app(5)								       Files								    app(5)

NAME

       app - Application resource file.

DESCRIPTION

       The  application  resource  file  specifies the resources an application uses, and how the application is started. There must always be one
       application resource file called Application.app for each application Application in the system.

       The file is read by the application controller when an application is loaded/started. It is also used by the functions in  systools  ,  for
       example when generating start scripts.

FILE SYNTAX

       The application resource file should be called Application.app where Application is the name of the application. The file should be located
       in the ebin directory for the application.

       It must contain one single Erlang term, which is called an application specification :

       {application, Application,
	 [{description,  Description},
	  {id,		 Id},
	  {vsn, 	 Vsn},
	  {modules,	 Modules},
	  {maxP,	 MaxP},
	  {maxT,	 MaxT},
	  {registered,	 Names},
	  {included_applications, Apps},
	  {applications, Apps},
	  {env, 	 Env},
	  {mod, 	 Start},
	  {start_phases, Phases}]}.

		    Value		 Default
		    -----		 -------
       Application  atom()		 -
       Description  string()		 ""
       Id	    string()		 ""
       Vsn	    string()		 ""
       Modules	    [Module]		 []
       MaxP	    int()		 infinity
       MaxT	    int()		 infinity
       Names	    [Name]		 []
       Apps	    [App]		 []
       Env	    [{Par,Val}] 	 []
       Start	    {Module,StartArgs}	 undefined
       Phases	    [{Phase,PhaseArgs}]  undefined
	 Module = Name = App = Par = Phase = atom()
	 Val = StartArgs = PhaseArgs = term()

       Application is the name of the application.

       For the application controller, all keys are optional. The respective default values are used for any omitted keys.

       The functions in systools require more information. If they are used, the following keys are mandatory: description , vsn , modules ,  reg-
       istered and applications . The other keys are ignored by systools .

	 description :
	   A one-line description of the application.

	 id :
	   Product identification, or similar.

	 vsn :
	   The version of the application.

	 modules :
	   All	modules  introduced by this application. systools uses this list when generating start scripts and tar files. A module can only be
	   defined in one application.

	 maxP :
	   Deprecated - will be ignored
	   The maximum number of processes allowed in the application.

	 maxT :
	   The maximum time in milliseconds that the application is allowed to run. After the specified time the  application  will  automatically
	   terminate.

	 registered :
	   All	names of registered processes started in this application. systools uses this list to detect name clashes between different appli-
	   cations.

	 included_applications :
	   All applications which are included by this application. When this application is started, all included application will  automatically
	   be  loaded,	but  not  started, by the application controller. It is assumed that the topmost supervisor of the included application is
	   started by a supervisor of this application.

	 applications :
	   All applications which must be started before this application is allowed to be started. systools uses this list  to  generate  correct
	   start scripts. Defaults to the empty list, but note that all applications have dependencies to (at least) kernel and stdlib .

	 env :
	   Configuration  parameters  used  by	the  application.  The	value  of  a  configuration  parameter	is  retrieved  by calling applica-
	   tion:get_env/1,2 . The values in the application resource file can be overridden by values in a configuration file (see config(5) )	or
	   by command line flags (see erl(1) ).

	 mod :
	   Specifies the application callback module and a start argument, see application(3erl) .

	   The mod key is necessary for an application implemented as a supervision tree, or the application controller will not know how to start
	   it. The mod key can be omitted for applications without processes, typically code libraries such as the application STDLIB.

	 start_phases :
	   A list of start phases and corresponding start arguments for the application. If this key is present, the application master will -	in
	   addition  to  the usual call to Module:start/2 - also call Module:start_phase(Phase,Type,PhaseArgs) for each start phase defined by the
	   start_phases key, and only after this extended start procedure will application:start(Application) return.

	   Start phases may be used to synchronize startup of an application and its included applications. In this case,  the	mod  key  must	be
	   specified as:

	 {mod, {application_starter,[Module,StartArgs]}}

	   The	application  master  will then call Module:start/2 for the primary application, followed by calls to Module:start_phase/3 for each
	   start phase (as defined for the primary application) both for the primary application and for each of  its  included  application,  for
	   which the start phase is defined.

	   This  implies  that	for an included application, the set of start phases must be a subset of the set of phases defined for the primary
	   application. Refer to OTP Design Principles for more information.

SEE ALSO

       application(3erl) , systools(3erl)

Ericsson AB							   kernel 2.14.3							    app(5)