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

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<!DOCTYPE comref SYSTEM "comref.dtd">

<comref>
  <header>
    <copyright>
      <year>1996</year><year>2010</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>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 wants 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 which 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 of ERTS version 5.8 (OTP-R14A) the runtime system will by
               default bind schedulers to logical processors using the
	       <c>default_bind</c> bind type if the amount of schedulers are
	       at least equal to the amount of logical processors configured,
	       binding of schedulers is supported, and a CPU topology is
	       available at startup.
	    </p><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 (as for example
	       another Erlang runtime system) also bind threads to
	       logical processors, there might be a performance penalty
	       instead. If this is the case you, are are advised to
	       unbind the schedulers using the
	       <seealso marker="#+sbt">+sbtu</seealso> command line argument,
	       or by invoking
	       <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type,
	       unbound)</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 the character <c><![CDATA[+]]></c> is
              interpreted as an <seealso marker="#emu_flags">emulator flag</seealso>.</p>
            <p>As indicated by the name, emulator flags controls
              the behavior of the emulator.</p>
          </item>
          <item>
            <p>Any argument starting with the character <c><![CDATA[-]]></c>
              (hyphen) is interpreted as a
              <seealso marker="#init_flags">flag</seealso> which should
              be passed to the Erlang part of the runtime system, more
              specifically to the <c><![CDATA[init]]></c> system process, see
              <seealso marker="init">init(3)</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>It can be noted that there are a small number of "-"
              flags 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. Additionally, the flag <c><![CDATA[-extra]]></c>
              causes everything that follows to become plain arguments.</p>
          </item>
        </list>
        <p>Example:</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 will cause 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>. Note that the list of user flags is
      not exhaustive, there may be additional, application specific
      flags which instead are documented 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">app(4)</seealso> and
          <seealso marker="kernel:application">application(3)</seealso>.</p>
      </item>
      <tag><marker id="args_file"><c><![CDATA[-args_file FileName]]></c></marker></tag>
      <item>
        <p>Command line arguments are read from the file <c><![CDATA[FileName]]></c>.
          The arguments read from the file replace the
          '<c><![CDATA[-args_file FileName]]></c>' flag on the resulting command line.</p>
        <p>The file <c><![CDATA[FileName]]></c> should be a plain text file and may
          contain comments and command line arguments. A comment begins
          with a # character and continues until next end of line character.
          Backslash (\\) is used as quoting character. All command line
          arguments accepted by <c><![CDATA[erl]]></c> are allowed, also the
          <c><![CDATA[-args_file FileName]]></c> flag. Be careful not to cause circular
          dependencies between files containing the <c><![CDATA[-args_file]]></c> flag,
          though.</p>
        <p>The <c><![CDATA[-extra]]></c> flag is treated specially. 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,
          i.e. 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 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">init(3)</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">systools:make_script/1,2</seealso>.</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">code(3)</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>. Not recommended - use
          <seealso marker="erlc">erlc</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">app(4)</seealso> and
          <seealso marker="kernel:application">application(3)</seealso>.</p>
      </item>
      <tag><marker id="connect_all"><c><![CDATA[-connect_all false]]></c></marker></tag>
      <item>
        <p>If this flag is present, <c><![CDATA[global]]></c> will not maintain a
          fully connected network of distributed Erlang nodes, and then
          global name registration cannot be used. See
          <seealso marker="kernel:global">global(3)</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.</p>
      </item>
      <tag><c><![CDATA[-emu_args]]></c></tag>
      <item>
        <p>Useful for debugging. Prints out the actual arguments
          sent to the 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
          the <c><![CDATA[DISPLAY]]></c> environment variable set to <c><![CDATA[gin:0]]></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">init(3)</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 heart beat monitoring of the Erlang runtime system.
          See <seealso marker="kernel:heart">heart(3)</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
          either of the connected nodes, i.e. neither 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">global_group(3)</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">erl_boot_server(3)</seealso>.
          This flag is mandatory if the <c><![CDATA[-loader inet]]></c> flag is
          present.</p>
        <p>The IP addresses must be given 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 the <c><![CDATA[-sname]]></c> or
          <c><![CDATA[-name]]></c> flag.</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)</marker></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 analysed using the module <c><![CDATA[instrument]]></c>.
