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<header>
<copyright>
<year>1996</year><year>2016</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
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Licensed under the Apache License, Version 2.0 (the "License");
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<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>Error 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>Error Logger Event Handlers</title>
<p>Two standard error logger event handlers are defined in
the Kernel application. These are described in
<seealso marker="error_logger"><c>error_logger(3)</c></seealso>.</p>
</section>
<section>
<title>Configuration</title>
<p>The following configuration parameters are defined for the Kernel
application. For more information about configuration parameters,
see file <seealso marker="app"><c>app(4)</c></seealso>.</p>
<taglist>
<tag><c>browser_cmd = string() | {M,F,A}</c></tag>
<item>
<p>When pressing the <em>Help</em> button in a tool such as Debugger,
the help text (an HTML file <c>File</c>) is by default
displayed in a Netscape browser, which is required to be
operational. This parameter can be used to change the command for
how to display the help text if another browser than Netscape
is preferred, or if another platform than Unix or Windows is
used.</p>
<p>If set to a string <c>Command</c>, the command
<c>"Command File"</c> is evaluated using
<seealso marker="os#cmd/1"><c>os:cmd/1</c></seealso>.</p>
<p>If set to a module-function-args tuple, <c>{M,F,A}</c>,
the call <c>apply(M,F,[File|A])</c> is evaluated.</p>
</item>
<tag><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
<seealso marker="application#load/2"><c>application:load/2</c></seealso>.</p>
</item>
<tag><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
<seealso marker="net_kernel"><c>net_kernel(3)</c></seealso>.</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
<seealso marker="net_kernel"><c>net_kernel(3)</c></seealso>.</p></item>
</taglist>
</item>
<tag><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
<seealso marker="application#permit/2"><c>application:permit/2</c></seealso>.</p>
</item>
<tag><c>error_logger = Value</c></tag>
<item>
<p><c>Value</c> is one of:</p>
<taglist>
<tag><c>tty</c></tag>
<item><p>Installs the standard event handler, which prints error
reports to <c>stdio</c>. This is the default option.</p></item>
<tag><c>{file, FileName}</c></tag>
<item><p>Installs the standard event handler, which prints error
reports to file <c>FileName</c>, where <c>FileName</c>
is a string.</p></item>
<tag><c>false</c></tag>
<item>
<p>No standard event handler is installed, but
the initial, primitive event handler is kept, printing
raw event messages to <c>tty</c>.</p>
</item>
<tag><c>silent</c></tag>
<item>
<p>Error logging is turned off.</p>
</item>
</taglist>
</item>
<tag><c>error_logger_format_depth = Depth</c></tag>
<item>
<marker id="error_logger_format_depth"></marker>
<p>Can be used to limit the size of the
formatted output from the error logger event handlers.</p>
<note><p>This configuration parameter was introduced in OTP 18.1
and is experimental. Based on user feedback, it
can be changed or improved in future releases, for example,
to gain better control over how to limit the size of the
formatted output. We have no plans to remove this
new feature entirely, unless it turns out to be
useless.</p></note>
<p><c>Depth</c> is a positive integer representing the maximum
depth to which terms are printed by the error logger event
handlers included in OTP. This
configuration parameter is used by the two event handlers
defined by the Kernel application and the two event
handlers in the SASL application.
(If you have implemented your own error handlers, this configuration
parameter has no effect on them.)</p>
<p><c>Depth</c> is used as follows: Format strings
passed to the event handlers are rewritten.
The format controls <c>~p</c> and <c>~w</c> are replaced with
<c>~P</c> and <c>~W</c>, respectively, and <c>Depth</c> is
used as the depth parameter. For details, see
<seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
in STDLIB.</p>
<note><p>A reasonable starting value for <c>Depth</c> is
<c>30</c>. We recommend to test crashing various processes in your
application, examine the logs from the crashes, and then
increase or decrease the value.</p></note>
</item>
<tag><c>global_groups = [GroupTuple]</c></tag>
<item>
<marker id="global_groups"></marker>
<p>Defines global groups, see
<seealso marker="global_group"><c>global_group(3)</c></seealso>.
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><c>inet_default_connect_options = [{Opt, Val}]</c></tag>
<item>
<p>Specifies default options for <c>connect</c> sockets,
see <seealso marker="inet"><c>inet(3)</c></seealso>.</p>
</item>
<tag><c>inet_default_listen_options = [{Opt, Val}]</c></tag>
<item>
<p>Specifies default options for <c>listen</c> (and
<c>accept</c>) sockets, see <seealso marker="inet"><c>inet(3)</c></seealso>.</p>
</item>
<tag><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 <seealso marker="inet"><c>inet(3)</c></seealso>.</p>
</item>
<tag><c>{inet_dist_listen_min, First}</c> and <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><c>{inet_dist_listen_options, Opts}</c></tag>
<item>
<marker id="inet_dist_listen_options"></marker>
<p>Defines a list of extra socket options to be used when opening the
listening socket for a distributed Erlang node.
