1erl(1) User Commands erl(1)
2
6 erl - The Erlang emulator.
7
9 The erl program starts an Erlang runtime system. The exact details (for
10 example, whether erl is a script or a program and which other programs
11 it calls) are system-dependent.
12 Windows users probably want to use the werl program instead, which runs
14 in its own window with scrollbars and supports command-line editing.
15 The erl program on Windows provides no line editing in its shell, and
16 on Windows 95 there is no way to scroll back to text that has scrolled
17 off the screen. The erl program must be used, however, in pipelines or
18 if you want to redirect standard input or output.
19 Note:
21 As from ERTS 5.9 (Erlang/OTP R15B) the runtime system does by default
22 not bind schedulers to logical processors. For more information, see
23 system flag +sbt.
24
27 erl <arguments>
28 Starts an Erlang runtime system.
30 The arguments can be divided into emulator flags, flags, and
32 plain arguments:
33 * Any argument starting with character + is interpreted as an
35 emulator flag.
36 As indicated by the name, emulator flags control the behav‐
38 ior of the emulator.
39 * Any argument starting with character - (hyphen) is inter‐
41 preted as a flag, which is to be passed to the Erlang part
42 of the runtime system, more specifically to the init system
43 process, see init(3).
44 The init process itself interprets some of these flags, the
46 init flags. It also stores any remaining flags, the user
47 flags. The latter can be retrieved by calling init:get_argu‐
48 ment/1.
49 A small number of "-" flags exist, which now actually are
51 emulator flags, see the description below.
52 * Plain arguments are not interpreted in any way. They are
54 also stored by the init process and can be retrieved by
55 calling init:get_plain_arguments/0. Plain arguments can oc‐
56 cur before the first flag, or after a -- flag. Also, the
57 -extra flag causes everything that follows to become plain
58 arguments.
59 Examples:
61 % erl +W w -sname arnie +R 9 -s my_init -extra +bertie
63 (arnie@host)1> init:get_argument(sname).
64 {ok,[["arnie"]]}
65 (arnie@host)2> init:get_plain_arguments().
66 ["+bertie"]
67 Here +W w and +R 9 are emulator flags. -s my_init is an init
69 flag, interpreted by init. -sname arnie is a user flag, stored
70 by init. It is read by Kernel and causes the Erlang runtime sys‐
71 tem to become distributed. Finally, everything after -extra
72 (that is, +bertie) is considered as plain arguments.
73 % erl -myflag 1
75 1> init:get_argument(myflag).
76 {ok,[["1"]]}
77 2> init:get_plain_arguments().
78 []
79 Here the user flag -myflag 1 is passed to and stored by the init
81 process. It is a user-defined flag, presumably used by some
82 user-defined application.
83
85 In the following list, init flags are marked "(init flag)". Unless oth‐
86 erwise specified, all other flags are user flags, for which the values
87 can be retrieved by calling init:get_argument/1. Notice that the list
88 of user flags is not exhaustive, there can be more application-specific
89 flags that instead are described in the corresponding application docu‐
90 mentation.
91 -- (init flag):
93 Everything following -- up to the next flag (-flag or +flag) is
94 considered plain arguments and can be retrieved using
95 init:get_plain_arguments/0.
96 -Application Par Val:
98 Sets the application configuration parameter Par to the value Val
99 for the application Application; see app(4) and application(3).
100 -args_file FileName:
102 Command-line arguments are read from the file FileName. The argu‐
103 ments read from the file replace flag '-args_file FileName' on the
104 resulting command line.
105 The file FileName is to be a plain text file and can contain com‐
107 ments and command-line arguments. A comment begins with a # charac‐
108 ter and continues until the next end of line character. Backslash
109 (\\) is used as quoting character. All command-line arguments ac‐
110 cepted by erl are allowed, also flag -args_file FileName. Be care‐
111 ful not to cause circular dependencies between files containing
112 flag -args_file, though.
113 The flag -extra is treated in special way. Its scope ends at the
115 end of the file. Arguments following an -extra flag are moved on
116 the command line into the -extra section, that is, the end of the
117 command line following after an -extra flag.
118 -async_shell_start:
120 The initial Erlang shell does not read user input until the system
121 boot procedure has been completed (Erlang/OTP 5.4 and later). This
122 flag disables the start synchronization feature and lets the shell
123 start in parallel with the rest of the system.
124 -boot File:
126 Specifies the name of the boot file, File.boot, which is used to
127 start the system; see init(3). Unless File contains an absolute
128 path, the system searches for File.boot in the current and
129 $ROOT/bin directories.
130 Defaults to $ROOT/bin/start.boot.
132 -boot_var Var Dir:
134 If the boot script contains a path variable Var other than $ROOT,
135 this variable is expanded to Dir. Used when applications are in‐
136 stalled in another directory than $ROOT/lib; see sys‐
137 tools:make_script/1,2 in SASL.
138 -code_path_cache:
140 Enables the code path cache of the code server; see code(3).
141 -compile Mod1 Mod2 ...:
143 Compiles the specified modules and then terminates (with non-zero
144 exit code if the compilation of some file did not succeed). Implies
145 -noinput.
146 Not recommended; use erlc instead.
148 -config Config [Config ...]:
150 Specifies the name of one or more configuration files, Config.con‐
151 fig, which is used to configure applications; see app(4) and appli‐
152 cation(3). See the documentation for the configuration file format
153 for a description of the configuration format and the order in
154 which configuration parameters are read.
155 -configfd FD [FD ...]:
157 Specifies the name of one or more file descriptors (called configu‐
158 ration file descriptors from here on) with configuration data for
159 applications; see app(4) and application(3). See the documentation
160 for the configuration file format for a description of the configu‐
161 ration format and the order in which configuration parameters are
162 read.
163 A configuration file descriptor will be read until its end and will
165 then be closed.
166 The content of a configuration file descriptor is stored so that it
168 can be reused when init:restart/0 or init:restart/1 is called.
169 The parameter -configfd 0 implies -noinput.
171 Note:
173 It is not recommended to use file descriptors 1 (standard output),
174 and 2 (standard error) together with -configfd as these file descrip‐
175 tors are typically used to print information to the console the pro‐
176 gram is running in.
177 Examples (Unix shell):
180 $ erl \ -noshell \ -configfd 3 \ -eval \ 'io:format("~p~n",[application:get_env(kernel, logger_level)]),erlang:halt()' 3< \ <(echo '[{kernel, [{logger_level, warning}]}].')
182 {ok,warning}
183 $ echo '[{kernel, [{logger_level, warning}]}].' > test1.config
186 $ echo '[{kernel, [{logger_level, error}]}].' > test2.config
187 $ erl \ -noshell \ -configfd 3 \ -configfd 4 \ -eval \ 'io:format("~p~n",[application:get_env(kernel, logger_level)]),erlang:halt()' \ 3< test1.config 4< test2.config
188 {ok,error}
189 -connect_all false:
192 If this flag is present, global does not maintain a fully connected
193 network of distributed Erlang nodes, and then global name registra‐
194 tion cannot be used; see global(3).
195 -cookie Cookie:
197 Obsolete flag without any effect and common misspelling for -set‐
198 cookie. Use -setcookie instead.
199 -detached:
201 Starts the Erlang runtime system detached from the system console.
202 Useful for running daemons and backgrounds processes. Implies
203 -noinput.
