.TH app 5 "kernel 2.15.1" "Ericsson AB" "Files"
.SH NAME
app \- Application resource file.
.SH DESCRIPTION
.LP
The \fIapplication resource file\fR\& specifies the resources an application uses, and how the application is started\&. There must always be one application resource file called \fIApplication\&.app\fR\& for each application \fIApplication\fR\& in the system\&.
.LP
The file is read by the application controller when an application is loaded/started\&. It is also used by the functions in \fIsystools\fR\&, for example when generating start scripts\&.
.SH "FILE SYNTAX"

.LP
The application resource file should be called \fIApplication\&.app\fR\& where \fIApplication\fR\& is the name of the application\&. The file should be located in the \fIebin\fR\& directory for the application\&.
.LP
It must contain one single Erlang term, which is called an \fIapplication specification\fR\&:
.LP
.nf

{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}   []
Phases       [{Phase,PhaseArgs}]  undefined
  Module = Name = App = Par = Phase = atom()
  Val = StartArgs = PhaseArgs = term()
.fi
.LP
\fIApplication\fR\& is the name of the application\&.
.LP
For the application controller, all keys are optional\&. The respective default values are used for any omitted keys\&.
.LP
The functions in \fIsystools\fR\& require more information\&. If they are used, the following keys are mandatory: \fIdescription\fR\&, \fIvsn\fR\&, \fImodules\fR\&, \fIregistered\fR\& and \fIapplications\fR\&\&. The other keys are ignored by \fIsystools\fR\&\&.
.RS 2
.TP 2
.B
\fIdescription\fR\&:
A one-line description of the application\&.
.TP 2
.B
\fIid\fR\&:
Product identification, or similar\&.
.TP 2
.B
\fIvsn\fR\&:
The version of the application\&.
.TP 2
.B
\fImodules\fR\&:
All modules introduced by this application\&. \fIsystools\fR\& uses this list when generating start scripts and tar files\&. A module can only be defined in one application\&.
.TP 2
.B
\fImaxP\fR\&:
\fIDeprecated - will be ignored\fR\& 
.br
The maximum number of processes allowed in the application\&.
.TP 2
.B
\fImaxT\fR\&:
The maximum time in milliseconds that the application is allowed to run\&. After the specified time the application will automatically terminate\&.
.TP 2
.B
\fIregistered\fR\&:
All names of registered processes started in this application\&. \fIsystools\fR\& uses this list to detect name clashes between different applications\&.
.TP 2
.B
\fIincluded_applications\fR\&:
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\&.
.TP 2
.B
\fIapplications\fR\&:
All applications which must be started before this application is allowed to be started\&. \fIsystools\fR\& uses this list to generate correct start scripts\&. Defaults to the empty list, but note that all applications have dependencies to (at least) \fIkernel\fR\& and \fIstdlib\fR\&\&.
.TP 2
.B
\fIenv\fR\&:
Configuration parameters used by the application\&. The value of a configuration parameter is retrieved by calling \fIapplication:get_env/1,2\fR\&\&. The values in the application resource file can be overridden by values in a configuration file (see \fIconfig(5)\fR\&) or by command line flags (see \fIerl(1)\fR\&)\&.
.TP 2
.B
\fImod\fR\&:
Specifies the application callback module and a start argument, see \fIapplication(3erl)\fR\&\&.
.RS 2
.LP
The \fImod\fR\& key is necessary for an application implemented as a supervision tree, or the application controller will not know how to start it\&. The \fImod\fR\& key can be omitted for applications without processes, typically code libraries such as the application STDLIB\&.
.RE

.TP 2
.B
\fIstart_phases\fR\&:
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 \fIModule:start/2\fR\& - also call \fIModule:start_phase(Phase,Type,PhaseArgs)\fR\& for each start phase defined by the \fIstart_phases\fR\& key, and only after this extended start procedure will \fIapplication:start(Application)\fR\& return\&.
.RS 2
.LP
Start phases may be used to synchronize startup of an application and its included applications\&. In this case, the \fImod\fR\& key must be specified as:
.RE

.LP
.nf

{mod, {application_starter,[Module,StartArgs]}}
.fi
.RS 2
.LP
The application master will then call \fIModule:start/2\fR\& for the primary application, followed by calls to \fIModule:start_phase/3\fR\& 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\&.
.RE

.RS 2
.LP
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 \fIOTP Design Principles\fR\& for more information\&.
.RE

.RE
.SH "SEE ALSO"

.LP
\fBapplication(3erl)\fR\&, systools(3erl)