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  <header>
    <copyright>
      <year>1996</year><year>2022</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
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    </legalnotice>

    <title>kernel</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <app>kernel</app>
  <appsummary>The Kernel application.</appsummary>
  <description>
    <p>The Kernel application has all the code necessary to run
      the Erlang runtime system: file servers, code servers,
      and so on.</p>
    <p>The Kernel application is the first application started. It is
      mandatory in the sense that the minimal system based on
      Erlang/OTP consists of Kernel and STDLIB. Kernel
      contains the following functional areas:</p>
    <list type="bulleted">
      <item>Start, stop, supervision, configuration, and distribution of applications</item>
      <item>Code loading</item>
      <item>Logging</item>
      <item>Global name service</item>
      <item>Supervision of Erlang/OTP</item>
      <item>Communication with sockets</item>
      <item>Operating system interface</item>
    </list>
  </description>

  <section>
    <title>Logger Handlers</title>
    <p>Two standard logger handlers are defined in
      the Kernel application. These are described in the
      <seeguide marker="logger_chapter">Kernel User's Guide</seeguide>,
      and in the <seeerl marker="logger_std_h"><c>logger_std_h(3)</c></seeerl>
      and <seeerl marker="logger_disk_log_h"><c>logger_disk_log_h(3)</c>
      </seeerl> manual pages.</p>
  </section>

  <section>
      <marker id="erl_signal_server"/>
      <title>OS Signal Event Handler</title>
      <p>Asynchronous OS signals may be subscribed to via the Kernel applications event manager
          (see <seeguide marker="system/design_principles:des_princ">OTP Design Principles</seeguide> and
          <seeerl marker="stdlib:gen_event"><c>gen_event(3)</c></seeerl>) registered as <c>erl_signal_server</c>.
          A default signal handler is installed which handles the following signals:</p>
          <taglist>
              <tag><c>sigusr1</c></tag>
              <item><p>The default handler will halt Erlang and produce a crashdump
                      with slogan "Received SIGUSR1".
                      This is equivalent to calling <c>erlang:halt("Received SIGUSR1")</c>.
              </p></item>

              <tag><c>sigquit</c></tag>
              <item><p>The default handler will halt Erlang immediately.
                      This is equivalent to calling <c>erlang:halt()</c>.
              </p></item>

              <tag><c>sigterm</c></tag>
              <item><p>The default handler will terminate Erlang normally.
                      This is equivalent to calling <c>init:stop()</c>.
              </p></item>
          </taglist>

          <section>
              <title>Events</title>
              <p>Any event handler added to <c>erl_signal_server</c> must handle the following events.</p>
              <taglist>
                  <tag><c>sighup</c></tag>
                  <item><p>Hangup detected on controlling terminal or death of controlling process</p></item>
                  <tag><c>sigquit</c></tag>
                  <item><p>Quit from keyboard</p></item>
                  <tag><c>sigabrt</c></tag>
                  <item><p>Abort signal from abort</p></item>
                  <tag><c>sigalrm</c></tag>
                  <item><p>Timer signal from alarm</p></item>
                  <tag><c>sigterm</c></tag>
                  <item><p>Termination signal</p></item>
                  <tag><c>sigusr1</c></tag>
                  <item><p>User-defined signal 1</p></item>
                  <tag><c>sigusr2</c></tag>
                  <item><p>User-defined signal 2</p></item>
                  <tag><c>sigchld</c></tag>
                  <item><p>Child process stopped or terminated</p></item>
                  <tag><c>sigstop</c></tag>
                  <item><p>Stop process</p></item>
                  <tag><c>sigtstp</c></tag>
                  <item><p>Stop typed at terminal</p></item>
              </taglist>