204 -emu_args:
206 Useful for debugging. Prints the arguments sent to the emulator.
207 -emu_flavor emu|jit|smp:
209 Start an emulator of a different flavor. Normally only one flavor
210 is available, more can be added by building specific flavors. The
211 currently available flavors are: emu and jit. The smp flavor is an
212 alias for the current default flavor. You can combine this flag
213 with --emu_type. You can get the current flavor at run-time using
214 erlang:system_info(emu_flavor). (The emulator with this flavor must
215 be built. You can build a specific flavor by doing make FLA‐
216 VOR=$FLAVOR in the Erlang/OTP source repository.)
217 -emu_type Type:
219 Start an emulator of a different type. For example, to start the
220 lock-counter emulator, use -emu_type lcnt. You can get the current
221 type at run-time using erlang:system_info(build_type). (The emula‐
222 tor of this type must already be built. Use the configure option
223 --enable-lock-counter to build the lock-counter emulator.)
224 -env Variable Value:
226 Sets the host OS environment variable Variable to the value Value
227 for the Erlang runtime system. Example:
228 % erl -env DISPLAY gin:0
230 In this example, an Erlang runtime system is started with environ‐
232 ment variable DISPLAY set to gin:0.
233 -epmd_module Module (init flag):
235 Configures the module responsible to communicate to epmd. Defaults
236 to erl_epmd.
237 -erl_epmd_port Port (init flag):
239 Configures the port used by erl_epmd to listen for connection and
240 connect to other nodes. See erl_epmd for more details. Defaults to
241 0.
242 -eval Expr (init flag):
244 Makes init evaluate the expression Expr; see init(3).
245 -extra (init flag):
247 Everything following -extra is considered plain arguments and can
248 be retrieved using init:get_plain_arguments/0.
249 -heart:
251 Starts heartbeat monitoring of the Erlang runtime system; see
252 heart(3).
253 -hidden:
255 Starts the Erlang runtime system as a hidden node, if it is run as
256 a distributed node. Hidden nodes always establish hidden connec‐
257 tions to all other nodes except for nodes in the same global group.
258 Hidden connections are not published on any of the connected nodes,
259 that is, none of the connected nodes are part of the result from
260 nodes/0 on the other node. See also hidden global groups;
261 global_group(3).
262 -hosts Hosts:
264 Specifies the IP addresses for the hosts on which Erlang boot
265 servers are running, see erl_boot_server(3). This flag is mandatory
266 if flag -loader inet is present.
267 The IP addresses must be specified in the standard form (four deci‐
269 mal numbers separated by periods, for example, "150.236.20.74".
270 Hosts names are not acceptable, but a broadcast address (preferably
271 limited to the local network) is.
272 -id Id:
274 Specifies the identity of the Erlang runtime system. If it is run
275 as a distributed node, Id must be identical to the name supplied
276 together with flag -sname or -name.
277 -init_debug:
279 Makes init write some debug information while interpreting the boot
280 script.
281 -instr (emulator flag):
283 Selects an instrumented Erlang runtime system (virtual machine) to
284 run, instead of the ordinary one. When running an instrumented run‐
285 time system, some resource usage data can be obtained and analyzed
286 using the instrument module. Functionally, it behaves exactly like
287 an ordinary Erlang runtime system.
288 -loader Loader:
290 Specifies the method used by erl_prim_loader to load Erlang modules
291 into the system; see erl_prim_loader(3). Two Loader methods are
292 supported:
293 * efile, which means use the local file system, this is the de‐
295 fault.
296 * inet, which means use a boot server on another machine. The flags
298 -id, -hosts and -setcookie must also be specified.
299 If Loader is something else, the user-supplied Loader port program
301 is started.
302 -make:
304 Makes the Erlang runtime system invoke make:all() in the current
305 working directory and then terminate; see make(3). Implies -noin‐
306 put.
307 -man Module:
309 Displays the manual page for the Erlang module Module. Only sup‐
310 ported on Unix.
311 -mode interactive | embedded:
313 Modules are auto loaded when they are first referenced if the run‐
314 time system runs in interactive mode, which is the default. In em‐
315 bedded mode modules are not auto loaded. The latter is recommended
316 when the boot script preloads all modules, as conventionally hap‐
317 pens in OTP releases. See code(3).
318 -name Name:
320 Makes the Erlang runtime system into a distributed node. This flag
321 invokes all network servers necessary for a node to become distrib‐
322 uted; see net_kernel(3). It is also ensured that epmd runs on the
323 current host before Erlang is started; see epmd(1) and the
324 -start_epmd option.
325 The node name will be Name@Host, where Host is the fully qualified
327 host name of the current host. For short names, use flag -sname in‐
328 stead.
329 If Name is set to undefined the node will be started in a special
331 mode optimized to be the temporary client of another node. The node
332 will then request a dynamic node name from the first node it con‐
333 nects to. Read more in Dynamic Node Name.
334 Warning:
336 Starting a distributed node without also specifying -proto_dist
337 inet_tls will expose the node to attacks that may give the attacker
338 complete access to the node and in extension the cluster. When using
339 un-secure distributed nodes, make sure that the network is configured
340 to keep potential attackers out.
341 -no_epmd:
344 Specifies that the distributed node does not need epmd at all.
345 This option ensures that the Erlang runtime system does not start
347 epmd and does not start the erl_epmd process for distribution ei‐
348 ther.
349 This option only works if Erlang is started as a distributed node
351 with the -proto_dist option using an alternative protocol for Er‐
352 lang distribution which does not rely on epmd for node registration
353 and discovery. For more information, see How to implement an Alter‐
354 native Carrier for the Erlang Distribution.
355 -noinput:
357 Ensures that the Erlang runtime system never tries to read any in‐
358 put. Implies -noshell.
359 -noshell:
361 Starts an Erlang runtime system with no shell. This flag makes it
362 possible to have the Erlang runtime system as a component in a se‐
363 ries of Unix pipes.
364 -nostick:
366 Disables the sticky directory facility of the Erlang code server;
367 see code(3).
368 -oldshell:
370 Invokes the old Erlang shell from Erlang/OTP 3.3. The old shell can
371 still be used.
372 -pa Dir1 Dir2 ...:
374 Adds the specified directories to the beginning of the code path,
375 similar to code:add_pathsa/1. Note that the order of the given di‐
376 rectories will be reversed in the resulting path.
377 As an alternative to -pa, if several directories are to be
379 prepended to the code path and the directories have a common parent
380 directory, that parent directory can be specified in environment
381 variable ERL_LIBS; see code(3).
382 -pz Dir1 Dir2 ...:
384 Adds the specified directories to the end of the code path, similar
385 to code:add_pathsz/1; see code(3).
386 -path Dir1 Dir2 ...:
388 Replaces the path specified in the boot script; see script(4).
389 -proto_dist Proto:
391 Specifies a protocol for Erlang distribution:
394 inet_tcp:
396 TCP over IPv4 (the default)
397 inet_tls:
399 Distribution over TLS/SSL, See the Using SSL for Erlang Distri‐
400 bution User's Guide for details on how to setup a secure distrib‐
401 uted node.
