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 This flag is deprecated and has been replaced by the kernel appli‐
193 cation parameter connect_all.
194 -cookie Cookie:
196 Obsolete flag without any effect and common misspelling for -set‐
197 cookie. Use -setcookie instead.
198 -detached:
200 Starts the Erlang runtime system detached from the system console.
201 Useful for running daemons and backgrounds processes. Implies
202 -noinput.
203 -disable-feature feature:
205 Disables the feature feature in the runtime system. The special
206 feature all can be used to disable all non permanent features.
207 -dist_listen true|false:
209 Specifies whether this node should be listening for incoming dis‐
210 tribution connections or not. By default a node will listen for in‐
211 coming connections. Setting this option to false implies -hidden.
212 -emu_args:
214 Useful for debugging. Prints the arguments sent to the emulator.
215 -emu_flavor emu|jit|smp:
217 Start an emulator of a different flavor. Normally only one flavor
218 is available, more can be added by building specific flavors. The
219 currently available flavors are: emu and jit. The smp flavor is an
220 alias for the current default flavor. You can combine this flag
221 with --emu_type. You can get the current flavor at run-time using
222 erlang:system_info(emu_flavor). (The emulator with this flavor must
223 be built. You can build a specific flavor by doing make FLA‐
224 VOR=$FLAVOR in the Erlang/OTP source repository.)
225 -emu_type Type:
227 Start an emulator of a different type. For example, to start the
228 lock-counter emulator, use -emu_type lcnt. You can get the current
229 type at run-time using erlang:system_info(build_type). (The emula‐
230 tor of this type must already be built. Use the configure option
231 --enable-lock-counter to build the lock-counter emulator.)
232 -enable-feature feature:
234 Enables the feature feature in the runtime system. The special fea‐
235 ture all can be used to enable all features.
236 -env Variable Value:
238 Sets the host OS environment variable Variable to the value Value
239 for the Erlang runtime system. Example:
240 % erl -env DISPLAY gin:0
242 In this example, an Erlang runtime system is started with environ‐
244 ment variable DISPLAY set to gin:0.
245 -epmd_module Module (init flag):
247 Configures the module responsible to communicate to epmd. Defaults
248 to erl_epmd.
249 -erl_epmd_port Port (init flag):
251 Configures the port used by erl_epmd to listen for connection and
252 connect to other nodes. See erl_epmd for more details. Defaults to
253 0.
254 -eval Expr (init flag):
256 Makes init evaluate the expression Expr; see init(3).
257 -extra (init flag):
259 Everything following -extra is considered plain arguments and can
260 be retrieved using init:get_plain_arguments/0.
261 -heart:
263 Starts heartbeat monitoring of the Erlang runtime system; see
264 heart(3).
265 -hidden:
267 Starts the Erlang runtime system as a hidden node, if it is run as
268 a distributed node. Hidden nodes always establish hidden connec‐
269 tions to all other nodes except for nodes in the same global group.
270 Hidden connections are not published on any of the connected nodes,
271 that is, none of the connected nodes are part of the result from
272 nodes/0 on the other node. See also hidden global groups;
273 global_group(3).
274 -hosts Hosts:
276 Specifies the IP addresses for the hosts on which Erlang boot
277 servers are running, see erl_boot_server(3). This flag is mandatory
278 if flag -loader inet is present.
279 The IP addresses must be specified in the standard form (four deci‐
281 mal numbers separated by periods, for example, "150.236.20.74".
282 Hosts names are not acceptable, but a broadcast address (preferably
283 limited to the local network) is.
284 -id Id:
286 Specifies the identity of the Erlang runtime system. If it is run
287 as a distributed node, Id must be identical to the name supplied
288 together with flag -sname or -name.
289 -init_debug:
291 Makes init write some debug information while interpreting the boot
292 script.