          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">erl_prim_loader(3)</seealso>.
          Two <c><![CDATA[Loader]]></c> methods are supported, <c><![CDATA[efile]]></c> and
          <c><![CDATA[inet]]></c>. <c><![CDATA[efile]]></c> means use the local file system,
          this is the default. <c><![CDATA[inet]]></c> means use a boot server on
          another machine, and the <c><![CDATA[-id]]></c>, <c><![CDATA[-hosts]]></c> and
          <c><![CDATA[-setcookie]]></c> flags must be specified as well. 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">make(3)</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>Indicates if the system should load code dynamically
          (<c><![CDATA[interactive]]></c>), or if all code should be loaded
          during system initialization (<c><![CDATA[embedded]]></c>), see
          <seealso marker="kernel:code">code(3)</seealso>. Defaults to
          <c><![CDATA[interactive]]></c>.</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">net_kernel(3)</seealso>.
          It is also ensured that <c><![CDATA[epmd]]></c> runs on the current host
          before Erlang is started. See
          <seealso marker="epmd">epmd(1)</seealso>.</p>
        <p>The name of the node 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 the <c><![CDATA[-sname]]></c> flag instead.</p>
      </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">code(3)</seealso>.</p>
      </item>
      <tag><c><![CDATA[-oldshell]]></c></tag>
      <item>
        <p>Invokes the old Erlang shell from Erlang 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 <c><![CDATA[code:add_pathsa/1]]></c>. See
          <seealso marker="kernel:code">code(3)</seealso>.
	  As an alternative to <c>-pa</c>, if several directories are
	  to be prepended to the code and the directories have a
	  common parent directory, that parent directory could be
	  specified in the <c>ERL_LIBS</c> environment variable.
	  See <seealso marker="kernel:code">code(3)</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">code(3)</seealso>.</p>
      </item>
      <tag><c><![CDATA[-remsh Node]]></c></tag>
      <item>
        <p>Starts Erlang with a remote shell connected to <c><![CDATA[Node]]></c>.</p>
      </item>
      <tag><c><![CDATA[-rsh Program]]></c></tag>
      <item>
        <p>Specifies an alternative to <c><![CDATA[rsh]]></c> for starting a slave
          node on a remote host. See
          <seealso marker="stdlib:slave">slave(3)</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">init(3)</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">init(3)</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">erlang:set_cookie/2</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> ms 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 DNS (Domain Name System) is not running. There can be no
          communication between nodes running with the <c><![CDATA[-sname]]></c>
          flag and those running with the <c><![CDATA[-name]]></c> flag, as node
          names must be unique in distributed Erlang systems.</p>
      </item>
      <tag><marker id="smp"><c><![CDATA[-smp [enable|auto|disable]]]></c></marker></tag>
      <item>
        <p><c>-smp enable</c> and <c>-smp</c> starts the Erlang runtime
	  system with SMP support enabled. This may fail if no runtime
	  system with SMP support is available. <c>-smp auto</c> starts
	  the Erlang runtime system with SMP support enabled if it is
	  available and more than one logical processor are detected.
	  <c>-smp disable</c> starts a runtime system without SMP support.
	  By default <c>-smp auto</c> will be used unless a conflicting
	  parameter has been passed, then <c>-smp disable</c> will be
	  used. Currently only the <c>-hybrid</c> parameter conflicts
	  with <c>-smp auto</c>.</p>
        <p><em>NOTE</em>: The runtime system with SMP support will not
          be available on all supported platforms. See also the
          <seealso marker="#+S">+S</seealso> flag.</p>
      </item>
      <tag><c><![CDATA[-version]]></c>(emulator flag)</tag>
      <item>
        <p>Makes the emulator print out 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></marker></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, i.e, 64
          kilobyte on 32-bit architectures. This small default size
          has been chosen since the amount of async-threads might
          be quite large. The default size is enough for drivers
          delivered with Erlang/OTP, but might not be sufficiently
          large for other dynamically linked in drivers that use the
          <seealso marker="erl_driver#driver_async">driver_async()</seealso>
          functionality. Note that the value passed is only a
          suggestion, and it might even be ignored on some
          platforms.</p>
      </item>
      <tag><marker id="async_thread_pool_size"><c><![CDATA[+A size]]></c></marker></tag>
      <item>
        <p>Sets the number of threads in async thread pool, valid range
          is 0-1024. Default is 0.</p>
      </item>
      <tag><c><![CDATA[+B [c | d | i]]]></c></tag>
      <item>
        <p>The <c><![CDATA[c]]></c> option makes <c><![CDATA[Ctrl-C]]></c> interrupt the current
          shell instead of invoking the emulator break handler.
