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 * Error logging
24 * Global name service
26 * Supervision of Erlang/OTP
28 * Communication with sockets
30 * Operating system interface
32
34 Two standard error logger event handlers are defined in the Kernel
35 application. These are described in error_logger(3).
36
38 Asynchronous OS signals may be subscribed to via the Kernel applica‐
39 tions event manager (see OTP Design Principles and gen_event(3)) regis‐
40 tered as erl_signal_server. A default signal handler is installed which
41 handles the following signals:
42 sigusr1:
44 The default handler will halt Erlang and produce a crashdump with
45 slogan "Received SIGUSR1". This is equivalent to calling
46 erlang:halt("Received SIGUSR1").
47 sigquit:
49 The default handler will halt Erlang immediately. This is equiva‐
50 lent to calling erlang:halt().
51 sigterm:
53 The default handler will terminate Erlang normally. This is equiva‐
54 lent to calling init:stop().
55 Events
57 Any event handler added to erl_signal_server must handle the following
58 events.
59 sighup:
61 Hangup detected on controlling terminal or death of controlling
62 process
63 sigquit:
65 Quit from keyboard
66 sigabrt:
68 Abort signal from abort
69 sigalrm:
71 Timer signal from alarm
72 sigterm:
74 Termination signal
75 sigusr1:
77 User-defined signal 1
78 sigusr2:
80 User-defined signal 2
81 sigchld:
83 Child process stopped or terminated
84 sigstop:
86 Stop process
87 sigtstp:
89 Stop typed at terminal
90 Setting OS signals are described in os:set_signal/2.
92
94 The following configuration parameters are defined for the Kernel
95 application. For more information about configuration parameters, see
96 file app(4).
97 browser_cmd = string() | {M,F,A}:
99 When pressing the Help button in a tool such as Debugger, the help
100 text (an HTML file File) is by default displayed in a Netscape
101 browser, which is required to be operational. This parameter can be
102 used to change the command for how to display the help text if
103 another browser than Netscape is preferred, or if another platform
104 than Unix or Windows is used.
105 If set to a string Command, the command "Command File" is evaluated
107 using os:cmd/1.
108 If set to a module-function-args tuple, {M,F,A}, the call
110 apply(M,F,[File|A]) is evaluated.
111 distributed = [Distrib]:
113 Specifies which applications that are distributed and on which
114 nodes they are allowed to execute. In this parameter:
115 * Distrib = {App,Nodes} | {App,Time,Nodes}
117 * App = atom()
119 * Time = integer()>0
121 * Nodes = [node() | {node(),...,node()}]
123 The parameter is described in application:load/2.
125 dist_auto_connect = Value:
127 Specifies when nodes are automatically connected. If this parameter
128 is not specified, a node is always automatically connected, for
129 example, when a message is to be sent to that node. Value is one
130 of:
131 never:
133 Connections are never automatically established, they must be
134 explicitly connected. See net_kernel(3).
135 once:
137 Connections are established automatically, but only once per
138 node. If a node goes down, it must thereafter be explicitly con‐
139 nected. See net_kernel(3).
140 permissions = [Perm]:
142 Specifies the default permission for applications when they are
143 started. In this parameter:
144 * Perm = {ApplName,Bool}
146 * ApplName = atom()
148 * Bool = boolean()
150 Permissions are described in application:permit/2.
152 error_logger = Value:
154 Value is one of:
155 tty:
157 Installs the standard event handler, which prints error reports
158 to stdio. This is the default option.
159 {file, FileName}:
161 Installs the standard event handler, which prints error reports
162 to file FileName, where FileName is a string. The file is opened
163 with encoding UTF-8.
164 false:
166 No standard event handler is installed, but the initial, primi‐
167 tive event handler is kept, printing raw event messages to tty.
168 silent:
170 Error logging is turned off.
171 error_logger_format_depth = Depth:
173 Can be used to limit the size of the formatted output from the
176 error logger event handlers.
177 Note:
179 This configuration parameter was introduced in OTP 18.1 and is exper‐
180 imental. Based on user feedback, it can be changed or improved in
181 future releases, for example, to gain better control over how to
182 limit the size of the formatted output. We have no plans to remove
183 this new feature entirely, unless it turns out to be useless.