402 inet6_tcp:
404 TCP over IPv6
405 For example, to start up IPv6 distributed nodes:
407 % erl -name test@ipv6node.example.com -proto_dist inet6_tcp
409 -remsh Node:
411 Starts Erlang with a remote shell connected to Node.
412 If no -name or -sname is given the node will be started using
414 -sname undefined. If Node does not contain a hostname, one is auto‐
415 matically taken from -name or -sname
416 Note:
418 Before OTP-23 the user needed to supply a valid -sname or -name for
419 -remsh to work. This is still the case if the target node is not run‐
420 ning OTP-23 or later.
421 -rsh Program:
424 Specifies an alternative to ssh for starting a slave node on a re‐
425 mote host; see slave(3).
426 -run Mod [Func [Arg1, Arg2, ...]] (init flag):
428 Makes init call the specified function. Func defaults to start. If
429 no arguments are provided, the function is assumed to be of arity
430 0. Otherwise it is assumed to be of arity 1, taking the list
431 [Arg1,Arg2,...] as argument. All arguments are passed as strings.
432 See init(3).
433 -s Mod [Func [Arg1, Arg2, ...]] (init flag):
435 Makes init call the specified function. Func defaults to start. If
436 no arguments are provided, the function is assumed to be of arity
437 0. Otherwise it is assumed to be of arity 1, taking the list
438 [Arg1,Arg2,...] as argument. All arguments are passed as atoms. See
439 init(3).
440 -setcookie Cookie:
442 Sets the magic cookie of the node to Cookie; see er‐
443 lang:set_cookie/2.
444 -setcookie Node Cookie:
446 Sets the magic cookie for Node to Cookie; see erlang:set_cookie/2.
447 -shutdown_time Time:
449 Specifies how long time (in milliseconds) the init process is al‐
450 lowed to spend shutting down the system. If Time milliseconds have
451 elapsed, all processes still existing are killed. Defaults to in‐
452 finity.
453 -sname Name:
455 Makes the Erlang runtime system into a distributed node, similar to
456 -name, but the host name portion of the node name Name@Host will be
457 the short name, not fully qualified.
458 This is sometimes the only way to run distributed Erlang if the Do‐
460 main Name System (DNS) is not running. No communication can exist
461 between nodes running with flag -sname and those running with flag
462 -name, as node names must be unique in distributed Erlang systems.
463 If Name is set to undefined the node will be started in a special
465 mode optimized to be the temporary client of another node. The node
466 will then request a dynamic node name from the first node it con‐
467 nects to. Read more in Dynamic Node Name.
468 Warning:
470 Starting a distributed node without also specifying -proto_dist
471 inet_tls will expose the node to attacks that may give the attacker
472 complete access to the node and in extension the cluster. When using
473 un-secure distributed nodes, make sure that the network is configured
474 to keep potential attackers out.
475 -start_epmd true | false:
478 Specifies whether Erlang should start epmd on startup. By default
479 this is true, but if you prefer to start epmd manually, set this to
480 false.
481 This only applies if Erlang is started as a distributed node, i.e.
483 if -name or -sname is specified. Otherwise, epmd is not started
484 even if -start_epmd true is given.
485 Note that a distributed node will fail to start if epmd is not run‐
487 ning.
488 -version (emulator flag):
490 Makes the emulator print its version number. The same as erl +V.
491
493 erl invokes the code for the Erlang emulator (virtual machine), which
494 supports the following flags:
495 +a size:
497 Suggested stack size, in kilowords, for threads in the async thread
498 pool. Valid range is 16-8192 kilowords. The default suggested stack
499 size is 16 kilowords, that is, 64 kilobyte on 32-bit architectures.
500 This small default size has been chosen because the number of async
501 threads can be large. The default size is enough for drivers deliv‐
502 ered with Erlang/OTP, but might not be large enough for other dy‐
503 namically linked-in drivers that use the driver_async() functional‐
504 ity. Notice that the value passed is only a suggestion, and it can
505 even be ignored on some platforms.
506 +A size:
508 Sets the number of threads in async thread pool. Valid range is
509 1-1024. The async thread pool is used by linked-in drivers to han‐
510 dle work that may take a very long time. Since OTP 21 there are
511 very few linked-in drivers in the default Erlang/OTP distribution
512 that uses the async thread pool. Most of them have been migrated to
513 dirty IO schedulers. Defaults to 1.
514 +B [c | d | i]:
516 Option c makes Ctrl-C interrupt the current shell instead of invok‐
517 ing the emulator break handler. Option d (same as specifying +B
518 without an extra option) disables the break handler. Option i makes
519 the emulator ignore any break signal.
520 If option c is used with oldshell on Unix, Ctrl-C will restart the
522 shell process rather than interrupt it.
523 Notice that on Windows, this flag is only applicable for werl, not
525 erl (oldshell). Notice also that Ctrl-Break is used instead of
526 Ctrl-C on Windows.
527 +c true | false:
529 Enables or disables time correction:
530 true:
532 Enables time correction. This is the default if time correction
533 is supported on the specific platform.
534 false:
536 Disables time correction.
537 For backward compatibility, the boolean value can be omitted. This
539 is interpreted as +c false.
540 +C no_time_warp | single_time_warp | multi_time_warp:
542 Sets time warp mode:
543 no_time_warp:
545 No time warp mode (the default)
546 single_time_warp:
548 Single time warp mode
549 multi_time_warp:
551 Multi-time warp mode
552 +d:
554 If the emulator detects an internal error (or runs out of memory),
555 it, by default, generates both a crash dump and a core dump. The
556 core dump is, however, not very useful as the content of process
557 heaps is destroyed by the crash dump generation.
558 Option +d instructs the emulator to produce only a core dump and no
560 crash dump if an internal error is detected.
561 Calling erlang:halt/1 with a string argument still produces a crash
563 dump. On Unix systems, sending an emulator process a SIGUSR1 signal
564 also forces a crash dump.
565 +dcg DecentralizedCounterGroupsLimit:
567 Limits the number of decentralized counter groups used by decen‐
568 tralized counters optimized for update operations in the Erlang
569 runtime system. By default, the limit is 256.
570 When the number of schedulers is less than or equal to the limit,
572 each scheduler has its own group. When the number of schedulers is
573 larger than the groups limit, schedulers share groups. Shared
574 groups degrade the performance for updating counters while many
575 reader groups degrade the performance for reading counters. So, the
576 limit is a tradeoff between performance for update operations and
577 performance for read operations. Each group consumes 64 bytes in
578 each counter.
579 Notice that a runtime system using decentralized counter groups
581 benefits from binding schedulers to logical processors, as the
582 groups are distributed better between schedulers with this option.
583 This option only affects decentralized counters used for the coun‐
585 ters that are keeping track of the memory consumption and the num‐
586 ber of terms in ETS tables of type ordered_set with the write_con‐
587 currency option activated.
588 +e Number:
590 Sets the maximum number of ETS tables. This limit is partially ob‐
591 solete.
592 +ec:
594 Forces option compressed on all ETS tables. Only intended for test
595 and evaluation.
596 +fnl:
598 The virtual machine works with filenames as if they are encoded us‐
599 ing the ISO Latin-1 encoding, disallowing Unicode characters with
600 code points > 255.
601 For more information about Unicode filenames, see section Unicode
603 Filenames in the STDLIB User's Guide. Notice that this value also
604 applies to command-line parameters and environment variables (see
605 section Unicode in Environment and Parameters in the STDLIB User's
606 Guide).
607 +fnu[{w|i|e}]:
609 The virtual machine works with filenames as if they are encoded us‐
610 ing UTF-8 (or some other system-specific Unicode encoding). This is
611 the default on operating systems that enforce Unicode encoding,
612 that is, Windows MacOS X and Android.