See <seealso marker="gen_tcp#listen/2"><c>gen_tcp:listen/2</c></seealso>.</p>
</item>
<tag><c>{inet_dist_connect_options, Opts}</c></tag>
<item>
<marker id="inet_dist_connect_options"></marker>
<p>Defines a list of extra socket options to be used when connecting to
other distributed Erlang nodes.
See <seealso marker="gen_tcp#connect/4"><c>gen_tcp:connect/4</c></seealso>.</p>
</item>
<tag><c>inet_parse_error_log = silent</c></tag>
<item>
<p>If set, no
<c>error_logger</c> messages are generated when erroneous
lines are found and skipped in the various Inet configuration
files.</p>
</item>
<tag><c>inetrc = Filename</c></tag>
<item>
<p>The name (string) of an Inet user configuration file. For details,
see section
<seealso marker="erts:inet_cfg"><c>Inet Configuration</c></seealso>
in the ERTS User's Guide.</p>
</item>
<tag><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><c>net_ticktime = TickTime</c></tag>
<item>
<marker id="net_ticktime"></marker>
<p>Specifies the <c>net_kernel</c> tick time. <c>TickTime</c>
is specified in seconds. Once every <c>TickTime/4</c> second, all
connected nodes are ticked (if anything else is written
to a node). If nothing is received from another node
within the last four tick times, that node is considered
to be down. This ensures that nodes that are not responding,
for reasons such as hardware errors, are considered to be
down.</p>
<p>The time <c>T</c>, in which a node that is not responding is
detected, is calculated as <c><![CDATA[MinT < T < MaxT]]></c>, where:</p>
<code type="none">
MinT = TickTime - TickTime / 4
MaxT = TickTime + TickTime / 4</code>
<p><c>TickTime</c> defaults to <c>60</c> (seconds). Thus,
<c><![CDATA[45 < T < 75]]></c> seconds.</p>
<p>Notice that <em>all</em> communicating nodes are to have the <em>same</em>
<c>TickTime</c> value specified.</p>
<p>Normally, a terminating node is detected immediately.</p>
</item>
<tag><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><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><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><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><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><c>start_boot_server = true | false</c></tag>
<item>
<p>Starts the <c>boot_server</c> if the parameter is <c>true</c>
(see <seealso marker="erl_boot_server"><c>erl_boot_server(3)</c></seealso>).
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><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><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 <seealso marker="disk_log"><c>disk_log(3)</c></seealso>).
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><c>start_pg2 = true | false</c></tag>
<item>
<marker id="start_pg2"></marker>
<p>Starts the <c>pg2</c> server (see
<seealso marker="pg2"><c>pg2(3)</c></seealso>) 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><c>start_timer = true | false</c></tag>
<item>
<p>Starts the <c>timer_server</c> if the parameter is
<c>true</c> (see <seealso marker="stdlib:timer"><c>timer(3)</c></seealso>).
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><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>
</taglist>
</section>
<section>
<title>See Also</title>
<p><seealso marker="app"><c>app(4)</c></seealso>,
<seealso marker="application"><c>application(3)</c></seealso>,
<seealso marker="code"><c>code(3)</c></seealso>,
<seealso marker="disk_log"><c>disk_log(3)</c></seealso>,
<seealso marker="erl_boot_server"><c>erl_boot_server(3)</c></seealso>,
<seealso marker="erl_ddll"><c>erl_ddll(3)</c></seealso>,
<seealso marker="error_logger"><c>error_logger(3)</c></seealso>,
<seealso marker="file"><c>file(3)</c></seealso>,
<seealso marker="global"><c>global(3)</c></seealso>,
<seealso marker="global_group"><c>global_group(3)</c></seealso>,
<seealso marker="heart"><c>heart(3)</c></seealso>,
<seealso marker="inet"><c>inet(3)</c></seealso>,
<seealso marker="net_kernel"><c>net_kernel(3)</c></seealso>,
<seealso marker="os"><c>os(3)</c></seealso>,
<seealso marker="pg2"><c>pg2(3)</c></seealso>,
<seealso marker="rpc"><c>rpc(3)</c></seealso>,
<seealso marker="seq_trace"><c>seq_trace(3)</c></seealso>,
<seealso marker="user"><c>user(3)</c></seealso>,
<seealso marker="stdlib:timer"><c>timer(3)</c></seealso></p>
</section>
</appref>
