path: root/erts/doc/src/erl.xml

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<!DOCTYPE comref SYSTEM "comref.dtd">

<comref>
  <header>
    <copyright>
      <year>1996</year><year>2018</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>erl</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>erl.xml</file>
  </header>
  <com>erl</com>
  <comsummary>The Erlang emulator.</comsummary>
  <description>
    <p>The <c><![CDATA[erl]]></c> program starts an Erlang runtime system.
      The exact details (for example, whether <c><![CDATA[erl]]></c> is a
      script or a program and which other programs it calls) are
      system-dependent.</p>

    <p>Windows users probably want to use the <c><![CDATA[werl]]></c> program
      instead, which runs in its own window with scrollbars and supports
      command-line editing. The <c><![CDATA[erl]]></c> program on Windows
      provides no line editing in its shell, and on Windows 95 there is no way
      to scroll back to text that has scrolled off the screen. The
      <c><![CDATA[erl]]></c> program must be used, however, in pipelines or if
      you want to redirect standard input or output.</p>

    <note>
      <p>As from ERTS 5.9 (Erlang/OTP R15B) the runtime system does by
        default <em>not</em> bind schedulers to logical processors.
	For more information, see system flag
	<seealso marker="#+sbt"><c>+sbt</c></seealso>.</p>
    </note>
  </description>

  <funcs>
    <func>
      <name>erl &lt;arguments></name>
      <fsummary>Start an Erlang runtime system.</fsummary>
      <desc>
	<p>Starts an Erlang runtime system.</p>
	<p>The arguments can be divided into <em>emulator flags</em>,
	  <em>flags</em>, and <em>plain arguments</em>:</p>
	<list type="bulleted">
	  <item>
	    <p>Any argument starting with character <c><![CDATA[+]]></c> is
	      interpreted as an
	      <seealso marker="#emu_flags">emulator flag</seealso>.</p>
	    <p>As indicated by the name, emulator flags control
	      the behavior of the emulator.</p>
	  </item>
	  <item>
	    <p>Any argument starting with character <c><![CDATA[-]]></c>
	      (hyphen) is interpreted as a
	      <seealso marker="#init_flags">flag</seealso>, which is to
	      be passed to the Erlang part of the runtime system, more
	      specifically to the <c><![CDATA[init]]></c> system process, see
	      <seealso marker="init"><c>init(3)</c></seealso>.</p>
	    <p>The <c><![CDATA[init]]></c> process itself interprets some of
	      these flags, the <em>init flags</em>. It also stores any
	      remaining flags, the <em>user flags</em>. The latter can be
	      retrieved by calling <c><![CDATA[init:get_argument/1]]></c>.</p>
	    <p>A small number of "-" flags exist, which now actually are
	      emulator flags, see the description below.</p>
	  </item>
	  <item>
	    <p>Plain arguments are not interpreted in any way. They are also
	      stored by the <c><![CDATA[init]]></c> process and can be retrieved
	      by calling <c><![CDATA[init:get_plain_arguments/0]]></c>.
	      Plain arguments can occur before the first flag, or after a
	      <c><![CDATA[--]]></c> flag. Also, the <c><![CDATA[-extra]]></c>
	      flag causes everything that follows to become plain arguments.</p>
	  </item>
	</list>
	<p><em>Examples:</em></p>
	<pre>
% <input>erl +W w -sname arnie +R 9 -s my_init -extra +bertie</input>
(arnie@host)1> <input>init:get_argument(sname).</input>
{ok,[["arnie"]]}
(arnie@host)2> <input>init:get_plain_arguments().</input>
["+bertie"]</pre>
        <p>Here <c><![CDATA[+W w]]></c> and <c><![CDATA[+R 9]]></c> are
	  emulator flags. <c><![CDATA[-s my_init]]></c> is an init flag,
	  interpreted by <c><![CDATA[init]]></c>.
	  <c><![CDATA[-sname arnie]]></c> is a user flag, stored by
	  <c><![CDATA[init]]></c>. It is read by Kernel and causes the
	  Erlang runtime system to become distributed. Finally, everything after
	  <c><![CDATA[-extra]]></c> (that is, <c><![CDATA[+bertie]]></c>) is
	  considered as plain arguments.</p>
	<pre>
% <input>erl -myflag 1</input>
1> <input>init:get_argument(myflag).</input>
{ok,[["1"]]}
2> <input>init:get_plain_arguments().</input>
[]</pre>
        <p>Here the user flag <c><![CDATA[-myflag 1]]></c> is passed to and
	  stored by the <c><![CDATA[init]]></c> process. It is a user-defined
	  flag, presumably used by some user-defined application.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="init_flags"></marker>
    <title>Flags</title>
    <p>In the following list, init flags are marked "(init flag)".
      Unless otherwise specified, all other flags are user flags, for
      which the values can be retrieved by calling
      <c><![CDATA[init:get_argument/1]]></c>. Notice that the list of user
      flags is not exhaustive, there can be more application-specific
      flags that instead are described in the corresponding
      application documentation.</p>
    <taglist>
      <tag><c><![CDATA[--]]></c> (init flag)</tag>
      <item>
        <p>Everything following <c><![CDATA[--]]></c> up to the next flag
          (<c><![CDATA[-flag]]></c> or <c><![CDATA[+flag]]></c>) is considered
          plain arguments and can be retrieved using
          <c><![CDATA[init:get_plain_arguments/0]]></c>.</p>
      </item>
      <tag><c><![CDATA[-Application Par Val]]></c></tag>
      <item>
        <p>Sets the application configuration parameter <c><![CDATA[Par]]></c>
          to the value <c><![CDATA[Val]]></c> for the application
          <c><![CDATA[Application]]></c>; see
          <seealso marker="kernel:app"><c>app(4)</c></seealso> and
          <seealso marker="kernel:application">
          <c>application(3)</c></seealso>.</p>
      </item>
      <tag><marker id="args_file"/><c><![CDATA[-args_file FileName]]></c></tag>
      <item>
        <p>Command-line arguments are read from the file
          <c><![CDATA[FileName]]></c>. The arguments read from the file replace
          flag '<c><![CDATA[-args_file FileName]]></c>' on the resulting
          command line.</p>
        <p>The file <c><![CDATA[FileName]]></c> is to be a plain text file and
          can contain comments and command-line arguments. A comment begins
          with a <c>#</c> character and continues until the next end of line
          character. Backslash (\\) is used as quoting character. All
          command-line arguments accepted by <c><![CDATA[erl]]></c> are allowed,
          also flag <c><![CDATA[-args_file FileName]]></c>. Be careful not to
          cause circular dependencies between files containing flag
          <c><![CDATA[-args_file]]></c>, though.</p>
        <p>The flag <c><![CDATA[-extra]]></c> is treated in special way. Its
          scope ends at the end of the file. Arguments following an
          <c><![CDATA[-extra]]></c> flag are moved on the command line into the
          <c><![CDATA[-extra]]></c> section, that is, the end of the command
          line following after an <c><![CDATA[-extra]]></c> flag.</p>
      </item>
      <tag><c><![CDATA[-async_shell_start]]></c></tag>
      <item>
        <p>The initial Erlang shell does not read user input until
          the system boot procedure has been completed (Erlang/OTP 5.4 and
          later). This flag disables the start synchronization feature
          and lets the shell start in parallel with the rest of
          the system.</p>
      </item>
      <tag><c><![CDATA[-boot File]]></c></tag>
      <item>
        <p>Specifies the name of the boot file, <c><![CDATA[File.boot]]></c>,
          which is used to start the system; see
          <seealso marker="init"><c>init(3)</c></seealso>. Unless
          <c><![CDATA[File]]></c> contains an absolute path, the system searches
          for <c><![CDATA[File.boot]]></c> in the current and 
          <c><![CDATA[$ROOT/bin]]></c> directories.</p>
        <p>Defaults to <c><![CDATA[$ROOT/bin/start.boot]]></c>.</p>
      </item>
      <tag><c><![CDATA[-boot_var Var Dir]]></c></tag>
      <item>
        <p>If the boot script contains a path variable <c><![CDATA[Var]]></c>
          other than <c><![CDATA[$ROOT]]></c>, this variable is expanded to
          <c><![CDATA[Dir]]></c>. Used when applications are installed in
          another directory than <c><![CDATA[$ROOT/lib]]></c>; see
          <seealso marker="sasl:systools#make_script/1">
          <c>systools:make_script/1,2</c></seealso> in SASL.</p>
      </item>
      <tag><c><![CDATA[-code_path_cache]]></c></tag>
      <item>
        <p>Enables the code path cache of the code server; see
          <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-compile Mod1 Mod2 ...]]></c></tag>
      <item>
        <p>Compiles the specified modules and then terminates (with
          non-zero exit code if the compilation of some file did not
          succeed). Implies <c><![CDATA[-noinput]]></c>.</p>
        <p>Not recommended; use <seealso marker="erlc"><c>erlc</c></seealso>
          instead.</p>
      </item>
      <tag><c><![CDATA[-config Config]]></c></tag>
      <item>
        <p>Specifies the name of a configuration file,
          <c><![CDATA[Config.config]]></c>, which is used to configure
          applications; see
          <seealso marker="kernel:app"><c>app(4)</c></seealso> and
          <seealso marker="kernel:application">
          <c>application(3)</c></seealso>.</p>
      </item>
      <tag><marker id="connect_all"/><c><![CDATA[-connect_all false]]></c></tag>
      <item>
        <p>If this flag is present, <c><![CDATA[global]]></c> does not maintain
          a fully connected network of distributed Erlang nodes, and then
          global name registration cannot be used; see
          <seealso marker="kernel:global"><c>global(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-cookie Cookie]]></c></tag>
      <item>
        <p>Obsolete flag without any effect and common misspelling for
          <c><![CDATA[-setcookie]]></c>. Use <c><![CDATA[-setcookie]]></c>
          instead.</p>
      </item>
      <tag><c><![CDATA[-detached]]></c></tag>
      <item>
        <p>Starts the Erlang runtime system detached from the system
          console. Useful for running daemons and backgrounds processes. Implies
          <c><![CDATA[-noinput]]></c>.</p>
      </item>
      <tag><c><![CDATA[-emu_args]]></c></tag>
      <item>
        <p>Useful for debugging. Prints the arguments sent to the emulator.</p>
      </item>
      <tag><c><![CDATA[-emu_type Type]]></c></tag>
      <item>
        <p>Start an emulator of a different type. For example, to start
	the lock-counter emualator, use <c>-emu_type lcnt</c>. (The emulator
	must already be built. Use the <c>configure</c> option
	<c>--enable-lock-counter</c> to build the lock-counter emulator.)</p>
      </item>
      <tag><c><![CDATA[-env Variable Value]]></c></tag>
      <item>
        <p>Sets the host OS environment variable <c><![CDATA[Variable]]></c> to
          the value <c><![CDATA[Value]]></c> for the Erlang runtime system.
