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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)