              <p>Setting OS signals are described in <seemfa marker="os#set_signal/2"><c>os:set_signal/2</c></seemfa>.</p>
          </section>
  </section>

  <section>
    <marker id="configuration"/>
    <title>Configuration</title>
    <p>The following configuration parameters are defined for the Kernel
      application. For more information about configuration parameters,
    see file <seefile marker="app"><c>app(4)</c></seefile>.</p>
    <taglist>
      <tag><marker id="distributed"/><c>distributed = [Distrib]</c></tag>
      <item>
        <p>Specifies which applications that are distributed and on which
          nodes they are allowed to execute. In this parameter:</p>
        <list type="bulleted">
          <item><c>Distrib = {App,Nodes} | {App,Time,Nodes}</c></item>
          <item><c>App = atom()</c></item>
          <item><c>Time = integer()>0</c></item>
          <item><c>Nodes = [node() | {node(),...,node()}]</c></item>
        </list>
        <p>The parameter is described in
	  <seemfa marker="application#load/2"><c>application:load/2</c></seemfa>.</p>
      </item>
      <tag><marker id="dist_auto_connect"/><c>dist_auto_connect = Value</c></tag>
      <item>
        <p>Specifies when nodes are automatically connected. If
          this parameter is not specified, a node is always
          automatically connected, for example, when a message is to be sent to
          that node. <c>Value</c> is one of:</p>
        <taglist>
          <tag><c>never</c></tag>
          <item><p>Connections are never automatically established, they
           must be explicitly connected. See
	   <seeerl marker="net_kernel"><c>net_kernel(3)</c></seeerl>.</p></item>
          <tag><c>once</c></tag>
          <item><p>Connections are established automatically, but only
           once per node. If a node goes down, it must thereafter be
           explicitly connected. See
	   <seeerl marker="net_kernel"><c>net_kernel(3)</c></seeerl>.</p></item>
        </taglist>
      </item>
      <tag><marker id="dist_listen"/><c>dist_listen = boolean()</c></tag>
      <item>
        <p>Specifies whether this node should be listening for incoming
        distribution connections. Using this option implies that the node
        also is <seecom marker="erts:erl#hidden"><c>-hidden</c></seecom>.</p>
      </item>
      <tag><marker id="permissions"/><c>permissions = [Perm]</c></tag>
      <item>
        <p>Specifies the default permission for applications when they
          are started. In this parameter:</p>
        <list type="bulleted">
          <item><c>Perm = {ApplName,Bool}</c></item>
          <item><c>ApplName = atom()</c></item>
          <item><c>Bool = boolean()</c></item>
        </list>
        <p>Permissions are described in
	  <seemfa marker="application#permit/2"><c>application:permit/2</c></seemfa>.</p>
      </item>
      <tag><marker id="logger"/><c>logger = [Config]</c></tag>
      <item>
        <p>Specifies the configuration
	  for <seeerl marker="logger">Logger</seeerl>, except the
	  primary log level, which is specified
	  with <seeapp marker="#logger_level"><c>logger_level</c></seeapp>,
	  and the compatibility
	  with <seeguide marker="sasl:error_logging">SASL Error
	  Logging</seeguide>, which is specified
	  with <seeapp marker="#logger_sasl_compatible">
	    <c>logger_sasl_compatible</c></seeapp>.</p>
        <p>The <c>logger </c> parameter is described in
          section <seeguide marker="logger_chapter#logger_parameter">
	    Logging</seeguide> in the Kernel User's Guide.</p>
      </item>
      <tag><marker id="logger_level"/><c>logger_level = Level</c></tag>
      <item>
	<p>Specifies the primary log level for Logger. Log events with
	  the same, or a more severe level, pass through the primary
	  log level check. See
	  section <seeguide marker="logger_chapter">Logging</seeguide>
	  in the Kernel User's Guide for more information about Logger
	  and log levels.</p>
	<p><c>Level = emergency | alert | critical | error | warning |
	    notice | info | debug | all | none</c></p>
	<p>To change the primary log level at runtime, use
          <seemfa marker="logger#set_primary_config/2">
