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NAME
kernel - The Kernel application.
DESCRIPTION
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 mandatory 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 applications
* Code loading
* Logging
* Error logging
* Global name service
* Supervision of Erlang/OTP
* Communication with sockets
* Operating system interface
ERROR LOGGER EVENT HANDLERS
Two standard error logger event handlers are defined in the Kernel application. These are described in
error_logger(3erl).
OS SIGNAL EVENT HANDLER
Asynchronous OS signals may be subscribed to via the Kernel applications event manager (see OTP Design
Principles and gen_event(3erl)) registered as erl_signal_server. A default signal handler is installed
which handles the following signals:
sigusr1:
The default handler will halt Erlang and produce a crashdump with slogan "Received SIGUSR1". This is
equivalent to calling erlang:halt("Received SIGUSR1").
sigquit:
The default handler will halt Erlang immediately. This is equivalent to calling erlang:halt().
sigterm:
The default handler will terminate Erlang normally. This is equivalent to calling init:stop().
Events
Any event handler added to erl_signal_server must handle the following events.
sighup:
Hangup detected on controlling terminal or death of controlling process
sigquit:
Quit from keyboard
sigabrt:
Abort signal from abort
sigalrm:
Timer signal from alarm
sigterm:
Termination signal
sigusr1:
User-defined signal 1
sigusr2:
User-defined signal 2
sigchld:
Child process stopped or terminated
sigstop:
Stop process
sigtstp:
Stop typed at terminal
Setting OS signals are described in os:set_signal/2.
CONFIGURATION
The following configuration parameters are defined for the Kernel application. For more information about
configuration parameters, see file app(5).
browser_cmd = string() | {M,F,A}:
When pressing the Help button in a tool such as Debugger, the help text (an HTML file File) 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.
If set to a string Command, the command "Command File" is evaluated using os:cmd/1.
If set to a module-function-args tuple, {M,F,A}, the call apply(M,F,[File|A]) is evaluated.
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 example, 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(3erl).
once:
Connections are established automatically, but only once per node. If a node goes down, it must
thereafter be explicitly connected. See net_kernel(3erl).
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.
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 file FileName, where FileName is
a string. The file is opened with encoding UTF-8.
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:
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 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.
Depth 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.)
Depth is used as follows: Format strings passed to the event handlers are rewritten. The format
controls ~p and ~w are replaced with ~P and ~W, respectively, and Depth is used as the depth
parameter. For details, see io:format/2 in STDLIB.
Note:
A reasonable starting value for Depth is 30. We recommend to test crashing various processes in your
application, examine the logs from the crashes, and then increase or decrease the value.
global_groups = [GroupTuple]:
Defines global groups, see global_group(3erl). In this parameter:
* 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(3erl).
inet_default_listen_options = [{Opt, Val}]:
Specifies default options for listen (and accept) sockets, see inet(3erl).
{inet_dist_use_interface, ip_address()}:
If the host of an Erlang node has many network interfaces, this parameter specifies which one to
listen on. For the type definition of ip_address(), see inet(3erl).
{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:listen/2.
{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 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. 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 operation 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 connection setup and handshake.
net_ticktime = TickTime:
Specifies the net_kernel tick time. TickTime is specified in seconds. Once every TickTime/4 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.
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 defaults to 60 (seconds). Thus, 45 < T < 75 seconds.
Notice that all communicating nodes are to have the same TickTime value specified.
Normally, a terminating node is detected immediately.
shutdown_timeout = integer() | infinity:
Specifies the time application_controller waits for an application to terminate during node shutdown.
If the timer expires, application_controller brutally kills application_master of the hanging
application. If this parameter is undefined, it defaults to infinity.
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
undefined, 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 undefined, no node synchronization is performed. This option ensures that
global is synchronized.
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(3erl)). This parameter is to be
set to true in an embedded system using this service.
Defaults to false.
boot_server_slaves = [SlaveIP]:
If configuration parameter start_boot_server 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:
'150.236.16.70', "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(3erl)). This parameter is to be set
to true in an embedded system using this service.
Defaults to false.
start_pg2 = true | false:
Starts the pg2 server (see pg2(3erl)) 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(3erl)). This parameter is to be set to
true in an embedded system using this service.
Defaults to false.
shell_history = enabled | disabled :
Specifies whether shell history should be logged to disk between usages of erl.
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 filename:basedir(user_cache, "erlang-history").
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.
source_search_rules = [DirRule] | [SuffixRule] :
Where:
* 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 and 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 directory 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 list.
SEE ALSO
app(5), application(3erl), code(3erl), disk_log(3erl), erl_boot_server(3erl), erl_ddll(3erl), error_logger(3erl), file(3erl), global(3erl), global_group(3erl), heart(3erl), inet(3erl), net_kernel(3erl), os(3erl), pg2(3erl), rpc(3erl), seq_trace(3erl), user(3erl), timer(3erl)