          The <c><![CDATA[d]]></c> option (same as specifying <c><![CDATA[+B]]></c> without an
          extra option) disables the break handler. The <c><![CDATA[i]]></c> option
          makes the emulator ignore any break signal.</p>
        <p>If the <c><![CDATA[c]]></c> option 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>Note that on Windows, this flag is only applicable for 
          <c><![CDATA[werl]]></c>, not <c><![CDATA[erl]]></c> (<c><![CDATA[oldshell]]></c>). Note also that
          <c><![CDATA[Ctrl-Break]]></c> is used instead of <c><![CDATA[Ctrl-C]]></c> on Windows.</p>
      </item>
      <tag><c><![CDATA[+c]]></c></tag>
      <item>
        <p>Disable compensation for sudden changes of system time.</p>
        <p>Normally, <c><![CDATA[erlang:now/0]]></c> will not immediately reflect
          sudden changes in the system time, in order to keep timers
          (including <c><![CDATA[receive-after]]></c>) working. Instead, the time
          maintained by <c><![CDATA[erlang:now/0]]></c> is slowly adjusted towards
          the new system time. (Slowly means in one percent adjustments;
          if the time is off by one minute, the time will be adjusted
          in 100 minutes.)</p>
        <p>When the <c><![CDATA[+c]]></c> option is given, this slow adjustment
          will not take place. Instead <c><![CDATA[erlang:now/0]]></c> will always
          reflect the current system time. Note that timers are based
          on <c><![CDATA[erlang:now/0]]></c>. If the system time jumps, timers
          then time out at the wrong time.</p>
      </item>
      <tag><c><![CDATA[+d]]></c></tag>
      <item>
        <p>If the emulator detects an internal error (or runs out of memory),
	it will by default generate both a crash dump and a core dump.
	The core dump will, however, not be very useful since the content
	of process heaps is destroyed by the crash dump generation.</p>

	<p>The <c>+d</c> option instructs the emulator to only produce a
	core dump and no crash dump if an internal error is detected.</p>

	<p>Calling <c>erlang:halt/1</c> with a string argument will still
	produce a crash dump.</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><c><![CDATA[+K true | false]]></c></tag>
      <item>
        <p>Enables or disables the kernel poll functionality if
          the emulator supports it. Default is <c><![CDATA[false]]></c> (disabled).
          If the emulator does not support kernel poll, and
          the <c><![CDATA[+K]]></c> flag is passed to the emulator, a warning is
          issued at startup.</p>
      </item>
      <tag><c><![CDATA[+l]]></c></tag>
      <item>
        <p>Enables auto load tracing, displaying info while loading
          code.</p>
      </item>
      <tag><marker id="erts_alloc"><c><![CDATA[+MFlag Value]]></c></marker></tag>
      <item>
        <p>Memory allocator specific flags, see
          <seealso marker="erts_alloc">erts_alloc(3)</seealso> for
          further information.</p>
      </item>
      <tag><marker id="max_processes"><c><![CDATA[+P Number]]></c></marker></tag>
      <item>
        <p>Sets the maximum number of concurrent processes for this
          system. <c><![CDATA[Number]]></c> must be in the range 16..134217727.
