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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.

       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
                   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, 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
          found.

       *  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
       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 "nisplus".
       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 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
       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 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 3.65 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/.



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