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<header>
<copyright>
<year>1996</year><year>2015</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
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<legalnotice>
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 is the first application started. It is
mandatory in the sense that the minimal system based on
Erlang/OTP consists of Kernel and STDLIB. The Kernel application
contains the following services:</p>
<list type="bulleted">
<item>application controller, see <seealso marker="application">application(3)</seealso></item>
<item><c>code</c></item>
<item><c>disk_log</c></item>
<item><c>dist_ac</c>, distributed application controller</item>
<item><c>erl_boot_server</c></item>
<item><c>erl_ddll</c></item>
<item><c>error_logger</c></item>
<item><c>error_logger_format_depth</c></item>
<item><c>file</c></item>
<item><c>global</c></item>
<item><c>global_group</c></item>
<item><c>heart</c></item>
<item><c>inet</c></item>
<item><c>net_kernel</c></item>
<item><c>os</c></item>
<item><c>pg2</c></item>
<item><c>rpc</c></item>
<item><c>seq_trace</c></item>
<item><c>user</c></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">error_logger(3)</seealso>.</p>
</section>
<section>
<title>Configuration</title>
<p>The following configuration parameters are defined for the Kernel
application. See <seealso marker="app">app(4)</seealso> for more
information about configuration parameters.</p>
<taglist>
<tag><c>browser_cmd = string() | {M,F,A}</c></tag>
<item>
<p>When pressing the Help button in a tool such as Debugger or
TV, the help text (an HTML file <c>File</c>) is by default
displayed in a Netscape browser which is required to be up and
running. This parameter can be used to change the command for
how to display the help text if another browser than Netscape
is preferred, or another platform than Unix or Windows is
used.</p>
<p>If set to a string <c>Command</c>, the command
<c>"Command File"</c> will be evaluated using <c>os:cmd/1</c>.</p>
<p>If set to a module-function-args tuple <c>{M,F,A}</c>,
the call <c>apply(M,F,[File|A])</c> will be evaluated.</p>
</item>
<tag><c>distributed = [Distrib]</c></tag>
<item>
<p>Specifies which applications are distributed and on which
nodes they may 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">application(3)</seealso>, function
<c>load/2</c>.</p>
</item>
<tag><c>dist_auto_connect = Value</c></tag>
<item>
<p>Specifies when nodes will be automatically connected. If
this parameter is not specified, a node is always
automatically connected, e.g when a message is to be sent to
that node. <c>Value</c> is one of:</p>
<taglist>
<tag><c>never</c></tag>
<item>Connections are never automatically established, they
must be explicitly connected. See
<seealso marker="net_kernel">net_kernel(3)</seealso>.</item>
<tag><c>once</c></tag>
<item>Connections will be established automatically, but only
once per node. If a node goes down, it must thereafter be
explicitly connected. See
<seealso marker="net_kernel">net_kernel(3)</seealso>.</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">application(3)</seealso>, function
<c>permit/2</c>.</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>Installs the standard event handler which prints error
reports to <c>stdio</c>. This is the default option.</item>
<tag><c>{file, FileName}</c></tag>
<item>Installs the standard event handler which prints error
reports to the file <c>FileName</c>, where <c>FileName</c>
is a string.</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 tty.</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>This parameter 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.
It is currently experimental. Based on user feedback it
may 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 entirely remove this
new feature, unless it turns out to be completely
useless. In OTP 19, the default may be changed to limit the
formatted output.</p></note>
<p><c>Depth</c> is a positive integer that is the maximum
depth to which terms are printed by the error logger event
handlers included in OTP. Specifically, the two event handlers
defined by the <c>Kernel</c> application and the two event
handlers in the <c>SASL</c> application will use this
configuration parameter. (If you have implemented you own
error handlers, this configuration parameter will have no
effect on them.)</p>
<p>The way <c>Depth</c> is used, is that format strings
string passed to the event handlers will be rewritten.
The "~p" and "~w" format controls will be replaced with
"~P" and "~W", respectively, and <c>Depth</c> will be
used as the depth parameter. See
<seealso marker="stdlib:io#format/2">io:format/2</seealso>.</p>
<note><p>A reasonable starting value for <c>Depth</c> is
<c>30</c>. You should test crashing various processes in your
application and examine the logs from the crashes, and then
either increase or decrease the value.</p></note>
</item>
<tag><c>global_groups = [GroupTuple]</c></tag>
<item>
<p>Defines global groups, see
<seealso marker="global_group">global_group(3)</seealso>.</p>
<list type="bulleted">
<item><c>GroupTuple = {GroupName, [Node]} | {GroupName, PublishType, [Node]}</c></item>
<item><c>GroupName = atom()</c></item>
<item><c>PublishType = normal | hidden</c></item>
<item><c>Node = node()</c></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">inet(3)</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">inet(3)</seealso>.</p>
</item>
<tag><c>{inet_dist_use_interface, ip_address()}</c></tag>
<item>
<p>If the host of an Erlang node has several network interfaces,
this parameter specifies which one to listen on. See
<seealso marker="inet">inet(3)</seealso> for the type definition
of <c>ip_address()</c>.</p>
</item>
<tag><c>{inet_dist_listen_min, First}</c></tag>
<item>
<p>See below.</p>
</item>
<tag><c>{inet_dist_listen_max, Last}</c></tag>
<item>
<p>Define 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>
<p>Define 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">gen_tcp:listen/2</seealso></p>
</item>
<tag><c>{inet_dist_connect_options, Opts}</c></tag>
<item>
<p>Define a list of extra socket options to be used when connecting to
other distributed Erlang nodes.