          Default is 32768.</p>
      </item>
      <tag><marker id="compat_rel"><c><![CDATA[+R ReleaseNumber]]></c></marker></tag>
      <item>
        <p>Sets the compatibility mode.</p>
        <p>The distribution mechanism is not backwards compatible by
          default. This flags 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[7..<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>
        <p>For example, an R10 node is not automatically compatible
          with an R9 node, but R10 nodes started with the <c><![CDATA[+R 9]]></c>
          flag can co-exist with R9 nodes in the same distributed
          Erlang system, they are R9-compatible.</p>
        <p>Note: Make sure 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>
        <p>For example: A distributed Erlang system can consist of
          R10 nodes, or of R9 nodes and R9-compatible R10 nodes, but
          not of R9 nodes, R9-compatible R10 nodes and "regular" R10
          nodes, as R9 and "regular" R10 nodes are not compatible.</p>
      </item>
      <tag><c><![CDATA[+r]]></c></tag>
      <item>
        <p>Force ets memory block to be moved on realloc.</p>
      </item>
      <tag><marker id="+rg"><c><![CDATA[+rg ReaderGroupsLimit]]></c></marker></tag>
      <item>
        <p>Limits the amount of reader groups used by read/write locks
	   optimized for read operations in the Erlang runtime system. By
	   default the reader groups limit equals 8.</p>
	<p>When the amount of schedulers is less than or equal to the reader
	   groups limit, each scheduler has its own reader group. When the
	   amount of schedulers is larger than the reader groups limit,
	   schedulers share reader groups. Shared reader groups degrades
	   read lock and read unlock performance while a large amount of
	   reader groups degrades write lock performance, so the limit is a
	   tradeoff between performance for read operations and performance
	   for write operations. Each reader group currently consumes 64 byte
	   in each read/write lock. Also note that a runtime system using
	   shared reader groups benefits from <seealso marker="#+sbt">binding
	   schedulers to logical processors</seealso>, since the reader groups
	   are distributed better between schedulers.</p>
      </item>
      <tag><marker id="+S"><c><![CDATA[+S Schedulers:SchedulerOnline]]></c></marker></tag>
      <item>
        <p>Sets the amount of scheduler threads to create and scheduler
	  threads to set online when SMP support has been enabled.
	  Valid range for both values are 1-1024. If the
          Erlang runtime system is able to determine the amount
          of logical processors configured and logical processors available,
	  <c>Schedulers</c> will default to logical processors configured,
	  and <c>SchedulersOnline</c> will default to logical processors
	  available; otherwise, the default values will be 1. <c>Schedulers</c>
	  may be omitted if <c>:SchedulerOnline</c> is not and vice versa. The
	  amount of schedulers online can be changed at run time via
	  <seealso marker="erlang#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>.
	</p>
        <p>This flag will be ignored if the emulator doesn't have
          SMP support enabled (see the <seealso marker="#smp">-smp</seealso>
          flag).</p>
      </item>
      <tag><c><![CDATA[+sFlag Value]]></c></tag>
      <item>
        <p>Scheduling specific flags.</p>
        <taglist>
          <tag><marker id="+sbt"><c>+sbt BindType</c></marker></tag>
          <item>
            <p>Set scheduler bind type. Currently valid <c>BindType</c>s:
	    </p>
	    <taglist>
	      <tag><c>u</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, unbound)</seealso>.
	      </p></item>
	      <tag><c>ns</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, no_spread)</seealso>.
	      </p></item>
	      <tag><c>ts</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, thread_spread)</seealso>.
	      </p></item>
	      <tag><c>ps</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, processor_spread)</seealso>.
	      </p></item>
	      <tag><c>s</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, spread)</seealso>.
	      </p></item>
	      <tag><c>nnts</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, no_node_thread_spread)</seealso>.
	      </p></item>
	      <tag><c>nnps</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, no_node_processor_spread)</seealso>.
	      </p></item>
	      <tag><c>tnnps</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, thread_no_node_processor_spread)</seealso>.
	      </p></item>
	      <tag><c>db</c></tag>
	      <item><p>Same as
	      <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, default_bind)</seealso>.
	      </p></item>
	    </taglist>
	    <p>Binding of schedulers is currently only supported on newer
	       Linux, Solaris, FreeBSD, and Windows systems.</p>
	    <p>If no CPU topology is available when the <c>+sbt</c> flag
	       is processed and <c>BindType</c> is any other type than
	       <c>u</c>, the runtime system will fail to start. CPU
	       topology can be defined using the
	       <seealso marker="#+sct">+sct</seealso> flag. Note
	       that the <c>+sct</c> flag may have to be passed before the
	       <c>+sbt</c> flag on the command line (in case no CPU topology
	       has been automatically detected).</p>
            <p>The runtime system will by default bind schedulers to logical
	       processors using the <c>default_bind</c> bind type if the amount
	       of schedulers are at least equal to the amount of logical
	       processors configured, binding of schedulers is supported,
	       and a CPU topology is available at startup.