            <c>logger:set_primary_config(level, Level)</c></seemfa>.</p>
	<p>Defaults to <c>notice</c>.</p>
      </item>
      <tag><marker id="logger_metadata"/><c>logger_metadata = Metadata</c></tag>
      <item>
	<p>Specifies primary metadata for log events.</p>
	<p><c>Metadata = map()</c></p>
	<p>Defaults to <c>#{}</c>.</p>
      </item>
      <tag><marker id="logger_sasl_compatible"/>
	<c>logger_sasl_compatible = true | false</c></tag>
      <item>
	<p>Specifies if Logger behaves backwards compatible with the
	  SASL error logging functionality from releases prior to
	  Erlang/OTP 21.0.</p>
	<p>If this parameter is set to <c>true</c>, the default Logger
	  handler does not log any progress-, crash-, or supervisor
	  reports. If the SASL application is then started, it adds a
	  Logger handler named <c>sasl</c>, which logs these events
	  according to values of the SASL configuration
	  parameter <c>sasl_error_logger</c>
	  and <c>sasl_errlog_type</c>.</p>
	<p>See section
	  <seeapp marker="sasl:sasl_app#deprecated_error_logger_config">
	    Deprecated Error Logger Event Handlers and
	 Configuration</seeapp> in the sasl(6) manual page for
	 information about the SASL configuration parameters.</p>
	<p>See section <seeguide marker="sasl:error_logging">SASL Error
	  Logging</seeguide> in the SASL User's Guide, and
	  section <seeguide marker="logger_chapter#compatibility">Backwards
	  Compatibility with error_logger</seeguide> in the Kernel
	  User's Guide for information about the SASL error logging
	  functionality, and how Logger can be backwards compatible
	  with this.</p>
	<p>Defaults to <c>false</c>.</p>
	<note>
	  <p>If this parameter is set to <c>true</c>,
	    <c>sasl_errlog_type</c> indicates that progress reports
	    shall be logged, and the configured primary log level
	    is <c>notice</c> or more severe, then SASL automatically
	    sets the primary log level to <c>info</c>. That is, this
	    setting can potentially overwrite the value of the Kernel
	    configuration parameter <c>logger_level</c>. This is to
	    allow progress reports, which have log level <c>info</c>,
	    to be forwarded to the handlers.</p>
	</note>
      </item>
      <tag><marker id="global_groups"/><c>global_groups = [GroupTuple]</c></tag>
      <item>
        <p>Defines global groups, see
	  <seeerl marker="global_group"><c>global_group(3)</c></seeerl>.
	In this parameter:</p>
        <list type="bulleted">
          <item><p><c>GroupTuple = {GroupName, [Node]} | {GroupName, PublishType, [Node]}</c></p></item>
          <item><p><c>GroupName = atom()</c></p></item>
          <item><p><c>PublishType = normal | hidden</c></p></item>
          <item><p><c>Node = node()</c></p></item>
        </list>
      </item>
      <tag><marker id="inet_default_connect_options"/><c>inet_default_connect_options = [{Opt, Val}]</c></tag>
      <item>
        <p>Specifies default options for <c>connect</c> sockets,
          see <seeerl marker="inet"><c>inet(3)</c></seeerl>.</p>
      </item>
      <tag><marker id="inet_default_listen_options"/><c>inet_default_listen_options = [{Opt, Val}]</c></tag>
      <item>
        <p>Specifies default options for <c>listen</c> (and
          <c>accept</c>) sockets, see <seeerl marker="inet"><c>inet(3)</c></seeerl>.</p>
      </item>
      <tag><marker id="inet_dist_use_interface"/><c>inet_dist_use_interface = ip_address()</c></tag>
      <item>
        <p>If the host of an Erlang node has many network interfaces,
          this parameter specifies which one to listen on. For the type definition
	  of <c>ip_address()</c>,
	  see <seeerl marker="inet"><c>inet(3)</c></seeerl>.</p>
      </item>
      <tag><marker id="inet_dist_listen"/><c>inet_dist_listen_min = First</c><br/><c>inet_dist_listen_max = Last</c></tag>
      <item>
        <p>Defines the <c>First..Last</c> port range for the listener
          socket of a distributed Erlang node.</p>
      </item>
      <tag><marker id="inet_dist_listen_options"/><c>inet_dist_listen_options = Opts</c></tag>
      <item>
        <p>Defines a list of extra socket options to be used when opening the
	  listening socket for a distributed Erlang node.