613 The +fnu switch can be followed by w, i, or e to control how
615 wrongly encoded filenames are to be reported:
616 * w means that a warning is sent to the error_logger whenever a
618 wrongly encoded filename is "skipped" in directory listings. This
619 is the default.
620 * i means that those wrongly encoded filenames are silently ig‐
622 nored.
623 * e means that the API function returns an error whenever a wrongly
625 encoded filename (or directory name) is encountered.
626 Notice that file:read_link/1 always returns an error if the link
628 points to an invalid filename.
629 For more information about Unicode filenames, see section Unicode
631 Filenames in the STDLIB User's Guide. Notice that this value also
632 applies to command-line parameters and environment variables (see
633 section Unicode in Environment and Parameters in the STDLIB User's
634 Guide).
635 +fna[{w|i|e}]:
637 Selection between +fnl and +fnu is done based on the current locale
638 settings in the OS. This means that if you have set your terminal
639 for UTF-8 encoding, the filesystem is expected to use the same en‐
640 coding for filenames. This is the default on all operating systems,
641 except Android, MacOS X and Windows.
642 The +fna switch can be followed by w, i, or e. This has effect if
644 the locale settings cause the behavior of +fnu to be selected; see
645 the description of +fnu above. If the locale settings cause the be‐
646 havior of +fnl to be selected, then w, i, or e have no effect.
647 For more information about Unicode filenames, see section Unicode
649 Filenames in the STDLIB User's Guide. Notice that this value also
650 applies to command-line parameters and environment variables (see
651 section Unicode in Environment and Parameters in the STDLIB User's
652 Guide).
653 +hms Size:
655 Sets the default heap size of processes to the size Size.
656 +hmbs Size:
658 Sets the default binary virtual heap size of processes to the size
659 Size.
660 +hmax Size:
662 Sets the default maximum heap size of processes to the size Size.
663 Defaults to 0, which means that no maximum heap size is used. For
664 more information, see process_flag(max_heap_size, MaxHeapSize).
665 +hmaxel true|false:
667 Sets whether to send an error logger message or not for processes
668 reaching the maximum heap size. Defaults to true. For more informa‐
669 tion, see process_flag(max_heap_size, MaxHeapSize).
670 +hmaxk true|false:
672 Sets whether to kill processes reaching the maximum heap size or
673 not. Default to true. For more information, see
674 process_flag(max_heap_size, MaxHeapSize).
675 +hpds Size:
677 Sets the initial process dictionary size of processes to the size
678 Size.
679 +hmqd off_heap|on_heap:
681 Sets the default value of the message_queue_data process flag. De‐
682 faults to on_heap. If +hmqd is not passed, on_heap will be the de‐
683 fault. For more information, see process_flag(message_queue_data,
684 MQD).
685 +IOp PollSets:
687 Sets the number of IO pollsets to use when polling for I/O. This
688 option is only used on platforms that support concurrent updates of
689 a pollset, otherwise the same number of pollsets are used as IO
690 poll threads. The default is 1.
691 +IOt PollThreads:
693 Sets the number of IO poll threads to use when polling for I/O. The
694 maximum number of poll threads allowed is 1024. The default is 1.
695 A good way to check if more IO poll threads are needed is to use
697 microstate accounting and see what the load of the IO poll thread
698 is. If it is high it could be a good idea to add more threads.
699 +IOPp PollSetsPercentage:
701 Similar to +IOp but uses percentages to set the number of IO
702 pollsets to create, based on the number of poll threads configured.
703 If both +IOPp and +IOp are used, +IOPp is ignored.
704 +IOPt PollThreadsPercentage:
706 Similar to +IOt but uses percentages to set the number of IO poll
707 threads to create, based on the number of schedulers configured. If
708 both +IOPt and +IOt are used, +IOPt is ignored.
709 +JPperf true|false:
711 Enables or disables support for the `perf` profiler when running
712 with the JIT on Linux. Defaults to false.
713 For more details about how to run perf see the perf support section
715 in the BeamAsm internal documentation.
716 +L:
718 Prevents loading information about source filenames and line num‐
719 bers. This saves some memory, but exceptions do not contain infor‐
720 mation about the filenames and line numbers.
721 +MFlag Value:
723 Memory allocator-specific flags. For more information, see erts_al‐
724 loc(3).
725 +pc Range:
727 Sets the range of characters that the system considers printable in
728 heuristic detection of strings. This typically affects the shell,
729 debugger, and io:format functions (when ~tp is used in the format
730 string).
731 Two values are supported for Range:
733 latin1:
735 The default. Only characters in the ISO Latin-1 range can be con‐
736 sidered printable. This means that a character with a code point
737 > 255 is never considered printable and that lists containing
738 such characters are displayed as lists of integers rather than
739 text strings by tools.
740 unicode:
742 All printable Unicode characters are considered when determining
743 if a list of integers is to be displayed in string syntax. This
744 can give unexpected results if, for example, your font does not
745 cover all Unicode characters.
746 See also io:printable_range/0 in STDLIB.
748 +P Number:
750 Sets the maximum number of simultaneously existing processes for
751 this system if a Number is passed as value. Valid range for Number
752 is [1024-134217727]
753 NOTE: The actual maximum chosen may be much larger than the Number
755 passed. Currently the runtime system often, but not always, chooses
756 a value that is a power of 2. This might, however, be changed in
757 the future. The actual value chosen can be checked by calling er‐
758 lang:system_info(process_limit).
759 The default value is 262144
761 +Q Number:
763 Sets the maximum number of simultaneously existing ports for this
764 system if a Number is passed as value. Valid range for Number is
765 [1024-134217727]
766 NOTE: The actual maximum chosen may be much larger than the actual
768 Number passed. Currently the runtime system often, but not always,
769 chooses a value that is a power of 2. This might, however, be
770 changed in the future. The actual value chosen can be checked by
771 calling erlang:system_info(port_limit).
772 The default value used is normally 65536. However, if the runtime
774 system is able to determine maximum amount of file descriptors that
775 it is allowed to open and this value is larger than 65536, the cho‐
776 sen value will increased to a value larger or equal to the maximum
777 amount of file descriptors that can be opened.
778 On Windows the default value is set to 8196 because the normal OS
780 limitations are set higher than most machines can handle.
781 +R ReleaseNumber:
783 Sets the compatibility mode.
784 The distribution mechanism is not backward compatible by default.
786 This flag sets the emulator in compatibility mode with an earlier
787 Erlang/OTP release ReleaseNumber. The release number must be in the
788 range <current release>-2..<current release>. This limits the emu‐
789 lator, making it possible for it to communicate with Erlang nodes
790 (as well as C- and Java nodes) running that earlier release.
791 Note:
793 Ensure that all nodes (Erlang-, C-, and Java nodes) of a distributed
794 Erlang system is of the same Erlang/OTP release, or from two differ‐
795 ent Erlang/OTP releases X and Y, where all Y nodes have compatibility
796 mode X.
797 +r:
800 Forces ETS memory block to be moved on realloc.
801 +rg ReaderGroupsLimit:
803 Limits the number of reader groups used by read/write locks opti‐
804 mized for read operations in the Erlang runtime system. By default
805 the reader groups limit is 64.
