kernel - The Kernel application.
Please see following description for synopsis
Erlang Application Definition kernel(7)
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 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-
cations
* Code loading
* Logging
* Global name service
* Supervision of Erlang/OTP
* Communication with sockets
* Operating system interface
LOGGER HANDLERS
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.
OS SIGNAL EVENT HANDLER
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:
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 equiva-
lent to calling erlang:halt().
sigterm:
The default handler will terminate Erlang normally. This is equiva-
lent 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(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
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(3).
once:
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-
patible.
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
information 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
error 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.
Note:
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,
[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 many network interfaces, this
parameter 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-
ten/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 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
received 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-
ity.
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
embedded 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
addresses:
SlaveIP = string() | atom | {integer(),integer(),integer(),inte-
ger()},
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(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
disabled.
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}:
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
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
list.
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.
DEPRECATED CONFIGURATION PARAMETERS
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.
error_logger:
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"}}}]'
error_logger_format_depth:
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.
SEE ALSO
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),
timer(3)
Ericsson AB kernel 8.2 kernel(7)