1kernel(7) Erlang Application Definition kernel(7)
2
6 kernel - The Kernel application.
7
9 The Kernel application has all the code necessary to run the Erlang
10 runtime system: file servers, code servers, and so on.
11 The Kernel application is the first application started. It is manda‐
13 tory in the sense that the minimal system based on Erlang/OTP consists
14 of Kernel and STDLIB. Kernel contains the following functional areas:
15 * Start, stop, supervision, configuration, and distribution of appli‐
17 cations
18 * Code loading
20 * Logging
22 * Global name service
24 * Supervision of Erlang/OTP
26 * Communication with sockets
28 * Operating system interface
30
32 Two standard logger handlers are defined in the Kernel application.
33 These are described in the Kernel User's Guide, and in the log‐
34 ger_std_h(3) and logger_disk_log_h(3) manual pages.
35
37 Asynchronous OS signals may be subscribed to via the Kernel applica‐
38 tions event manager (see OTP Design Principles and gen_event(3)) regis‐
39 tered as erl_signal_server. A default signal handler is installed which
40 handles the following signals:
41 sigusr1:
43 The default handler will halt Erlang and produce a crashdump with
44 slogan "Received SIGUSR1". This is equivalent to calling
45 erlang:halt("Received SIGUSR1").
46 sigquit:
48 The default handler will halt Erlang immediately. This is equiva‐
49 lent to calling erlang:halt().
50 sigterm:
52 The default handler will terminate Erlang normally. This is equiva‐
53 lent to calling init:stop().
54 Events
56 Any event handler added to erl_signal_server must handle the following
57 events.
58 sighup:
60 Hangup detected on controlling terminal or death of controlling
61 process
62 sigquit:
64 Quit from keyboard
65 sigabrt:
67 Abort signal from abort
68 sigalrm:
70 Timer signal from alarm
71 sigterm:
73 Termination signal
74 sigusr1:
76 User-defined signal 1
77 sigusr2:
79 User-defined signal 2
80 sigchld:
82 Child process stopped or terminated
83 sigstop:
85 Stop process
86 sigtstp:
88 Stop typed at terminal
89 Setting OS signals are described in os:set_signal/2.
91
93 The following configuration parameters are defined for the Kernel
94 application. For more information about configuration parameters, see
95 file app(4).
96 distributed = [Distrib]:
98 Specifies which applications that are distributed and on which
99 nodes they are allowed to execute. In this parameter:
100 * Distrib = {App,Nodes} | {App,Time,Nodes}
102 * App = atom()
104 * Time = integer()>0
106 * Nodes = [node() | {node(),...,node()}]
108 The parameter is described in application:load/2.
110 dist_auto_connect = Value:
112 Specifies when nodes are automatically connected. If this parameter
113 is not specified, a node is always automatically connected, for
114 example, when a message is to be sent to that node. Value is one
115 of:
116 never:
118 Connections are never automatically established, they must be
119 explicitly connected. See net_kernel(3).
120 once:
122 Connections are established automatically, but only once per
123 node. If a node goes down, it must thereafter be explicitly con‐
124 nected. See net_kernel(3).
125 permissions = [Perm]:
127 Specifies the default permission for applications when they are
128 started. In this parameter:
129 * Perm = {ApplName,Bool}
131 * ApplName = atom()
133 * Bool = boolean()
135 Permissions are described in application:permit/2.
137 logger = [Config]:
139 Specifies the configuration for Logger, except the primary log
140 level, which is specified with logger_level, and the compatibility
141 with SASL Error Logging, which is specified with logger_sasl_com‐
142 patible.
143 The logger parameter is described in section Logging in the Ker‐
145 nel User's Guide.
146 logger_level = Level:
148 Specifies the primary log level for Logger. Log events with the
149 same, or a more severe level, pass through the primary log level
150 check. See section Logging in the Kernel User's Guide for more
151 information about Logger and log levels.
152 Level = emergency | alert | critical | error | warning | notice |
154 info | debug | all | none
155 To change the primary log level at runtime, use logger:set_pri‐
157 mary_config(level, Level).
158 Defaults to notice.
160 logger_sasl_compatible = true | false:
162 Specifies if Logger behaves backwards compatible with the SASL
163 error logging functionality from releases prior to Erlang/OTP 21.0.
164 If this parameter is set to true, the default Logger handler does
166 not log any progress-, crash-, or supervisor reports. If the SASL
167 application is then started, it adds a Logger handler named sasl,
168 which logs these events according to values of the SASL configura‐
169 tion parameter sasl_error_logger and sasl_errlog_type.
170 See section Deprecated Error Logger Event Handlers and Configura‐
172 tion in the sasl(6) manual page for information about the SASL con‐
173 figuration parameters.
174 See section SASL Error Logging in the SASL User's Guide, and sec‐
176 tion Backwards Compatibility with error_logger in the Kernel User's
177 Guide for information about the SASL error logging functionality,
178 and how Logger can be backwards compatible with this.