	  See <seemfa marker="gen_tcp#listen/2"><c>gen_tcp:listen/2</c></seemfa>.</p>
      </item>
      <tag><marker id="inet_dist_connect_options"/><c>inet_dist_connect_options = Opts</c></tag>
      <item>
        <p>Defines a list of extra socket options to be used when connecting to
	  other distributed Erlang nodes.
	  See <seemfa marker="gen_tcp#connect/4"><c>gen_tcp:connect/4</c></seemfa>.</p>
      </item>
      <tag><marker id="inet_parse_error_log"/><c>inet_parse_error_log = silent</c></tag>
      <item>
        <p>If set, no log events are issued when erroneous lines are
          found and skipped in the various Inet configuration
          files.</p>
      </item>
      <tag><marker id="inetrc"/><c>inetrc = Filename</c></tag>
      <item>
        <p>The name (string) of an Inet user configuration file. For details,
	see section
	<seeguide marker="erts:inet_cfg"><c>Inet Configuration</c></seeguide>
	in the ERTS User's Guide.</p>
      </item>
      <tag><marker id="net_setuptime"/><c>net_setuptime = SetupTime</c></tag>
      <item>
        <marker id="net_setuptime"></marker>
        <p><c>SetupTime</c> must be a positive integer or floating point
          number, and is interpreted as the maximum allowed time
          for each network operation during connection setup to another
          Erlang node. The maximum allowed value is <c>120</c>. If higher values
          are specified, <c>120</c> is used. Default is 7 seconds if the variable
          is not specified, or if the value is incorrect (for example, not a number).</p>
        <p>Notice that this value does not limit the total connection
          setup time, but rather each individual network operation during
          the connection setup and handshake.</p>
      </item>
      <tag><marker id="net_ticker_spawn_options"/><c>net_ticker_spawn_options = Opts</c></tag>
      <item>
        <p>
          Defines a list of extra spawn options for net ticker processes. There exist
          one such process for each connection to another node. A net ticker process is
          responsible for supervising the connection it is associated with. These
          processes also execute the distribution handshake protocol when setting up
          connections. When there is a large number of distribution connections,
          setting up garbage collection options can be helpful to reduce memory usage.
          Default is <c>[link, {priority, max}]</c>, and these two options cannot be
          changed. The <c>monitor</c> and <c>{monitor, MonitorOpts}</c> options are
          not allowed and will be dropped if present. See the documentation of the
          <seemfa marker="erts:erlang#spawn_opt/4"><c>erlang:spawn_opt/4</c></seemfa>
          BIF for information about valid options. If the <c>Opts</c> list is not
          a proper list, or containing invalid options the setup of connections
          will fail.
        </p>
        <p>
          Note that the behavior described above is only true if the distribution
          carrier protocol used is implemented as described in
 	  <seeguide marker="erts:alt_dist#distribution_module">ERTS
	  User's Guide ➜ How to implement an Alternative Carrier
	  for the Erlang Distribution ➜ Distribution Module</seeguide> without
          further alterations. The implementer of the distribution carrier protocol
          used, may have chosen to ignore the <c>net_ticker_spawn_options</c> parameter
          or altered its behavior. Currently all distribution modules shipped with OTP
          do, however, behave as described above.
