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nsswitch.conf(5)					      nsswitch.conf(5)

       nsswitch.conf - name-service switch configuration file

       The  nsswitch.conf  file	 specifies how the nsdispatch(3) (name-service
       switch dispatcher) routines in the C library should operate.

       The configuration file controls how a process looks  up	various	 data‐
       bases   containing  information	regarding  hosts,  users  (passwords),
       groups, net-groups, etc.	 Each database comes from a  source  (such  as
       local  files,  DNS,  and	 NIS), and the order to look up the sources is
       specified in nsswitch.conf.

       Each entry in nsswitch.conf consists of a database name,	 and  a	 space
       separated  list	of sources.  Each source can have an optional trailing
       criterion that determines whether the next listed source	 is  used,  or
       the  search  terminates at the current source.  Each criterion consists
       of one or more status codes, and actions to take if  that  status  code

       The  following  sources	may  be used: Description Local files, such as
       /etc/hosts and /etc/passwd.  Internet Domain  Name  System.   ``hosts''
       and  `networks'	use IN class entries, all other databases use HS class
       (Hesiod) entries.  NIS (formerly YP) support `+/-'  in  the  ``passwd''
       and ``group'' databases. If this is present, it must be the only source
       for that entry.

       The following databases use the switch: Used  by	 getesdfent()  getesd‐
       vent()  getesfient()  getespwent()  getestcent()	 getgrent() gethostby‐
       name() getnetgrent() getnetbyname() getpwent() getprotobyname()	getrp‐
       cent() getnameinfo()

   Status Codes
       The following status codes are available: Codes The requested entry was
       found.  The entry was not present at this source.  The source  is  busy
       and  may respond to retires.  The source is not responding, or entry is

       For each of the status codes, one if two actions is possible:  Descrip‐
       tion Try the next source.  Return with the current result.

   Format of the File
       A BNF description of the syntax of nsswitch.conf is:

       <entry>	      ::= <database> ":" [<source> [<criteria>]]*
	<criteria>     ::= "[" <criterion>+ "]"
       <criterion>    ::= <status> "=" <action>
	  <status>	 ::= "success" | "notfound" | "unavail" | "tryagain"
	  <action>	 ::= "return" | "continue"

       Each  entry starts on a new line in the file.  A `#' delimits a comment
       to end of line.	Blank lines are ignored.  A `\' at the end of  a  line
       escapes	the  newline, and causes the next line to be a continuation of
       the  current line.  All entries are case-insensitive.

       The default criteria is to return on ``success'', and continue on  any‐
       thing  else  (i.e,  [success=return  notfound=continue unavail=continue
       tryagain=continue] ).

   Compat Mode: +/- syntax
       In historical multi-source implementations, the `+' and `-'  characters
       are  used  to specify the importing of user password and group informa‐
       tion from NIS.  Although nsswitch.conf provides alternative methods  of
       accessing  distributed sources such as NIS, specifying a sole source of
       ``compat'' will provide the historical behaviour.

       An alternative source for the information accessed  via	`+/-'  can  be
       used  by specifying ``passwd_compat: source''.  ``source'' in this case
       can be `dns', `nis', or any other source except for `files'  and	 `com‐

       Historically, many of the databases had enumeration functions, often of
       the form getXXXent().  These made sense	when  the  databases  were  in
       local   files, but don't make sense or have lesser relevance when there
       are possibly multiple sources, each of an unknown size.	The interfaces
       are still provided for compatibility, but the source may not be able to
       provide complete entries, or duplicate entries may be retrieved if mul‐
       tiple sources that contain similar information are specified.

       To  ensure compatibility with previous and current implementations, the
       ``compat'' source must appear alone for a given database.

   Default Source Lists
       If, for any reason, nsswitch.conf doesn't exist, or it has  missing  or
       corrupt	entries,  nsdispatch(3)	 will default to an entry of ``files''
       for the requested database.  Exceptions are: Default Source List compat
       nis files dns files [notfound=return] nis compat nis


       To  look	 up hosts in /etc/hosts and then from the DNS, and lookup user
       information from NIS then files, use:

       hosts:	  files dns
       passwd:	  nis [notfound=return] files
       group:	  nis [notfound=return] files

       The criteria ``[notfound=return]'' sets a policy of "if the user is not
       found  in  nis, don't try files."  This treats nis as the authoritative
       source of information, except when the server is down.

       getesdfent(3),  getesdvent(3),  getesfient(3),  getespwent(3),  getest‐
       cent(3),	 getgrent()getprent(3), gethostbyname(3), getnetgrent(3), get‐
       netbyname(3), getpwent(3),  getprotobyname(3),  getnameinfo(3),	nsdis‐


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