	    </p>
	    <p><em>NOTE:</em> 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 (as for example another Erlang runtime
	       system) also bind threads to logical processors, there might be a
	       performance penalty instead. If this is the case you, are advised
	       to unbind the schedulers using the <c>+sbtu</c> command line
	       argument, or by invoking
	       <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type,
	       unbound)</seealso>.</p>
	    <p>For more information, see
	    <seealso marker="erlang#system_flag_scheduler_bind_type">erlang:system_flag(scheduler_bind_type, SchedulerBindType)</seealso>.
	    </p>
          </item>
          <tag><marker id="+sct"><c>+sct CpuTopology</c></marker></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>Upper-case letters signify real identifiers and lower-case
	       letters signify fake identifiers only used for description
	       of the topology. Identifiers passed as real identifiers may
	       be used by the runtime system when trying to access specific
	       hardware and if they are not correct the behavior is
	       undefined. Faked logical CPU identifiers are not accepted
	       since there is no point in defining the CPU topology without
	       real logical CPU identifiers. Thread, core, processor, and
	       node identifiers may be left out. If left out, thread id
	       defaults to <c>t0</c>, core id defaults to <c>c0</c>,
	       processor id defaults to <c>p0</c>, and node id will
	       be left undefined. Either each logical processor must 
	       belong to one and 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 have to 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 imply the hierarchy of the
	        CPU topology. Valid orders are either
		<c><![CDATA[<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>]]></c>,
		or
		<c><![CDATA[<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>]]></c>.
		That is, thread is part of a core which is part of a processor
		which is part of a NUMA node, or thread is part of a core which
		is part of a NUMA node which is part of a processor. A cpu
		topology can consist of both processor external, and processor
		internal NUMA nodes as long as each logical processor belongs
		to one and only one NUMA node. If <c><![CDATA[<ProcessorIds>]]></c>
		is left out, its default position will be 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> have to be a list
	             of identifiers.</item>
	       <item>At least one other identifier type apart from
		     <c><![CDATA[<LogicalIds>]]></c> also have to have a
		     list of identifiers.</item>
	       <item>All lists of identifiers have to produce the
	             same amount of identifiers.</item>
             </list>
	     <p>A simple example. A single quad core processor may be
	        described this way:</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 little more complicated example. Two quad core
	        processors. Each processor in its own NUMA node.
		The ordering of logical processors is a little weird.
		This in order 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 okay
	        to pass a CPU topology that is not a correct
		description of the CPU topology. When used with
		care this can actually be very useful. This in
		order 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 amount 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>Note 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_flag_cpu_topology">erlang:system_flag(cpu_topology, CpuTopology)</seealso>.</p>
          </item>
	  <tag><marker id="+swt"><c>+swt very_low|low|medium|high|very_high</c></marker></tag>
	  <item>
             <p>Set scheduler wakeup threshold. Default is <c>medium</c>.
	        The threshold determines when to wake up sleeping schedulers
		when more work than can be handled by currently awake schedulers
		exist. A low threshold will cause earlier wakeups, and a high
		threshold will cause later wakeups. Early wakeups will
		distribute work over multiple schedulers faster, but work will
		more easily bounce between schedulers.
	     </p>
             <p><em>NOTE:</em> This flag may be removed or changed at any time
	        without prior notice.
	     </p>
	  </item>
	  <tag><marker id="sched_thread_stack_size"><c><![CDATA[+sss size]]></c></marker></tag>
	  <item>
	    <p>Suggested stack size, in kilowords, for scheduler threads.