        </p>
      </item>
      <tag><marker id="net_tickintensity"/><c>net_tickintensity = NetTickIntensity</c></tag>
      <item>
        <p><i>Net tick intensity</i> specifies how many ticks to send during a
        <seeapp marker="#net_ticktime">net tick time</seeapp> period when
        no other data is sent over a connection to another node. This also
        determines how often to check for data from the other node. The
        higher net tick intensity, the closer to the chosen net tick time period
        the node will detect an unresponsive node. The net tick intensity
        defaults to <c>4</c>. The value of <c>NetTickIntensity</c> should be
        an integer in the range <c>4..1000</c>. If the <c>NetTickIntensity</c>
        is not an integer or an integer less than <c>4</c>, <c>4</c> will
        silently be used. If <c>NetTickIntensity</c> is an integer larger than
        <c>1000</c>, <c>1000</c> will silently be used.
        </p>
        <note>
          <p>Note that all communicating nodes are expected to use the same
          <i>net tick intensity</i> as well as the same <i>net tick time</i>.</p>
        </note>
        <warning>
          <p>Be careful not to set a too high net tick intensity, since you
          can overwhelm the node with work if it is set too high.</p>
        </warning>
      </item>
      <tag><marker id="net_ticktime"/><c>net_ticktime = NetTickTime</c></tag>
      <item>
        <p>Specifies the <i>net tick time</i> in seconds. This is the
	approximate time a connected node may be unresponsive until it is
	considered down and thereby disconnected.</p>
        <p>Net tick time together with <seeapp marker="#net_tickintensity">net
        tick intensity</seeapp> determines an interval <c>TickInterval =
        NetTickTime/NetTickIntensity</c>. Once every <c>TickInterval</c> seconds,
        each connected node is ticked if nothing has been sent to it during that
        last <c>TickInterval</c> seconds. A tick is a small package sent on the
        connection.
        A connected node is considered to be down if no ticks or payload packages
        have been received during the last <c>NetTickIntensity</c> number of
        <c>TickInterval</c> seconds intervals. This ensures that nodes that
        are not responding, for reasons such as hardware errors, are considered
        to be down.</p>
        <p>As the availability is only checked every <c>TickInterval</c> seconds,
	the actual time <c>T</c> a node have been unresponsive when
	detected may vary between <c>MinT</c> and <c>MaxT</c>,
	where:</p>
        <code type="none">
MinT = NetTickTime - NetTickTime / NetTickIntensity
MaxT = NetTickTime + NetTickTime / NetTickIntensity</code>
        <p><c>NetTickTime</c> defaults to <c>60</c> seconds and
        <c>NetTickIntensity</c> defaults to <c>4</c>. Thus,
        <c><![CDATA[45 < T < 75]]></c> seconds.</p>
        <note>
        <p>Notice that <em>all</em> communicating nodes are to have the
	<em>same</em> <c>NetTickTime</c> and <c>NetTickIntensity</c> values
        specified, as it determines both the frequency of outgoing ticks and
        the expected frequency of incominging ticks.</p>
        </note>
        <p><c>NetTickTime</c> needs to be a multiple of <c>NetTickIntensity</c>.
        If the configured values are not, <c>NetTickTime</c> will internally be
        rounded up to the nearest millisecond.
        <seemfa marker="net_kernel#get_net_ticktime/0"><c>net_kernel:get_net_ticktime()</c></seemfa>
        will, however, report net tick time truncated to the nearest second.
        </p>
        <p>Normally, a terminating node is detected immediately by the transport
	protocol (like TCP/IP).</p>
      </item>
      <tag><marker id="prevent_overlapping_partitions"/>
      <c>prevent_overlapping_partitions = true | false</c></tag>
      <item>
        <p>
          If enabled (<c>true</c>), <c>global</c> will actively prevent
          overlapping partitions from forming when connections are lost
          between nodes. This fix is enabled by default. If you are about
          to disable this fix, make sure to read the
          <seeerl marker="kernel:global#prevent_overlapping_partitions">
            <c>global(3)</c></seeerl> documentation about this fix for
            more important information about this.