184 Depth is a positive integer representing the maximum depth to which
187 terms are printed by the error logger event handlers included in
188 OTP. This configuration parameter is used by the two event handlers
189 defined by the Kernel application and the two event handlers in the
190 SASL application. (If you have implemented your own error handlers,
191 this configuration parameter has no effect on them.)
192 Depth is used as follows: Format strings passed to the event han‐
194 dlers are rewritten. The format controls ~p and ~w are replaced
195 with ~P and ~W, respectively, and Depth is used as the depth param‐
196 eter. For details, see io:format/2 in STDLIB.
197 Note:
199 A reasonable starting value for Depth is 30. We recommend to test
200 crashing various processes in your application, examine the logs from
201 the crashes, and then increase or decrease the value.
202 global_groups = [GroupTuple]:
205 Defines global groups, see global_group(3). In this parameter:
208 * GroupTuple = {GroupName, [Node]} | {GroupName, PublishType,
210 [Node]}
211 * GroupName = atom()
213 * PublishType = normal | hidden
215 * Node = node()
217 inet_default_connect_options = [{Opt, Val}]:
219 Specifies default options for connect sockets, see inet(3).
220 inet_default_listen_options = [{Opt, Val}]:
222 Specifies default options for listen (and accept) sockets, see
223 inet(3).
224 {inet_dist_use_interface, ip_address()}:
226 If the host of an Erlang node has many network interfaces, this
227 parameter specifies which one to listen on. For the type definition
228 of ip_address(), see inet(3).
229 {inet_dist_listen_min, First} and {inet_dist_listen_max, Last}:
231 Defines the First..Last port range for the listener socket of a
232 distributed Erlang node.
233 {inet_dist_listen_options, Opts}:
235 Defines a list of extra socket options to be used when opening the
238 listening socket for a distributed Erlang node. See gen_tcp:lis‐
239 ten/2.
240 {inet_dist_connect_options, Opts}:
242 Defines a list of extra socket options to be used when connecting
245 to other distributed Erlang nodes. See gen_tcp:connect/4.
246 inet_parse_error_log = silent:
248 If set, no error_logger messages are generated when erroneous lines
249 are found and skipped in the various Inet configuration files.
250 inetrc = Filename:
252 The name (string) of an Inet user configuration file. For details,
253 see section Inet Configuration in the ERTS User's Guide.
254 net_setuptime = SetupTime:
256 SetupTime must be a positive integer or floating point number, and
259 is interpreted as the maximum allowed time for each network opera‐
260 tion during connection setup to another Erlang node. The maximum
261 allowed value is 120. If higher values are specified, 120 is used.
262 Default is 7 seconds if the variable is not specified, or if the
263 value is incorrect (for example, not a number).
264 Notice that this value does not limit the total connection setup
266 time, but rather each individual network operation during the con‐
267 nection setup and handshake.
268 net_ticktime = TickTime:
270 Specifies the net_kernel tick time. TickTime is specified in sec‐
273 onds. Once every TickTime/4 second, all connected nodes are ticked
274 (if anything else is written to a node). If nothing is received
275 from another node within the last four tick times, that node is
276 considered to be down. This ensures that nodes that are not
277 responding, for reasons such as hardware errors, are considered to
278 be down.
279 The time T, in which a node that is not responding is detected, is
281 calculated as MinT < T < MaxT, where:
282 MinT = TickTime - TickTime / 4
284 MaxT = TickTime + TickTime / 4
285 TickTime defaults to 60 (seconds). Thus, 45 < T < 75 seconds.
287 Notice that all communicating nodes are to have the same TickTime
289 value specified.
290 Normally, a terminating node is detected immediately.
292 shutdown_timeout = integer() | infinity:
294 Specifies the time application_controller waits for an application
295 to terminate during node shutdown. If the timer expires, applica‐
296 tion_controller brutally kills application_master of the hanging
297 application. If this parameter is undefined, it defaults to infin‐
298 ity.
299 sync_nodes_mandatory = [NodeName]:
301 Specifies which other nodes that must be alive for this node to
302 start properly. If some node in the list does not start within the
303 specified time, this node does not start either. If this parameter
304 is undefined, it defaults to [].
305 sync_nodes_optional = [NodeName]:
307 Specifies which other nodes that can be alive for this node to
308 start properly. If some node in this list does not start within the
309 specified time, this node starts anyway. If this parameter is unde‐
310 fined, it defaults to the empty list.