806 When the number of schedulers is less than or equal to the reader
808 groups limit, each scheduler has its own reader group. When the
809 number of schedulers is larger than the reader groups limit, sched‐
810 ulers share reader groups. Shared reader groups degrade read lock
811 and read unlock performance while many reader groups degrade write
812 lock performance. So, the limit is a tradeoff between performance
813 for read operations and performance for write operations. Each
814 reader group consumes 64 byte in each read/write lock.
815 Notice that a runtime system using shared reader groups benefits
817 from binding schedulers to logical processors, as the reader groups
818 are distributed better between schedulers.
819 +S Schedulers:SchedulerOnline:
821 Sets the number of scheduler threads to create and scheduler
822 threads to set online. The maximum for both values is 1024. If the
823 Erlang runtime system is able to determine the number of logical
824 processors configured and logical processors available, Schedulers
825 defaults to logical processors configured, and SchedulersOnline de‐
826 faults to logical processors available; otherwise the default val‐
827 ues are 1. If the emulator detects that it is subject to a CPU
828 quota, the default value for SchedulersOnline will be limited ac‐
829 cordingly.
830 Schedulers can be omitted if :SchedulerOnline is not and con‐
832 versely. The number of schedulers online can be changed at runtime
833 through erlang:system_flag(schedulers_online, SchedulersOnline).
834 If Schedulers or SchedulersOnline is specified as a negative num‐
836 ber, the value is subtracted from the default number of logical
837 processors configured or logical processors available, respec‐
838 tively.
839 Specifying value 0 for Schedulers or SchedulersOnline resets the
841 number of scheduler threads or scheduler threads online, respec‐
842 tively, to its default value.
843 +SP SchedulersPercentage:SchedulersOnlinePercentage:
845 Similar to +S but uses percentages to set the number of scheduler
846 threads to create, based on logical processors configured, and
847 scheduler threads to set online, based on logical processors avail‐
848 able. Specified values must be > 0. For example, +SP 50:25 sets the
849 number of scheduler threads to 50% of the logical processors con‐
850 figured, and the number of scheduler threads online to 25% of the
851 logical processors available. SchedulersPercentage can be omitted
852 if :SchedulersOnlinePercentage is not and conversely. The number of
853 schedulers online can be changed at runtime through erlang:sys‐
854 tem_flag(schedulers_online, SchedulersOnline).
855 This option interacts with +S settings. For example, on a system
857 with 8 logical cores configured and 8 logical cores available, the
858 combination of the options +S 4:4 +SP 50:25 (in either order) re‐
859 sults in 2 scheduler threads (50% of 4) and 1 scheduler thread on‐
860 line (25% of 4).
861 +SDcpu DirtyCPUSchedulers:DirtyCPUSchedulersOnline:
863 Sets the number of dirty CPU scheduler threads to create and dirty
864 CPU scheduler threads to set online. The maximum for both values is
865 1024, and each value is further limited by the settings for normal
866 schedulers:
867 * The number of dirty CPU scheduler threads created cannot exceed
869 the number of normal scheduler threads created.
870 * The number of dirty CPU scheduler threads online cannot exceed
872 the number of normal scheduler threads online.
873 For details, see the +S and +SP. By default, the number of dirty
875 CPU scheduler threads created equals the number of normal scheduler
876 threads created, and the number of dirty CPU scheduler threads on‐
877 line equals the number of normal scheduler threads online. DirtyC‐
878 PUSchedulers can be omitted if :DirtyCPUSchedulersOnline is not and
879 conversely. The number of dirty CPU schedulers online can be
880 changed at runtime through erlang:system_flag(dirty_cpu_sched‐
881 ulers_online, DirtyCPUSchedulersOnline).
882 The amount of dirty CPU schedulers is limited by the amount of nor‐
884 mal schedulers in order to limit the effect on processes executing
885 on ordinary schedulers. If the amount of dirty CPU schedulers was
886 allowed to be unlimited, dirty CPU bound jobs would potentially
887 starve normal jobs.
888 Typical users of the dirty CPU schedulers are large garbage collec‐
890 tions, json protocol encode/decoders written as nifs and matrix ma‐
891 nipulation libraries.
892 You can use msacc(3) in order to see the current load of the dirty
894 CPU schedulers threads and adjust the number used accordingly.
895 +SDPcpu DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercent‐
897 age:
898 Similar to +SDcpu but uses percentages to set the number of dirty
899 CPU scheduler threads to create and the number of dirty CPU sched‐
900 uler threads to set online. Specified values must be > 0. For exam‐
901 ple, +SDPcpu 50:25 sets the number of dirty CPU scheduler threads
902 to 50% of the logical processors configured and the number of dirty
903 CPU scheduler threads online to 25% of the logical processors
904 available. DirtyCPUSchedulersPercentage can be omitted if :DirtyC‐
905 PUSchedulersOnlinePercentage is not and conversely. The number of
906 dirty CPU schedulers online can be changed at runtime through er‐
907 lang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOn‐
908 line).
909 This option interacts with +SDcpu settings. For example, on a sys‐
911 tem with 8 logical cores configured and 8 logical cores available,
912 the combination of the options +SDcpu 4:4 +SDPcpu 50:25 (in either
913 order) results in 2 dirty CPU scheduler threads (50% of 4) and 1
914 dirty CPU scheduler thread online (25% of 4).
915 +SDio DirtyIOSchedulers:
917 Sets the number of dirty I/O scheduler threads to create. Valid
918 range is 1-1024. By default, the number of dirty I/O scheduler
919 threads created is 10.
920 The amount of dirty IO schedulers is not limited by the amount of
922 normal schedulers like the amount of dirty CPU schedulers. This
923 since only I/O bound work is expected to execute on dirty I/O
924 schedulers. If the user should schedule CPU bound jobs on dirty I/O
925 schedulers, these jobs might starve ordinary jobs executing on or‐
926 dinary schedulers.
927 Typical users of the dirty IO schedulers are reading and writing to
929 files.
930 You can use msacc(3) in order to see the current load of the dirty
932 IO schedulers threads and adjust the number used accordingly.
933 +sFlag Value:
935 Scheduling specific flags.
936 +sbt BindType:
938 Sets scheduler bind type.
939 Schedulers can also be bound using flag +stbt. The only differ‐
941 ence between these two flags is how the following errors are han‐
942 dled:
943 * Binding of schedulers is not supported on the specific plat‐
945 form.
946 * No available CPU topology. That is, the runtime system was not
948 able to detect the CPU topology automatically, and no user-de‐
949 fined CPU topology was set.
950 If any of these errors occur when +sbt has been passed, the run‐
952 time system prints an error message, and refuses to start. If any
953 of these errors occur when +stbt has been passed, the runtime
954 system silently ignores the error, and start up using unbound
955 schedulers.
956 Valid BindTypes:
958 u:
960 unbound - Schedulers are not bound to logical processors, that
961 is, the operating system decides where the scheduler threads
962 execute, and when to migrate them. This is the default.
963 ns:
965 no_spread - Schedulers with close scheduler identifiers are
966 bound as close as possible in hardware.
967 ts:
969 thread_spread - Thread refers to hardware threads (such as In‐
970 tel's hyper-threads). Schedulers with low scheduler identi‐
971 fiers, are bound to the first hardware thread of each core,
972 then schedulers with higher scheduler identifiers are bound to
973 the second hardware thread of each core,and so on.
