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
       remaining 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.

       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 functions.

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

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

       services    Network services, used by getservent(3) and related functions.

       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 presence 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  "nis-
       plus".	For  the  hosts  database,  you can additionally specify "dns".  For the passwd, group, and shadow databases, you can additionally
       specify "compat" (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
       preceding 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 "continue".

	   unavail     The service is permanently unavailable.	This can mean either that the required file cannot be read, or, for  network  ser-
		       vices, 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 connec-
		       tions.  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.

	   continue    Call the next lookup function.

   Compatibility mode (compat)
       The NSS "compat" service is similar to "files" except that it additionally permits special entries in /etc/passwd  for  granting  users	or
       members 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 specifying "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 Service (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 mecha-
       nism, 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 3.44 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								    2012-04-14							  NSSWITCH.CONF(5)