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authorErlang/OTP <otp@erlang.org>2009-11-20 14:54:40 +0000
committerErlang/OTP <otp@erlang.org>2009-11-20 14:54:40 +0000
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The R13B03 release.OTP_R13B03
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+<?xml version="1.0" encoding="latin1" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+ <header>
+ <copyright>
+ <year>1996</year><year>2009</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ The contents of this file are subject to the Erlang Public License,
+ Version 1.1, (the "License"); you may not use this file except in
+ compliance with the License. You should have received a copy of the
+ Erlang Public License along with this software. If not, it can be
+ retrieved online at http://www.erlang.org/.
+
+ Software distributed under the License is distributed on an "AS IS"
+ basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ the License for the specific language governing rights and limitations
+ under the License.
+
+ </legalnotice>
+
+ <title>init</title>
+ <prepared></prepared>
+ <docno></docno>
+ <date></date>
+ <rev></rev>
+ <file>init.xml</file>
+ </header>
+ <module>init</module>
+ <modulesummary>Coordination of System Startup</modulesummary>
+ <description>
+ <p>The <c>init</c> module is pre-loaded and contains the code for
+ the <c>init</c> system process which coordinates the start-up of
+ the system. The first function evaluated at start-up is
+ <c>boot(BootArgs)</c>, where <c>BootArgs</c> is a list of command
+ line arguments supplied to the Erlang runtime system from
+ the local operating system. See
+ <seealso marker="erts:erl">erl(1)</seealso>.</p>
+ <p><c>init</c> reads the boot script which contains instructions on
+ how to initiate the system. See
+ <seealso marker="sasl:script">script(4)</seealso> for more
+ information about boot scripts.</p>
+ <p><c>init</c> also contains functions to restart, reboot, and stop
+ the system.</p>
+ </description>
+ <funcs>
+ <func>
+ <name>boot(BootArgs) -> void()</name>
+ <fsummary>Start the Erlang runtime system</fsummary>
+ <type>
+ <v>BootArgs = [binary()]</v>
+ </type>
+ <desc>
+ <p>Starts the Erlang runtime system. This function is called
+ when the emulator is started and coordinates system start-up.</p>
+ <p><c>BootArgs</c> are all command line arguments except
+ the emulator flags, that is, flags and plain arguments. See
+ <seealso marker="erts:erl">erl(1)</seealso>.</p>
+ <p><c>init</c> itself interprets some of the flags, see
+ <seealso marker="#flags">Command Line Flags</seealso> below.
+ The remaining flags ("user flags") and plain arguments are
+ passed to the <c>init</c> loop and can be retrieved by calling
+ <c>get_arguments/0</c> and <c>get_plain_arguments/0</c>,
+ respectively.</p>
+ </desc>
+ </func>
+ <func>
+ <name>get_args() -> [Arg]</name>
+ <fsummary>Get all non-flag command line arguments</fsummary>
+ <type>
+ <v>Arg = atom()</v>
+ </type>
+ <desc>
+ <p>Returns any plain command line arguments as a list of atoms
+ (possibly empty). It is recommended that
+ <c>get_plain_arguments/1</c> is used instead, because of
+ the limited length of atoms.</p>
+ </desc>
+ </func>
+ <func>
+ <name>get_argument(Flag) -> {ok, Arg} | error</name>
+ <fsummary>Get the values associated with a command line user flag</fsummary>
+ <type>
+ <v>Flag = atom()</v>
+ <v>Arg = [Values]</v>
+ <v>&nbsp;Values = [string()]</v>
+ </type>
+ <desc>
+ <p>Returns all values associated with the command line user flag
+ <c>Flag</c>. If <c>Flag</c> is provided several times, each
+ <c>Values</c> is returned in preserved order.</p>
+ <pre>
+% <input>erl -a b c -a d</input>
+...
