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           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
           *  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/  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
           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".
           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.
               +@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.


           A service named SERVICE is implemented by a shared object library named
  that resides in /lib.
               /etc/nsswitch.conf       NSS configuration file.
               /lib/  implements "compat" source.
               /lib/      implements "db" source.
               /lib/     implements "dns" source.
               /lib/   implements "files" source.
               /lib/  implements "hesiod" source.
               /lib/     implements "nis" source.
               /lib/ implements "nisplus" source.


           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)

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


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