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kernel(7)		 Erlang	Application Definition		     kernel(7)

       kernel -	The Kernel application.

       The  Kernel  application	 has  all the code necessary to	run the	Erlang
       runtime system: file servers, code servers, and so on.

       The Kernel application is the first application started.	It  is	manda-
       tory  in	the sense that the minimal system based	on Erlang/OTP consists
       of Kernel and STDLIB. Kernel contains the following functional areas:

	 * Start, stop,	supervision, configuration, and	distribution of	appli-

	 * Code	loading

	 * Logging

	 * Global name service

	 * Supervision of Erlang/OTP

	 * Communication with sockets

	 * Operating system interface

       Two  standard  logger  handlers	are defined in the Kernel application.
       These are described in  the  Kernel  User's  Guide,  and	 in  the  log-
       ger_std_h(3) and	logger_disk_log_h(3) manual pages.

       Asynchronous  OS	 signals  may be subscribed to via the Kernel applica-
       tions event manager (see	OTP Design Principles and gen_event(3))	regis-
       tered as	erl_signal_server. A default signal handler is installed which
       handles the following signals:

	   The default handler will halt Erlang	and produce a  crashdump  with
	   slogan  "Received  SIGUSR1".	 This  is  equivalent  to  calling er-
	   lang:halt("Received SIGUSR1").

	   The default handler will halt Erlang	immediately. This  is  equiva-
	   lent	to calling erlang:halt().

	   The default handler will terminate Erlang normally. This is equiva-
	   lent	to calling init:stop().

       Any event handler added to erl_signal_server must handle	the  following

	   Hangup  detected  on	 controlling  terminal or death	of controlling

	   Quit	from keyboard

	   Abort signal	from abort

	   Timer signal	from alarm

	   Termination signal

	   User-defined	signal 1

	   User-defined	signal 2

	   Child process stopped or terminated

	   Stop	process

	   Stop	typed at terminal

       Setting OS signals are described	in os:set_signal/2.

       The following configuration parameters are defined for the  Kernel  ap-
       plication.  For	more  information  about configuration parameters, see
       file app(4).

	 distributed = [Distrib]:
	   Specifies which applications	that  are  distributed	and  on	 which
	   nodes they are allowed to execute. In this parameter:

	   * Distrib = {App,Nodes} | {App,Time,Nodes}

	   * App = atom()

	   * Time = integer()_0

	   * Nodes = [node() | {node(),...,node()}]

	   The parameter is described in application:load/2.

	 dist_auto_connect = Value:
	   Specifies when nodes	are automatically connected. If	this parameter
	   is not specified, a node is always automatically connected, for ex-
	   ample, when a message is to be sent to that node. Value is one of:

	     Connections are never automatically established, they must	be ex-
	     plicitly connected. See net_kernel(3).

	     Connections are established  automatically,  but  only  once  per
	     node.  If a node goes down, it must thereafter be explicitly con-
	     nected. See net_kernel(3).

	 dist_listen = boolean():
	   Specifies whether this node should be listening for	incoming  dis-
	   tribution connections. Using	this option implies that the node also
	   is -hidden.

	 permissions = [Perm]:
	   Specifies the default permission for	 applications  when  they  are
	   started. In this parameter:

	   * Perm = {ApplName,Bool}

	   * ApplName =	atom()

	   * Bool = boolean()

	   Permissions are described in	application:permit/2.

	 logger	= [Config]:
	   Specifies  the  configuration  for  Logger,	except the primary log
	   level, which	is specified with logger_level,	and the	 compatibility
	   with	 SASL  Error Logging, which is specified with logger_sasl_com-

	   The logger  parameter is described in section  Logging in the  Ker-
	   nel User's Guide.

	 logger_level =	Level:
	   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 Logging in the Kernel User's Guide for more in-
	   formation about Logger and log levels.

	   Level = emergency | alert | critical	| error	| warning |  notice  |
	   info	| debug	| all |	none

	   To  change  the  primary  log level at runtime, use logger:set_pri-
	   mary_config(level, Level).

	   Defaults to notice.

	 logger_metadata = Metadata:
	   Specifies primary metadata for log events.

	   Metadata = map()

	   Defaults to #{}.

	 logger_sasl_compatible	= true | false:
	   Specifies if	Logger behaves backwards compatible with the SASL  er-
	   ror logging functionality from releases prior to Erlang/OTP 21.0.

	   If  this  parameter is set to true, 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 sasl,
	   which logs these events according to	values of the SASL  configura-
	   tion	parameter sasl_error_logger and	sasl_errlog_type.

	   See	section	 Deprecated Error Logger Event Handlers	and Configura-
	   tion	in the sasl(6) manual page for information about the SASL con-
	   figuration parameters.

	   See	section	 SASL Error Logging in the SASL	User's Guide, and sec-
	   tion	Backwards Compatibility	with error_logger in the Kernel	User's
	   Guide  for  information about the SASL error	logging	functionality,
	   and how Logger can be backwards compatible with this.

	   Defaults to false.