974 ps:
976 processor_spread - Schedulers are spread like thread_spread,
977 but also over physical processor chips.
978 s:
980 spread - Schedulers are spread as much as possible.
981 nnts:
983 no_node_thread_spread - Like thread_spread, but if multiple
984 Non-Uniform Memory Access (NUMA) nodes exist, schedulers are
985 spread over one NUMA node at a time, that is, all logical pro‐
986 cessors of one NUMA node are bound to schedulers in sequence.
987 nnps:
989 no_node_processor_spread - Like processor_spread, but if multi‐
990 ple NUMA nodes exist, schedulers are spread over one NUMA node
991 at a time, that is, all logical processors of one NUMA node are
992 bound to schedulers in sequence.
993 tnnps:
995 thread_no_node_processor_spread - A combination of
996 thread_spread, and no_node_processor_spread. Schedulers are
997 spread over hardware threads across NUMA nodes, but schedulers
998 are only spread over processors internally in one NUMA node at
999 a time.
1000 db:
1002 default_bind - Binds schedulers the default way. Defaults to
1003 thread_no_node_processor_spread (which can change in the fu‐
1004 ture).
1005 Binding of schedulers is only supported on newer Linux, Solaris,
1007 FreeBSD, and Windows systems.
1008 If no CPU topology is available when flag +sbt is processed and
1010 BindType is any other type than u, the runtime system fails to
1011 start. CPU topology can be defined using flag +sct. Notice that
1012 flag +sct can have to be passed before flag +sbt on the command
1013 line (if no CPU topology has been automatically detected).
1014 The runtime system does by default not bind schedulers to logical
1016 processors.
1017 Note:
1019 If the Erlang runtime system is the only operating system process
1020 that binds threads to logical processors, this improves the perfor‐
1021 mance of the runtime system. However, if other operating system
1022 processes (for example another Erlang runtime system) also bind
1023 threads to logical processors, there can be a performance penalty
1024 instead. This performance penalty can sometimes be severe. If so,
1025 you are advised not to bind the schedulers.
1026 How schedulers are bound matters. For example, in situations when
1029 there are fewer running processes than schedulers online, the
1030 runtime system tries to migrate processes to schedulers with low
1031 scheduler identifiers. The more the schedulers are spread over
1032 the hardware, the more resources are available to the runtime
1033 system in such situations.
1034 Note:
1036 If a scheduler fails to bind, this is often silently ignored, as it
1037 is not always possible to verify valid logical processor identi‐
1038 fiers. If an error is reported, it is reported to the error_logger.
1039 If you want to verify that the schedulers have bound as requested,
1040 call erlang:system_info(scheduler_bindings).
1041 +sbwt none|very_short|short|medium|long|very_long:
1044 Sets scheduler busy wait threshold. Defaults to medium. The
1045 threshold determines how long schedulers are to busy wait when
1046 running out of work before going to sleep.
1047 Note:
1049 This flag can be removed or changed at any time without prior no‐
1050 tice.
1051 +sbwtdcpu none|very_short|short|medium|long|very_long:
1054 As +sbwt but affects dirty CPU schedulers. Defaults to short.
1055 Note:
1057 This flag can be removed or changed at any time without prior no‐
1058 tice.
1059 +sbwtdio none|very_short|short|medium|long|very_long:
1062 As +sbwt but affects dirty IO schedulers. Defaults to short.
1063 Note:
1065 This flag can be removed or changed at any time without prior no‐
1066 tice.
1067 +scl true|false:
1070 Enables or disables scheduler compaction of load. By default
1071 scheduler compaction of load is enabled. When enabled, load bal‐
1072 ancing strives for a load distribution, which causes as many
1073 scheduler threads as possible to be fully loaded (that is, not
1074 run out of work). This is accomplished by migrating load (for ex‐
1075 ample, runnable processes) into a smaller set of schedulers when
1076 schedulers frequently run out of work. When disabled, the fre‐
1077 quency with which schedulers run out of work is not taken into
1078 account by the load balancing logic.
1079 +scl false is similar to +sub true, but +sub true also balances
1081 scheduler utilization between schedulers.
1082 +sct CpuTopology:
1084 * <Id> = integer(); when 0 =< <Id> =< 65535
1087 * <IdRange> = <Id>-<Id>
1089 * <IdOrIdRange> = <Id> | <IdRange>
1091 * <IdList> = <IdOrIdRange>,<IdOrIdRange> | <IdOrIdRange>
1093 * <LogicalIds> = L<IdList>
1095 * <ThreadIds> = T<IdList> | t<IdList>
1097 * <CoreIds> = C<IdList> | c<IdList>
1099 * <ProcessorIds> = P<IdList> | p<IdList>
1101 * <NodeIds> = N<IdList> | n<IdList>
1103 * <IdDefs> = <LogicalIds><ThreadIds><CoreIds><Proces‐
1105 sorIds><NodeIds> | <LogicalIds><ThreadIds><Cor‐
1106 eIds><NodeIds><ProcessorIds>
1107 * CpuTopology = <IdDefs>:<IdDefs> | <IdDefs>
1109 Sets a user-defined CPU topology. The user-defined CPU topology
1111 overrides any automatically detected CPU topology. The CPU topol‐
1112 ogy is used when binding schedulers to logical processors.
1113 Uppercase letters signify real identifiers and lowercase letters
1115 signify fake identifiers only used for description of the topol‐
1116 ogy. Identifiers passed as real identifiers can be used by the
1117 runtime system when trying to access specific hardware; if they
1118 are incorrect the behavior is undefined. Faked logical CPU iden‐
1119 tifiers are not accepted, as there is no point in defining the
1120 CPU topology without real logical CPU identifiers. Thread, core,
1121 processor, and node identifiers can be omitted. If omitted, the
1122 thread ID defaults to t0, the core ID defaults to c0, the proces‐
1123 sor ID defaults to p0, and the node ID is left undefined. Either
1124 each logical processor must belong to only one NUMA node, or no
1125 logical processors must belong to any NUMA nodes.
1126 Both increasing and decreasing <IdRange>s are allowed.
1128 NUMA node identifiers are system wide. That is, each NUMA node on
1130 the system must have a unique identifier. Processor identifiers
1131 are also system wide. Core identifiers are processor wide. Thread
1132 identifiers are core wide.
1133 The order of the identifier types implies the hierarchy of the
1135 CPU topology. The valid orders are as follows:
1136 * <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>, that
1138 is, thread is part of a core that is part of a processor, which
1139 is part of a NUMA node.
1140 * <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>, that
1142 is, thread is part of a core that is part of a NUMA node, which
1143 is part of a processor.
1144 A CPU topology can consist of both processor external, and pro‐
1146 cessor internal NUMA nodes as long as each logical processor be‐
1147 longs to only one NUMA node. If <ProcessorIds> is omitted, its
1148 default position is before <NodeIds>. That is, the default is
1149 processor external NUMA nodes.
1150 If a list of identifiers is used in an <IdDefs>:
1152 * <LogicalIds> must be a list of identifiers.
1154 * At least one other identifier type besides <LogicalIds> must
1156 also have a list of identifiers.
1157 * All lists of identifiers must produce the same number of iden‐
1159 tifiers.
1160 A simple example. A single quad core processor can be described
1162 as follows:
1163 % erl +sct L0-3c0-3
1165 1> erlang:system_info(cpu_topology).