311 sync_nodes_timeout = integer() | infinity:
313 Specifies the time (in milliseconds) that this node waits for the
314 mandatory and optional nodes to start. If this parameter is unde‐
315 fined, no node synchronization is performed. This option ensures
316 that global is synchronized.
317 start_dist_ac = true | false:
319 Starts the dist_ac server if the parameter is true. This parameter
320 is to be set to true for systems using distributed applications.
321 Defaults to false. If this parameter is undefined, the server is
323 started if parameter distributed is set.
324 start_boot_server = true | false:
326 Starts the boot_server if the parameter is true (see
327 erl_boot_server(3)). This parameter is to be set to true in an
328 embedded system using this service.
329 Defaults to false.
331 boot_server_slaves = [SlaveIP]:
333 If configuration parameter start_boot_server is true, this parame‐
334 ter can be used to initialize boot_server with a list of slave IP
335 addresses:
336 SlaveIP = string() | atom | {integer(),integer(),integer(),inte‐
338 ger()},
339 where 0 <= integer() <=255.
341 Examples of SlaveIP in atom, string, and tuple form:
343 '150.236.16.70', "150,236,16,70", {150,236,16,70}.
345 Defaults to [].
347 start_disk_log = true | false:
349 Starts the disk_log_server if the parameter is true (see
350 disk_log(3)). This parameter is to be set to true in an embedded
351 system using this service.
352 Defaults to false.
354 start_pg2 = true | false:
356 Starts the pg2 server (see pg2(3)) if the parameter is true. This
359 parameter is to be set to true in an embedded system that uses this
360 service.
361 Defaults to false.
363 start_timer = true | false:
365 Starts the timer_server if the parameter is true (see timer(3)).
366 This parameter is to be set to true in an embedded system using
367 this service.
368 Defaults to false.
370 shell_history = enabled | disabled :
372 Specifies whether shell history should be logged to disk between
373 usages of erl.
374 shell_history_drop = [string()]:
376 Specific log lines that should not be persisted. For example
377 ["q().", "init:stop()."] will allow to ignore commands that shut
378 the node down. Defaults to [].
379 shell_history_file_bytes = integer():
381 how many bytes the shell should remember. By default, the value is
382 set to 512kb, and the minimal value is 50kb.
383 shell_history_path = string():
385 Specifies where the shell history files will be stored. defaults to
386 the user's cache directory as returned by file‐
387 name:basedir(user_cache, "erlang-history").
388 shutdown_func = {Mod, Func}:
390 Where:
391 * Mod = atom()
393 * Func = atom()
395 Sets a function that application_controller calls when it starts to
397 terminate. The function is called as Mod:Func(Reason), where Reason
398 is the terminate reason for application_controller, and it must
399 return as soon as possible for application_controller to terminate
400 properly.
401 source_search_rules = [DirRule] | [SuffixRule] :
403 Where:
406 * DirRule = {ObjDirSuffix,SrcDirSuffix}
408 * SuffixRule = {ObjSuffix,SrcSuffix,[DirRule]}
410 * ObjDirSuffix = string()
412 * SrcDirSuffix = string()
414 * ObjSuffix = string()
416 * SrcSuffix = string()
418 Specifies a list of rules for use by filelib:find_file/2
420 filelib:find_source/2 If this is set to some other value than the
421 empty list, it replaces the default rules. Rules can be simple
422 pairs of directory suffixes, such as {"ebin", "src"}, which are
423 used by filelib:find_file/2, or triples specifying separate direc‐
424 tory suffix rules depending on file name extensions, for example
425 [{".beam", ".erl", [{"ebin", "src"}]}, which are used by
426 filelib:find_source/2. Both kinds of rules can be mixed in the
427 list.
428 The interpretation of ObjDirSuffix and SrcDirSuffix is as follows:
430 if the end of the directory name where an object is located matches
431 ObjDirSuffix, then the name created by replacing ObjDirSuffix with
432 SrcDirSuffix is expanded by calling filelib:wildcard/1, and the
433 first regular file found among the matches is the source file.
434
436 app(4), application(3), code(3), disk_log(3), erl_boot_server(3),
437 erl_ddll(3), error_logger(3), file(3), global(3), global_group(3),
438 heart(3), inet(3), net_kernel(3), os(3), pg2(3), rpc(3), seq_trace(3),
439 user(3), timer(3)
440Ericsson AB kernel 5.4.3.2 kernel(7)