          Example:</p>
        <pre>
% <input>erl -env DISPLAY gin:0</input></pre>
        <p>In this example, an Erlang runtime system is started with
          environment variable <c><![CDATA[DISPLAY]]></c> set to
          <c><![CDATA[gin:0]]></c>.</p>
      </item>
      <tag><c><![CDATA[-epmd_module Module]]></c> (init flag)</tag>
      <item>
        <p>Configures the module responsible to communicate to
          <seealso marker="epmd">epmd</seealso>. Defaults to <c>erl_epmd</c>.</p>
      </item>
      <tag><c><![CDATA[-eval Expr]]></c> (init flag)</tag>
      <item>
        <p>Makes <c><![CDATA[init]]></c> evaluate the expression
          <c><![CDATA[Expr]]></c>; see
          <seealso marker="init"><c>init(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-extra]]></c> (init flag)</tag>
      <item>
        <p>Everything following <c><![CDATA[-extra]]></c> is considered plain
          arguments and can be retrieved using
          <c><![CDATA[init:get_plain_arguments/0]]></c>.</p>
      </item>
      <tag><c><![CDATA[-heart]]></c></tag>
      <item>
        <p>Starts heartbeat monitoring of the Erlang runtime system;
          see <seealso marker="kernel:heart">
          <c>heart(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-hidden]]></c></tag>
      <item>
        <p>Starts the Erlang runtime system as a hidden node, if it is
          run as a distributed node. Hidden nodes always establish
          hidden connections to all other nodes except for nodes in the
          same global group. Hidden connections are not published on
          any of the connected nodes, that is, none of the connected
          nodes are part of the result from <c><![CDATA[nodes/0]]></c> on the
          other node. See also hidden global groups;
          <seealso marker="kernel:global_group">
          <c>global_group(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-hosts Hosts]]></c></tag>
      <item>
        <p>Specifies the IP addresses for the hosts on which Erlang boot servers
          are running, see <seealso marker="kernel:erl_boot_server">
          <c>erl_boot_server(3)</c></seealso>. This flag
          is mandatory if flag <c><![CDATA[-loader inet]]></c> is present.</p>
        <p>The IP addresses must be specified in the standard form (four
          decimal numbers separated by periods, for example,
          <c><![CDATA["150.236.20.74"]]></c>. Hosts names are not acceptable,
          but a broadcast address (preferably limited to the local network)
          is.</p>
      </item>
      <tag><c><![CDATA[-id Id]]></c></tag>
      <item>
        <p>Specifies the identity of the Erlang runtime system. If it is
          run as a distributed node, <c><![CDATA[Id]]></c> must be identical to
          the name supplied together with flag <c><![CDATA[-sname]]></c> or
          <c><![CDATA[-name]]></c>.</p>
      </item>
      <tag><c><![CDATA[-init_debug]]></c></tag>
      <item>
        <p>Makes <c><![CDATA[init]]></c> write some debug information while
          interpreting the boot script.</p>
      </item>
      <tag><marker id="instr"/><c><![CDATA[-instr]]></c> (emulator flag)</tag>
      <item>
        <p>Selects an instrumented Erlang runtime system (virtual
          machine) to run, instead of the ordinary one. When running an
          instrumented runtime system, some resource usage data can be
          obtained and analyzed using the <c><![CDATA[instrument]]></c> module.
          Functionally, it behaves exactly like an ordinary Erlang
          runtime system.</p>
      </item>
      <tag><c><![CDATA[-loader Loader]]></c></tag>
      <item>
        <p>Specifies the method used by <c><![CDATA[erl_prim_loader]]></c> to
          load Erlang modules into the system; see
          <seealso marker="erl_prim_loader"><c>erl_prim_loader(3)</c></seealso>.
          Two <c><![CDATA[Loader]]></c> methods are supported:</p>
        <list type="bulleted">
          <item>
            <p><c><![CDATA[efile]]></c>, which means use the local file system,
              this is the default.</p>
          </item>
          <item>
            <p><c><![CDATA[inet]]></c>, which means use a boot server on
              another machine. The flags <c><![CDATA[-id]]></c>,
              <c><![CDATA[-hosts]]></c> and <c><![CDATA[-setcookie]]></c> must
              also be specified.</p>
          </item>
        </list>
        <p>If <c><![CDATA[Loader]]></c> is something else, the user-supplied
          <c><![CDATA[Loader]]></c> port program is started.</p>
      </item>
      <tag><c><![CDATA[-make]]></c></tag>
      <item>
        <p>Makes the Erlang runtime system invoke <c><![CDATA[make:all()]]></c>
          in the current working directory and then terminate; see
          <seealso marker="tools:make"><c>make(3)</c></seealso>. Implies
          <c><![CDATA[-noinput]]></c>.</p>
      </item>
      <tag><c><![CDATA[-man Module]]></c></tag>
      <item>
        <p>Displays the manual page for the Erlang module
          <c><![CDATA[Module]]></c>. Only supported on Unix.</p>
      </item>
      <tag><c><![CDATA[-mode interactive | embedded]]></c></tag>
      <item>
        <p>Modules are auto loaded when they are first referenced if the
          runtime system runs in <c><![CDATA[interactive]]></c> mode, which is
          the default. In <c><![CDATA[embedded]]></c> mode modules are not auto
          loaded. The latter is recommended when the boot script preloads all
          modules, as conventionally happens in OTP releases. See
          <seealso marker="kernel:code"><c>code(3)</c></seealso></p>.
      </item>
      <tag><c><![CDATA[-name Name]]></c></tag>
      <item>
        <p>Makes the Erlang runtime system into a distributed node.
          This flag invokes all network servers necessary for a node to
          become distributed; see <seealso marker="kernel:net_kernel">
          <c>net_kernel(3)</c></seealso>. It is also ensured that
          <c><![CDATA[epmd]]></c> runs on the current host before Erlang is
          started; see <seealso marker="epmd"><c>epmd(1)</c></seealso>.and the
          <seealso marker="#start_epmd"><c>-start_epmd</c></seealso> option.</p>
        <p>The node name will be <c><![CDATA[Name@Host]]></c>, where
          <c><![CDATA[Host]]></c> is the fully qualified host name of the
          current host. For short names, use flag <c><![CDATA[-sname]]></c>
          instead.</p>
        <warning>
          <p>
            Starting a distributed node without also specifying
            <seealso marker="#proto_dist"><c>-proto_dist inet_tls</c></seealso>
            will expose the node to attacks that may give the attacker
            complete access to the node and in extension the cluster.
            When using un-secure distributed nodes, make sure that the
            network is configured to keep potential attackers out.
          </p>
        </warning>
      </item>
      <tag><c><![CDATA[-noinput]]></c></tag>
      <item>
        <p>Ensures that the Erlang runtime system never tries to read
          any input. Implies <c><![CDATA[-noshell]]></c>.</p>
      </item>
      <tag><c><![CDATA[-noshell]]></c></tag>
      <item>
        <p>Starts an Erlang runtime system with no shell. This flag
          makes it possible to have the Erlang runtime system as a
          component in a series of Unix pipes.</p>
      </item>
      <tag><c><![CDATA[-nostick]]></c></tag>
      <item>
        <p>Disables the sticky directory facility of the Erlang code
          server; see
          <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-oldshell]]></c></tag>
      <item>
        <p>Invokes the old Erlang shell from Erlang/OTP 3.3. The old shell
          can still be used.</p>
      </item>
      <tag><c><![CDATA[-pa Dir1 Dir2 ...]]></c></tag>
      <item>
        <p>Adds the specified directories to the beginning of the code
          path, similar to <seealso marker="kernel:code#add_pathsa/1">
	  <c><![CDATA[code:add_pathsa/1]]></c></seealso>. Note that the
	  order of the given directories will be reversed in the
	  resulting path.</p>
	<p>As an alternative to <c>-pa</c>, if several directories are
	  to be prepended to the code path and the directories have a
	  common parent directory, that parent directory can be
	  specified in environment variable <c>ERL_LIBS</c>; see
	  <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-pz Dir1 Dir2 ...]]></c></tag>
      <item>
        <p>Adds the specified directories to the end of the code path,
          similar to <c><![CDATA[code:add_pathsz/1]]></c>; see
          <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-path Dir1 Dir2 ...]]></c></tag>
      <item>
        <p>Replaces the path specified in the boot script; see
          <seealso marker="sasl:script"><c>script(4)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-proto_dist Proto]]></c></tag>
      <item>
        <marker id="proto_dist"/>
        <p>Specifies a protocol for Erlang distribution:</p>
        <taglist>
          <tag><c>inet_tcp</c></tag>
          <item>TCP over IPv4 (the default)</item>
          <tag><c>inet_tls</c></tag>
          <item>Distribution over TLS/SSL, See the
            <seealso marker="ssl:ssl_distribution">
              Using SSL for Erlang Distribution</seealso> User's Guide
              for details on how to setup a secure distributed node.
