kernel

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:

• application controller, see application(3)
• code
• disk_log
• dist_ac, distributed application controller
• erl_boot_server
• erl_ddll
• error_logger
• error_logger_format_depth
• file
• global
• global_group
• heart
• inet
• net_kernel
• os
• pg2
• rpc
• seq_trace
• user

Two standard error logger event handlers are defined in the Kernel application. These are described in error_logger(3).

The following configuration parameters are defined for the Kernel application. See app(4) for more information about configuration parameters.

browser_cmd = string() | {M,F,A}

When pressing the Help button in a tool such as Debugger or TV, the help text (an HTML file File) 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.

If set to a string Command, the command "Command File" will be evaluated using os:cmd/1.

If set to a module-function-args tuple {M,F,A}, the call apply(M,F,[File|A]) will be evaluated.

distributed = [Distrib]

Specifies which applications are distributed and on which nodes they may 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(3), function load/2.

dist_auto_connect = Value

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. Value is one of:

never

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

once

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

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(3), function permit/2.

error_logger = Value

Value is one of:

tty

Installs the standard event handler which prints error reports to stdio. This is the default option.

{file, FileName}

Installs the standard event handler which prints error reports to the file FileName, where FileName is a string.

false

No standard event handler is installed, but the initial, primitive event handler is kept, printing raw event messages to tty.

silent

Error logging is turned off.

error_logger_format_depth = Depth

This parameter can be used to limit the size of the formatted output from the error logger event handlers.

Note

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.

Depth 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 Kernel application and the two event handlers in the SASL application will use this configuration parameter. (If you have implemented you own error handlers, this configuration parameter will have no effect on them.)

The way Depth 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 Depth will be used as the depth parameter. See io:format/2.

Note

A reasonable starting value for Depth is 30. You should test crashing various processes in your application and examine the logs from the crashes, and then either increase or decrease the value.

global_groups = [GroupTuple]

Defines global groups, see global_group(3).

• GroupTuple = {GroupName, [Node]} | {GroupName, PublishType, [Node]}
• 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(3).

{inet_dist_use_interface, ip_address()}

If the host of an Erlang node has several network interfaces, this parameter specifies which one to listen on. See inet(3) for the type definition of ip_address().

{inet_dist_listen_min, First}

See below.

{inet_dist_listen_max, Last}

Define the First..Last port range for the listener socket of a distributed Erlang node.

{inet_dist_listen_options, Opts}

Define a list of extra socket options to be used when opening the listening socket for a distributed Erlang node. See gen_tcp:listen/2

{inet_dist_connect_options, Opts}

Define 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 this configuration parameter is set, no error_logger messages are generated when erroneous lines are found and skipped in the various Inet configuration files.

inetrc = Filename

The name (string) of an Inet user configuration file. See ERTS User's Guide, Inet configuration.

net_setuptime = SetupTime

SetupTime 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.

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

net_ticktime = TickTime

Specifies the net_kernel tick time. TickTime is given in seconds. Once every TickTime/4 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.

The time T, in which a node that is not responding is detected, is calculated as: MinT < T < MaxT where:

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

TickTime is by default 60 (seconds). Thus, 45 < T < 75 seconds.

Note: All communicating nodes should have the same TickTime value specified.

Note: Normally, a terminating node is detected immediately.

shutdown_timeout = integer() | infinity

Specifies the time application_controller will wait for an application to terminate during node shutdown. If the timer expires, application_controller will brutally kill application_master of the hanging application. If this parameter is undefined, it defaults to infinity.

sync_nodes_mandatory = [NodeName]

Specifies which other nodes must 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 [].

sync_nodes_optional = [NodeName]

Specifies which other nodes can 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.

sync_nodes_timeout = integer() | infinity

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 global is synchronized.

start_dist_ac = true | false

Starts the dist_ac server if the parameter is true. This parameter should be set to true for systems that use distributed applications.

The default value is false. If this parameter is undefined, the server is started if the 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 should be set to true in an embedded system which uses this service.

The default value is false.

boot_server_slaves = [SlaveIP]

If the start_boot_server configuration parameter is true, this parameter can be used to initialize boot_server with a list of slave IP addresses. SlaveIP = string() | atom | {integer(),integer(),integer(),integer()}

where 0 <= integer() <=255.

Examples of SlaveIP in atom, string and tuple form are:
'150.236.16.70', "150,236,16,70", {150,236,16,70}.

The default value is [].

start_disk_log = true | false

Starts the disk_log_server if the parameter is true (see disk_log(3)). This parameter should be set to true in an embedded system which uses this service.

The default value is false.

start_pg2 = true | false

Starts the pg2 server (see pg2(3)) if the parameter is true. This parameter should be set to true in an embedded system which uses this service.

The default value is false.

start_timer = true | false

Starts the timer_server if the parameter is true (see timer(3)). This parameter should be set to true in an embedded system which uses this service.

The default value is false.

shutdown_func = {Mod, Func}

Where:

• 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 return as soon as possible for application_controller to terminate properly.

app(4), application(3), code(3), disk_log(3), erl_boot_server(3), erl_ddll(3), error_logger(3), file(3), global(3), global_group(3), heart(3), inet(3), net_kernel(3), os(3), pg2(3), rpc(3), seq_trace(3), timer(3), user(3)