1166 [{processor,[{core,{logical,0}},
1167 {core,{logical,1}},
1168 {core,{logical,2}},
1169 {core,{logical,3}}]}]
1170 A more complicated example with two quad core processors, each
1172 processor in its own NUMA node. The ordering of logical proces‐
1173 sors is a bit weird. This to give a better example of identifier
1174 lists:
1175 % erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1
1177 1> erlang:system_info(cpu_topology).
1178 [{node,[{processor,[{core,{logical,0}},
1179 {core,{logical,1}},
1180 {core,{logical,3}},
1181 {core,{logical,2}}]}]},
1182 {node,[{processor,[{core,{logical,7}},
1183 {core,{logical,4}},
1184 {core,{logical,6}},
1185 {core,{logical,5}}]}]}]
1186 As long as real identifiers are correct, it is OK to pass a CPU
1188 topology that is not a correct description of the CPU topology.
1189 When used with care this can be very useful. This to trick the
1190 emulator to bind its schedulers as you want. For example, if you
1191 want to run multiple Erlang runtime systems on the same machine,
1192 you want to reduce the number of schedulers used and manipulate
1193 the CPU topology so that they bind to different logical CPUs. An
1194 example, with two Erlang runtime systems on a quad core machine:
1195 % erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
1197 % erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two
1198 In this example, each runtime system have two schedulers each on‐
1200 line, and all schedulers online will run on different cores. If
1201 we change to one scheduler online on one runtime system, and
1202 three schedulers online on the other, all schedulers online will
1203 still run on different cores.
1204 Notice that a faked CPU topology that does not reflect how the
1206 real CPU topology looks like is likely to decrease the perfor‐
1207 mance of the runtime system.
1208 For more information, see erlang:system_info(cpu_topology).
1210 +sfwi Interval:
1212 Sets scheduler-forced wakeup interval. All run queues are scanned
1213 each Interval milliseconds. While there are sleeping schedulers
1214 in the system, one scheduler is woken for each non-empty run
1215 queue found. Interval default to 0, meaning this feature is dis‐
1216 abled.
1217 Note:
1219 This feature has been introduced as a temporary workaround for
1220 long-executing native code, and native code that does not bump re‐
1221 ductions properly in OTP. When these bugs have been fixed, this
1222 flag will be removed.
1223 +spp Bool:
1226 Sets default scheduler hint for port parallelism. If set to true,
1227 the virtual machine schedules port tasks when it improves paral‐
1228 lelism in the system. If set to false, the virtual machine tries
1229 to perform port tasks immediately, improving latency at the ex‐
1230 pense of parallelism. Default to false. The default used can be
1231 inspected in runtime by calling erlang:system_info(port_parallel‐
1232 ism). The default can be overridden on port creation by passing
1233 option parallelism to erlang:open_port/2.
1234 +sss size:
1236 Suggested stack size, in kilowords, for scheduler threads. Valid
1237 range is 20-8192 kilowords. The default suggested stack size is
1238 128 kilowords.
1239 +sssdcpu size:
1241 Suggested stack size, in kilowords, for dirty CPU scheduler
1242 threads. Valid range is 20-8192 kilowords. The default suggested
1243 stack size is 40 kilowords.
1244 +sssdio size:
1246 Suggested stack size, in kilowords, for dirty IO scheduler
1247 threads. Valid range is 20-8192 kilowords. The default suggested
1248 stack size is 40 kilowords.
1249 +stbt BindType:
1251 Tries to set the scheduler bind type. The same as flag +sbt ex‐
1252 cept how some errors are handled. For more information, see +sbt.
1253 +sub true|false:
1255 Enables or disables scheduler utilization balancing of load. By
1256 default scheduler utilization balancing is disabled and instead
1257 scheduler compaction of load is enabled, which strives for a load
1258 distribution that causes as many scheduler threads as possible to
1259 be fully loaded (that is, not run out of work). When scheduler
1260 utilization balancing is enabled, the system instead tries to
1261 balance scheduler utilization between schedulers. That is, strive
1262 for equal scheduler utilization on all schedulers.
1263 +sub true is only supported on systems where the runtime system
1265 detects and uses a monotonically increasing high-resolution
1266 clock. On other systems, the runtime system fails to start.
1267 +sub true implies +scl false. The difference between +sub true
1269 and +scl false is that +scl false does not try to balance the
1270 scheduler utilization.
1271 +swct very_eager|eager|medium|lazy|very_lazy:
1273 Sets scheduler wake cleanup threshold. Defaults to medium. Con‐
1274 trols how eager schedulers are to be requesting wakeup because of
1275 certain cleanup operations. When a lazy setting is used, more
1276 outstanding cleanup operations can be left undone while a sched‐
1277 uler is idling. When an eager setting is used, schedulers are
1278 more frequently woken, potentially increasing CPU-utilization.
1279 Note:
1281 This flag can be removed or changed at any time without prior no‐
1282 tice.
1283 +sws default|legacy:
1286 Sets scheduler wakeup strategy. Default strategy changed in ERTS
1287 5.10 (Erlang/OTP R16A). This strategy was known as proposal in
1288 Erlang/OTP R15. The legacy strategy was used as default from R13
1289 up to and including R15.
1290 Note:
1292 This flag can be removed or changed at any time without prior no‐
1293 tice.
1294 +swt very_low|low|medium|high|very_high:
1297 Sets scheduler wakeup threshold. Defaults to medium. The thresh‐
1298 old determines when to wake up sleeping schedulers when more work
1299 than can be handled by currently awake schedulers exists. A low
1300 threshold causes earlier wakeups, and a high threshold causes
1301 later wakeups. Early wakeups distribute work over multiple sched‐
1302 ulers faster, but work does more easily bounce between sched‐
1303 ulers.
1304 Note:
1306 This flag can be removed or changed at any time without prior no‐
1307 tice.
1308 +swtdcpu very_low|low|medium|high|very_high:
1311 As +swt but affects dirty CPU schedulers. Defaults to medium.
1312 Note:
1314 This flag can be removed or changed at any time without prior no‐
1315 tice.
1316 +swtdio very_low|low|medium|high|very_high:
1319 As +swt but affects dirty IO schedulers. Defaults to medium.
1320 Note:
1322 This flag can be removed or changed at any time without prior no‐
1323 tice.
1324 +t size:
1327 Sets the maximum number of atoms the virtual machine can handle.
1328 Defaults to 1,048,576.
1329 +T Level:
1331 Enables modified timing and sets the modified timing level. Valid
1332 range is 0-9. The timing of the runtime system is changed. A high
1333 level usually means a greater change than a low level. Changing the
1334 timing can be very useful for finding timing-related bugs.
1335 Modified timing affects the following:
1337 Process spawning:
1339 A process calling spawn, spawn_link, spawn_monitor, or spawn_opt
1340 is scheduled out immediately after completing the call. When
1341 higher modified timing levels are used, the caller also sleeps
1342 for a while after it is scheduled out.
1343 Context reductions:
1345 The number of reductions a process is allowed to use before it is
1346 scheduled out is increased or reduced.
1347 Input reductions:
1349 The number of reductions performed before checking I/O is in‐
1350 creased or reduced.
1351 Note:
1353 Performance suffers when modified timing is enabled. This flag is
1354 only intended for testing and debugging.
1355 return_to and return_from trace messages are lost when tracing on the
1357 spawn BIFs.
