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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 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)
                   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 func-
                   tions.
       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-
                   tions.
       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 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=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  "con-
                       tinue".
           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 addition-
       ally permits special entries in /etc/passwd for granting users or  mem-
       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.
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  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.
SEE ALSO
       getent(1), nss(5)
COLOPHON
       This  page  is  part of release 3.53 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                             2013-02-12                  NSSWITCH.CONF(5)