179 Defaults to false.
181 Note:
183 If this parameter is set to true, sasl_errlog_type indicates that
184 progress reports shall be logged, and the configured primary log
185 level is notice or more severe, then SASL automatically sets the pri‐
186 mary log level to info. That is, this setting can potentially over‐
187 write the value of the Kernel configuration parameter logger_level.
188 This is to allow progress reports, which have log level info, to be
189 forwarded to the handlers.
190 global_groups = [GroupTuple]:
193 Defines global groups, see global_group(3). In this parameter:
196 * GroupTuple = {GroupName, [Node]} | {GroupName, PublishType,
198 [Node]}
199 * GroupName = atom()
201 * PublishType = normal | hidden
203 * Node = node()
205 inet_default_connect_options = [{Opt, Val}]:
207 Specifies default options for connect sockets, see inet(3).
208 inet_default_listen_options = [{Opt, Val}]:
210 Specifies default options for listen (and accept) sockets, see
211 inet(3).
212 {inet_dist_use_interface, ip_address()}:
214 If the host of an Erlang node has many network interfaces, this
215 parameter specifies which one to listen on. For the type definition
216 of ip_address(), see inet(3).
217 {inet_dist_listen_min, First} and {inet_dist_listen_max, Last}:
219 Defines the First..Last port range for the listener socket of a
220 distributed Erlang node.
221 {inet_dist_listen_options, Opts}:
223 Defines a list of extra socket options to be used when opening the
226 listening socket for a distributed Erlang node. See gen_tcp:lis‐
227 ten/2.
228 {inet_dist_connect_options, Opts}:
230 Defines a list of extra socket options to be used when connecting
233 to other distributed Erlang nodes. See gen_tcp:connect/4.
234 inet_parse_error_log = silent:
236 If set, no log events are issued when erroneous lines are found and
237 skipped in the various Inet configuration files.
238 inetrc = Filename:
240 The name (string) of an Inet user configuration file. For details,
241 see section Inet Configuration in the ERTS User's Guide.
242 net_setuptime = SetupTime:
244 SetupTime must be a positive integer or floating point number, and
247 is interpreted as the maximum allowed time for each network opera‐
248 tion during connection setup to another Erlang node. The maximum
249 allowed value is 120. If higher values are specified, 120 is used.
250 Default is 7 seconds if the variable is not specified, or if the
251 value is incorrect (for example, not a number).
252 Notice that this value does not limit the total connection setup
254 time, but rather each individual network operation during the con‐
255 nection setup and handshake.
256 net_ticktime = TickTime:
258 Specifies the net_kernel tick time in seconds. This is the approxi‐
261 mate time a connected node may be unresponsive until it is consid‐
262 ered down and thereby disconnected.
263 Once every TickTime/4 seconds, each connected node is ticked if
265 nothing has been sent to it during that last TickTime/4 interval. A
266 tick is a small package sent on the connection. A connected node is
267 considered to be down if no ticks or payload packages have been
268 received during the last four TickTime/4 intervals. This ensures
269 that nodes that are not responding, for reasons such as hardware
270 errors, are considered to be down.
271 As the availability is only checked every TickTime/4 seconds, the
273 actual time T a node have been unresponsive when detected may vary
274 between MinT and MaxT, where:
275 MinT = TickTime - TickTime / 4
277 MaxT = TickTime + TickTime / 4
278 TickTime defaults to 60 seconds. Thus, 45 < T < 75 seconds.
280 Notice that all communicating nodes are to have the same TickTime
282 value specified, as it determines both the frequency of outgoing
283 ticks and the expected frequency of incominging ticks.
284 Normally, a terminating node is detected immediately by the trans‐
286 port protocol (like TCP/IP).
287 shutdown_timeout = integer() | infinity:
289 Specifies the time application_controller waits for an application
290 to terminate during node shutdown. If the timer expires, applica‐
291 tion_controller brutally kills application_master of the hanging
292 application. If this parameter is undefined, it defaults to infin‐
293 ity.
294 sync_nodes_mandatory = [NodeName]:
296 Specifies which other nodes that must be alive for this node to
297 start properly. If some node in the list does not start within the
298 specified time, this node does not start either. If this parameter
299 is undefined, it defaults to [].
300 sync_nodes_optional = [NodeName]:
302 Specifies which other nodes that can be alive for this node to
303 start properly. If some node in this list does not start within the
304 specified time, this node starts anyway. If this parameter is unde‐
305 fined, it defaults to the empty list.
306 sync_nodes_timeout = integer() | infinity:
308 Specifies the time (in milliseconds) that this node waits for the
309 mandatory and optional nodes to start. If this parameter is unde‐
310 fined, no node synchronization is performed. This option ensures
311 that global is synchronized.
312 start_distribution = true | false:
314 Starts all distribution services, such as rpc, global, and net_ker‐
315 nel if the parameter is true. This parameter is to be set to false
316 for systems who want to disable all distribution functionality.
317 Defaults to true.
319 start_dist_ac = true | false:
321 Starts the dist_ac server if the parameter is true. This parameter
322 is to be set to true for systems using distributed applications.
