NSSWITCH.CONF(5)					      BSD File Formats Manual						  NSSWITCH.CONF(5)

NAME

     nsswitch.conf -- name-service switch configuration file

DESCRIPTION

     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,
     netgroups, 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 occurs.

   Sources
     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 (Hes-
			    iod) entries.
	   mdnsd	    Use mdnsd(8) for ``hosts'' lookups, acting as both a system-wide cache for normal unicast DNS as well as providing
			    multicast DNS (``zeroconf'') lookups.
	   multicast_dns    Use mdnsd(8) only for multicast DNS ``hosts'' lookups.  This would normally be used in conjunction with ``dns'', which
			    would then provide unicast DNS resolver functions.
	   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.

   Databases
     The following databases are used by the following C library functions:
	   Database    Used by
	   group       getgrent(3)
	   hosts       gethostbyname(3)
	   netgroup    getnetgrent(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.

   Actions
     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
     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 anything 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 'compat'.

   Notes
     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
     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
	   netgroup	    files [notfound=return] nis
	   passwd	    compat
	   passwd_compat    nis

FILES

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

EXAMPLES

     To lookup 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 notfound in nis, don't try files."  This treats nis as the authoritative
     source of information, except when the server is down.

SEE ALSO

     getent(1), nsdispatch(3), resolv.conf(5), named(8), ypbind(8)

HISTORY

     The nsswitch.conf file format first appeared in NetBSD 1.4.

AUTHORS

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

BSD
								 October 25, 2009							       BSD