+1> <input>init:get_argument(a).</input>
+{ok,[["b","c"],["d"]]}</pre>
+ <p>There are also a number of flags, which are defined
+ automatically and can be retrieved using this function:</p>
+ <taglist>
+ <tag><c>root</c></tag>
+ <item>
+ <p>The installation directory of Erlang/OTP, <c>$ROOT</c>.</p>
+ <pre>
+2> <input>init:get_argument(root).</input>
+{ok,[["/usr/local/otp/releases/otp_beam_solaris8_r10b_patched"]]}</pre>
+ </item>
+ <tag><c>progname</c></tag>
+ <item>
+ <p>The name of the program which started Erlang.</p>
+ <pre>
+3> <input>init:get_argument(progname).</input>
+{ok,[["erl"]]}</pre>
+ </item>
+ <tag><c>home</c></tag>
+ <item>
+ <p>The home directory.</p>
+ <pre>
+4> <input>init:get_argument(home).</input>
+{ok,[["/home/harry"]]}</pre>
+ </item>
+ </taglist>
+ <p>Returns <c>error</c> if there is no value associated with
+ <c>Flag</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>get_arguments() -> Flags</name>
+ <fsummary>Get all command line user flags</fsummary>
+ <type>
+ <v>Flags = [{Flag, Values}]</v>
+ <v>&nbsp;Flag = atom()</v>
+ <v>&nbsp;Values = [string()]</v>
+ </type>
+ <desc>
+ <p>Returns all command line flags, as well as the system
+ defined flags, see <c>get_argument/1</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>get_plain_arguments() -> [Arg]</name>
+ <fsummary>Get all non-flag command line arguments</fsummary>
+ <type>
+ <v>Arg = string()</v>
+ </type>
+ <desc>
+ <p>Returns any plain command line arguments as a list of strings
+ (possibly empty).</p>
+ </desc>
+ </func>
+ <func>
+ <name>get_status() -> {InternalStatus, ProvidedStatus}</name>
+ <fsummary>Get system status information</fsummary>
+ <type>
+ <v>InternalStatus = starting | started | stopping</v>
+ <v>ProvidedStatus = term()</v>
+ </type>
+ <desc>
+ <p>The current status of the <c>init</c> process can be
+ inspected. During system startup (initialization),
+ <c>InternalStatus</c> is <c>starting</c>, and
+ <c>ProvidedStatus</c> indicates how far the boot script has
+ been interpreted. Each <c>{progress, Info}</c> term
+ interpreted in the boot script affects <c>ProvidedStatus</c>,
+ that is, <c>ProvidedStatus</c> gets the value of <c>Info</c>.</p>
+ </desc>
+ </func>
+ <func>
+ <name>reboot() -> void()</name>
+ <fsummary>Take down and restart an Erlang node smoothly</fsummary>
+ <desc>
+ <p>All applications are taken down smoothly, all code is
+ unloaded, and all ports are closed before the system
+ terminates. If the <c>-heart</c> command line flag was given,
+ the <c>heart</c> program will try to reboot the system. Refer
+ to <c>heart(3)</c> for more information.</p>
+ <p>To limit the shutdown time, the time <c>init</c> is allowed
+ to spend taking down applications, the <c>-shutdown_time</c>
+ command line flag should be used.</p>
+ </desc>
+ </func>
+ <func>
+ <name>restart() -> void()</name>
+ <fsummary>Restart the running Erlang node</fsummary>
+ <desc>
+ <p>The system is restarted <em>inside</em> 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 <c>BootArgs</c>
+ are used again.</p>
+ <p>To limit the shutdown time, the time <c>init</c> is allowed
+ to spend taking down applications, the <c>-shutdown_time</c>
+ command line flag should be used.</p>
+ </desc>
+ </func>
+ <func>
+ <name>script_id() -> Id</name>
+ <fsummary>Get the identity of the used boot script</fsummary>
+ <type>
+ <v>Id = term()</v>
+ </type>
+ <desc>
+ <p>Get the identity of the boot script used to boot the system.
+ <c>Id</c> can be any Erlang term. In the delivered boot
+ scripts, <c>Id</c> is <c>{Name, Vsn}</c>. <c>Name</c> and
+ <c>Vsn</c> are strings.</p>
+ </desc>
+ </func>
+ <func>
+ <name>stop() -> void()</name>
+ <fsummary>Take down an Erlang node smoothly</fsummary>
+ <desc>
+ <p>All applications are taken down smoothly, all code is
+ unloaded, and all ports are closed before the system
+ terminates. If the <c>-heart</c> command line flag was given,
+ the <c>heart</c> program is terminated before the Erlang node
+ terminates. Refer to <c>heart(3)</c> for more information.</p>
+ <p>To limit the shutdown time, the time <c>init</c> is allowed
+ to spend taking down applications, the <c>-shutdown_time</c>
+ command line flag should be used.</p>
+ </desc>
+ </func>
+ <func>
+ <name>stop(Status) -> void()</name>
+ <fsummary>Take down an Erlang node smoothly</fsummary>
+ <type>
+ <v>Status = int()>=0 | string()</v>
+ </type>
+ <desc>
+ <p>All applications are taken down smoothly, all code is
+ unloaded, and all ports are closed before the system
+ terminates by calling <c>halt(Status)</c>. If the
+ <c>-heart</c> command line flag was given, the <c>heart</c>
+ program is terminated before the Erlang node
+ terminates. Refer to <c>heart(3)</c> for more
+ information.</p>
+ <p>To limit the shutdown time, the time <c>init</c> is allowed
