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NAME

       config - Configuration file.

DESCRIPTION

       A  configuration  file contains values for configuration parameters for
       the applications in the system. The erl command line  argument  -config
       Name  tells  the  system  to  use data in the system configuration file
       Name.config.

       Configuration parameter values in the configuration file will  override
       the  values  in the application resource files (see app(4)). The values
       in the configuration file can be overridden by command line flags  (see
       erl(1)).

       The  value  of  a  configuration  parameter  is  retrieved  by  calling
       application:get_env/1, 2.

FILE SYNTAX

       The configuration file should be called Name.config where  Name  is  an
       arbitrary name.

       The  .config  file  contains  one  single Erlang term. The file has the
       following syntax:

       [{Application1, [{Par11, Val11}, ..]},
        ..
        {ApplicationN, [{ParN1, ValN1}, ..]}].

         * Application = atom() is the name of the application.

         * Par = atom() is the name of a configuration parameter.

         * Val = term() is the value of a configuration parameter.

sys.config

       When starting Erlang in embedded mode, it is assumed that  exactly  one
       system  configuration  file is used, named sys.config. This file should
       be located in $ROOT/releases/Vsn, where $ROOT is  the  Erlang/OTP  root
       installation directory and Vsn is the release version.

       Release  handling  relies  on  this  assumption.  When installing a new
       release version, the new sys.config is read  and  used  to  update  the
       application configurations.

       This  means that specifying another, or additional, .config files would
       lead to inconsistent update of application  configurations.  Therefore,
       in  Erlang 5.4/OTP R10B, the syntax of sys.config was extended to allow
       pointing out other .config files:

       [{Application, [{Par, Val}]} | File].

         * File = string() is the name of another .config file. The  extension
           .config  may be omitted. It is recommended to use absolute paths. A
           relative path is relative the  current  working  directory  of  the
           emulator.

       When   traversing   the  contents  of  sys.config  and  a  filename  is
       encountered, its contents are read and merged with the result  so  far.
       When an application configuration tuple {Application, Env} is found, it
       is merged with the result so far. Merging means that new parameters are
       added and existing parameter values overwritten. Example:

       sys.config:

       [{myapp,[{par1,val1},{par2,val2}]},
        "/home/user/myconfig"].

       myconfig.config:

       [{myapp,[{par2,val3},{par3,val4}]}].

       This will yield the following environment for myapp:

       [{par1,val1},{par2,val3},{par3,val4}]

       The  behaviour  if  a file specified in sys.config does not exist or is
       erroneous in some other way,  is  backwards  compatible.  Starting  the
       runtime  system  will  fail.  Installing a new release version will not
       fail, but an error message is given and the erroneous file is  ignored.

SEE ALSO

       app(4), erl(1), OTP Design Principles

AUTHORS

       Martin Björklund - support@erlang.ericsson.se
       Gunilla Arendt - support@erlang.ericsson.se