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 nsswitch.conf(4)					    nsswitch.conf(4)




 NAME
      nsswitch.conf - configuration file for the name-service switch

 SYNOPSIS
      /etc/nsswitch.conf

 DESCRIPTION
      The operating system uses a number of "databases" of information about
      hosts, users (passwd), groups and so forth.  Data for these can come
      from a variety of sources:  host-names and -addresses, for example,
      may be found in /etc/hosts, NIS, NIS+ or DNS.  One or more sources may
      be used for each database; the sources and their lookup order are
      specified in the /etc/nsswitch.conf file.

      The following databases use the switch:

	   Database	     Used by
	   aliases	     sendmail
	   automount	     automount
	   group	     getgrnam()
	   hosts	     gethostbyname()
	   netgroup	     innetgr()
	   networks	     getnetbyname()
	   passwd	     getpwnam(), getspnam()
	   protocols	     getprotobyname()
	   publickey	     getpublickey(), secure_rpc()
	   rpc		     getrpcbyname()
	   sendmailvars	     sendmail
	   services	     getservbyname()

      The following sources may be used:

	   Source	   Uses
	   files	   /etc/hosts, /etc/passwd, and so forth
	   nis		   NIS (YP)
	   nisplus	   NIS+
	   dns		   Valid only for hosts; uses the Internet Domain
			   Name Service.
	   compat	   Valid only for passwd and group; implements "+"
			   and "-".
			   (See "Interaction with +/- syntax" below)

      There is an entry in /etc/nsswitch.conf for each database.  Typically
      these entries will be simple, like "protocols: files" or "networks:
      files nisplus".  However, when multiple sources are specified it is
      sometimes necessary to define precisely the circumstances under which
      each source will be tried.  A source can return one of the following
      codes:

	   Status	   Meaning




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 nsswitch.conf(4)					    nsswitch.conf(4)




	   SUCCESS	   Requested database entry was found
	   UNAVAIL	   Source is not responding or corrupted
	   NOTFOUND	   Source responded "no such entry"
	   TRYAGAIN	   Source is busy, might respond to retries

      For each status code, two actions are possible:

	   Action	   Meaning
	   continue	   Try the next source in the list
	   return	   Return now

      The complete syntax of an entry is

	   <entry>     ::= <database> ":" [<source> [<criteria>]]* <source>
	   <criteria>  ::= "[" <criterion>+ "]"
	   <criterion> ::= <status> "=" <action>
	   <status>    ::= "success" | "notfound" | "unavail" | "tryagain"
	   <action>    ::= "return"  | "continue"

      Each entry occupies a single line in the file.  Lines that are blank,
      or that start with white space character are ignored.  Everything on a
      line following a # character is also ignored; the # character can
      begin anywhere in a line, to be used to begin comments.  The
      <database> and <source> names are case-sensitive, but <action> and
      <status> names are case-insensitive.

      The library functions contain compiled-in default entries that are
      used if the appropriate entry in nsswitch.conf is absent or
      syntactically incorrect.

      The default criteria are to continue on anything except SUCCESS; in
      other words, [SUCCESS=return NOTFOUND=continue UNAVAIL=continue
      TRYAGAIN=continue].

      The default, or explicitly specified, criteria are meaningless
      following the last source in an entry; and are ignored since the
      action is always to return to the caller irrespective of the status
      code the source returns.

    Interaction with netconfig
      In order to ensure that they all return consistent results based on
      the inet family of entries, gethostbyname(), getservbyname(), and
      netdir_getbyname() functions are all implemented in terms of the same
      internal switch library functions. These functions obtain the system-
      wide source lookup policy for hosts and services based on the inet
      family entries in netconfig().  For services and hosts only the "-" in
      the last column, which represents nametoaddr libraries, is supported.

