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NAME
init - Coordination of system startup.
DESCRIPTION
This module is preloaded and contains the code for the init system process that
coordinates the startup of the system. The first function evaluated at startup 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. For
more information about boot scripts, see script(5).
init also contains functions to restart, reboot, and stop the system.
DATA TYPES
mode() = embedded | interactive
Code loading mode.
EXPORTS
boot(BootArgs) -> no_return()
Types:
BootArgs = [binary()]
Starts the Erlang runtime system. This function is called when the emulator is
started and coordinates system startup.
BootArgs are all command-line arguments except the emulator flags, that is, flags
and plain arguments; see erl(1).
init interprets some of the flags, see section 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_argument(Flag) -> {ok, Arg} | error
Types:
Flag = atom()
Arg = [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. Example:
% erl -a b c -a d
...
1> init:get_argument(a).
{ok,[["b","c"],["d"]]}
The following flags 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 (on Unix, the value of $HOME):
4> init:get_argument(home).
{ok,[["/home/harry"]]}
Returns error if no value is associated with Flag.
get_arguments() -> Flags
Types:
Flags = [{Flag :: atom(), Values :: [string()]}]
Returns all command-line flags and 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 = internal_status()
ProvidedStatus = term()
internal_status() = starting | started | stopping
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() -> ok
All applications are taken down smoothly, all code is unloaded, and all ports are
closed before the system terminates. If command-line flag -heart was specified, the
heart program tries to reboot the system. For more information, see heart(3erl).
To limit the shutdown time, the time init is allowed to spend taking down
applications, command-line flag -shutdown_time is to be used.
restart() -> ok
The same as restart([]).
restart(Opts :: [{mode, mode()}]) -> ok
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 when restarting the system unless the mode option is
given, allowing the code loading mode to be set to either embedded or interactive.
All other BootArgs remain the same.
To limit the shutdown time, the time init is allowed to spend taking down
applications, command-line flag -shutdown_time is to be used.
script_id() -> Id
Types:
Id = term()
Gets 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() -> ok
The same as stop(0).
stop(Status) -> ok
Types:
Status = integer() >= 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 command-line flag
-heart was specified, the heart program is terminated before the Erlang node
terminates. For more information, see heart(3erl).
To limit the shutdown time, the time init is allowed to spend taking down
applications, command-line flag -shutdown_time is to be used.
COMMAND-LINE FLAGS
Warning:
The support for loading of code from archive files is experimental. The only purpose of
releasing it before it is ready is to obtain early feedback. The file format, semantics,
interfaces, and so on, can 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:
Can be set to strict or relaxed. It controls how each directory in the code path is to
be interpreted:
* Strictly as it appears in the boot script, or
* init is to 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. For more information about interpretation of
boot scripts, see script(5). The flag has also a similar effect on how the code server
works; see code(3erl).
-epmd_module Module:
Specifies the module to use for registration and lookup of node names. Defaults to
erl_epmd.
-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. In the following example
Erlang is used 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 terminate 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 that
does not return blocks 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 that
does not return blocks further processing; to avoid this, use some variant of spawn in
such cases.
Because of the limited length of atoms, it is recommended to use -run 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)