293 -instr (emulator flag):
295 Selects an instrumented Erlang runtime system (virtual machine) to
296 run, instead of the ordinary one. When running an instrumented run‐
297 time system, some resource usage data can be obtained and analyzed
298 using the instrument module. Functionally, it behaves exactly like
299 an ordinary Erlang runtime system.
300 -loader Loader:
302 Specifies the method used by erl_prim_loader to load Erlang modules
303 into the system; see erl_prim_loader(3). Two Loader methods are
304 supported:
305 * efile, which means use the local file system, this is the de‐
307 fault.
308 * inet, which means use a boot server on another machine. The flags
310 -id, -hosts and -setcookie must also be specified.
311 If Loader is something else, the user-supplied Loader port program
313 is started.
314 -make:
316 Makes the Erlang runtime system invoke make:all() in the current
317 working directory and then terminate; see make(3). Implies -noin‐
318 put.
319 -man Module:
321 Displays the manual page for the Erlang module Module. Only sup‐
322 ported on Unix.
323 -mode interactive | embedded:
325 Modules are auto loaded when they are first referenced if the run‐
326 time system runs in interactive mode, which is the default. In em‐
327 bedded mode modules are not auto loaded. The latter is recommended
328 when the boot script preloads all modules, as conventionally hap‐
329 pens in OTP releases. See code(3).
330 -name Name:
332 Makes the Erlang runtime system into a distributed node. This flag
333 invokes all network servers necessary for a node to become distrib‐
334 uted; see net_kernel(3). It also ensures that epmd runs on the cur‐
335 rent host before Erlang is started (see epmd(1) and the -start_epmd
336 option) and that a magic cookie has been set (see -setcookie).
337 The node name will be Name@Host, where Host is the fully qualified
339 host name of the current host. For short names, use flag -sname in‐
340 stead.
341 If Name is set to undefined the node will be started in a special
343 mode optimized to be the temporary client of another node. The node
344 will then request a dynamic node name from the first node it con‐
345 nects to. Read more in Dynamic Node Name.
346 Warning:
348 Starting a distributed node without also specifying -proto_dist
349 inet_tls will expose the node to attacks that may give the attacker
350 complete access to the node and in extension the cluster. When using
351 un-secure distributed nodes, make sure that the network is configured
352 to keep potential attackers out.
353 -no_epmd:
356 Specifies that the distributed node does not need epmd at all.
357 This option ensures that the Erlang runtime system does not start
359 epmd and does not start the erl_epmd process for distribution ei‐
360 ther.
361 This option only works if Erlang is started as a distributed node
363 with the -proto_dist option using an alternative protocol for Er‐
364 lang distribution which does not rely on epmd for node registration
365 and discovery. For more information, see How to implement an Alter‐
366 native Carrier for the Erlang Distribution.
367 -noinput:
369 Ensures that the Erlang runtime system never tries to read any in‐
370 put. Implies -noshell.
371 -noshell:
373 Starts an Erlang runtime system with no shell. This flag makes it
374 possible to have the Erlang runtime system as a component in a se‐
375 ries of Unix pipes.
376 -nostick:
378 Disables the sticky directory facility of the Erlang code server;
379 see code(3).
380 -oldshell:
382 Invokes the old Erlang shell from Erlang/OTP 3.3. The old shell can
383 still be used.
384 -pa Dir1 Dir2 ...:
386 Adds the specified directories to the beginning of the code path,
387 similar to code:add_pathsa/1. Note that the order of the given di‐
388 rectories will be reversed in the resulting path.
389 As an alternative to -pa, if several directories are to be
391 prepended to the code path and the directories have a common parent
392 directory, that parent directory can be specified in environment
393 variable ERL_LIBS; see code(3).
394 -pz Dir1 Dir2 ...:
396 Adds the specified directories to the end of the code path, similar
397 to code:add_pathsz/1; see code(3).