            Valid range is 4-8192 kilowords. The default stack size
            is OS dependent.</p>
	  </item>
        </taglist>
      </item>
      <tag><marker id="+t"><c><![CDATA[+t size]]></c></marker></tag>
      <item>
        <p>Set the maximum number of atoms the VM can handle. Default is 1048576.</p>
      </item>
      <tag><marker id="+T"><c><![CDATA[+T Level]]></c></marker></tag>
      <item>
        <p>Enables modified timing and sets the modified timing level.
          Currently valid range is 0-9. The timing of the runtime system
          will change. 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>Currently, modified timing affects the following:</p>
        <taglist>
          <tag>Process spawning</tag>
          <item>
            <p>A process calling <c><![CDATA[spawn]]></c>, <c><![CDATA[spawn_link]]></c>,
              <c><![CDATA[spawn_monitor]]></c>, or <c><![CDATA[spawn_opt]]></c> will be scheduled
              out immediately after completing the call. When higher modified
              timing levels are used, the caller will also sleep for a while
              after being scheduled out.</p>
          </item>
          <tag>Context reductions</tag>
          <item>The amount of reductions a process is a allowed to
           use before being scheduled out is increased or reduced.</item>
          <tag>Input reductions</tag>
          <item>The amount of reductions performed before checking I/O
           is increased or reduced.</item>
        </taglist>
        <p><em>NOTE:</em> Performance will suffer when modified timing
          is enabled. This flag is <em>only</em> intended for testing and
          debugging. Also note that <c><![CDATA[return_to]]></c> and <c><![CDATA[return_from]]></c>
          trace messages will be lost when tracing on the spawn BIFs. This
          flag may be removed or changed at any time without prior notice.</p>
      </item>
      <tag><c><![CDATA[+V]]></c></tag>
      <item>
        <p>Makes the emulator print out its version number.</p>
      </item>
      <tag><c><![CDATA[+v]]></c></tag>
      <item>
        <p>Verbose.</p>
      </item>
      <tag><c><![CDATA[+W w | i]]></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 either to errors (default), warnings 
          (<c><![CDATA[+W w]]></c>), or info reports (<c><![CDATA[+W i]]></c>). The current
          mapping can be retrieved using
          <c><![CDATA[error_logger:warning_map/0]]></c>. See
          <seealso marker="kernel:error_logger#warning_map/0">error_logger(3)</seealso>
          for further information.</p>
      </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 will be the file name of the crash dump file.
          If the variable is not set, the name of the crash dump file will
          be <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 will use the value of this variable to set the nice value
          for the process, thus lowering its priority. The allowable range is
          1 through 39 (higher values will be replaced with 39). The highest
          value, 39, will give 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 will be allowed to spend writing a crash dump. When
          the given number of seconds have elapsed, the emulator will be
          terminated by a SIGALRM signal.</p>
      </item>
      <tag><c><![CDATA[ERL_AFLAGS]]></c></tag>
      <item>
        <p>The content of this environment variable will be added to the
          beginning of the command line for <c><![CDATA[erl]]></c>.</p>
        <p>The <c><![CDATA[-extra]]></c> flag is treated specially. 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
          the <c><![CDATA[-extra]]></c> section, i.e. the end of the command line
          following after an <c><![CDATA[-extra]]></c> flag.</p>
      </item>
      <tag><c><![CDATA[ERL_ZFLAGS]]></c>and <c><![CDATA[ERL_FLAGS]]></c></tag>
      <item>
        <p>The content of these environment variables will be added to the
          end of the command line for <c><![CDATA[erl]]></c>.</p>
        <p>The <c><![CDATA[-extra]]></c> flag is treated specially. 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
          the <c><![CDATA[-extra]]></c> section, i.e. the end of the command line
          following after an <c><![CDATA[-extra]]></c> flag.</p>
      </item>
      <tag><c><![CDATA[ERL_LIBS]]></c></tag>
      <item>
        <p>This environment variable contains a list of additional library
	  directories that the code server will search for applications and
	  add to the code path.
  	  See <seealso marker="kernel:code">code(3)</seealso>.</p>
      </item>
      <tag><c><![CDATA[ERL_EPMD_PORT]]></c></tag>
      <item>
        <p>This environment variable can contain the port number to use when
          communicating with <seealso marker="epmd">epmd</seealso>. The default
          port will work 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 epmd port number.</p>
      </item>
    </taglist>
  </section>

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