    Interaction with NIS+ YP-compatibility Mode
      The NIS+ server can be run in "YP-compatibility mode", where it
      handles NIS (YP) requests as well as NIS+ requests.  In this case, the



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 nsswitch.conf(4)					    nsswitch.conf(4)




      clients get much the same results from the "nis" source as from
      "nisplus";  however, "nisplus" is recommended instead of "nis".

    Interaction with NIS (YP) server in DNS-forwarding Mode
      The NIS (YP) server can be run in "DNS-forwarding mode", where it
      forwards lookup requests to DNS for host-names and -addresses that do
      not exist in its database.  In this case, specifying "nis" as a source
      for "hosts" is sufficient to get DNS lookups; "dns" need not be
      specified explicitly as a source.

      The NIS+ server in "YP-compatibility mode" can also be run in "DNS-
      forwarding mode" (see rpc.nisd(1M)).  Forwarding is effective only for
      requests originating from its YP clients; "hosts" policy on these
      clients should be configured appropriately.

    Interaction with +/- syntax
      Releases prior to HP-UX 10.30 did not have the name-service switch
      support for passwd and group but did allow the user some policy
      control.	In /etc/passwd one could have entries of the form +user
      (include the specified user from NIS passwd.byname), -user (exclude
      the specified user) and + (include everything, except excluded users,
      from NIS passwd.byname).	The desired behavior was often "everything
      in the file followed by everything in NIS", expressed by a solitary +
      at the end of /etc/passwd.  The switch provides an alternative for
      this case ("passwd: files nis") that does not require + entries in
      /etc/passwd

      If this is not sufficient, the "compat" source provides full +/-
      semantics.  It reads /etc/passwd for getpwnam() functions and, if it
      finds +/- entries, invokes an appropriate source.	 By default the
      source is "nis", but this may be overridden by specifying "nisplus" as
      the source for the pseudo-database passwd_compat.

      The compat source also provides full +/- semantics for group; the
      relevant pseudo-database is group_compat.

    Useful Configurations
      The compiled-in default entries for all databases use NIS (YP) as the
      enterprise level name-service and are identical to those in the
      default configuration of this file:

	   passwd:	   files nis
	   group:	   files nis
	   hosts:	   nis [NOTFOUND=return] files
	   networks:	   nis [NOTFOUND=return] files
	   protocols:	   nis [NOTFOUND=return] files
	   rpc:		   nis [NOTFOUND=return] files
	   publickey:	   nis [NOTFOUND=return] files
	   netgroup:	   nis
	   automount:	   files nis




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	   aliases:	   files nis
	   services:	   files nis
	   sendmailvars:   files

      The policy "nis [NOTFOUND=return] files" implies "if nis is UNAVAIL,
      continue on to files, and if nis returns NOTFOUND, return to the
      caller; in other words, treat nis as the authoritative source of
      information and try files only if nis is down."

      If compatibility with the +/- syntax for passwd and group is required,
      simply modify the entries for passwd and group to:

	   passwd:	   compat
	   group:	   compat

      If NIS+ is the enterprise level name-service, the default
      configuration should be modified to use nisplus instead of nis for
      every database on client machines.  The file /etc/nsswitch.nisplus
      contains a sample configuration that can be copied to
      /etc/nsswitch.conf to set this policy.

      If the use of +/- syntax is desired in conjunction with nisplus, use
      the following four entries:

	   passwd:	   compat
	   passwd_compat:  nisplus
	   group:	   compat
	   group_compat:   nisplus

      In order to get information from the Internet Domain Name Service for
      hosts that are not listed in the enterprise level name-service, NIS+,
      use the following configuration and set up the /etc/resolv.conf file
      (see resolver(4) for more details):

	   hosts:	   nisplus dns [NOTFOUND=return] files

    Enumeration -- getXXXent()
      Many of the databases have enumeration functions: passwd has
      getpwent(), hosts has gethostent(), and so on.  These were reasonable
      when the only source was files but often make little sense for
      hierarchically structured sources that contain large numbers of
      entries, much less for multiple sources.	The interfaces are still
      provided and the implementations strive to provide reasonable results,
      but the data returned may be incomplete (enumeration for hosts is
      simply not supported by the dns source), inconsistent (if multiple
      sources are used), formatted in an unexpected fashion (for a host with
      a canonical name and three aliases, the nisplus source will return
      four hostents, and they may not be consecutive), or very expensive
      (enumerating a passwd database of 5000 users is probably a bad idea).
      Furthermore, multiple threads in the same process using the same
      reentrant enumeration function (getXXXent_r() are supported) share the



