init(3erl)						     Erlang Module Definition							init(3erl)

NAME

       init - Coordination of System Startup

DESCRIPTION

       The  init  module  is  pre-loaded and contains the code for the init system process which coordinates the start-up of the system. The first
       function evaluated at start-up is boot(BootArgs) , where BootArgs is a list of command line arguments supplied to the Erlang runtime system
       from the local operating system. See erl(1) .

       init  reads  the  boot  script  which  contains	instructions  on how to initiate the system. See script(5) for more information about boot
       scripts.

       init also contains functions to restart, reboot, and stop the system.

EXPORTS

       boot(BootArgs) -> void()

	      Types  BootArgs = [binary()]

	      Starts the Erlang runtime system. This function is called when the emulator is started and coordinates system start-up.

	      BootArgs are all command line arguments except the emulator flags, that is, flags and plain arguments. See erl(1) .

	      init itself interprets some of the flags, see Command Line Flags below. The remaining flags ("user flags") and plain  arguments  are
	      passed to the init loop and can be retrieved by calling get_arguments/0 and get_plain_arguments/0 , respectively.

       get_args() -> [Arg]

	      Types  Arg = atom()

	      Returns  any  plain command line arguments as a list of atoms (possibly empty). It is recommended that get_plain_arguments/1 is used
	      instead, because of the limited length of atoms.

       get_argument(Flag) -> {ok, Arg} | error

	      Types  Flag = atom()
		     Arg = [Values]
		     Values = [string()]

	      Returns all values associated with the command line user flag Flag . If Flag is provided several times, each Values is  returned	in
	      preserved order.

	      % erl -a b c -a d
	      1> init:get_argument(a).
	      {ok,[["b","c"],["d"]]}

	      There are also a number of flags, which are defined automatically and can be retrieved using this function:

		root :
		  The installation directory of Erlang/OTP, $ROOT .

		2> init:get_argument(root).
		{ok,[["/usr/local/otp/releases/otp_beam_solaris8_r10b_patched"]]}

		progname :
		  The name of the program which started Erlang.

		3> init:get_argument(progname).
		{ok,[["erl"]]}

		home :
		  The home directory.

		4> init:get_argument(home).
		{ok,[["/home/harry"]]}

	      Returns error if there is no value associated with Flag .

       get_arguments() -> Flags

	      Types  Flags = [{Flag, Values}]
		     Flag = atom()
		     Values = [string()]

	      Returns all command line flags, as well as the system defined flags, see get_argument/1 .

       get_plain_arguments() -> [Arg]

	      Types  Arg = string()

	      Returns any plain command line arguments as a list of strings (possibly empty).

       get_status() -> {InternalStatus, ProvidedStatus}

	      Types  InternalStatus = starting | started | stopping
		     ProvidedStatus = term()

	      The  current  status  of the init process can be inspected. During system startup (initialization), InternalStatus is starting , and
	      ProvidedStatus indicates how far the boot script has been interpreted. Each {progress, Info} term interpreted  in  the  boot  script
	      affects ProvidedStatus , that is, ProvidedStatus gets the value of Info .

       reboot() -> void()

	      All applications are taken down smoothly, all code is unloaded, and all ports are closed before the system terminates. If the -heart
	      command line flag was given, the heart program will try to reboot the system. Refer to heart(3erl) for more information.

	      To limit the shutdown time, the time init is allowed to spend taking down applications, the -shutdown_time command line flag  should
	      be used.

       restart() -> void()

	      The  system  is restarted inside the running Erlang node, which means that the emulator is not restarted. All applications are taken
	      down smoothly, all code is unloaded, and all ports are closed before the system is  booted  again  in  the  same	way  as  initially
	      started. The same BootArgs are used again.

	      To  limit the shutdown time, the time init is allowed to spend taking down applications, the -shutdown_time command line flag should
	      be used.

       script_id() -> Id

	      Types  Id = term()

	      Get the identity of the boot script used to boot the system. Id can be any Erlang term. In the delivered boot scripts, Id is  {Name,
	      Vsn} . Name and Vsn are strings.

       stop() -> void()

	      All applications are taken down smoothly, all code is unloaded, and all ports are closed before the system terminates. If the -heart
	      command line flag was given, the heart program is terminated before the Erlang node terminates. Refer to heart(3erl) for more infor-
	      mation.