        </p>
      </item>
      <tag><marker id="shutdown_timeout"/><c>shutdown_timeout = integer() | infinity</c></tag>
      <item>
        <p>Specifies the time <c>application_controller</c> waits
          for an application to terminate during node shutdown. If the
          timer expires, <c>application_controller</c> brutally
          kills <c>application_master</c> of the hanging
          application. If this parameter is undefined, it defaults
          to <c>infinity</c>.</p>
      </item>
      <tag><marker id="sync_nodes_mandatory"/><c>sync_nodes_mandatory = [NodeName]</c></tag>
      <item>
        <p>Specifies which other nodes that <em>must</em> be alive
          for this node to start properly. If some node in the list
          does not start within the specified time, this node does not
          start either. If this parameter is undefined, it defaults to
          <c>[]</c>.</p>
      </item>
      <tag><marker id="sync_nodes_optional"/><c>sync_nodes_optional = [NodeName]</c></tag>
      <item>
        <p>Specifies which other nodes that <em>can</em> be alive
          for this node to start properly. If some node in this list
          does not start within the specified time, this node starts
          anyway. If this parameter is undefined, it defaults to
          the empty list.</p>
      </item>
      <tag><marker id="sync_nodes_timeout"/><c>sync_nodes_timeout = integer() | infinity</c></tag>
      <item>
        <p>Specifies the time (in milliseconds) that this node
          waits for the mandatory and optional nodes to start. If
          this parameter is undefined, no node synchronization is
          performed. This option ensures that <c>global</c> is
          synchronized.</p>
      </item>
      <tag><marker id="start_distribution"/><c>start_distribution = true | false</c></tag>
      <item>
        <p>Starts all distribution services, such as <c>rpc</c>,
          <c>global</c>, and <c>net_kernel</c> if the parameter is
          <c>true</c>. This parameter is to be set to <c>false</c>
          for systems who want to disable all distribution functionality.</p>
        <p>Defaults to <c>true</c>.</p>
      </item>
      <tag><marker id="start_dist_ac"/><c>start_dist_ac = true | false</c></tag>
      <item>
        <p>Starts the <c>dist_ac</c> server if the parameter is
          <c>true</c>. This parameter is to be set to <c>true</c> for
          systems using distributed applications.</p>
        <p>Defaults to <c>false</c>.  If this parameter is
          undefined, the server is started if parameter
          <c>distributed</c> is set.</p>
      </item>
      <tag><marker id="start_boot_server"/><c>start_boot_server = true | false</c></tag>
      <item>
        <p>Starts the <c>boot_server</c> if the parameter is <c>true</c>
          (see <seeerl marker="erl_boot_server"><c>erl_boot_server(3)</c></seeerl>).
	  This parameter is to be set to <c>true</c> in an embedded system
	  using this service.</p>
        <p>Defaults to <c>false</c>.</p>
      </item>
      <tag><marker id="boot_server_slaves"/><c>boot_server_slaves = [SlaveIP]</c></tag>
      <item>
        <p>If configuration parameter <c>start_boot_server</c> is
          <c>true</c>, this parameter can be used to initialize
          <c>boot_server</c> with a list of slave IP addresses:</p>
	<p>
          <c>SlaveIP = string() | atom | {integer(),integer(),integer(),integer()}</c>,</p>
        <p>where <c><![CDATA[0 <= integer() <=255]]></c>.</p>
        <p>Examples of <c>SlaveIP</c> in atom, string, and tuple form:</p>
	<p><c>'150.236.16.70', "150,236,16,70", {150,236,16,70}</c>.</p>
        <p>Defaults to <c>[]</c>.</p>
      </item>
      <tag><marker id="start_disk_log"/><c>start_disk_log = true | false</c></tag>
      <item>
        <p>Starts the <c>disk_log_server</c> if the parameter is
          <c>true</c> (see <seeerl marker="disk_log"><c>disk_log(3)</c></seeerl>).
