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 override the values in the application  resource
       files  (see  app(5)).  The  values in the configuration file can be overridden by command-line flags (see
       erts:erl(1)).

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

FILE SYNTAX

       The configuration file is to be called Name.config, where Name is any name.

       File .config contains a single Erlang term and has the following syntax:

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

         Application = atom():
           Application name.

         Par = atom():
           Name of a configuration parameter.

         Val = term():
           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 is to 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 .config file, or more .config files, leads to inconsistent update of
       application configurations. There is, however, a syntax for sys.config that  allows  pointing  out  other
       .config files:

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

         File = string():
           Name  of  another  .config  file. Extension .config can be omitted. It is recommended to use absolute
           paths. If a relative path is used, File is searched, first, relative from sys.config directory,  then
           relative  to the current working directory of the emulator, for backward compatibility. This allow to
           use a sys.config pointing out other .config files in a release or in a node  started  manually  using
           -config ... with same result whatever the current working directory.

       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 yields the following environment for myapp:

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

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

SEE ALSO

       app(5), erts:erl(1), OTP Design Principles

Ericsson AB                                       kernel 6.5.1                                         config(5)