1358 This flag can be removed or changed at any time without prior notice.
1360 +v:
1363 Verbose.
1364 +V:
1366 Makes the emulator print its version number.
1367 +W w | i | e:
1369 Sets the mapping of warning messages for error_logger. Messages
1370 sent to the error logger using one of the warning routines can be
1371 mapped to errors (+W e), warnings (+W w), or information reports
1372 (+W i). Defaults to warnings. The current mapping can be retrieved
1373 using error_logger:warning_map/0. For more information, see er‐
1374 ror_logger:warning_map/0 in Kernel.
1375 +zFlag Value:
1377 Miscellaneous flags:
1378 +zdbbl size:
1380 Sets the distribution buffer busy limit (dist_buf_busy_limit) in
1381 kilobytes. Valid range is 1-2097151. Defaults to 1024.
1382 A larger buffer limit allows processes to buffer more outgoing
1384 messages over the distribution. When the buffer limit has been
1385 reached, sending processes will be suspended until the buffer
1386 size has shrunk. The buffer limit is per distribution channel. A
1387 higher limit gives lower latency and higher throughput at the ex‐
1388 pense of higher memory use.
1389 +zdntgc time:
1391 Sets the delayed node table garbage collection time (de‐
1392 layed_node_table_gc) in seconds. Valid values are either infinity
1393 or an integer in the range 0-100000000. Defaults to 60.
1394 Node table entries that are not referred linger in the table for
1396 at least the amount of time that this parameter determines. The
1397 lingering prevents repeated deletions and insertions in the ta‐
1398 bles from occurring.
1399 +zosrl limit:
1401 Sets a limit on the amount of outstanding requests made by a sys‐
1402 tem process orchestrating system wide changes. Valid range of
1403 this limit is [1, 134217727]. See erlang:system_flag(outstand‐
1404 ing_system_requests_limit, Limit) for more information.
1405
1407 ERL_CRASH_DUMP:
1408 If the emulator needs to write a crash dump, the value of this
1409 variable is the filename of the crash dump file. If the variable is
1410 not set, the name of the crash dump file is erl_crash.dump in the
1411 current directory.
1412 ERL_CRASH_DUMP_NICE:
1414 Unix systems: If the emulator needs to write a crash dump, it uses
1415 the value of this variable to set the nice value for the process,
1416 thus lowering its priority. Valid range is 1-39 (higher values are
1417 replaced with 39). The highest value, 39, gives the process the
1418 lowest priority.
1419 ERL_CRASH_DUMP_SECONDS:
1421 Unix systems: This variable gives the number of seconds that the
1422 emulator is allowed to spend writing a crash dump. When the given
1423 number of seconds have elapsed, the emulator is terminated.
1424 ERL_CRASH_DUMP_SECONDS=0:
1426 If the variable is set to 0 seconds, the runtime system does not
1427 even attempt to write the crash dump file. It only terminates.
1428 This is the default if option -heart is passed to erl and
1429 ERL_CRASH_DUMP_SECONDS is not set.
1430 ERL_CRASH_DUMP_SECONDS=S:
1432 If the variable is set to a positive value S, wait for S seconds
1433 to complete the crash dump file and then terminates the runtime
1434 system with a SIGALRM signal.
1435 ERL_CRASH_DUMP_SECONDS=-1:
1437 A negative value causes the termination of the runtime system to
1438 wait indefinitely until the crash dump file has been completly
1439 written. This is the default if option -heart is not passed to
1440 erl and ERL_CRASH_DUMP_SECONDS is not set.
1441 See also heart(3).
1443 ERL_CRASH_DUMP_BYTES:
1445 This variable sets the maximum size of a crash dump file in bytes.
1446 The crash dump will be truncated if this limit is exceeded. If the
1447 variable is not set, no size limit is enforced by default. If the
1448 variable is set to 0, the runtime system does not even attempt to
1449 write a crash dump file.
1450 Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).
1452 ERL_AFLAGS:
1454 The content of this variable is added to the beginning of the com‐
1455 mand line for erl.
1456 Flag -extra is treated in a special way. Its scope ends at the end
1458 of the environment variable content. Arguments following an -extra
1459 flag are moved on the command line into section -extra, that is,
1460 the end of the command line following an -extra flag.
1461 ERL_ZFLAGS and ERL_FLAGS:
1463 The content of these variables are added to the end of the command
1464 line for erl.
1465 Flag -extra is treated in a special way. Its scope ends at the end
1467 of the environment variable content. Arguments following an -extra
1468 flag are moved on the command line into section -extra, that is,
1469 the end of the command line following an -extra flag.
1470 ERL_LIBS:
1472 Contains a list of additional library directories that the code
1473 server searches for applications and adds to the code path; see
1474 code(3).
1475 ERL_EPMD_ADDRESS:
1477 Can be set to a comma-separated list of IP addresses, in which case
1478 the epmd daemon listens only on the specified address(es) and on
1479 the loopback address (which is implicitly added to the list if it
1480 has not been specified).
1481 ERL_EPMD_PORT:
1483 Can contain the port number to use when communicating with epmd.
1484 The default port works fine in most cases. A different port can be
1485 specified to allow nodes of independent clusters to co-exist on the
1486 same host. All nodes in a cluster must use the same epmd port num‐
1487 ber.
1488
1490 On Unix systems, the Erlang runtime will interpret two types of sig‐
1491 nals.
1492 SIGUSR1:
1494 A SIGUSR1 signal forces a crash dump.
1495 SIGTERM:
1497 A SIGTERM will produce a stop message to the init process. This is
1498 equivalent to a init:stop/0 call.
1499 Introduced in ERTS 8.3 (Erlang/OTP 19.3)
1501 The signal SIGUSR2 is reserved for internal usage. No other signals are
1503 handled.
1504
1506 The standard Erlang/OTP system can be reconfigured to change the de‐
1507 fault behavior on startup.
1508 The .erlang startup file:
1510 When Erlang/OTP is started, the system searches for a file named
1511 .erlang in the user's home directory.
1512 If an .erlang file is found, it is assumed to contain valid Erlang
1514 expressions. These expressions are evaluated as if they were input
1515 to the shell.
1516 A typical .erlang file contains a set of search paths, for example:
1518 io:format("executing user profile in HOME/.erlang\n",[]).
1520 code:add_path("/home/calvin/test/ebin").
1521 code:add_path("/home/hobbes/bigappl-1.2/ebin").
1522 io:format(".erlang rc finished\n",[]).
1523 user_default and shell_default:
1525 Functions in the shell that are not prefixed by a module name are
1526 assumed to be functional objects (funs), built-in functions (BIFs),
1527 or belong to the module user_default or shell_default.
1528 To include private shell commands, define them in a module user_de‐
1530 fault and add the following argument as the first line in the .er‐
1531 lang file:
1532 code:load_abs("..../user_default").
1534 erl:
1536 If the contents of .erlang are changed and a private version of
1537 user_default is defined, the Erlang/OTP environment can be custom‐
1538 ized. More powerful changes can be made by supplying command-line
1539 arguments in the startup script erl. For more information, see
1540 init(3).
1541
1543 epmd(1), erl_prim_loader(3), erts_alloc(3), init(3), application(3),
1544 auth(3), code(3), erl_boot_server(3), heart(3), net_kernel(3), make(3)
1545Ericsson AB erts 12.3.2.1 erl(1)