          </item>
          <tag><c>inet6_tcp</c></tag>
          <item>TCP over IPv6</item>
        </taglist>
        <p>For example, to start up IPv6 distributed nodes:</p>
<pre>
% <input>erl -name [email protected] -proto_dist inet6_tcp</input></pre>
      </item>
      <tag><c><![CDATA[-remsh Node]]></c></tag>
      <item>
        <p>Starts Erlang with a remote shell connected to
          <c><![CDATA[Node]]></c>. Requires either <c><![CDATA[-name]]></c>
          or <c><![CDATA[-sname]]></c> to be given. If <c><![CDATA[Node]]></c>
          does not contain a hostname, one is automatically taken from
          <c><![CDATA[-name]]></c> or <c><![CDATA[-sname]]></c></p>
      </item>
      <tag><c><![CDATA[-rsh Program]]></c></tag>
      <item>
        <p>Specifies an alternative to <c><![CDATA[ssh]]></c> for starting a
          slave node on a remote host; see
          <seealso marker="stdlib:slave"><c>slave(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-run Mod [Func [Arg1, Arg2, ...]]]]></c> (init
        flag)</tag>
      <item>
        <p>Makes <c><![CDATA[init]]></c> call the specified function.
          <c><![CDATA[Func]]></c> defaults to <c><![CDATA[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><![CDATA[[Arg1,Arg2,...]]]></c> as argument. All arguments are
          passed as strings. See <seealso marker="init">
          <c>init(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-s Mod [Func [Arg1, Arg2, ...]]]]></c> (init flag)</tag>
      <item>
        <p>Makes <c><![CDATA[init]]></c> call the specified function.
          <c><![CDATA[Func]]></c> defaults to <c><![CDATA[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><![CDATA[[Arg1,Arg2,...]]]></c> as argument. All arguments are
          passed as atoms. See <seealso marker="init">
          <c>init(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-setcookie Cookie]]></c></tag>
      <item>
        <p>Sets the magic cookie of the node to <c><![CDATA[Cookie]]></c>; see
          <seealso marker="erlang#set_cookie/2">
          <c>erlang:set_cookie/2</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[-shutdown_time Time]]></c></tag>
      <item>
        <p>Specifies how long time (in milliseconds) the <c><![CDATA[init]]></c>
          process is allowed to spend shutting down the system. If
          <c><![CDATA[Time]]></c> milliseconds have elapsed, all processes still
          existing are killed. Defaults to <c><![CDATA[infinity]]></c>.</p>
      </item>
      <tag><c><![CDATA[-sname Name]]></c></tag>
      <item>
        <p>Makes the Erlang runtime system into a distributed node, similar to
          <c><![CDATA[-name]]></c>, but the host name portion of the node
          name <c><![CDATA[Name@Host]]></c> will be the short name, not fully
          qualified.</p>
        <p>This is sometimes the only way to run distributed Erlang if
          the Domain Name System (DNS) is not running. No communication can
          exist between nodes running with flag <c><![CDATA[-sname]]></c>
          and those running with flag <c><![CDATA[-name]]></c>, as node
          names must be unique in distributed Erlang systems.</p>
        <warning>
          <p>
            Starting a distributed node without also specifying
            <seealso marker="#proto_dist"><c>-proto_dist inet_tls</c></seealso>
            will expose the node to attacks that may give the attacker
            complete access to the node and in extension the cluster.
            When using un-secure distributed nodes, make sure that the
            network is configured to keep potential attackers out.
          </p>
        </warning>
      </item>
      <tag><marker id="start_epmd"/><c>-start_epmd true | false</c></tag>
      <item>

        <p>Specifies whether Erlang should start
          <seealso marker="epmd">epmd</seealso> on startup. By default
          this is <c>true</c>, but if you prefer to start epmd
          manually, set this to <c>false</c>.</p>

        <p>This only applies if Erlang is started as a distributed node,
          i.e. if <c>-name</c> or <c>-sname</c> is specified. Otherwise,
          epmd is not started even if <c>-start_epmd true</c> is given.</p>

        <p>Note that a distributed node will fail to start if epmd is
          not running.</p>
      </item>
      <tag><c><![CDATA[-version]]></c> (emulator flag)</tag>
      <item>
        <p>Makes the emulator print its version number. The same
          as <c><![CDATA[erl +V]]></c>.</p>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="emu_flags"></marker>
    <title>Emulator Flags</title>
    <p><c><![CDATA[erl]]></c> invokes the code for the Erlang emulator (virtual
      machine), which supports the following flags:</p>
    <taglist>
      <tag><marker id="async_thread_stack_size"/>
        <c><![CDATA[+a size]]></c></tag>
      <item>
        <p>Suggested stack size, in kilowords, for threads in the
          async thread pool. Valid range is 16-8192 kilowords. The
          default suggested stack size is 16 kilowords, that is, 64
          kilobyte on 32-bit architectures. This small default size
          has been chosen because the number of async threads can
          be large. The default size is enough for drivers
          delivered with Erlang/OTP, but might not be large
          enough for other dynamically linked-in drivers that use the
          <seealso marker="erl_driver#driver_async">
          <c>driver_async()</c></seealso> functionality.
          Notice that the value passed is only a suggestion,
          and it can even be ignored on some platforms.</p>
      </item>
      <tag><marker id="async_thread_pool_size"/><c><![CDATA[+A size]]></c></tag>
      <item>
        <p>Sets the number of threads in async thread pool. Valid range
          is 0-1024. Defaults to 1.</p>
      </item>
      <tag><c><![CDATA[+B [c | d | i]]]></c></tag>
      <item>
        <p>Option <c><![CDATA[c]]></c> makes <c><![CDATA[Ctrl-C]]></c>
          interrupt the current shell instead of invoking the emulator break
          handler. Option <c><![CDATA[d]]></c> (same as specifying
          <c><![CDATA[+B]]></c> without an extra option) disables the break
          handler. Option <c><![CDATA[i]]></c> makes the emulator ignore any
          break signal.</p>
        <p>If option <c><![CDATA[c]]></c> is used with
          <c><![CDATA[oldshell]]></c> on Unix, <c><![CDATA[Ctrl-C]]></c> will
          restart the shell process rather than interrupt it.</p>
        <p>Notice that on Windows, this flag is only applicable for
          <c><![CDATA[werl]]></c>, not <c><![CDATA[erl]]></c>
          (<c><![CDATA[oldshell]]></c>). Notice also that
          <c><![CDATA[Ctrl-Break]]></c> is used instead of
          <c><![CDATA[Ctrl-C]]></c> on Windows.</p>
      </item>
      <tag><marker id="+c"/><c><![CDATA[+c true | false]]></c></tag>
      <item>
        <p>Enables or disables
          <seealso marker="time_correction#Time_Correction">time
          correction</seealso>:</p>
	<taglist>
	  <tag><c>true</c></tag>
          <item>Enables time correction. This is the default if
            time correction is supported on the specific platform.</item>
          <tag><c>false</c></tag>
          <item>Disables time correction.</item>
          </taglist>
        <p>For backward compatibility, the boolean value can be omitted.
          This is interpreted as <c>+c false</c>.</p>
      </item>
      <tag><marker id="+C_"/><c><![CDATA[+C no_time_warp | single_time_warp |
        multi_time_warp]]></c></tag>
      <item>
        <p>Sets <seealso marker="time_correction#Time_Warp_Modes">time warp
          mode</seealso>:</p>
        <taglist>
        <tag><c>no_time_warp</c></tag>
          <item><seealso marker="time_correction#No_Time_Warp_Mode">
            No time warp mode</seealso> (the default)</item>
          <tag><c>single_time_warp</c></tag>
          <item><seealso marker="time_correction#Single_Time_Warp_Mode">
            Single time warp mode</seealso></item>
          <tag><c>multi_time_warp</c></tag>
          <item><seealso marker="time_correction#Multi_Time_Warp_Mode">
            Multi-time warp mode</seealso></item>
      </taglist>
      </item>
      <tag><c><![CDATA[+d]]></c></tag>
      <item>
        <p>If the emulator detects an internal error (or runs out of memory),
          it, by default, generates both a crash dump and a core dump.
          The core dump is, however, not very useful as the content
          of process heaps is destroyed by the crash dump generation.</p>
        <p>Option <c>+d</c> instructs the emulator to produce only a
          core dump and no crash dump if an internal error is detected.</p>
        <p>Calling <seealso marker="erlang#halt/1">
          <c>erlang:halt/1</c></seealso> with a string argument still
          produces a crash dump. On Unix systems, sending an emulator process
          a <c>SIGUSR1</c> signal also forces a crash dump.</p>
      </item>
      <tag><marker id="+dcg"/><c><![CDATA[+rg DecentralizedCounterGroupsLimit]]></c></tag>
      <item>
        <p>Limits the number of decentralized counter groups used by
           decentralized counters optimized for update operations in the
           Erlang runtime system. By default, the limit is 256.</p>
        <p>When the number of schedulers is less than or equal to the
           limit, each scheduler has its own group. When the
           number of schedulers is larger than the groups limit,
           schedulers share groups. Shared groups degrade
           the performance for updating counters while many reader groups
           degrade the performance for reading counters. So, the limit is a tradeoff
           between performance for update operations and performance for
           read operations. Each group consumes 64 bytes in each
           counter.</p>
        <p>Notice that a runtime system using decentralized
           counter groups benefits from <seealso marker="#+sbt">binding
           schedulers to logical processors</seealso>, as the groups are
           distributed better between schedulers with this option.</p>
        <p>This option only affects decentralized counters used for
           the counters that are keeping track of the memory consumption
           and the number of terms in ETS tables of type ordered_set with
           the write_concurrency option activated.</p>
      </item>
      <tag><marker id="+e"/><c><![CDATA[+e Number]]></c></tag>
      <item>
        <p>Sets the maximum number of ETS tables. This limit is
	<seealso marker="stdlib:ets#max_ets_tables">partially obsolete</seealso>.
	</p>
      </item>
      <tag><c><![CDATA[+ec]]></c></tag>
      <item>
        <p>Forces option <c>compressed</c> on all ETS tables.