	 If this parameter is set to  true,  sasl_errlog_type  indicates  that
	 progress  reports  shall  be  logged,	and the	configured primary log
	 level is notice or more severe, then SASL automatically sets the pri-
	 mary  log  level to info. That	is, this setting can potentially over-
	 write the value of the	Kernel configuration  parameter	 logger_level.
	 This  is  to allow progress reports, which have log level info, to be
	 forwarded to the handlers.

	 global_groups = [GroupTuple]:

	   Defines global groups, see global_group(3). In this parameter:

	   * GroupTuple	 =  {GroupName,	 [Node]}  |  {GroupName,  PublishType,

	   * GroupName = atom()

	   * PublishType = normal | hidden

	   * Node = node()

	 inet_default_connect_options =	[{Opt, Val}]:
	   Specifies default options for connect sockets, see inet(3).

	 inet_default_listen_options = [{Opt, Val}]:
	   Specifies  default  options	for  listen  (and accept) sockets, see

	 {inet_dist_use_interface, ip_address()}:
	   If the host of an Erlang node has many network interfaces, this pa-
	   rameter  specifies  which one to listen on. For the type definition
	   of ip_address(), see	inet(3).

	 {inet_dist_listen_min,	First} and {inet_dist_listen_max, Last}:
	   Defines the First..Last port	range for the  listener	 socket	 of  a
	   distributed Erlang node.

	 {inet_dist_listen_options, Opts}:

	   Defines  a list of extra socket options to be used when opening the
	   listening socket for	a distributed Erlang  node.  See  gen_tcp:lis-

	 {inet_dist_connect_options, Opts}:

	   Defines  a  list of extra socket options to be used when connecting
	   to other distributed	Erlang nodes. See gen_tcp:connect/4.

	 inet_parse_error_log =	silent:
	   If set, no log events are issued when erroneous lines are found and
	   skipped in the various Inet configuration files.

	 inetrc	= Filename:
	   The	name (string) of an Inet user configuration file. For details,
	   see section Inet Configuration in the ERTS User's Guide.

	 net_setuptime = SetupTime:

	   SetupTime must be a positive	integer	or floating point number,  and
	   is  interpreted as the maximum allowed time for each	network	opera-
	   tion	during connection setup	to another Erlang  node.  The  maximum
	   allowed  value is 120. If higher values are specified, 120 is used.
	   Default is 7	seconds	if the variable	is not specified,  or  if  the
	   value is incorrect (for example, not	a number).

	   Notice  that	 this  value does not limit the	total connection setup
	   time, but rather each individual network operation during the  con-
	   nection setup and handshake.

	 net_ticktime =	TickTime:

	   Specifies the net_kernel tick time in seconds. This is the approxi-
	   mate	time a connected node may be unresponsive until	it is  consid-
	   ered	down and thereby disconnected.

	   Once	 every	TickTime/4  seconds,  each connected node is ticked if
	   nothing has been sent to it during that last	TickTime/4 interval. 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 re-
	   ceived during the last four TickTime/4 intervals. This ensures that
	   nodes that are not responding, for reasons such as hardware errors,
	   are considered to be	down.

	   As  the  availability is only checked every TickTime/4 seconds, the
	   actual time T a node	have been unresponsive when detected may  vary
	   between MinT	and MaxT, where:

	 MinT =	TickTime - TickTime / 4
	 MaxT =	TickTime + TickTime / 4

	   TickTime defaults to	60 seconds. Thus, 45 _ T _ 75 seconds.

	   Notice  that	 all communicating nodes are to	have the same TickTime
	   value specified, as it determines both the  frequency  of  outgoing
	   ticks and the expected frequency of incominging ticks.

	   Normally,  a	terminating node is detected immediately by the	trans-
	   port	protocol (like TCP/IP).

	 shutdown_timeout = integer() |	infinity:
	   Specifies the time application_controller waits for an  application
	   to  terminate  during node shutdown.	If the timer expires, applica-
	   tion_controller brutally kills application_master  of  the  hanging
	   application.	 If this parameter is undefined, it defaults to	infin-

	 sync_nodes_mandatory =	[NodeName]:
	   Specifies which other nodes that must 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	[].

	 sync_nodes_optional = [NodeName]:
	   Specifies  which  other  nodes  that	 can 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 unde-
	   fined, it defaults to the empty list.

	 sync_nodes_timeout = integer()	| infinity:
	   Specifies the time (in milliseconds)	that this node waits  for  the
	   mandatory  and  optional nodes to start. If this parameter is unde-
	   fined, no node synchronization is performed.	 This  option  ensures
	   that	global is synchronized.

	 start_distribution = true | false:
	   Starts all distribution services, such as rpc, global, and net_ker-
	   nel if the parameter	is true. This parameter	is to be set to	 false
	   for systems who want	to disable all distribution functionality.

	   Defaults to true.

	 start_dist_ac = true |	false:
	   Starts  the dist_ac server if the parameter is true.	This parameter
	   is to be set	to true	for systems using distributed applications.

	   Defaults to false. If this parameter	is undefined,  the  server  is
	   started if parameter	distributed is set.

	 start_boot_server = true | false:
	   Starts   the	  boot_server	if   the   parameter   is   true  (see
	   erl_boot_server(3)).	This parameter is to be	set to true in an  em-
	   bedded system using this service.

