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NSSWITCH.CONF(5)	    BSD	File Formats Manual	      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 databases
     containing	information regarding hosts, users (passwords),	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 sep-
     arated list of sources.  Each source can have an optional trailing	crite-
     rion 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 occurs.

     The following sources are implemented:

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

     The following databases are used by the following C library functions:

     Database  Used by
     group     getgrent(3)
     hosts     gethostbyname(3)
     networks  getnetbyname(3)
     passwd    getpwent(3)
     shells    getusershell(3)

   Status codes
     The following status codes	are available:

     Status    Description
     success   The requested entry was found.
     notfound  The entry is not	present	at this	source.
     tryagain  The source is busy, and may respond to retries.
     unavail   The source is not responding, or	entry is corrupt.

     For each of the status codes, one of two actions is possible:

     Action    Description
     continue  Try the next source
     return    Return with the current result

   Format of 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	es-
     capes 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 anything
     else (i.e,	[success=return	notfound=continue unavail=continue

   Compat mode:	+/- syntax
     In	historical multi-source	implementations, the `+' and `-' characters
     are used to specify the importing of user password	and group information
     from NIS.	Although nsswitch.conf provides	alternative methods of access-
     ing 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 `compat'.

     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 pos-
     sibly multiple sources, each of an	unknown	size.  The interfaces are
     still provided for	compatibility, but the source may not be able to pro-
     vide complete entries, or duplicate entries may be	retrieved if multiple
     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:

     Database	    Default source list
     group	    compat
     group_compat   nis
     hosts	    files dns
     passwd	    compat
     passwd_compat  nis

     /etc/nsswitch.conf	 The file nsswitch.conf	resides	in /etc.

     To	lookup hosts in	/etc/hosts and then from the DNS, and lookup user in-
     formation 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.

     nsdispatch(3), resolv.conf(5), named(8), ypbind(8)

     The nsswitch.conf file format first appeared in FreeBSD 5.0.  It was im-
     ported from the NetBSD Project, where it appeared first in	NetBSD 1.4.

     Luke Mewburn <> wrote this	freely distributable name-ser-
     vice switch implementation, using ideas from the ULTRIX svc.conf(5) and
     Solaris nsswitch.conf(4) manual pages.

BSD				 June 21, 2004				   BSD


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