          Only intended for test and evaluation.</p>
      </item>
      <tag><marker id="file_name_encoding"></marker>
        <c><![CDATA[+fnl]]></c></tag>
      <item>
        <p>The virtual machine works with filenames as if they are encoded
          using the ISO Latin-1 encoding, disallowing Unicode characters with
          code points &gt; 255.</p>
        <p>For more information about Unicode filenames, see section
          <seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
          Filenames</seealso> in the STDLIB User's Guide. Notice that
          this value also applies to command-line parameters and environment
          variables (see section <seealso
          marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
          Unicode in Environment and Parameters</seealso> in the STDLIB
          User's Guide).</p>
      </item>
      <tag><c><![CDATA[+fnu[{w|i|e}]]]></c></tag>
      <item>
        <p>The virtual machine works with filenames as if they are encoded
          using UTF-8 (or some other system-specific Unicode encoding). This is
          the default on operating systems that enforce Unicode encoding, that
          is, Windows and MacOS X.</p>
        <p>The <c>+fnu</c> switch can be followed by <c>w</c>, <c>i</c>, or
          <c>e</c> to control how wrongly encoded filenames are to be
          reported:</p>
        <list type="bulleted">
          <item>
            <p><c>w</c> means that a warning is sent to the <c>error_logger</c>
              whenever a wrongly encoded filename is "skipped" in directory
              listings. This is the default.</p>
          </item>
          <item>
            <p><c>i</c> means that those wrongly encoded filenames are silently
              ignored.</p>
          </item>
          <item>
            <p><c>e</c> means that the API function returns an error whenever a
              wrongly encoded filename (or directory name) is encountered.</p>
          </item>
        </list>
        <p>Notice that <seealso marker="kernel:file#read_link/1">
          <c>file:read_link/1</c></seealso> always returns an error if the link
          points to an invalid filename.</p>
        <p>For more information about Unicode filenames, see section
          <seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
          Filenames</seealso> in the STDLIB User's Guide. Notice that
          this value also applies to command-line parameters and environment
          variables (see section <seealso
          marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
          Unicode in Environment and Parameters</seealso> in the STDLIB
          User's Guide).</p>
      </item>
      <tag><c><![CDATA[+fna[{w|i|e}]]]></c></tag>
      <item>
        <p>Selection between <c>+fnl</c> and <c>+fnu</c> is done based
          on the current locale settings in the OS. This means that if you
          have set your terminal for UTF-8 encoding, the filesystem is
          expected to use the same encoding for filenames. This is
          default on all operating systems, except MacOS X and Windows.</p>
        <p>The <c>+fna</c> switch can be followed by <c>w</c>, <c>i</c>, or
          <c>e</c>. This has effect if the locale settings cause the behavior
          of <c>+fnu</c> to be selected; see the description of <c>+fnu</c>
          above. If the locale settings cause the behavior of <c>+fnl</c> to be
          selected, then <c>w</c>, <c>i</c>, or <c>e</c> have no effect.</p>
        <p>For more information about Unicode filenames, see section
          <seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
          Filenames</seealso> in the STDLIB User's Guide. Notice that
          this value also applies to command-line parameters and environment
          variables (see section <seealso
          marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
          Unicode in Environment and Parameters</seealso> in the STDLIB
          User's Guide).</p>
      </item>
      <tag><c><![CDATA[+hms Size]]></c></tag>
      <item>
        <p>Sets the default heap size of processes to the size
          <c><![CDATA[Size]]></c>.</p>
      </item>
      <tag><c><![CDATA[+hmbs Size]]></c></tag>
      <item>
        <p>Sets the default binary virtual heap size of processes to the size
          <c><![CDATA[Size]]></c>.</p>
      </item>
      <tag><marker id="+hmax"/><c><![CDATA[+hmax Size]]></c></tag>
      <item>
        <p>Sets the default maximum heap size of processes to the size
          <c><![CDATA[Size]]></c>. Defaults to <c>0</c>, which means that no
          maximum heap size is used. For more information, see
          <seealso marker="erlang#process_flag_max_heap_size">
          <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
      </item>
      <tag><marker id="+hmaxel"/><c><![CDATA[+hmaxel true|false]]></c></tag>
      <item>
        <p>Sets whether to send an error logger message or not for processes
          reaching the maximum heap size. Defaults to <c>true</c>.
          For more information, see
          <seealso marker="erlang#process_flag_max_heap_size">
          <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
      </item>
      <tag><marker id="+hmaxk"/><c><![CDATA[+hmaxk true|false]]></c></tag>
      <item>
        <p>Sets whether to kill processes reaching the maximum heap size or not.
          Default to <c>true</c>. For more information, see
          <seealso marker="erlang#process_flag_max_heap_size">
          <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[+hpds Size]]></c></tag>
      <item>
        <p>Sets the initial process dictionary size of processes to the size
          <c><![CDATA[Size]]></c>.</p>
      </item>
      <tag><marker id="+hmqd"/><c>+hmqd off_heap|on_heap</c></tag>
      <item>
        <p>Sets the default value for process flag <c>message_queue_data</c>.
          Defaults to <c>on_heap</c>. If <c>+hmqd</c> is not
	  passed, <c>on_heap</c> will be the default. For more information, see
          <seealso marker="erlang#process_flag_message_queue_data">
          <c>process_flag(message_queue_data, MQD)</c></seealso>.</p>
      </item>
      <tag><marker id="+IOp"/><c>+IOp PollSets</c></tag>
      <item>
        <p>Sets the number of IO pollsets to use when polling for I/O.
          This option is only used on platforms that support concurrent
          updates of a pollset, otherwise the same number of pollsets
          are used as IO poll threads.
          The default is 1.
        </p>
      </item>
      <tag><marker id="+IOt"/><c>+IOt PollThreads</c></tag>
      <item>
        <p>Sets the number of IO poll threads to use when polling for I/O.
          The maximum number of poll threads allowed is 1024. The default is 1.
        </p>
        <p>A good way to check if more IO poll threads are needed is to use
          <seealso marker="runtime_tools:msacc">microstate accounting</seealso>
          and see what the load of the IO poll thread is. If it is high it could
          be a good idea to add more threads.</p>
      </item>
      <tag><marker id="+IOPp"/><c>+IOPp PollSetsPercentage</c></tag>
      <item>
        <p>Similar to <seealso marker="#+IOp"><c>+IOp</c></seealso> but uses
          percentages to set the number of IO pollsets to create, based on the
          number of poll threads configured. If both <c>+IOPp</c> and <c>+IOp</c>
          are used, <c>+IOPp</c> is ignored.
        </p>
      </item>
      <tag><marker id="+IOPt"/><c>+IOPt PollThreadsPercentage</c></tag>
      <item>
        <p>Similar to <seealso marker="#+IOt"><c>+IOt</c></seealso> but uses
          percentages to set the number of IO poll threads to create, based on
          the number of schedulers configured. If both <c>+IOPt</c> and
          <c>+IOt</c> are used, <c>+IOPt</c> is ignored.
        </p>
      </item>
      <tag><c><![CDATA[+l]]></c></tag>
      <item>
        <p>Enables autoload tracing, displaying information while loading
          code.</p>
      </item>
      <tag><c><![CDATA[+L]]></c></tag>
      <item>
        <p>Prevents loading information about source filenames and line
          numbers. This saves some memory, but exceptions do not contain
          information about the filenames and line numbers.</p>
      </item>
      <tag><marker id="erts_alloc"/><c><![CDATA[+MFlag Value]]></c></tag>
      <item>
        <p>Memory allocator-specific flags. For more information, see
          <seealso marker="erts_alloc"><c>erts_alloc(3)</c></seealso>.</p>
      </item>
      <tag><marker id="+pc"/><marker id="printable_character_range"/>
        <c><![CDATA[+pc Range]]></c></tag>
      <item>
        <p>Sets the range of characters that the system considers printable in
          heuristic detection of strings. This typically affects the shell,
          debugger, and <c>io:format</c> functions (when <c>~tp</c> is used in
          the format string).</p> 
        <p>Two values are supported for <c>Range</c>:</p>
        <taglist>
          <tag><c>latin1</c></tag>
          <item>The default. Only characters in the ISO Latin-1 range can be
            considered printable. This means that a character with a code point
            &gt; 255 is never considered printable and that lists containing
            such characters are displayed as lists of integers rather than text
            strings by tools.</item>
          <tag><c>unicode</c></tag>
          <item>All printable Unicode characters are considered when
            determining if a list of integers is to be displayed in
            string syntax. This can give unexpected results if, for
            example, your font does not cover all Unicode characters.</item>
        </taglist>
        <p>See also <seealso marker="stdlib:io#printable_range/0">
          <c>io:printable_range/0</c></seealso> in STDLIB.</p>
      </item>
      <tag><marker id="+P"/><marker id="max_processes"/><c><![CDATA[+P Number]]></c></tag>
      <item>
	<p>Sets the maximum number of simultaneously existing processes for this
          system if a <c>Number</c> is passed as value. Valid range for
	<c>Number</c> is <c>[1024-134217727]</c></p>
	<p><em>NOTE</em>: The actual maximum chosen may be much larger than
	the <c>Number</c> passed. Currently the runtime system often,
	but not always, chooses a value that is a power of 2. This might,
	however, be changed in the future. The actual value chosen can be
	checked by calling
	<seealso marker="erlang#system_info_process_limit">erlang:system_info(process_limit)</seealso>.</p>
	<p>The default value is <c>262144</c></p>
      </item>
      <tag><marker id="+Q"/><marker id="max_ports"/><c><![CDATA[+Q Number]]></c></tag>
      <item>
	<p>Sets the maximum number of simultaneously existing ports for this
          system if a Number is passed as value. Valid range for <c>Number</c>
	is <c>[1024-134217727]</c></p>
	<p><em>NOTE</em>: The actual maximum chosen may be much larger than
	the actual <c>Number</c> passed. Currently the runtime system often,
	but not always, chooses a value that is a power of 2. This might,
	however, be changed in the future. The actual value chosen can be
	checked by calling
	<seealso marker="erlang#system_info_port_limit">erlang:system_info(port_limit)</seealso>.</p>
	<p>The default value used is normally <c>65536</c>. However, if
	the runtime system is able to determine maximum amount of file
	descriptors that it is allowed to open and this value is larger
	than <c>65536</c>, the chosen value will increased to a value
	larger or equal to the maximum amount of file descriptors that
	can be opened.</p>
	<p>On Windows the default value is set to <c>8196</c> because the
	normal OS limitations are set higher than most machines can handle.</p>
      </item>
      <tag><marker id="compat_rel"/><c><![CDATA[+R ReleaseNumber]]></c></tag>
      <item>
        <p>Sets the compatibility mode.</p>
        <p>The distribution mechanism is not backward compatible by
          default. This flag sets the emulator in compatibility mode
          with an earlier Erlang/OTP release <c><![CDATA[ReleaseNumber]]></c>.