See <seealso marker="gen_tcp#connect/4">gen_tcp:connect/4</seealso></p>
</item>
<tag><c>inet_parse_error_log = silent</c></tag>
<item>
<p>If this configuration parameter is 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. See
ERTS User's Guide, Inet configuration.</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 will be interpreted as the maximally allowed time
for each network operation during connection setup to another
Erlang node. The maximum allowed value is 120; if higher values
are given, 120 will be used. The default value if the variable
is not given, or if the value is incorrect (e.g. not a number),
is 7 seconds.</p>
<p>Note 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 given in seconds. Once every <c>TickTime/4</c> second, all
connected nodes are ticked (if anything else has been written
to a node) and if nothing has been received from another node
within the last four (4) tick times that node is considered
to be down. This ensures that nodes which 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> is by default 60 (seconds). Thus,
<c><![CDATA[45 < T < 75]]></c> seconds.</p>
<p><em>Note:</em> All communicating nodes should have the same
<c>TickTime</c> value specified.</p>
<p><em>Note:</em> 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> will wait
for an application to terminate during node shutdown. If the
timer expires, <c>application_controller</c> will brutally
kill <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 <em>must</em> be alive in order
for this node to start properly. If some node in the list
does not start within the specified time, this node will not
start either. If this parameter is undefined, it defaults to
[].</p>
</item>
<tag><c>sync_nodes_optional = [NodeName]</c></tag>
<item>
<p>Specifies which other nodes <em>can</em> be alive in order
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 amount of time (in milliseconds) this node
will wait for the mandatory and optional nodes to start. If
this parameter is undefined, no node synchronization is
performed. This option also makes sure 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 should be set to <c>true</c> for
systems that use distributed applications.</p>
<p>The default value is <c>false</c>. If this parameter is
undefined, the server is started if the 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">erl_boot_server(3)</seealso>).
This parameter should be
set to <c>true</c> in an embedded system which uses this
service.</p>
<p>The default value is <c>false</c>.</p>
</item>
<tag><c>boot_server_slaves = [SlaveIP]</c></tag>
<item>
<p>If the <c>start_boot_server</c> configuration parameter is
<c>true</c>, this parameter can be used to initialize
<c>boot_server</c> with a list of slave IP addresses.
<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
are: <br></br>
<c>'150.236.16.70', "150,236,16,70", {150,236,16,70}</c>.</p>
<p>The default value is <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">disk_log(3)</seealso>).
This parameter should be
set to true in an embedded system which uses this service.</p>
<p>The default value is <c>false</c>.</p>
</item>
<tag><c>start_pg2 = true | false</c></tag>
<item>
<p>Starts the <c>pg2</c> server (see
<seealso marker="pg2">pg2(3)</seealso>) if
the parameter is <c>true</c>. This parameter should be set to
<c>true</c> in an embedded system which uses this service.</p>
<p>The default value is <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">timer(3)</seealso>).
This parameter should be
set to <c>true</c> in an embedded system which uses this
service.</p>
<p>The default value is <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">app(4)</seealso>,
<seealso marker="application">application(3)</seealso>,
<seealso marker="code">code(3)</seealso>,
<seealso marker="disk_log">disk_log(3)</seealso>,
<seealso marker="erl_boot_server">erl_boot_server(3)</seealso>,
<seealso marker="erl_ddll">erl_ddll(3)</seealso>,
<seealso marker="error_logger">error_logger(3)</seealso>,
<seealso marker="file">file(3)</seealso>,
<seealso marker="global">global(3)</seealso>,
<seealso marker="global_group">global_group(3)</seealso>,
<seealso marker="heart">heart(3)</seealso>,
<seealso marker="inet">inet(3)</seealso>,
<seealso marker="net_kernel">net_kernel(3)</seealso>,
<seealso marker="os">os(3)</seealso>,
<seealso marker="pg2">pg2(3)</seealso>,
<seealso marker="rpc">rpc(3)</seealso>,
<seealso marker="seq_trace">seq_trace(3)</seealso>,
<seealso marker="stdlib:timer">timer(3)</seealso>,
<seealso marker="user">user(3)</seealso></p>
</section>
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