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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 1.2 2003/06/17 04:30:05 dillon Exp $
39 .Nd NIS database server
47 is an RPC-based service designed to allow a number of UNIX-based
48 machines to share a common set of configuration files.
50 requiring a system administrator to update several copies of files
56 which tend to require frequent changes in most environments,
58 allows groups of computers to share one set of data which can be
59 updated from a single location.
63 program is the server that distributes
65 databases to client systems within an
70 domain must have its domainname set to
71 one of the domains served by
76 The clients must also run
78 in order to attach to a particular server, since it is possible to
79 have several servers within a single
83 The databases distributed by
86 .Pa /var/yp/[domainname]
89 is the name of the domain being served.
91 such directories with different domainnames, and you need only one
93 daemon to handle them all.
97 as they are often called,
100 using several system files as source.
101 The database files are in
103 format to help speed retrieval when there are many records involved.
106 the maps are always readable and writable only by root for security
108 Technically this is only necessary for the password
109 maps, but since the data in the other maps can be found in
110 other world-readable files anyway, it doesn't hurt and it's considered
111 good general practice.
115 program is started by
117 if it has been enabled in
120 There are some problems associated with distributing a
126 normally only stores encrypted passwords
128 .Pa /etc/master.passwd ,
129 which is readable and writable only by root.
133 map, this security feature would be completely defeated.
135 To make up for this, the
140 .Pa master.passwd.byname
142 .Pa master.passwd.byuid
143 maps in a special way.
144 When the server receives a request to access
145 either of these two maps, it will check the TCP port from which the
146 request originated and return an error if the port number is greater
148 Since only the superuser is allowed to bind to TCP ports
149 with values less than 1024, the server can use this test to determine
150 whether or not the access request came from a privileged user.
151 Any requests made by non-privileged users are therefore rejected.
157 standard C library will only attempt to retrieve
159 .Pa master.passwd.byname
161 .Pa master.passwd.byuid
162 maps for the superuser: if a normal user calls any of these functions,
167 maps will be accessed instead.
168 The latter two maps are constructed by
172 file and stripping out the password fields, and are therefore
173 safe to pass on to unprivileged users.
174 In this way, the shadow password
175 aspect of the protected
177 database is maintained through
180 .Ss Setting Up Master and Slave Servers
182 is a convenient script that will help setup master and slave
186 There are two problems inherent with password shadowing in
190 .Bl -enum -offset indent
193 .Sq TCP port less than 1024
194 test is trivial to defeat for users with
195 unrestricted access to machines on your network (even those machines
196 which do not run UNIX-based operating systems).
203 have no support for password shadowing (which is most of them), you
204 will have to disable the password shadowing entirely by uncommenting the
207 .Pa /var/yp/Makefile .
208 This will cause the standard
212 maps to be generated with valid encrypted password fields, which is
213 necessary in order for
215 clients to perform user
216 authentication through
221 In general, any remote user can issue an RPC to
223 and retrieve the contents of your
225 maps, provided the remote user
226 knows your domain name.
227 To prevent such unauthorized transactions,
229 supports a feature called
231 which can be used to restrict access to a given set of hosts.
234 will attempt to load the securenets information from a file
236 .Pa /var/yp/securenets .
237 (Note that this path varies depending on the path specified with
240 option, which is explained below.)
241 This file contains entries
242 that consist of a network specification and a network mask separated
246 are considered to be comments.
248 sample securenets file might look like this:
249 .Bd -unfilled -offset indent
250 # allow connections from local host -- mandatory
251 127.0.0.1 255.255.255.255
252 # allow connections from any host
253 # on the 192.168.128.0 network
254 192.168.128.0 255.255.255.0
255 # allow connections from any host
256 # between 10.0.0.0 to 10.0.15.255
257 10.0.0.0 255.255.240.0
262 receives a request from an address that matches one of these rules,
263 it will process the request normally.
264 If the address fails to match
265 a rule, the request will be ignored and a warning message will be
268 .Pa /var/yp/securenets
271 will allow connections from any host.
275 program also has support for Wietse Venema's
277 package, though it is not compiled in by default since
280 package is not distributed with
286 you can easily recompile
289 This allows the administrator to use the tcpwrapper
291 .Pa ( /etc/hosts.allow
293 .Pa /etc/hosts.deny )
294 for access control instead of
295 .Pa /var/yp/securenets .
297 Note: while both of these access control mechanisms provide some
298 security, they, like the privileged port test, are both vulnerable
303 .Ss NIS v1 compatibility
306 has some support for serving
312 implementation only uses the
314 v2 protocol, however other implementations
315 include support for the v1 protocol for backwards compatibility
319 daemons supplied with these systems will try to establish a binding
322 v1 server even though they may never actually need it (and they may
323 persist in broadcasting in search of one even after they receive a
324 response from a v2 server). Note that while
325 support for normal client calls is provided, this version of
327 does not handle v1 map transfer requests; consequently, it cannot
328 be used as a master or slave in conjunction with older
331 only support the v1 protocol.
332 Fortunately, there probably aren't any
333 such servers still in use today.
334 .Ss NIS servers that are also NIS clients
335 Care must be taken when running
337 in a multi-server domain where the server machines are also
340 It is generally a good idea to force the servers to
341 bind to themselves rather than allowing them to broadcast bind
342 requests and possibly become bound to each other: strange failure
343 modes can result if one server goes down and
344 others are dependent upon on it.
345 (Eventually all the clients will
346 time out and attempt to bind to other servers, but the delay
347 involved can be considerable and the failure mode is still present
348 since the servers might bind to each other all over again).
352 man page for details on how to force it to bind to a particular
355 The following options are supported by
359 This option affects the way
361 handles yp_match requests for the
368 can't find an entry for a given host in its hosts maps, it will
369 return an error and perform no further processing.
374 will go one step further: rather than giving up immediately, it
375 will try to resolve the hostname or address using a DNS nameserver
377 If the query is successful,
379 will construct a fake database record and return it to the client,
380 thereby making it seem as though the client's yp_match request
383 This feature is provided for compatibility with SunOS 4.1.x,
384 which has brain-damaged resolver functions in its standard C
385 library that depend on
387 for hostname and address resolution.
390 resolver can be configured to do DNS
391 queries directly, therefore it is not necessary to enable this
392 option when serving only
397 Cause the server to run in debugging mode.
400 reports only unusual errors (access violations, file access failures)
404 In debug mode, the server does not background
405 itself and prints extra status messages to stderr for each
406 request that it receives.
407 Also, while running in debug mode,
409 will not spawn any additional subprocesses as it normally does
410 when handling yp_all requests or doing DNS lookups.
412 often take a fair amount of time to complete and are therefore handled
413 in subprocesses, allowing the parent server process to go on handling
415 This makes it easier to trace the server with
422 maps are stored under
426 flag may be used to specify an alternate
429 the system administrator to move the map files to a different place
430 within the filesystem.
433 .Bl -tag -width Pa -compact
434 .It Pa /var/yp/[domainname]/[maps]
438 .It Pa /etc/host.conf
439 resolver configuration file
440 .It Pa /var/yp/securenets
441 host access control file
446 .Xr rpc.yppasswdd 8 ,
453 .An Bill Paul Aq wpaul@ctr.columbia.edu