	  This parameter is to be set to <c>true</c> in an embedded system
	  using this service.</p>
        <p>Defaults to <c>false</c>.</p>
      </item>
      <tag><marker id="start_pg"/><c>start_pg = true | false</c></tag>
      <item>
        <marker id="start_pg"></marker>
        <p>Starts the default <c>pg</c> scope server (see
          <seeerl marker="pg"><c>pg(3)</c></seeerl>) if
          the parameter is <c>true</c>. This parameter is to be set to
          <c>true</c> in an embedded system that uses this service.</p>
        <p>Defaults to <c>false</c>.</p>
      </item>
      <tag><marker id="start_timer"/><c>start_timer = true | false</c></tag>
      <item>
        <p>Starts the <c>timer_server</c> if the parameter is
          <c>true</c> (see <seeerl marker="stdlib:timer"><c>timer(3)</c></seeerl>).
	  This parameter is to be set to <c>true</c> in an embedded system
	  using this service.</p>
        <p>Defaults to <c>false</c>.</p>
      </item>
      <tag><marker id="shell_history"/><c>shell_history = enabled | disabled | module()</c></tag>
      <item>
        <p>Specifies whether shell history should be logged to disk
           between usages of <c>erl</c> (<c>enabled</c>), not logged
           at all (<c>disabled</c>), or a user-specified module will
           be used to log shell history. This module should export
           <c>load() -> [string()]</c> returning a list of strings to
           load in the shell when it starts, and <c>add(iodata()) -> ok.</c>
           called every time new line is entered in the shell. By default
           logging is disabled.</p>
      </item>
      <tag><marker id="shell_history_drop"/><c>shell_history_drop = [string()]</c></tag>
      <item>
        <p>Specific log lines that should not be persisted. For
           example <c>["q().", "init:stop()."]</c> will allow to
           ignore commands that shut the node down. Defaults to
           <c>[]</c>.</p>
      </item>
      <tag><marker id="shell_history_file_bytes"/><c>shell_history_file_bytes = integer()</c></tag>
      <item>
        <p>How many bytes the shell should remember. By default, the
           value is set to 512kb, and the minimal value is 50kb.</p>
      </item>
      <tag><marker id="shell_history_path"/><c>shell_history_path = string()</c></tag>
      <item>
        <p>Specifies where the shell history files will be stored.
           defaults to the user's cache directory as returned by
           <c>filename:basedir(user_cache, "erlang-history")</c>.</p>
      </item>
      <tag><marker id="shutdown_func"/><c>shutdown_func = {Mod, Func}</c></tag>
      <item>
        <p>Where:</p>
        <list type="bulleted">
          <item><c>Mod = atom()</c></item>
          <item><c>Func = atom()</c></item>
        </list>
        <p>Sets a function that <c>application_controller</c> calls
          when it starts to terminate. The function is called as
          <c>Mod:Func(Reason)</c>, where <c>Reason</c> is the terminate
          reason for <c>application_controller</c>, and it must
          return as soon as possible for <c>application_controller</c>
          to terminate properly.</p>
      </item>
      <tag><marker id="source_search_rules"/><c>source_search_rules = [DirRule] | [SuffixRule] </c></tag>
      <item>
	<marker id="source_search_rules"></marker>
        <p>Where:</p>
        <list type="bulleted">
          <item><c>DirRule = {ObjDirSuffix,SrcDirSuffix}</c></item>
          <item><c>SuffixRule = {ObjSuffix,SrcSuffix,[DirRule]}</c></item>
          <item><c>ObjDirSuffix = string()</c></item>
          <item><c>SrcDirSuffix = string()</c></item>
          <item><c>ObjSuffix = string()</c></item>
          <item><c>SrcSuffix = string()</c></item>
        </list>
        <p>Specifies a list of rules for use by
	  <seemfa marker="stdlib:filelib#find_file/2">
	  <c>filelib:find_file/2</c></seemfa>
	  <seemfa marker="stdlib:filelib#find_source/2">
	  <c>filelib:find_source/2</c></seemfa>
          If this is set to some other value
          than the empty list, it replaces the default rules. Rules can be
          simple pairs of directory suffixes, such as <c>{"ebin",
          "src"}</c>, which are used by <c>filelib:find_file/2</c>, or
          triples specifying separate directory suffix rules depending on
          file name extensions, for example <c>[{".beam", ".erl", [{"ebin",
          "src"}]}</c>, which are used by <c>filelib:find_source/2</c>. Both
          kinds of rules can be mixed in the list.</p>
	  <p>The interpretation of <c>ObjDirSuffix</c> and <c>SrcDirSuffix</c>
	  is as follows: if the end of the directory name where an
	  object is located matches <c>ObjDirSuffix</c>, then the
	  name created by replacing <c>ObjDirSuffix</c> with
	  <c>SrcDirSuffix</c> is expanded by calling
	  <seemfa marker="stdlib:filelib#wildcard/1">
	  <c>filelib:wildcard/1</c></seemfa>, and the first regular
	  file found among the matches is the source file.