323 Defaults to false. If this parameter is undefined, the server is
325 started if parameter distributed is set.
326 start_boot_server = true | false:
328 Starts the boot_server if the parameter is true (see
329 erl_boot_server(3)). This parameter is to be set to true in an
330 embedded system using this service.
331 Defaults to false.
333 boot_server_slaves = [SlaveIP]:
335 If configuration parameter start_boot_server is true, this parame‐
336 ter can be used to initialize boot_server with a list of slave IP
337 addresses:
338 SlaveIP = string() | atom | {integer(),integer(),integer(),inte‐
340 ger()},
341 where 0 <= integer() <=255.
343 Examples of SlaveIP in atom, string, and tuple form:
345 '150.236.16.70', "150,236,16,70", {150,236,16,70}.
347 Defaults to [].
349 start_disk_log = true | false:
351 Starts the disk_log_server if the parameter is true (see
352 disk_log(3)). This parameter is to be set to true in an embedded
353 system using this service.
354 Defaults to false.
356 start_pg2 = true | false:
358 Starts the pg2 server (see pg2(3)) if the parameter is true. This
361 parameter is to be set to true in an embedded system that uses this
362 service.
363 Defaults to false.
365 start_timer = true | false:
367 Starts the timer_server if the parameter is true (see timer(3)).
368 This parameter is to be set to true in an embedded system using
369 this service.
370 Defaults to false.
372 shell_history = enabled | disabled :
374 Specifies whether shell history should be logged to disk between
375 usages of erl.
376 shell_history_drop = [string()]:
378 Specific log lines that should not be persisted. For example
379 ["q().", "init:stop()."] will allow to ignore commands that shut
380 the node down. Defaults to [].
381 shell_history_file_bytes = integer():
383 how many bytes the shell should remember. By default, the value is
384 set to 512kb, and the minimal value is 50kb.
385 shell_history_path = string():
387 Specifies where the shell history files will be stored. defaults to
388 the user's cache directory as returned by file‐
389 name:basedir(user_cache, "erlang-history").
390 shutdown_func = {Mod, Func}:
392 Where:
393 * Mod = atom()
395 * Func = atom()
397 Sets a function that application_controller calls when it starts to
399 terminate. The function is called as Mod:Func(Reason), where Reason
400 is the terminate reason for application_controller, and it must
401 return as soon as possible for application_controller to terminate
402 properly.
403 source_search_rules = [DirRule] | [SuffixRule] :
405 Where:
408 * DirRule = {ObjDirSuffix,SrcDirSuffix}
410 * SuffixRule = {ObjSuffix,SrcSuffix,[DirRule]}
412 * ObjDirSuffix = string()
414 * SrcDirSuffix = string()
416 * ObjSuffix = string()
418 * SrcSuffix = string()
420 Specifies a list of rules for use by filelib:find_file/2
422 filelib:find_source/2 If this is set to some other value than the
423 empty list, it replaces the default rules. Rules can be simple
424 pairs of directory suffixes, such as {"ebin", "src"}, which are
425 used by filelib:find_file/2, or triples specifying separate direc‐
426 tory suffix rules depending on file name extensions, for example
427 [{".beam", ".erl", [{"ebin", "src"}]}, which are used by
428 filelib:find_source/2. Both kinds of rules can be mixed in the
429 list.
430 The interpretation of ObjDirSuffix and SrcDirSuffix is as follows:
432 if the end of the directory name where an object is located matches
433 ObjDirSuffix, then the name created by replacing ObjDirSuffix with
434 SrcDirSuffix is expanded by calling filelib:wildcard/1, and the
435 first regular file found among the matches is the source file.
436
438 In Erlang/OTP 21.0, a new API for logging was added. The old error_log‐
439 ger event manager, and event handlers running on this manager, still
440 work, but they are no longer used by default.
441 The following application configuration parameters can still be set,
443 but they are only used if the corresponding configuration parameters
444 for Logger are not set.
445 error_logger:
447 Replaced by setting the type, and possibly file and modes parame‐
448 ters of the default logger_std_h handler. Example:
449 erl -kernel logger '[{handler,default,logger_std_h,#{config=>#{file=>"/tmp/erlang.log"}}}]'
451 error_logger_format_depth:
454 Replaced by setting the depth parameter of the default handlers
455 formatter. Example:
456 erl -kernel logger '[{handler,default,logger_std_h,#{formatter=>{logger_formatter,#{legacy_header=>true,template=>[{logger_formatter,header},"\n",msg,"\n"],depth=>10}}}]'
458 See Backwards compatibility with error_logger for more information.
461
463 app(4), application(3), code(3), disk_log(3), erl_boot_server(3),
464 erl_ddll(3), file(3), global(3), global_group(3), heart(3), inet(3),
465 logger(3), net_kernel(3), os(3), pg2(3), rpc(3), seq_trace(3), user(3),
466 timer(3)
467Ericsson AB kernel 6.5 kernel(7)