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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  ap-
       plication resource file called Application.app for each application Ap-
       plication 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 exam-
       ple when	generating start scripts.

FILE SYNTAX
       The application resource	file is	to be  called  Application.app,	 where
       Application  is	the application	name. The file is to be	located	in di-
       rectory ebin for	the application.

       The file	must contain a single Erlang term, which is called an applica-
       tion 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},
	  {runtime_dependencies, RTDeps}]}.

		    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}	 []
       Phases	    [{Phase,PhaseArgs}]	 undefined
       RTDeps	    [ApplicationVersion] []

       Module =	Name = App = Par = Phase = atom()
       Val = StartArgs = PhaseArgs = term()
       ApplicationVersion = string()

	 Application:
	   Application name.

       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

	 * registered

	 * applications

       The other keys are ignored by systools.

	 description:
	   A one-line description of the application.

	 id:
	   Product identification, or similar.

	 vsn:
	   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 -	is ignored

	   Maximum number of processes allowed in the application.

	 maxT:
	   Maximum  time,  in milliseconds, that the application is allowed to
	   run.	After the specified time, the application terminates automati-
	   cally.

	 registered:
	   All names of	registered processes started in	this application. sys-
	   tools uses this list	to detect name clashes between	different  ap-
	   plications.

	 included_applications:
	   All	applications  included by this application. When this applica-
	   tion	is started, all	included  applications	are  loaded  automati-
	   cally,  but	not  started, by the application controller. It	is as-
	   sumed that the top-most supervisor of the included  application  is
	   started by a	supervisor of this application.

	 applications:
	   All	applications  that  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 notice that all ap-
	   plications 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(4)) or
	   by command-line flags (see erts:erl(1)).

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

	   Key	mod  is	necessary for an application implemented as a supervi-
	   sion	tree, otherwise	the application	controller does	not  know  how
	   to start it.	mod can	be omitted for applications without processes,
	   typically code libraries, for example, STDLIB.

	 start_phases:
	   A list of start phases and corresponding start  arguments  for  the
	   application.	If this	key is present,	the application	master,	in ad-
	   dition to  the  usual  call	to  Module:start/2,  also  calls  Mod-
	   ule:start_phase(Phase,Type,PhaseArgs)  for each start phase defined
	   by key start_phases.	Only after this	extended start procedure,  ap-
	   plication:start(Application)	returns.

	   Start  phases  can be used to synchronize startup of	an application
	   and its included applications. In this case,	key mod	must be	speci-
	   fied	as follows:

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

	   The	application  master  then calls	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 applications,  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  pri-
	   mary	application. For more information, see OTP Design Principles.

	 runtime_dependencies:
	   A  list of application versions that	the application	depends	on. An
	   example of such an application version is "kernel-3.0". Application
	   versions  specified	as  runtime  dependencies are minimum require-
	   ments. That is, a larger application	version	than the one specified
	   in  the dependency satisfies	the requirement. For information about
	   how to compare application versions,	see section  Versions  in  the
	   System Principles User's Guide.

	   Notice  that	 the  application version specifies a source code ver-
	   sion. One more, indirect, requirement is that the installed	binary
	   application of the specified	version	is built so that it is compat-
	   ible	with the rest of the system.

	   Some	dependencies can only be required in specific runtime  scenar-
	   ios.	When such optional dependencies	exist, these are specified and
	   documented in the corresponding "App" documentation of the specific
	   application.

     Warning:
	 The  runtime_dependencies key was introduced in OTP 17.0. The type of
	 its value might be subject to changes during the OTP 17 release.

     Warning:
	 All runtime dependencies specified in OTP applications	during the OTP
	 17  release  may  not	be  completely correct.	This is	actively being
	 worked	on. Declared runtime dependencies in OTP applications are  ex-
	 pected	to be correct in OTP 18.

SEE ALSO
       application(3), systools(3)

Ericsson AB			  kernel 6.3				app(5)

NAME | DESCRIPTION | FILE SYNTAX | SEE ALSO

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