config(4)                             FILES                            config(4)

       config - Configuration file.

       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

       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

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

       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.

       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

       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

       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:





       This will yield the following environment for myapp:


       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.

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

Ericsson AB                      kernel  2.12.3                        config(4)