          The release number must be in the range
          <c><![CDATA[<current release>-2..<current release>]]></c>. This
          limits the emulator, making it possible for it to communicate
          with Erlang nodes (as well as C- and Java nodes) running that
          earlier release.</p>
        <note>
          <p>Ensure that all nodes (Erlang-,  C-, and Java nodes) of
            a distributed Erlang system is of the same Erlang/OTP release,
            or from two different Erlang/OTP releases X and Y, where
            <em>all</em> Y nodes have compatibility mode X.</p>
        </note>
      </item>
      <tag><c><![CDATA[+r]]></c></tag>
      <item>
        <p>Forces ETS memory block to be moved on realloc.</p>
      </item>
      <tag><marker id="+rg"/><c><![CDATA[+rg ReaderGroupsLimit]]></c></tag>
      <item>
        <p>Limits the number of reader groups used by read/write locks
          optimized for read operations in the Erlang runtime system. By
          default the reader groups limit is 64.</p>
        <p>When the number of schedulers is less than or equal to the reader
          groups limit, each scheduler has its own reader group. When the
          number of schedulers is larger than the reader groups limit,
          schedulers share reader groups. Shared reader groups degrade
          read lock and read unlock performance while many
          reader groups degrade write lock performance. So, the limit is a
          tradeoff between performance for read operations and performance
          for write operations. Each reader group consumes 64 byte
          in each read/write lock.</p>
        <p>Notice that a runtime system using shared reader groups benefits from
          <seealso marker="#+sbt">binding schedulers to logical
          processors</seealso>, as the reader groups are distributed better
          between schedulers.</p>
      </item>
      <tag><marker id="+S"/>
        <c><![CDATA[+S Schedulers:SchedulerOnline]]></c></tag>
      <item>
        <p>Sets the number of scheduler threads to create and scheduler threads
          to set online. The maximum for both
          values is 1024. If the Erlang runtime system is able to determine the
          number of logical processors configured and logical processors
          available, <c>Schedulers</c> defaults to logical processors
          configured, and <c>SchedulersOnline</c> defaults to logical processors
          available; otherwise the default values are 1. <c>Schedulers</c> can
          be omitted if <c>:SchedulerOnline</c> is not and conversely. The
          number of schedulers online can be changed at runtime through
          <seealso marker="erlang#system_flag_schedulers_online">
          <c>erlang:system_flag(schedulers_online,
          SchedulersOnline)</c></seealso>.</p>
        <p>If <c>Schedulers</c> or <c>SchedulersOnline</c> is specified as a
          negative number, the value is subtracted from the default number of
          logical processors configured or logical processors available,
          respectively.</p>
        <p>Specifying value <c>0</c> for <c>Schedulers</c> or
          <c>SchedulersOnline</c> resets the number of scheduler threads or
          scheduler threads online, respectively, to its default value.</p>
      </item>
      <tag><marker id="+SP"/><c><![CDATA[+SP
        SchedulersPercentage:SchedulersOnlinePercentage]]></c></tag>
      <item>
        <p>Similar to <seealso marker="#+S"><c>+S</c></seealso> but uses
          percentages to set the number of scheduler threads to create, based
          on logical processors configured, and scheduler threads to set online,
          based on logical processors available.
          Specified values must be &gt; 0. For example,
          <c>+SP 50:25</c> sets the number of scheduler threads to 50% of the
          logical processors configured, and the number of scheduler threads
          online to 25% of the logical processors available.
          <c>SchedulersPercentage</c> can be omitted if
          <c>:SchedulersOnlinePercentage</c> is not and conversely. The number
          of schedulers online can be changed at runtime through
          <seealso marker="erlang#system_flag_schedulers_online">
          <c>erlang:system_flag(schedulers_online,
          SchedulersOnline)</c></seealso>.</p>
        <p>This option interacts with <seealso marker="#+S"><c>+S</c></seealso>
          settings. For example, on a system with 8 logical cores configured
          and 8 logical cores available, the combination of the options
          <c>+S 4:4 +SP 50:25</c> (in either order) results in 2 scheduler
          threads (50% of 4) and 1 scheduler thread online (25% of 4).</p>
      </item>
      <tag><marker id="+SDcpu"/><c><![CDATA[+SDcpu
        DirtyCPUSchedulers:DirtyCPUSchedulersOnline]]></c></tag>
      <item>
        <p>Sets the number of dirty CPU scheduler threads to create and dirty
          CPU scheduler threads to set online.
          The maximum for both values is 1024, and each value is
          further limited by the settings for normal schedulers:</p>
        <list type="bulleted">
          <item>The number of dirty CPU scheduler threads created cannot exceed
            the number of normal scheduler threads created.</item>
          <item>The number of dirty CPU scheduler threads online cannot exceed
            the number of normal scheduler threads online.</item>
        </list>
        <p>For details, see the <seealso marker="#+S"><c>+S</c></seealso> and
          <seealso marker="#+SP"><c>+SP</c></seealso>. By default, the number
          of dirty CPU scheduler threads created equals the number of normal
          scheduler threads created, and the number of dirty CPU scheduler
          threads online equals the number of normal scheduler threads online.
          <c>DirtyCPUSchedulers</c> can be omitted if
          <c>:DirtyCPUSchedulersOnline</c> is not and conversely. The number of
          dirty CPU schedulers online can be changed at runtime through
          <seealso marker="erlang#system_flag_dirty_cpu_schedulers_online">
          <c>erlang:system_flag(dirty_cpu_schedulers_online,
          DirtyCPUSchedulersOnline)</c></seealso>.</p>
	<p>The amount of dirty CPU schedulers is limited by the amount of
	  normal schedulers in order to limit the effect on processes
	  executing on ordinary schedulers. If the amount of dirty CPU
	  schedulers was allowed to be unlimited, dirty CPU bound jobs would
	  potentially starve normal jobs.</p>
      </item>
      <tag><marker id="+SDPcpu"/><c><![CDATA[+SDPcpu
        DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercentage]]></c></tag>
      <item>
        <p>Similar to <seealso marker="#+SDcpu"><c>+SDcpu</c></seealso> but
          uses percentages to set the number of dirty CPU scheduler threads to
          create and the number of dirty CPU scheduler threads to set online.
          Specified values must be
          &gt; 0. For example, <c>+SDPcpu 50:25</c> sets the number of dirty
          CPU scheduler threads to 50% of the logical processors configured
          and the number of dirty CPU scheduler threads online to 25% of the
          logical processors available. <c>DirtyCPUSchedulersPercentage</c> can
          be omitted if <c>:DirtyCPUSchedulersOnlinePercentage</c> is not and
          conversely. The number of dirty CPU schedulers online can be changed
          at runtime through
          <seealso marker="erlang#system_flag_dirty_cpu_schedulers_online">
          <c>erlang:system_flag(dirty_cpu_schedulers_online,
          DirtyCPUSchedulersOnline)</c></seealso>.</p>
        <p>This option interacts with <seealso
          marker="#+SDcpu"><c>+SDcpu</c></seealso> settings. For example, on a
          system with 8 logical cores configured and 8 logical cores available,
          the combination of the options <c>+SDcpu 4:4 +SDPcpu 50:25</c> (in
          either order) results in 2 dirty CPU scheduler threads (50% of 4) and
          1 dirty CPU scheduler thread online (25% of 4).</p>
      </item>
      <tag><marker id="+SDio"/><c><![CDATA[+SDio DirtyIOSchedulers]]></c></tag>
      <item>
        <p>Sets the number of dirty I/O scheduler threads to create.
          Valid range is 0-1024. By
          default, the number of dirty I/O scheduler threads created is 10,
          same as the default number of threads in the <seealso
          marker="#async_thread_pool_size">async thread pool</seealso>.</p>
	<p>The amount of dirty IO schedulers is not limited by the amount of
	  normal schedulers <seealso marker="#+SDcpu">like the amount of
	  dirty CPU schedulers</seealso>. This since only I/O bound work is
	  expected to execute on dirty I/O schedulers. If the user should schedule CPU
	  bound jobs on dirty I/O schedulers, these jobs might starve ordinary
	  jobs executing on ordinary schedulers.</p>
      </item>
      <tag><c><![CDATA[+sFlag Value]]></c></tag>
      <item>
        <p>Scheduling specific flags.</p>
        <taglist>
          <tag><marker id="+sbt"/><c>+sbt BindType</c></tag>
          <item>
            <p>Sets scheduler bind type.</p>
            <p>Schedulers can also be bound using flag
              <seealso marker="#+stbt"><c>+stbt</c></seealso>. The only
              difference between these two flags is how the following errors
              are handled:</p>
            <list type="bulleted">
              <item>Binding of schedulers is not supported on the specific
                platform.</item>
              <item>No available CPU topology. That is, the runtime system was
                not able to detect the CPU topology automatically, and no
                <seealso marker="#+sct">user-defined CPU topology</seealso>
                was set.</item>
            </list>
            <p>If any of these errors occur when <c>+sbt</c> has been passed,
              the runtime system prints an error message, and refuses to
              start. If any of these errors occur when <c>+stbt</c> has been
              passed, the runtime system silently ignores the error, and
              start up using unbound schedulers.</p>
            <p>Valid <c>BindType</c>s:</p>
            <taglist>
              <tag><c>u</c></tag>
              <item><c>unbound</c> - Schedulers are not bound to logical
                processors, that is, the operating system decides where the
                scheduler threads execute, and when to migrate them. This is
                the default.
              </item>
              <tag><c>ns</c></tag>
              <item><c>no_spread</c> - Schedulers with close scheduler
                identifiers are bound as close as possible in hardware.
