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config(5) Files config(5) 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(5) ). The val- ues 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 appli- cation configurations. This means that specifying another, or additional, .config files would lead to inconsistent update of application configurations. There- fore, 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(5) , erl(1) , OTP Design Principles Ericsson AB kernel 2.14.3 config(5)