	      To  limit the shutdown time, the time init is allowed to spend taking down applications, the -shutdown_time command line flag should
	      be used.

       stop(Status) -> void()

	      Types  Status = int()>=0 | string()

	      All applications are taken down smoothly, all code is unloaded, and all ports are closed before the  system  terminates  by  calling
	      halt(Status)  .  If the -heart command line flag was given, the heart program is terminated before the Erlang node terminates. Refer
	      to heart(3erl) for more information.

	      To limit the shutdown time, the time init is allowed to spend taking down applications, the -shutdown_time command line flag  should
	      be used.

COMMAND LINE FLAGS

   Warning:
       The  support for loading of code from archive files is experimental. The sole purpose of releasing it before it is ready is to obtain early
       feedback. The file format, semantics, interfaces etc. may be changed in a future release. The -code_path_choice flag is also experimental.

       The init module interprets the following command line flags:

	 -- :
	   Everything following -- up to the next flag is considered plain arguments and can be retrieved using get_plain_arguments/0 .

	 -code_path_choice Choice :
	   This flag can be set to strict or relaxed . It controls whether each directory in the code path should be interpreted  strictly  as	it
	   appears  in the boot script or if init should be more relaxed and try to find a suitable directory if it can choose from a regular ebin
	   directory and an ebin directory in an archive file. This flag is particular useful when you want to elaborate with  code  loading  from
	   archives  without editing the boot script . See script(5) for more information about interpretation of boot scripts. The flag does also
	   have a similar affect on how the code server works. See code(3erl) .

	 -eval Expr :
	   Scans, parses and evaluates an arbitrary expression Expr during system initialization. If any of these steps fail (syntax error,  parse
	   error or exception during evaluation), Erlang stops with an error message. Here is an example that seeds the random number generator:

	 % erl -eval '{X,Y,Z}' = now(), random:seed(X,Y,Z).'

	   This example uses Erlang as a hexadecimal calculator:

	 % erl -noshell -eval 'R = 16#1F+16#A0, io:format("~.16B~n", [R])' \
	 -s erlang halt
	 BF

	   If  multiple  -eval	expressions are specified, they are evaluated sequentially in the order specified. -eval expressions are evaluated
	   sequentially with -s and -run function calls (this also in the order specified). As with -s and -run , an evaluation that does not ter-
	   minate, blocks the system initialization process.

	 -extra :
	   Everything following -extra is considered plain arguments and can be retrieved using get_plain_arguments/0 .

	 -run Mod [Func [Arg1, Arg2, ...]] :
	   Evaluates the specified function call during system initialization. Func defaults to start . If no arguments are provided, the function
	   is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list [Arg1,Arg2,...] as argument. All  arguments  are
	   passed as strings. If an exception is raised, Erlang stops with an error message.

	   Example:

	 % erl -run foo -run foo bar -run foo bar baz 1 2

	   This starts the Erlang runtime system and evaluates the following functions:

	 foo:start()
	 foo:bar()
	 foo:bar(["baz", "1", "2"]).

	   The	functions  are	executed sequentially in an initialization process, which then terminates normally and passes control to the user.
	   This means that a -run call which does not return will block further processing; to avoid this, use	some  variant  of  spawn  in  such
	   cases.

	 -s Mod [Func [Arg1, Arg2, ...]] :
	   Evaluates the specified function call during system initialization. Func defaults to start . If no arguments are provided, the function
	   is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list [Arg1,Arg2,...] as argument. All  arguments  are
	   passed as atoms. If an exception is raised, Erlang stops with an error message.

	   Example:

	 % erl -s foo -s foo bar -s foo bar baz 1 2

	   This starts the Erlang runtime system and evaluates the following functions:

	 foo:start()
	 foo:bar()
	 foo:bar([baz, '1', '2']).

	   The	functions  are	executed sequentially in an initialization process, which then terminates normally and passes control to the user.
	   This means that a -s call which does not return will block further processing; to avoid this, use some variant of spawn in such cases.

	   Due to the limited length of atoms, it is recommended that -run be used instead.

EXAMPLE

       % erl -- a b -children thomas claire -ages 7 3 -- x y

       1> init:get_plain_arguments().
       ["a","b","x","y"]
       2> init:get_argument(children).
       {ok,[["thomas","claire"]]}
       3> init:get_argument(ages).
       {ok, [["7","3"]]}
       4> init:get_argument(silly).
       error

SEE ALSO

       erl_prim_loader(3erl) , heart(3erl)

Ericsson AB							    erts 5.8.3								init(3erl)