              </item>
              <tag><c>ts</c></tag>
              <item><c>thread_spread</c> - Thread refers to hardware threads
                (such as Intel's hyper-threads). Schedulers with low scheduler
                identifiers, are bound to the first hardware thread of
                each core, then schedulers with higher scheduler identifiers
                are bound to the second hardware thread of each core,and so on.
              </item>
              <tag><c>ps</c></tag>
              <item><c>processor_spread</c> - Schedulers are spread like
                <c>thread_spread</c>, but also over physical processor chips.
              </item>
              <tag><c>s</c></tag>
              <item><c>spread</c> - Schedulers are spread as much as possible.
              </item>
              <tag><c>nnts</c></tag>
              <item><c>no_node_thread_spread</c> - Like <c>thread_spread</c>,
                but if multiple Non-Uniform Memory Access (NUMA) nodes exist,
                schedulers are spread over one NUMA node at a time,
                that is, all logical processors of one NUMA node are bound
                to schedulers in sequence.
              </item>
              <tag><c>nnps</c></tag>
              <item><c>no_node_processor_spread</c> - Like
                <c>processor_spread</c>, but if multiple NUMA nodes exist,
                schedulers are spread over one NUMA node at a time, that is,
                all logical processors of one NUMA node are bound to
                schedulers in sequence.
              </item>
              <tag><c>tnnps</c></tag>
              <item><c>thread_no_node_processor_spread</c> - A combination of
                <c>thread_spread</c>, and <c>no_node_processor_spread</c>.
                Schedulers are spread over hardware threads across NUMA
                nodes, but schedulers are only spread over processors
                internally in one NUMA node at a time.
              </item>
              <tag><c>db</c></tag>
              <item><c>default_bind</c> - Binds schedulers the default way.
                Defaults to <c>thread_no_node_processor_spread</c>
                (which can change in the future).
              </item>
            </taglist>
            <p>Binding of schedulers is only supported on newer
              Linux, Solaris, FreeBSD, and Windows systems.</p>
            <p>If no CPU topology is available when flag <c>+sbt</c>
              is processed and <c>BindType</c> is any other type than
              <c>u</c>, the runtime system fails to start. CPU
              topology can be defined using flag
              <seealso marker="#+sct"><c>+sct</c></seealso>. Notice
              that flag <c>+sct</c> can have to be passed before flag
              <c>+sbt</c> on the command line (if no CPU topology
              has been automatically detected).</p>
            <p>The runtime system does by default <em>not</em> bind schedulers
              to logical processors.</p>
            <note>
              <p>If the Erlang runtime system is the only operating system
                process that binds threads to logical processors, this
                improves the performance of the runtime system. However,
                if other operating system processes (for example
                another Erlang runtime system) also bind threads to
                logical processors, there can be a performance penalty
                instead. This performance penalty can sometimes be
                severe. If so, you are advised not to
                bind the schedulers.</p>
            </note>
            <p>How schedulers are bound matters. For example, in
              situations when there are fewer running processes than
              schedulers online, the runtime system tries to migrate
              processes to schedulers with low scheduler identifiers.
              The more the schedulers are spread over the hardware,
              the more resources are available to the runtime
              system in such situations.</p>
            <note>
              <p>If a scheduler fails to bind, this is
                often silently ignored, as it is not always
                possible to verify valid logical processor identifiers. If
                an error is reported, it is reported to the
                <c>error_logger</c>. If you want to verify that the
                schedulers have bound as requested, call
                <seealso marker="erlang#system_info_scheduler_bindings">
                <c>erlang:system_info(scheduler_bindings)</c></seealso>.</p>
            </note>
          </item>
          <tag><marker id="+sbwt"/>
            <c>+sbwt none|very_short|short|medium|long|very_long</c></tag>
          <item>
            <p>Sets scheduler busy wait threshold. Defaults to <c>medium</c>.
              The threshold determines how long schedulers are to busy
              wait when running out of work before going to sleep.</p>
            <note>
              <p>This flag can be removed or changed at any time
                without prior notice.</p>
            </note>
          </item>
          <tag><marker id="+sbwtdcpu"/>
            <c>+sbwtdcpu none|very_short|short|medium|long|very_long</c></tag>
          <item>
            <p>As <seealso marker="#+sbwt"><c>+sbwt</c></seealso> but affects
              dirty CPU schedulers. Defaults to <c>short</c>.</p>
            <note>
              <p>This flag can be removed or changed at any time
                without prior notice.</p>
            </note>
          </item>
          <tag><marker id="+sbwtdio"/>
            <c>+sbwtdio none|very_short|short|medium|long|very_long</c></tag>
          <item>
            <p>As <seealso marker="#+sbwt"><c>+sbwt</c></seealso> but affects
              dirty IO schedulers. Defaults to <c>short</c>.</p>
            <note>
              <p>This flag can be removed or changed at any time
                without prior notice.</p>
            </note>
          </item>
<tag><marker id="+scl"/><c>+scl true|false</c></tag>
          <item>
            <p>Enables or disables scheduler compaction of load. By default
              scheduler compaction of load is enabled. When enabled, load
              balancing strives for a load distribution, which causes
              as many scheduler threads as possible to be fully loaded (that is,
              not run out of work). This is accomplished by migrating load
              (for example, runnable processes) into a smaller set of schedulers
              when schedulers frequently run out of work. When disabled,
              the frequency with which schedulers run out of work is
              not taken into account by the load balancing logic.</p>
            <p><c>+scl false</c> is similar to
              <seealso marker="#+sub"><c>+sub true</c></seealso>, but
              <c>+sub true</c> also balances scheduler utilization
              between schedulers.</p>
          </item>
          <tag><marker id="+sct"/><c>+sct CpuTopology</c></tag>
          <item>
            <list type="bulleted">
              <item><c><![CDATA[<Id> = integer(); when 0 =< <Id> =< 65535]]></c>
              </item>
              <item><c><![CDATA[<IdRange> = <Id>-<Id>]]></c></item>
              <item><c><![CDATA[<IdOrIdRange> = <Id> | <IdRange>]]></c></item>
              <item><c><![CDATA[<IdList> = <IdOrIdRange>,<IdOrIdRange> |
                <IdOrIdRange>]]></c></item>
              <item><c><![CDATA[<LogicalIds> = L<IdList>]]></c></item>
              <item><c><![CDATA[<ThreadIds> = T<IdList> | t<IdList>]]></c>
              </item>
              <item><c><![CDATA[<CoreIds> = C<IdList> | c<IdList>]]></c></item>
              <item><c><![CDATA[<ProcessorIds> = P<IdList> | p<IdList>]]></c>
              </item>
              <item><c><![CDATA[<NodeIds> = N<IdList> | n<IdList>]]></c></item>
              <item><c><![CDATA[<IdDefs> =
                <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds> |
                <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>]]></c>
              </item>
              <item><c><![CDATA[CpuTopology = <IdDefs>:<IdDefs> |
                <IdDefs>]]></c></item>
            </list>
            <p>Sets a user-defined CPU topology. The user-defined
              CPU topology overrides any automatically detected
              CPU topology. The CPU topology is used when
              <seealso marker="#+sbt">binding schedulers to logical
              processors</seealso>.</p>
            <p>Uppercase letters signify real identifiers and lowercase
	      letters signify fake identifiers only used for description
              of the topology. Identifiers passed as real identifiers can
              be used by the runtime system when trying to access specific
              hardware; if they are incorrect the behavior is
              undefined. Faked logical CPU identifiers are not accepted,
              as there is no point in defining the CPU topology without
              real logical CPU identifiers. Thread, core, processor, and
              node identifiers can be omitted. If omitted, the thread ID
              defaults to <c>t0</c>, the core ID defaults to <c>c0</c>,
              the processor ID defaults to <c>p0</c>, and the node ID is
              left undefined. Either each logical processor must 
              belong to only one NUMA node, or no logical
              processors must belong to any NUMA nodes.</p>
            <p>Both increasing and decreasing <c><![CDATA[<IdRange>]]></c>s
              are allowed.</p>
            <p>NUMA node identifiers are system wide. That is, each NUMA
              node on the system must have a unique identifier. Processor
              identifiers are also system wide. Core identifiers are
              processor wide. Thread identifiers are core wide.</p>
            <p>The order of the identifier types implies the hierarchy of the
              CPU topology. The valid orders are as follows:</p>
            <list type="bulleted">
              <item>
                <p><c><![CDATA[<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>]]></c>,
                  that is, thread is part of a core that is part of a processor,
                  which is part of a NUMA node.</p>
              </item>
              <item>
                <p><c><![CDATA[<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>]]></c>,
                  that is, thread is part of a core that is part of a NUMA node,
                  which is part of a processor.</p>
              </item>
            </list>
            <p>A CPU topology can consist of both processor external, and
              processor internal NUMA nodes as long as each logical processor
              belongs to only one NUMA node. If
              <c><![CDATA[<ProcessorIds>]]></c> is omitted, its default position
              is before <c><![CDATA[<NodeIds>]]></c>. That is, the default is
              processor external NUMA nodes.</p>
            <p>If a list of identifiers is used in an
              <c><![CDATA[<IdDefs>]]></c>:</p>
            <list type="bulleted">
              <item><c><![CDATA[<LogicalIds>]]></c> must be a list
                of identifiers.</item>
              <item>At least one other identifier type besides
                <c><![CDATA[<LogicalIds>]]></c> must also have a
                list of identifiers.</item>
              <item>All lists of identifiers must produce the
                same number of identifiers.</item>
            </list>
            <p>A simple example. A single quad core processor can be
              described as follows:</p>
<pre>
% <input>erl +sct L0-3c0-3</input>
1> <input>erlang:system_info(cpu_topology).</input>
[{processor,[{core,{logical,0}},
             {core,{logical,1}},
             {core,{logical,2}},
             {core,{logical,3}}]}]</pre>
            <p>A more complicated example with two quad core
              processors, each processor in its own NUMA node.
              The ordering of logical processors is a bit weird.
