .Sh AUTHORS
459 .An Bill Paul Aq wpaul@ctr.columbia.edu