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41 .Nd name-service switch configuration file
45 file specifies how the
47 (name-service switch dispatcher) routines in the C library should operate.
49 The configuration file controls how a process looks up various databases
50 containing information regarding hosts, users (passwords), groups, etc.
51 Each database comes from a source (such as local files, DNS,
53 and cache), and the order to look up the sources is specified in
58 consists of a database name, and a space separated list of sources.
59 Each source can have an optional trailing criterion that determines
60 whether the next listed source is used, or the search terminates at
62 Each criterion consists of one or more status codes, and actions to
63 take if that status code occurs.
65 The following sources are implemented:
67 .Bl -tag -width Source -compact
76 Internet Domain Name System.
82 class entries, all other databases use
84 class (Hesiod) entries.
95 If this is present, it must be the only source for that entry.
102 The following databases are used by the following C library functions:
104 .Bl -tag -width networks -compact
116 .Xr gethostbyaddr 3 ,
117 .Xr gethostbyaddr_r 3 ,
118 .Xr gethostbyname 3 ,
119 .Xr gethostbyname2 3 ,
120 .Xr gethostbyname_r 3 ,
121 .Xr getipnodebyaddr 3 ,
122 .Xr getipnodebyname 3
125 .Xr getnetbyaddr_r 3 ,
141 .Xr getrpcbynumber 3 ,
144 .Xr getprotobyname 3 ,
145 .Xr getprotobynumber 3 ,
153 The following status codes are available:
155 .Bl -tag -width tryagain -compact
159 The requested entry was found.
161 The entry is not present at this source.
163 The source is busy, and may respond to retries.
165 The source is not responding, or entry is corrupt.
168 For each of the status codes, one of two actions is possible:
170 .Bl -tag -width continue -compact
176 Return with the current result
181 description of the syntax of
185 .Bl -tag -width <criterion> -compact
188 <database> ":" [<source> [<criteria>]]*
194 <status> "=" <action>
197 "success" | "notfound" | "unavail" | "tryagain"
200 "return" | "continue"
203 Each entry starts on a new line in the file.
206 delimits a comment to end of line.
207 Blank lines are ignored.
210 at the end of a line escapes the newline, and causes the next line to
211 be a continuation of the current line.
212 All entries are case-insensitive.
214 The default criteria is to return on
216 and continue on anything else (i.e,
217 .Li "[success=return notfound=continue unavail=continue tryagain=continue]" ) .
219 You can enable caching for the particular database by specifying
221 as the first source in the
224 You should also enable caching for this database in
226 If for the particular query
228 source returns success, no further sources are queried.
229 On the other hand, if there are no previously cached data, the
230 query result will be placed into the cache right after
231 all other sources are processed.
236 daemon to be running.
237 .Ss Compat mode: +/- syntax
238 In historical multi-source implementations, the
242 characters are used to specify the importing of user password and
243 group information from
247 provides alternative methods of accessing distributed sources such as
249 specifying a sole source of
251 will provide the historical behaviour.
253 An alternative source for the information accessed via
255 can be used by specifying
256 .Dq passwd_compat: source .
262 any other source except for
267 Historically, many of the databases had enumeration functions, often of
270 These made sense when the databases were in local files, but do not make
271 sense or have lesser relevance when there are possibly multiple sources,
272 each of an unknown size.
273 The interfaces are still provided for compatibility, but the source
274 may not be able to provide complete entries, or duplicate entries may
275 be retrieved if multiple sources that contain similar information are
278 To ensure compatibility with previous and current implementations, the
280 source must appear alone for a given database.
281 .Ss Default source lists
284 does not exist, or it has missing or corrupt entries,
286 will default to an entry of
288 for the requested database.
291 .Bl -tag -width services_compat -compact
293 .Sy "Default source list"
310 .Bl -tag -width /etc/nsswitch.conf -compact
311 .It Pa /etc/nsswitch.conf
318 To lookup hosts in cache, then in
320 and then from the DNS, and lookup user information from
324 .Bl -tag -width passwd: -compact
328 nis [notfound=return] files
330 nis [notfound=return] files
334 .Dq [notfound=return]
335 sets a policy of "if the user is notfound in nis, do not try files."
336 This treats nis as the authoritative source of information, except
337 when the server is down.
339 If system got compiled with
347 provides stubs for compatibility with NSS modules
353 However, these stubs only support the use of the
368 file format first appeared in
370 It was imported from the
372 Project, where it appeared first in
377 wrote this freely distributable name-service switch implementation,