init
Coordination of System Startup
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(4) for more
information about boot scripts.
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 start-up.
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_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.
%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
Flags = [{Flag :: atom(), Values :: [string()]}]
Returns all command line flags, as well as 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 the -heart
command line flag was given,
the heart
program will try to reboot the system. Refer
to heart(3)
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() -> 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, the -shutdown_time
command line flag should be used.
script_id() -> Id
Id = term()
Get 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
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(3)
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.
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 the
-heart
command line flag was given, the heart
program is terminated before the Erlang node
terminates. Refer to heart(3)
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(4) for more information
about interpretation of boot scripts. The flag does also have
a similar affect on how the code server works. See code(3).
-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 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 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