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 nsswitch.conf(4)					    nsswitch.conf(4)




      same enumeration position; if they interleave calls, they will
      enumerate disjoint subsets of the same database.

      In general the use of the enumeration functions is deprecated.  In the
      case of passwd, and group, it may sometimes be appropriate to use
      fgetgrent(), fgetpwent(), and fgetspent() (see getgrent(3C), and
      getpwent(3C), respectively), which use only the files source.

 WARNINGS
      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.

      Programs that use the getXXbyYY() functions cannot be linked
      statically since the implementation of these functions requires
      dynamic linker functionality to access the shared objects
      /usr/lib/nss_SSS.sl.1 at run time.

      The use of both nis and nisplus as sources for the same database is
      strongly discouraged since both the name-services are expected to
      store similar information and the lookups on the database may yield
      different results depending on which name-service is operational at
      the time of the request.

      Misspelled names of sources and databases will be treated as
      legitimate names of (most likely nonexistent) sources and databases.

      The following functions do not use the switch: fgetgrent(),
      fgetpwent(), fgetspent(), getpw(), and putpwent().

      Applications linked with libc.1 will display different default actions
      for NOTFOUND and TRYAGAIN.  Applications linked with libc.1 will have
      the switch search terminate if the Name Service returns a result of
      NOTFOUND or TRYAGAIN.

      This will be an issue for exisiting nsswitch.conf files that specify
      name service lookup criteria that contains no <criterion> between
      <source> entries.

      Example: hosts: dns files

      For applications linked with libc.1, the fallback to files will only
      occur if DNS returns UNAVAIL.  For all other applications, the
      fallback to files will occur unless DNS returns SUCCESS.

      For applications linked with libc.1 and other applications to have the
      same behavior, a <criterion> must be specified between <source>.

      For libc.1 behavior:





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      hosts: dns [NOTFOUND=return TRYAGAIN=return] files

      For the default system behavior:

      hosts: dns [NOTFOUND=continue TRYAGAIN=continue] files

 AUTHOR
      nsswitch.conf was developed by Sun Microsystems, Inc.

 FILES
      A source named SSS is implemented by a shared object named nss_SSS.1
      that resides in /usr/lib.

      /etc/nsswitch.conf		   configuration file
      /usr/lib/nss_compat.1		   implements "compat" source
      /usr/lib/nss_dns.1		   implements "dns" source
      /usr/lib/nss_files.1		   implements "files" source
      /usr/lib/nss_nis.1		   implements "nis" source
      /usr/lib/nss_nisplus.1		   implements "nisplus" source
      /etc/netconfig			   configuration file for netdir()
					   functions that redirects
					   hosts/services policy to the
					   switch
      /etc/nsswitch.files		   sample configuration file that
					   uses "files" only
      /etc/nsswitch.nis			   sample configuration file that
					   uses "files" and "nis"
      /etc/nsswitch.nisplus		   sample configuration file that
					   uses "files" and "nisplus"

 SEE ALSO
      nis+(1), automount(1M), rpc.nisd(1M), sendmail(1M), getgrent(3C),
      getpwent(3C), gethostent(3N), getnetent(3N), getnetgrent(3C),
      getprotoent(3N), getpublickey(3N), getrpcent(3C), getservent(3N),
      netdir(3N), secure_rpc(3N), netconfig(4), resolver(4), ypfiles(4).



















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