	</p>

      </item>
    </taglist>
  </section>

  <section>
    <title>Deprecated Configuration Parameters</title>
    <p>In Erlang/OTP 21.0, a new API for logging was added. The
      old <c>error_logger</c> event manager, and event handlers
      running on this manager, still work, but they are no longer used
      by default.</p>
    <p>The following application configuration parameters can still be
      set, but they are only used if the corresponding configuration
      parameters for Logger are not set.</p>
    <taglist>
      <tag><c>error_logger</c></tag>
      <item>Replaced by setting the <seeerl
      marker="logger_std_h#type"><c>type</c></seeerl>, and possibly
      <seeerl marker="logger_std_h#file"><c>file</c></seeerl> and
      <seeerl marker="logger_std_h#modes"><c>modes</c></seeerl>
      parameters of the default <c>logger_std_h</c> handler. Example:
      <code type="none">
erl -kernel logger '[{handler,default,logger_std_h,#{config=>#{file=>"/tmp/erlang.log"}}}]'
      </code>
      </item>
      <tag><c>error_logger_format_depth</c></tag>
      <item>Replaced by setting the <seeerl marker="logger_formatter#depth"><c>depth</c></seeerl>
      parameter of the default handlers formatter. Example:
      <code type="none">
erl -kernel logger '[{handler,default,logger_std_h,#{formatter=>{logger_formatter,#{legacy_header=>true,template=>[{logger_formatter,header},"\n",msg,"\n"],depth=>10}}}]'
      </code>
      </item>
    </taglist>
    <p>See <seeguide marker="logger_chapter#compatibility">Backwards
	compatibility with error_logger</seeguide> for more
      information.</p>
  </section>

  <section>
    <title>See Also</title>
    <p><seefile marker="app"><c>app(4)</c></seefile>,
      <seeerl marker="application"><c>application(3)</c></seeerl>,
      <seeerl marker="code"><c>code(3)</c></seeerl>,
      <seeerl marker="disk_log"><c>disk_log(3)</c></seeerl>,
      <seeerl marker="erl_boot_server"><c>erl_boot_server(3)</c></seeerl>,
      <seeerl marker="erl_ddll"><c>erl_ddll(3)</c></seeerl>,
      <seeerl marker="file"><c>file(3)</c></seeerl>,
      <seeerl marker="global"><c>global(3)</c></seeerl>,
      <seeerl marker="global_group"><c>global_group(3)</c></seeerl>,
      <seeerl marker="heart"><c>heart(3)</c></seeerl>,
      <seeerl marker="inet"><c>inet(3)</c></seeerl>,
      <seeerl marker="logger"><c>logger(3)</c></seeerl>,
      <seeerl marker="net_kernel"><c>net_kernel(3)</c></seeerl>,
      <seeerl marker="os"><c>os(3)</c></seeerl>,
      <seeerl marker="pg"><c>pg(3)</c></seeerl>,
      <seeerl marker="rpc"><c>rpc(3)</c></seeerl>,
      <seeerl marker="seq_trace"><c>seq_trace(3)</c></seeerl>,
      <seeerl marker="user"><c>user(3)</c></seeerl>,
      <seeerl marker="stdlib:timer"><c>timer(3)</c></seeerl></p>
  </section>
</appref>
