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

       nsswitch.conf - Name Service Switch configuration file

       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)

       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

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

       protocols   Network protocols, used by getprotoent(3) and related func-

       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-

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

       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, for example, "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

       *  Optional  actions to perform if a particular result is obtained from
	  the preceding service, for example, "[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 => success | notfound | unavail | tryagain
	   ACTION => return | continue | merge

       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-

	   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.

	   merge       [SUCCESS=merge] is used between two  database  entries.
		       When  a	group is located in the first of the two group
		       entries, processing will continue on to the  next  one.
		       If  the	group is also found in the next entry (and the
		       group name and GID are an exact match), the member list
		       of  the	second entry will be added to the group object
		       to be returned.	Available since glibc 2.24.

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

	   For passwd and shadow databases:

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

	       +@netgroup  Include all users in the given netgroup.

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

	       -@netgroup  Exclude all users in the given netgroup.

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

	   For group database:

	       +group	   Include the specified group from the NIS group map.

	       -group	   Exclude the specified group from the NIS group map.

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

       By default, the source is "nis", but this may be overridden by specify-
       ing any NSS service except  "compat"  itself  as	 the  source  for  the
       pseudo-databases passwd_compat, group_compat, and shadow_compat.

       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.

       The following files are read  when  "files"  source  is	specified  for
       respective databases:

	   aliases     /etc/aliases
	   ethers      /etc/ethers
	   group       /etc/group
	   hosts       /etc/hosts
	   initgroups  /etc/group
	   netgroup    /etc/netgroup
	   networks    /etc/networks
	   passwd      /etc/passwd
	   protocols   /etc/protocols
	   publickey   /etc/publickey
	   rpc	       /etc/rpc
	   services    /etc/services
	   shadow      /etc/shadow

       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.

       getent(1), nss(5)

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Linux				  2016-03-15		      NSSWITCH.CONF(5)