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NSSWITCH.CONF(5)	   Linux Programmer's Manual	      NSSWITCH.CONF(5)

NAME
       nsswitch.conf - Name Service Switch configuration file

DESCRIPTION
       The  Name  Service Switch (NSS) configuration file, /etc/nsswitch.conf,
       is used by the GNU C Library to determine the  sources  from  which  to
       obtain  name-service  information in a range of categories, and in what
       order.  Each category of information is identified by a database name.

       The file is plain ASCII text, with columns separated by spaces  or  tab
       characters.  The first column specifies the database name.  The remain‐
       ing columns describe the order of sources to query and a limited set of
       actions that can be performed by lookup result.

       The following databases are understood by the GNU C Library:

       aliases	   Mail aliases, used by getaliasent(3) and related functions.

       ethers	   Ethernet numbers.

       group	   Groups of users, used by getgrent(3) and related functions.

       hosts	   Host	 names	and  numbers,  used  by	 gethostbyname(3)  and
		   related functions.

       initgroups  Supplementary group access list,  used  by  getgrouplist(3)
		   function.

       netgroup	   Network-wide	 list  of  hosts  and  users,  used for access
		   rules.  C libraries before glibc  2.1  supported  netgroups
		   only over NIS.

       networks	   Network names and numbers, used by getnetent(3) and related
		   functions.

       passwd	   User passwords, used by getpwent(3) and related functions.

       protocols   Network protocols, used by getprotoent(3) and related func‐
		   tions.

       publickey   Public and secret keys for Secure_RPC used by NFS and NIS+.

       rpc	   Remote  procedure call names and numbers, used by getrpcby‐
		   name(3) and related functions.

       services	   Network services, used by getservent(3) and	related	 func‐
		   tions.

       shadow	   Shadow  user	 passwords,  used  by  getspnam(3) and related
		   functions.

       Here is an example /etc/nsswitch.conf file:

	   passwd:	   compat
	   group:	   compat
	   shadow:	   compat

	   hosts:	   dns [!UNAVAIL=return] files
	   networks:	   nis [NOTFOUND=return] files
	   ethers:	   nis [NOTFOUND=return] files
	   protocols:	   nis [NOTFOUND=return] files
	   rpc:		   nis [NOTFOUND=return] files
	   services:	   nis [NOTFOUND=return] files

       The first column is the database name.  The remaining columns specify:

       *  One or more service specifications e.g., "files",  "db",  or	"nis".
	  The  order of the services on the line determines the order in which
	  those services will be queried, in turn, until a result is found.

       *  Optional actions to perform if a particular result is obtained  from
	  the preceding service, e.g., "[NOTFOUND=return]".

       The service specifications supported on your system depend on the pres‐
       ence of shared libraries,  and  are  therefore  extensible.   Libraries
       called  /lib/libnss_SERVICE.so.X	 will provide the named SERVICE.  On a
       standard installation, you can use "files", "db", "nis", and "nisplus".
       For  the	 hosts	database, you can additionally specify "dns".  For the
       passwd, group, and shadow databases, you can additionally specify "com‐
       pat" (see Compatibility mode below).  The version number X may be 1 for
       glibc 2.0, or 2 for glibc 2.1 and later.	 On  systems  with  additional
       libraries  installed,  you  may have access to further services such as
       "hesiod", "ldap", "winbind" and "wins".

       An action may also be specified following a service specification.  The
       action  modifies the behavior following a result obtained from the pre‐
       ceding data source.  Action items take the general form:

	   [STATUS=ACTION]
	   [!STATUS=ACTION]

       where

	   STATUS => success | notfound | unavail | tryagain
	   ACTION => return | continue

       The ! negates the test, matching all possible results  except  the  one
       specified.  The case of the keywords is not significant.

       The  STATUS  value is matched against the result of the lookup function
       called by the preceding service specification, and can be one of:

	   success     No error occurred and the requested entry is  returned.
		       The default action for this condition is "return".

	   notfound    The  lookup  succeeded, but the requested entry was not
		       found.  The default action for this condition is	 "con‐
		       tinue".

	   unavail     The  service is permanently unavailable.	 This can mean
		       either that the required file cannot be read,  or,  for
		       network	services,  that the server is not available or
		       does not allow queries.	The default  action  for  this
		       condition is "continue".

	   tryagain    The  service  is	 temporarily  unavailable.  This could
		       mean a file is locked  or  a  server  currently	cannot
		       accept  more  connections.  The default action for this
		       condition is "continue".

       The ACTION value can be one of:

	   return      Return a result now.  Do not call  any  further	lookup
		       functions.  However, for compatibility reasons, if this
		       is the selected action for the group database  and  the
		       notfound	 status,  and  the configuration file does not
		       contain the initgroups line, the next  lookup  function
		       is always called, without affecting the search result.

	   continue    Call the next lookup function.

   Compatibility mode (compat)
       The NSS "compat" service is similar to "files" except that it addition‐
       ally permits special entries in /etc/passwd for granting users or  mem‐
       bers  of	 netgroups  access  to	the system.  The following entries are
       valid in this mode:

	   +user       Include the specified user from the NIS passwd map.

	   +user:::::: Include the specified user from the NIS passwd map, but
		       override with non-empty passwd fields.

	   +@netgroup  Include all users in the given netgroup.

	   -user       Exclude the specified user from the NIS passwd map.

	   -@netgroup  Exclude all users in the given netgroup.

	   +	       Include	every  user,  except previously excluded ones,
		       from the NIS passwd map.

       By default the source is "nis", but this may be overridden by  specify‐
       ing  "nisplus"  as  the	source for the pseudo-databases passwd_compat,
       group_compat, and shadow_compat.

FILES
       A service named SERVICE is implemented by a shared object library named
       libnss_SERVICE.so.X that resides in /lib.

	   /etc/nsswitch.conf	    NSS configuration file.
	   /lib/libnss_compat.so.X  implements "compat" source.
	   /lib/libnss_db.so.X	    implements "db" source.
	   /lib/libnss_dns.so.X	    implements "dns" source.
	   /lib/libnss_files.so.X   implements "files" source.
	   /lib/libnss_hesiod.so.X  implements "hesiod" source.
	   /lib/libnss_nis.so.X	    implements "nis" source.
	   /lib/libnss_nisplus.so.X implements "nisplus" source.

NOTES
       Within  each  process  that uses nsswitch.conf, the entire file is read
       only once.  If the file is later changed,  the  process	will  continue
       using the old configuration.

       Traditionally,  there was only a single source for service information,
       often in the form of a single configuration file	 (e.g.,	 /etc/passwd).
       However,	 as  other name services, such as the Network Information Ser‐
       vice (NIS) and the Domain Name Service (DNS), became popular, a	method
       was  needed  that would be more flexible than fixed search orders coded
       into the C library.  The Name Service Switch mechanism, which was based
       on  the	mechanism used by Sun Microsystems in the Solaris 2 C library,
       introduced a cleaner solution to the problem.

SEE ALSO
       getent(1), nss(5)

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2013-02-12		      NSSWITCH.CONF(5)
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