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38 .Nd NIS database server
46 is an RPC-based service designed to allow a number of UNIX-based
47 machines to share a common set of configuration files.
49 requiring a system administrator to update several copies of files
55 which tend to require frequent changes in most environments,
57 allows groups of computers to share one set of data which can be
58 updated from a single location.
62 program is the server that distributes
64 databases to client systems within an
69 domain must have its domainname set to
70 one of the domains served by
75 The clients must also run
77 in order to attach to a particular server, since it is possible to
78 have several servers within a single
82 The databases distributed by
85 .Pa /var/yp/[domainname]
88 is the name of the domain being served.
90 such directories with different domainnames, and you need only one
92 daemon to handle them all.
96 as they are often called,
99 using several system files as source.
100 The database files are in
102 format to help speed retrieval when there are many records involved.
105 the maps are always readable and writable only by root for security
107 Technically this is only necessary for the password
108 maps, but since the data in the other maps can be found in
109 other world-readable files anyway, it doesn't hurt and it's considered
110 good general practice.
114 program is started by
116 if it has been enabled in
119 There are some problems associated with distributing a
125 normally only stores encrypted passwords
127 .Pa /etc/master.passwd ,
128 which is readable and writable only by root.
132 map, this security feature would be completely defeated.
134 To make up for this, the
139 .Pa master.passwd.byname
141 .Pa master.passwd.byuid
142 maps in a special way.
143 When the server receives a request to access
144 either of these two maps, it will check the TCP port from which the
145 request originated and return an error if the port number is greater
147 Since only the superuser is allowed to bind to TCP ports
148 with values less than 1024, the server can use this test to determine
149 whether or not the access request came from a privileged user.
150 Any requests made by non-privileged users are therefore rejected.
156 standard C library will only attempt to retrieve
158 .Pa master.passwd.byname
160 .Pa master.passwd.byuid
161 maps for the superuser: if a normal user calls any of these functions,
166 maps will be accessed instead.
167 The latter two maps are constructed by
171 file and stripping out the password fields, and are therefore
172 safe to pass on to unprivileged users.
173 In this way, the shadow password
174 aspect of the protected
176 database is maintained through
179 .Ss Setting Up Master and Slave Servers
181 is a convenient script that will help setup master and slave
185 There are two problems inherent with password shadowing in
189 .Bl -enum -offset indent
192 .Sq TCP port less than 1024
193 test is trivial to defeat for users with
194 unrestricted access to machines on your network (even those machines
195 which do not run UNIX-based operating systems).
202 have no support for password shadowing (which is most of them), you
203 will have to disable the password shadowing entirely by uncommenting the
206 .Pa /var/yp/Makefile .
207 This will cause the standard
211 maps to be generated with valid encrypted password fields, which is
212 necessary in order for
214 clients to perform user
215 authentication through
220 In general, any remote user can issue an RPC to
222 and retrieve the contents of your
224 maps, provided the remote user
225 knows your domain name.
226 To prevent such unauthorized transactions,
228 supports a feature called
230 which can be used to restrict access to a given set of hosts.
233 will attempt to load the securenets information from a file
235 .Pa /var/yp/securenets .
236 (Note that this path varies depending on the path specified with
239 option, which is explained below.)
240 This file contains entries
241 that consist of a network specification and a network mask separated
245 are considered to be comments.
247 sample securenets file might look like this:
248 .Bd -unfilled -offset indent
249 # allow connections from local host -- mandatory
250 127.0.0.1 255.255.255.255
251 # allow connections from any host
252 # on the 192.168.128.0 network
253 192.168.128.0 255.255.255.0
254 # allow connections from any host
255 # between 10.0.0.0 to 10.0.15.255
256 10.0.0.0 255.255.240.0
261 receives a request from an address that matches one of these rules,
262 it will process the request normally.
263 If the address fails to match
264 a rule, the request will be ignored and a warning message will be
267 .Pa /var/yp/securenets
270 will allow connections from any host.
274 program also has support for Wietse Venema's
277 This allows the administrator to use the tcpwrapper
279 .Pa ( /etc/hosts.allow
281 .Pa /etc/hosts.deny )
282 for access control instead of
283 .Pa /var/yp/securenets .
285 Note: while both of these access control mechanisms provide some
286 security, they, like the privileged port test, are both vulnerable
291 .Ss NIS v1 compatibility
294 has some support for serving
300 implementation only uses the
302 v2 protocol, however other implementations
303 include support for the v1 protocol for backwards compatibility
307 daemons supplied with these systems will try to establish a binding
310 v1 server even though they may never actually need it (and they may
311 persist in broadcasting in search of one even after they receive a
312 response from a v2 server). Note that while
313 support for normal client calls is provided, this version of
315 does not handle v1 map transfer requests; consequently, it cannot
316 be used as a master or slave in conjunction with older
319 only support the v1 protocol.
320 Fortunately, there probably aren't any
321 such servers still in use today.
322 .Ss NIS servers that are also NIS clients
323 Care must be taken when running
325 in a multi-server domain where the server machines are also
328 It is generally a good idea to force the servers to
329 bind to themselves rather than allowing them to broadcast bind
330 requests and possibly become bound to each other: strange failure
331 modes can result if one server goes down and
332 others are dependent upon on it.
333 (Eventually all the clients will
334 time out and attempt to bind to other servers, but the delay
335 involved can be considerable and the failure mode is still present
336 since the servers might bind to each other all over again).
340 man page for details on how to force it to bind to a particular
343 The following options are supported by
347 This option affects the way
349 handles yp_match requests for the
356 can't find an entry for a given host in its hosts maps, it will
357 return an error and perform no further processing.
362 will go one step further: rather than giving up immediately, it
363 will try to resolve the hostname or address using a DNS nameserver
365 If the query is successful,
367 will construct a fake database record and return it to the client,
368 thereby making it seem as though the client's yp_match request
371 This feature is provided for compatiblity with SunOS 4.1.x,
372 which has brain-damaged resolver functions in its standard C
373 library that depend on
375 for hostname and address resolution.
378 resolver can be configured to do DNS
379 queries directly, therefore it is not necessary to enable this
380 option when serving only
385 Cause the server to run in debugging mode.
388 reports only unusual errors (access violations, file access failures)
392 In debug mode, the server does not background
393 itself and prints extra status messages to stderr for each
394 request that it receives.
395 Also, while running in debug mode,
397 will not spawn any additional subprocesses as it normally does
398 when handling yp_all requests or doing DNS lookups.
400 often take a fair amount of time to complete and are therefore handled
401 in subprocesses, allowing the parent server process to go on handling
403 This makes it easier to trace the server with
410 maps are stored under
414 flag may be used to specify an alternate
417 the system administrator to move the map files to a different place
418 within the filesystem.
421 .Bl -tag -width Pa -compact
422 .It Pa /var/yp/[domainname]/[maps]
426 .It Pa /etc/nsswitch.conf
427 name switch configuration file
428 .It Pa /var/yp/securenets
429 host access control file
435 .Xr rpc.yppasswdd 8 ,
442 .An Bill Paul Aq wpaul@ctr.columbia.edu