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/1
Starts the Erlang runtime system. This function is called when the emulator is started and coordinates system start-up.
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/1
Returns all values associated with the command line user flag
%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:
rootThe installation directory of Erlang/OTP, $ROOT.
2> init:get_argument(root).
{ok,[["/usr/local/otp/releases/otp_beam_solaris8_r10b_patched"]]}
prognameThe name of the program which started Erlang.
3> init:get_argument(progname).
{ok,[["erl"]]}
homeThe home directory.
4> init:get_argument(home).
{ok,[["/home/harry"]]}
Returns error if there is no value associated with
Flag.
get_arguments/0
Returns all command line flags, as well as the system
defined flags, see get_argument/1.
get_plain_arguments/0
Returns any plain command line arguments as a list of strings (possibly empty).
get_status/0
The current status of the init process can be
inspected. During system startup (initialization),
starting, and
{progress, Info} term
interpreted in the boot script affects Info.
reboot/0
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/0
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/0
Get the identity of the boot script used to boot the system.
{Name, Vsn}. Name and
Vsn are strings.
stop/0
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/1
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 ChoiceThis 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 ExprScans, 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 haltBF
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.
-extraEverything 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