+ to spend taking down applications, the <c>-shutdown_time</c>
+ command line flag should be used.</p>
+ </desc>
+ </func>
+ </funcs>
+
+ <section>
+ <marker id="flags"></marker>
+ <title>Command Line Flags</title>
+ <warning><p>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
+ <c>-code_path_choice</c> flag is also experimental.</p></warning>
+
+ <p>The <c>init</c> module interprets the following command line
+ flags:</p>
+
+ <taglist>
+ <tag><c>--</c></tag>
+ <item>
+ <p>Everything following <c>--</c> up to the next flag is
+ considered plain arguments and can be retrieved using
+ <c>get_plain_arguments/0</c>.</p>
+ </item>
+ <tag><c>-code_path_choice Choice</c></tag>
+ <item>
+ <p>This flag can be set to <c>strict</c> or <c>relaxed</c>. It
+ controls whether each directory in the code path should be
+ interpreted strictly as it appears in the <c>boot script</c> or if
+ <c>init</c> 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 <c>boot script</c>. See <seealso
+ marker="sasl:script">script(4)</seealso> for more information
+ about interpretation of boot scripts. The flag does also have
+ a similar affect on how the code server works. See <seealso
+ marker="kernel:code">code(3)</seealso>.</p>
+
+ </item>
+ <tag><c>-eval Expr</c></tag>
+ <item>
+ <p>Scans, parses and evaluates an arbitrary expression
+ <c>Expr</c> 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:</p>
+ <pre>
+% <input>erl -eval '{X,Y,Z}' = now(), random:seed(X,Y,Z).'</input></pre>
+ <p>This example uses Erlang as a hexadecimal calculator:</p>
+ <pre>
+% <input>erl -noshell -eval 'R = 16#1F+16#A0, io:format("~.16B~n", [R])' \\</input>
+<input>-s erlang halt</input>
+BF</pre>
+ <p>If multiple <c>-eval</c> expressions are specified, they
+ are evaluated sequentially in the order specified.
+ <c>-eval</c> expressions are evaluated sequentially with
+ <c>-s</c> and <c>-run</c> function calls (this also in
+ the order specified). As with <c>-s</c> and <c>-run</c>, an
+ evaluation that does not terminate, blocks the system
+ initialization process.</p>
+ </item>
+ <tag><c>-extra</c></tag>
+ <item>
+ <p>Everything following <c>-extra</c> is considered plain
+ arguments and can be retrieved using
+ <c>get_plain_arguments/0</c>.</p>
+ </item>
+ <tag><c>-run Mod [Func [Arg1, Arg2, ...]]</c></tag>
+ <item>
+ <p>Evaluates the specified function call during system
+ initialization. <c>Func</c> defaults to <c>start</c>. 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
+ <c>[Arg1,Arg2,...]</c> as argument. All arguments are passed
+ as strings. If an exception is raised, Erlang stops with an
+ error message.</p>
+ <p>Example:</p>
+ <pre>
+% <input>erl -run foo -run foo bar -run foo bar baz 1 2</input></pre>
+ <p>This starts the Erlang runtime system and evaluates
+ the following functions:</p>
+ <code type="none">
+foo:start()
+foo:bar()
+foo:bar(["baz", "1", "2"]).</code>
+ <p>The functions are executed sequentially in an initialization
+ process, which then terminates normally and passes control to
+ the user. This means that a <c>-run</c> call which does not
+ return will block further processing; to avoid this, use
+ some variant of <c>spawn</c> in such cases.</p>
+ </item>
+ <tag><c>-s Mod [Func [Arg1, Arg2, ...]]</c></tag>
+ <item>
+ <p>Evaluates the specified function call during system
+ initialization. <c>Func</c> defaults to <c>start</c>. 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
+ <c>[Arg1,Arg2,...]</c> as argument. All arguments are passed
+ as atoms. If an exception is raised, Erlang stops with an
+ error message.</p>
+ <p>Example:</p>
+ <pre>
+% <input>erl -s foo -s foo bar -s foo bar baz 1 2</input></pre>
+ <p>This starts the Erlang runtime system and evaluates
+ the following functions:</p>
+ <code type="none">
+foo:start()
+foo:bar()
+foo:bar([baz, '1', '2']).</code>
+ <p>The functions are executed sequentially in an initialization
+ process, which then terminates normally and passes control to
+ the user. This means that a <c>-s</c> call which does not
+ return will block further processing; to avoid this, use
+ some variant of <c>spawn</c> in such cases.</p>
+ <p>Due to the limited length of atoms, it is recommended that
+ <c>-run</c> be used instead.</p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Example</title>
+ <pre>
+% <input>erl -- a b -children thomas claire -ages 7 3 -- x y</input>
+...
+
+1> <input>init:get_plain_arguments().</input>
+["a","b","x","y"]
+2> <input>init:get_argument(children).</input>
+{ok,[["thomas","claire"]]}
+3> <input>init:get_argument(ages).</input>
+{ok, [["7","3"]]}
+4> <input>init:get_argument(silly).</input>
+error</pre>
+ </section>
+
+ <section>
+ <title>SEE ALSO</title>
+ <p><seealso marker="erl_prim_loader">erl_prim_loader(3)</seealso>,
+ <seealso marker="kernel:heart">heart(3)</seealso></p>
+ </section>
+</erlref>
+