In addition to the postgresql.conf file
      already mentioned, PostgreSQL uses
      two other manually-edited configuration files, which control
      client authentication (their use is discussed in Chapter 20).  By default, all three
      configuration files are stored in the database cluster's data
      directory.  The parameters described in this section allow the
      configuration files to be placed elsewhere.  (Doing so can ease
      administration.  In particular it is often easier to ensure that
      the configuration files are properly backed-up when they are
      kept separate.)
     
data_directory (string)
      
       #Specifies the directory to use for data storage. This parameter can only be set at server start.
config_file (string)
      
       #
         Specifies the main server configuration file
         (customarily called postgresql.conf).
         This parameter can only be set on the postgres command line.
       
hba_file (string)
      
       #
         Specifies the configuration file for host-based authentication
         (customarily called pg_hba.conf).
         This parameter can only be set at server start.
       
ident_file (string)
      
       #
         Specifies the configuration file for user name mapping
         (customarily called pg_ident.conf).
         This parameter can only be set at server start.
         See also Section 20.2.
       
external_pid_file (string)
      
       #Specifies the name of an additional process-ID (PID) file that the server should create for use by server administration programs. This parameter can only be set at server start.
      In a default installation, none of the above parameters are set
      explicitly.  Instead, the
      data directory is specified by the -D command-line
      option or the PGDATA environment variable, and the
      configuration files are all found within the data directory.
     
      If you wish to keep the configuration files elsewhere than the
      data directory, the postgres -D
      command-line option or PGDATA environment variable
      must point to the directory containing the configuration files,
      and the data_directory parameter must be set in
      postgresql.conf (or on the command line) to show
      where the data directory is actually located.  Notice that
      data_directory overrides -D and
      PGDATA for the location
      of the data directory, but not for the location of the configuration
      files.
     
      If you wish, you can specify the configuration file names and locations
      individually using the parameters config_file,
      hba_file and/or ident_file.
      config_file can only be specified on the
      postgres command line, but the others can be
      set within the main configuration file.  If all three parameters plus
      data_directory are explicitly set, then it is not necessary
      to specify -D or PGDATA.
     
      When setting any of these parameters, a relative path will be interpreted
      with respect to the directory in which postgres
      is started.