Coordination of system startup.
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(4)
.
init
also contains functions to restart, reboot, and stop
the system.
Functions
boot(BootArgs) -> no_return()
BootArgs = [binary()]
Starts the Erlang runtime system. This function is called when the emulator is started and coordinates system startup.
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
Flag = atom()
Arg = [Values :: [string()]]
Returns all values associated with the command-line user flag
. If
is provided
several times, each
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:
4> init:get_argument(home).
{ok,[["/home/harry"]]}
Returns error
if no value is associated with Flag
.
get_arguments() -> Flags
Flags = [{Flag :: atom(), Values :: [string()]}]
Returns all command-line flags and the system-defined flags, see
get_argument/1
.
get_plain_arguments() -> [Arg]
Arg = string()
Returns any plain command-line arguments as a list of strings (possibly empty).
get_status() -> {InternalStatus, ProvidedStatus}
InternalStatus = internal_status()
ProvidedStatus = term()
internal_status() = starting | started | stopping
The current status of the init
process can be
inspected. During system startup (initialization),
is starting
, and
indicates how far the boot
script has been interpreted. Each {progress, Info}
term
interpreted in the boot script affects
, that is,
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(3)
.
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 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, command-line flag
-shutdown_time
is to be used.
script_id() -> Id
Id = term()
Gets the identity of the boot script used to boot the system.
can be any Erlang term. In the delivered boot
scripts,
is {Name, Vsn}
. Name
and Vsn
are strings.
stop() -> ok
The same as
stop(0)
.
stop(Status) -> ok
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(
. If
command-line flag -heart
was specified, the heart
program is terminated before the Erlang node terminates.
For more information, see
heart(3)
.
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 regularebin
directory and anebin
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(4)
.
The flag has also a similar effect on how the code server works; see
code(3)
.
-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