              This to give a better example of identifier lists:</p>
<pre>
% <input>erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1</input>
1> <input>erlang:system_info(cpu_topology).</input>
[{node,[{processor,[{core,{logical,0}},
                    {core,{logical,1}},
                    {core,{logical,3}},
                    {core,{logical,2}}]}]},
 {node,[{processor,[{core,{logical,7}},
                    {core,{logical,4}},
                    {core,{logical,6}},
                    {core,{logical,5}}]}]}]</pre>
            <p>As long as real identifiers are correct, it is OK
              to pass a CPU topology that is not a correct
              description of the CPU topology. When used with
              care this can be very useful. This
              to trick the emulator to bind its schedulers
              as you want. For example, if you want to run multiple
              Erlang runtime systems on the same machine, you
              want to reduce the number of schedulers used and
              manipulate the CPU topology so that they bind to
              different logical CPUs. An example, with two Erlang
              runtime systems on a quad core machine:</p>
<pre>
% <input>erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one</input>
% <input>erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two</input></pre>
            <p>In this example, each runtime system have two
              schedulers each online, and all schedulers online
              will run on different cores. If we change to one
              scheduler online on one runtime system, and three
              schedulers online on the other, all schedulers
              online will still run on different cores.</p>
            <p>Notice that a faked CPU topology that does not reflect
              how the real CPU topology looks like is likely to
              decrease the performance of the runtime system.</p>
            <p>For more information, see
              <seealso marker="erlang#system_info_cpu_topology">
              <c>erlang:system_info(cpu_topology)</c></seealso>.</p>
          </item>
          <tag><marker id="+sfwi"/><c>+sfwi Interval</c></tag>
          <item>
            <p>Sets scheduler-forced wakeup interval. All run queues are
              scanned each <c>Interval</c> milliseconds. While there are
              sleeping schedulers in the system, one scheduler is woken
              for each non-empty run queue found. <c>Interval</c> default
              to <c>0</c>, meaning this feature is disabled.</p>
            <note>
              <p>This feature has been introduced as a temporary workaround
                for long-executing native code, and native code that does not
                bump reductions properly in OTP. When these bugs have be fixed,
                this flag will be removed.</p>
            </note>
          </item>
          <tag><marker id="+spp"/><c>+spp Bool</c></tag>
          <item>
            <p>Sets default scheduler hint for port parallelism. If set to
              <c>true</c>, the virtual machine schedules port tasks when it
              improves parallelism in the system. If set to <c>false</c>, the
              virtual machine tries to perform port tasks immediately,
              improving latency at the expense of parallelism. Default to
              <c>false</c>. The default used can be inspected in runtime by
              calling <seealso marker="erlang#system_info_port_parallelism">
              <c>erlang:system_info(port_parallelism)</c></seealso>.
              The default can be overridden on port creation by passing option
              <seealso marker="erlang#open_port_parallelism">
              <c>parallelism</c></seealso> to
              <seealso marker="erlang#open_port/2">
              <c>erlang:open_port/2</c></seealso></p>.
          </item>
          <tag><marker id="sched_thread_stack_size"/>
            <c><![CDATA[+sss size]]></c></tag>
          <item>
            <p>Suggested stack size, in kilowords, for scheduler threads.
              Valid range is 20-8192 kilowords. The default suggested
	      stack size is 128 kilowords.</p>
          </item>
          <tag><marker id="dcpu_sched_thread_stack_size"/>
            <c><![CDATA[+sssdcpu size]]></c></tag>
          <item>
            <p>Suggested stack size, in kilowords, for dirty CPU scheduler
	      threads. Valid range is 20-8192 kilowords. The default
	      suggested stack size is 40 kilowords.</p>
          </item>
          <tag><marker id="dio_sched_thread_stack_size"/>
            <c><![CDATA[+sssdio size]]></c></tag>
          <item>
            <p>Suggested stack size, in kilowords, for dirty IO scheduler
	      threads. Valid range is 20-8192 kilowords. The default
	      suggested stack size is 40 kilowords.</p>
          </item>
          <tag><marker id="+stbt"/><c>+stbt BindType</c></tag>
          <item>
            <p>Tries to set the scheduler bind type. The same as flag
              <seealso marker="#+sbt"><c>+sbt</c></seealso> except
              how some errors are handled. For more information, see
              <seealso marker="#+sbt"><c>+sbt</c></seealso>.</p>
          </item>
          <tag><marker id="+sub"/><c>+sub true|false</c></tag>
          <item>
            <p>Enables or disables
              <seealso marker="erts:erlang#statistics_scheduler_wall_time">
              scheduler utilization</seealso> balancing of load. By default
              scheduler utilization balancing is disabled and instead scheduler
              compaction of load is enabled, which strives for a load
              distribution that causes as many scheduler threads as possible
              to be fully loaded (that is, not run out of work). When scheduler
              utilization balancing is enabled, the system instead tries to
              balance scheduler utilization between schedulers. That is,
              strive for equal scheduler utilization on all schedulers.</p>
            <p><c>+sub true</c> is only supported on systems where the runtime
              system detects and uses a monotonically increasing high-resolution
              clock. On other systems, the runtime system fails to start.</p>
            <p><c>+sub true</c> implies <seealso marker="#+scl">
              <c>+scl false</c></seealso>. The difference between
              <c>+sub true</c> and <c>+scl false</c> is that <c>+scl false</c>
              does not try to balance the scheduler utilization.</p>
          </item>
          <tag><marker id="+swct"/>
            <c>+swct very_eager|eager|medium|lazy|very_lazy</c></tag>
          <item>
            <p>Sets scheduler wake cleanup threshold. Defaults to <c>medium</c>.
              Controls how eager schedulers are to be requesting
              wakeup because of certain cleanup operations. When a lazy setting
              is used, more outstanding cleanup operations can be left undone
              while a scheduler is idling. When an eager setting is used,
              schedulers are more frequently woken, potentially increasing
              CPU-utilization.</p>
            <note>
              <p>This flag can be removed or changed at any time without prior
                notice.</p>
            </note>
          </item>
          <tag><marker id="+sws"/><c>+sws default|legacy</c></tag>
          <item>
            <p>Sets scheduler wakeup strategy. Default strategy changed in
              ERTS 5.10 (Erlang/OTP R16A). This strategy was known as
              <c>proposal</c> in Erlang/OTP R15. The <c>legacy</c> strategy
              was used as default from R13 up to and including R15.</p>
            <note>
              <p>This flag can be removed or changed at any time without prior
                notice.</p>
            </note>
          </item>
          <tag><marker id="+swt"/>
            <c>+swt very_low|low|medium|high|very_high</c></tag>
          <item>
            <p>Sets scheduler wakeup threshold. Defaults to <c>medium</c>.
              The threshold determines when to wake up sleeping schedulers
              when more work than can be handled by currently awake schedulers
              exists. A low threshold causes earlier wakeups, and a high
              threshold causes later wakeups. Early wakeups distribute work
              over multiple schedulers faster, but work does more easily bounce
              between schedulers.</p>
            <note>
              <p>This flag can be removed or changed at any time without prior
                notice.</p>
            </note>
          </item>
          <tag><marker id="+swtdcpu"/>
            <c>+swtdcpu very_low|low|medium|high|very_high</c></tag>
          <item>
            <p>As <seealso marker="#+swt"><c>+swt</c></seealso> but
              affects dirty CPU schedulers. Defaults to <c>medium</c>.</p>
            <note>
              <p>This flag can be removed or changed at any time
                without prior notice.</p>
            </note>
          </item>
          <tag><marker id="+swtdio"/>
            <c>+swtdio very_low|low|medium|high|very_high</c></tag>
          <item>
            <p>As <seealso marker="#+swt"><c>+swt</c></seealso> but affects
              dirty IO schedulers. Defaults to <c>medium</c>.</p>
            <note>
              <p>This flag can be removed or changed at any time
                without prior notice.</p>
            </note>
          </item>
        </taglist>
      </item>
      <tag><marker id="+t"/><c><![CDATA[+t size]]></c></tag>
      <item>
        <p>Sets the maximum number of atoms the virtual machine can handle.
          Defaults to 1,048,576.</p>
      </item>
      <tag><marker id="+T"/><c><![CDATA[+T Level]]></c></tag>
      <item>
        <p>Enables modified timing and sets the modified timing level. Valid
          range is 0-9. The timing of the runtime system is changed. A high
          level usually means a greater change than a low level. Changing the
          timing can be very useful for finding timing-related bugs.</p>
        <p>Modified timing affects the following:</p>
        <taglist>
          <tag>Process spawning</tag>
          <item>A process calling <c><![CDATA[spawn]]></c>,
            <c><![CDATA[spawn_link]]></c>, <c><![CDATA[spawn_monitor]]></c>,
            or <c><![CDATA[spawn_opt]]></c> is scheduled out immediately
            after completing the call. When higher modified timing levels are
            used, the caller also sleeps for a while after it is scheduled out.
          </item>
          <tag>Context reductions</tag>
          <item>The number of reductions a process is allowed to use before it
            is scheduled out is increased or reduced.
          </item>
          <tag>Input reductions</tag>
          <item>The number of reductions performed before checking I/O is
            increased or reduced.
          </item>
        </taglist>
        <note>
          <p>Performance suffers when modified timing is enabled. This flag is
            <em>only</em> intended for testing and debugging.</p>
          <p><c><![CDATA[return_to]]></c> and <c><![CDATA[return_from]]></c>
            trace messages are lost when tracing on the spawn BIFs.</p>
          <p>This flag can be removed or changed at any time without prior
            notice.</p>
        </note>
      </item>
      <tag><c><![CDATA[+v]]></c></tag>
      <item>
        <p>Verbose.</p>
      </item>
      <tag><c><![CDATA[+V]]></c></tag>
      <item>
        <p>Makes the emulator print its version number.</p>
      </item>
      <tag><c><![CDATA[+W w | i | e]]></c></tag>
      <item>
        <p>Sets the mapping of warning messages for
          <c><![CDATA[error_logger]]></c>. Messages sent to the error logger
          using one of the warning routines can be mapped to errors
          (<c><![CDATA[+W e]]></c>), warnings (<c><![CDATA[+W w]]></c>), or
          information reports (<c><![CDATA[+W i]]></c>). Defaults to warnings.