	   Defaults to false.

	 boot_server_slaves = [SlaveIP]:
	   If  configuration parameter start_boot_server is true, this parame-
	   ter can be used to initialize boot_server with a list of  slave  IP

	   SlaveIP  =  string()	 | atom	| {integer(),integer(),integer(),inte-

	   where 0 _= integer()	_=255.

	   Examples of SlaveIP in atom,	string,	and tuple form:

	   '', "150,236,16,70", {150,236,16,70}.

	   Defaults to [].

	 start_disk_log	= true | false:
	   Starts  the	disk_log_server	 if  the  parameter   is   true	  (see
	   disk_log(3)).  This	parameter  is to be set	to true	in an embedded
	   system using	this service.

	   Defaults to false.

	 start_pg = true | false:

	   Starts the default pg scope server (see pg(3)) if the parameter  is
	   true.  This	parameter  is  to be set to true in an embedded	system
	   that	uses this service.

	   Defaults to false.

	 start_timer = true | false:
	   Starts the timer_server if the parameter is	true  (see  timer(3)).
	   This	 parameter  is	to  be set to true in an embedded system using
	   this	service.

	   Defaults to false.

	 shell_history = enabled | disabled | module():
	   Specifies whether shell history should be logged  to	 disk  between
	   usages  of  erl (enabled), not logged at all	(disabled), or a user-
	   specified module will be used to log	 shell	history.  This	module
	   should  export  load() -_ [string()]	returning a list of strings to
	   load	in the shell when it starts, and add(iodata()) -_  ok.	called
	   every  time new line	is entered in the shell. By default logging is

	 shell_history_drop = [string()]:
	   Specific log	lines  that  should  not  be  persisted.  For  example
	   ["q().",  "init:stop()."]  will  allow to ignore commands that shut
	   the node down. Defaults to [].

	 shell_history_file_bytes = integer():
	   How many bytes the shell should remember. By	default, the value  is
	   set to 512kb, and the minimal value is 50kb.

	 shell_history_path = string():
	   Specifies where the shell history files will	be stored. defaults to
	   the	 user's	   cache    directory	 as    returned	   by	 file-
	   name:basedir(user_cache, "erlang-history").

	 shutdown_func = {Mod, Func}:

	   * Mod = atom()

	   * Func = atom()

	   Sets	a function that	application_controller calls when it starts to
	   terminate. The function is called as	Mod:Func(Reason), where	Reason
	   is the terminate reason for application_controller, and it must re-
	   turn	as soon	as possible for	 application_controller	 to  terminate

	 source_search_rules = [DirRule] | [SuffixRule]	:


	   * DirRule = {ObjDirSuffix,SrcDirSuffix}

	   * SuffixRule	= {ObjSuffix,SrcSuffix,[DirRule]}

	   * ObjDirSuffix = string()

	   * SrcDirSuffix = string()

	   * ObjSuffix = string()

	   * SrcSuffix = string()

	   Specifies   a   list	  of  rules  for  use  by  filelib:find_file/2
	   filelib:find_source/2 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	 {"ebin",  "src"},  which  are
	   used	 by filelib:find_file/2, or triples specifying separate	direc-
	   tory	suffix rules depending on file name  extensions,  for  example
	   [{".beam",	".erl",	  [{"ebin",   "src"}]},	  which	 are  used  by
	   filelib:find_source/2. Both kinds of	rules  can  be	mixed  in  the

	   The	interpretation of ObjDirSuffix and SrcDirSuffix	is as follows:
	   if the end of the directory name where an object is located matches
	   ObjDirSuffix,  then the name	created	by replacing ObjDirSuffix with
	   SrcDirSuffix	is expanded by	calling	 filelib:wildcard/1,  and  the
	   first regular file found among the matches is the source file.

       In Erlang/OTP 21.0, a new API for logging was added. The	old error_log-
       ger event manager, and event handlers running on	 this  manager,	 still
       work, but they are no longer used by default.

       The  following  application  configuration parameters can still be set,
       but they	are only used if the  corresponding  configuration  parameters
       for Logger are not set.

	   Replaced  by	 setting the type, and possibly	file and modes parame-
	   ters	of the default logger_std_h handler. Example:

	 erl -kernel logger '[{handler,default,logger_std_h,#{config=>#{file=>"/tmp/erlang.log"}}}]'

	   Replaced by setting the depth parameter  of	the  default  handlers
	   formatter. Example:

	 erl -kernel logger '[{handler,default,logger_std_h,#{formatter=>{logger_formatter,#{legacy_header=>true,template=>[{logger_formatter,header},"\n",msg,"\n"],depth=>10}}}]'

       See Backwards compatibility with	error_logger for more information.

       app(4),	 application(3),   code(3),  disk_log(3),  erl_boot_server(3),
       erl_ddll(3), file(3), global(3),	 global_group(3),  heart(3),  inet(3),
       logger(3),  net_kernel(3), os(3), pg(3),	rpc(3),	seq_trace(3), user(3),

Ericsson AB			  kernel 8.2			     kernel(7)


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