          The current mapping can be retrieved using
          <c><![CDATA[error_logger:warning_map/0]]></c>. For more information,
          see <seealso marker="kernel:error_logger#warning_map/0">
          <c>error_logger:warning_map/0</c></seealso> in Kernel.</p>
      </item>
      <tag><c><![CDATA[+zFlag Value]]></c></tag>
      <item>
        <p>Miscellaneous flags:</p>
        <taglist>
          <tag><marker id="+zdbbl"/><c>+zdbbl size</c></tag>
          <item>
            <p>Sets the distribution buffer busy limit
              (<seealso marker="erlang#system_info_dist_buf_busy_limit">
              <c>dist_buf_busy_limit</c></seealso>)
              in kilobytes. Valid range is 1-2097151. Defaults to 1024.</p>
            <p>A larger buffer limit allows processes to buffer
              more outgoing messages over the distribution. When the
              buffer limit has been reached, sending processes will be
              suspended until the buffer size has shrunk. The buffer
              limit is per distribution channel. A higher limit
              gives lower latency and higher throughput at the expense
              of higher memory use.</p>
          </item>
          <tag><marker id="+zdntgc"/><c>+zdntgc time</c></tag>
          <item>
            <p>Sets the delayed node table garbage collection time
              (<seealso marker="erlang#system_info_delayed_node_table_gc">
              <c>delayed_node_table_gc</c></seealso>)
              in seconds. Valid values are either <c>infinity</c> or
              an integer in the range 0-100000000. Defaults to 60.</p>
            <p>Node table entries that are not referred linger
              in the table for at least the amount of time that this
              parameter determines. The lingering prevents repeated
              deletions and insertions in the tables from occurring.</p>
          </item>
        </taglist>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="environment_variables"></marker>
    <title>Environment Variables</title>
    <taglist>
      <tag><c><![CDATA[ERL_CRASH_DUMP]]></c></tag>
      <item>
        <p>If the emulator needs to write a crash dump, the value of this
          variable is the filename of the crash dump file.
          If the variable is not set, the name of the crash dump file is
          <c><![CDATA[erl_crash.dump]]></c> in the current directory.</p>
      </item>
      <tag><c><![CDATA[ERL_CRASH_DUMP_NICE]]></c></tag>
      <item>
      <p><em>Unix systems</em>: If the emulator needs to write a crash dump,
        it uses the value of this variable to set the nice value
        for the process, thus lowering its priority. Valid range is
        1-39 (higher values are replaced with 39). The highest
        value, 39, gives the process the lowest priority.</p>
      </item>
      <tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS]]></c></tag>
      <item>
        <p><em>Unix systems</em>: This variable gives the number of seconds
          that the emulator is allowed to spend writing a crash dump. When the
          given number of seconds have elapsed, the emulator is terminated.</p>
        <taglist>
          <tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=0]]></c></tag>
	  <item>If the variable is set to <c>0</c> seconds, the runtime system does
            not even attempt to write the crash dump file. It only terminates.
	    This is the default if option <c>-heart</c> is passed to <c>erl</c>
	    and <c>ERL_CRASH_DUMP_SECONDS</c> is not set.
	  </item>
          <tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=S]]></c></tag>
          <item>If the variable is set to a positive value <c>S</c>,
	    wait for <c>S</c> seconds to complete the crash dump file and
            then terminates the runtime system with a <c>SIGALRM</c> signal.
          </item>
          <tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=-1]]></c></tag>
          <item>A negative value causes the termination of the runtime system
	    to wait indefinitely until the crash dump file has been completly
	    written. This is the default if option <c>-heart</c> is <em>not</em>
	    passed to <c>erl</c> and <c>ERL_CRASH_DUMP_SECONDS</c> is not set.
          </item>
        </taglist>
        <p>See also <seealso marker="kernel:heart"><c>heart(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[ERL_CRASH_DUMP_BYTES]]></c></tag>
      <item>
      <p>This variable sets the maximum size of a crash dump file in bytes.
        The crash dump will be truncated if this limit is exceeded. If the
	variable is not set, no size limit is enforced by default. If the
	variable is set to <c>0</c>, the runtime system does not even attempt
	to write a crash dump file.</p>
      <p>Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).</p>
      </item>
      <tag><marker id="ERL_AFLAGS"/><c><![CDATA[ERL_AFLAGS]]></c></tag>
      <item>
        <p>The content of this variable is added to the beginning of the
          command line for <c><![CDATA[erl]]></c>.</p>
        <p>Flag <c><![CDATA[-extra]]></c> is treated in a special way. Its
          scope ends at the end of the environment variable content. Arguments
          following an <c><![CDATA[-extra]]></c> flag are moved on the command
          line into section <c><![CDATA[-extra]]></c>, that is, the end of the
          command line following an <c><![CDATA[-extra]]></c> flag.</p>
      </item>
      <tag><marker id="ERL_ZFLAGS"/><c><![CDATA[ERL_ZFLAGS]]></c> and
        <marker id="ERL_FLAGS"/><c><![CDATA[ERL_FLAGS]]></c></tag>
      <item>
        <p>The content of these variables are added to the end of the command
          line for <c><![CDATA[erl]]></c>.</p>
        <p>Flag <c><![CDATA[-extra]]></c> is treated in a special way. Its
          scope ends at the end of the environment variable content. Arguments
          following an <c><![CDATA[-extra]]></c> flag are moved on the command
          line into section <c><![CDATA[-extra]]></c>, that is, the end of the
          command line following an <c><![CDATA[-extra]]></c> flag.</p>
      </item>
      <tag><c><![CDATA[ERL_LIBS]]></c></tag>
      <item>
        <p>Contains a list of additional library directories that the code
          server searches for applications and adds to the code path; see
          <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
      </item>
      <tag><c><![CDATA[ERL_EPMD_ADDRESS]]></c></tag>
      <item>
        <p>Can be set to a comma-separated list of IP addresses, in which case
          the <seealso marker="epmd"><c>epmd</c></seealso> daemon listens only
          on the specified address(es) and on the loopback address (which is
          implicitly added to the list if it has not been specified).</p>
      </item>
      <tag><c><![CDATA[ERL_EPMD_PORT]]></c></tag>
      <item>
        <p>Can contain the port number to use when communicating with
          <seealso marker="epmd"><c>epmd</c></seealso>. The default port works
          fine in most cases. A different port can be specified
          to allow nodes of independent clusters to co-exist on the same host.
          All nodes in a cluster must use the same <c>epmd</c> port number.</p>
      </item>
    </taglist>
  </section>

  <section>
      <marker id="signals"></marker>
      <title>Signals</title>
      <p>On Unix systems, the Erlang runtime will interpret two types of signals.</p>
      <taglist>
          <tag><c>SIGUSR1</c></tag>
          <item>
              <p>A <c>SIGUSR1</c> signal forces a crash dump.</p>
          </item>
          <tag><c>SIGTERM</c></tag>
          <item>
              <p>A <c>SIGTERM</c> will produce a <c>stop</c> message to the <c>init</c> process.
                  This is equivalent to a <c>init:stop/0</c> call.</p>
              <p>Introduced in ERTS 8.3 (Erlang/OTP 19.3)</p>
          </item>
      </taglist>
      <p>The signal <c>SIGUSR2</c> is reserved for internal usage. No other signals are handled.</p>
  </section>

  <section>
    <marker id="configuration"></marker>
    <title>Configuration</title>
    <p>The standard Erlang/OTP system can be reconfigured to change the default
      behavior on startup.</p>
    <taglist>
      <tag>The <c>.erlang</c> startup file</tag>
      <item>
        <p>When Erlang/OTP is started, the system searches for a file named
        <c>.erlang</c> in the user's home directory.</p>
        <p>If an <c>.erlang</c> file is found, it is assumed to contain valid
          Erlang expressions. These expressions are evaluated as if they were
          input to the shell.</p>
        <p>A typical <c>.erlang</c> file contains a set of search paths, for
          example:</p>
    <code type="none"><![CDATA[
io:format("executing user profile in HOME/.erlang\n",[]).
code:add_path("/home/calvin/test/ebin").
code:add_path("/home/hobbes/bigappl-1.2/ebin").
io:format(".erlang rc finished\n",[]).    ]]></code>
      </item>
      <tag>user_default and shell_default</tag>
      <item>
        <p>Functions in the shell that are not prefixed by a module name are
          assumed to be functional objects (funs), built-in functions (BIFs),
          or belong to the module <c>user_default</c> or
          <c>shell_default</c>.</p>
        <p>To include private shell commands, define them in a module
          <c>user_default</c> and add the following argument as the first line
          in the <c>.erlang</c> file:</p>
        <code type="none"><![CDATA[
code:load_abs("..../user_default").    ]]></code>
      </item>
      <tag>erl</tag>
      <item>
        <p>If the contents of <c>.erlang</c> are changed and a private version
          of <c>user_default</c> is defined, the Erlang/OTP environment can be
          customized. More powerful changes can be made by supplying
          command-line arguments in the startup script <c>erl</c>. For more
          information, see <seealso marker="init"><c>init(3)</c></seealso>.</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>See Also</title>
    <p><seealso marker="epmd"><c>epmd(1)</c></seealso>,
      <seealso marker="erl_prim_loader"><c>erl_prim_loader(3)</c></seealso>,
      <seealso marker="erts_alloc"><c>erts_alloc(3)</c></seealso>,
      <seealso marker="init"><c>init(3)</c></seealso>,
      <seealso marker="kernel:application">
        <c>application(3)</c></seealso>,
      <seealso marker="kernel:auth"><c>auth(3)</c></seealso>,
      <seealso marker="kernel:code"><c>code(3)</c></seealso>,
      <seealso marker="kernel:erl_boot_server">
        <c>erl_boot_server(3)</c></seealso>,
      <seealso marker="kernel:heart"><c>heart(3)</c></seealso>,
      <seealso marker="kernel:net_kernel"><c>net_kernel(3)</c></seealso>,
      <seealso marker="tools:make"><c>make(3)</c></seealso></p>
  </section>
</comref>