398 -path Dir1 Dir2 ...:
400 Replaces the path specified in the boot script; see script(4).
401 -proto_dist Proto:
403 Specifies a protocol for Erlang distribution:
406 inet_tcp:
408 TCP over IPv4 (the default)
409 inet_tls:
411 Distribution over TLS/SSL, See the Using SSL for Erlang Distri‐
412 bution User's Guide for details on how to setup a secure distrib‐
413 uted node.
414 inet6_tcp:
416 TCP over IPv6
417 For example, to start up IPv6 distributed nodes:
419 % erl -name test@ipv6node.example.com -proto_dist inet6_tcp
421 -remsh Node:
423 Starts Erlang with a remote shell connected to Node.
424 If no -name or -sname is given the node will be started using
426 -sname undefined. If Node does not contain a hostname, one is auto‐
427 matically taken from -name or -sname
428 Note:
430 Before OTP-23 the user needed to supply a valid -sname or -name for
431 -remsh to work. This is still the case if the target node is not run‐
432 ning OTP-23 or later.
433 Note:
436 The connecting node needs to have a proper shell with terminal emula‐
437 tion. This means that UNIX users must use an Erlang compiled with
438 terminal capabilities and Windows users must use werl(1).
439 -rsh Program:
442 Specifies an alternative to ssh for starting a slave node on a re‐
443 mote host; see slave(3).
444 -run Mod [Func [Arg1, Arg2, ...]] (init flag):
446 Makes init call the specified function. Func defaults to start. If
447 no arguments are provided, the function is assumed to be of arity
448 0. Otherwise it is assumed to be of arity 1, taking the list
449 [Arg1,Arg2,...] as argument. All arguments are passed as strings.
450 See init(3).
451 -s Mod [Func [Arg1, Arg2, ...]] (init flag):
453 Makes init call the specified function. Func defaults to start. If
454 no arguments are provided, the function is assumed to be of arity
455 0. Otherwise it is assumed to be of arity 1, taking the list
456 [Arg1,Arg2,...] as argument. All arguments are passed as atoms. See
457 init(3).
458 -setcookie Cookie:
460 Sets the magic cookie of the node to Cookie; see er‐
461 lang:set_cookie/1. See see section Distributed Erlang in the Erlang
462 Reference Manual for more details.
463 -setcookie Node Cookie:
465 Sets the magic cookie for Node to Cookie; see erlang:set_cookie/2.
466 -shutdown_time Time:
468 Specifies how long time (in milliseconds) the init process is al‐
469 lowed to spend shutting down the system. If Time milliseconds have
470 elapsed, all processes still existing are killed. Defaults to in‐
471 finity.
472 -sname Name:
474 Makes the Erlang runtime system into a distributed node, similar to
475 -name, but the host name portion of the node name Name@Host will be
476 the short name, not fully qualified.
477 This is sometimes the only way to run distributed Erlang if the Do‐
479 main Name System (DNS) is not running. No communication can exist
480 between nodes running with flag -sname and those running with flag
481 -name, as node names must be unique in distributed Erlang systems.
482 If Name is set to undefined the node will be started in a special
484 mode optimized to be the temporary client of another node. The node
485 will then request a dynamic node name from the first node it con‐
486 nects to. Read more in Dynamic Node Name.
487 Warning:
489 Starting a distributed node without also specifying -proto_dist
490 inet_tls will expose the node to attacks that may give the attacker
491 complete access to the node and in extension the cluster. When using
492 un-secure distributed nodes, make sure that the network is configured
493 to keep potential attackers out.
494 -start_epmd true | false:
497 Specifies whether Erlang should start epmd on startup. By default
498 this is true, but if you prefer to start epmd manually, set this to
499 false.
500 This only applies if Erlang is started as a distributed node, i.e.
502 if -name or -sname is specified. Otherwise, epmd is not started
503 even if -start_epmd true is given.
504 Note that a distributed node will fail to start if epmd is not run‐
506 ning.
507 -version (emulator flag):
509 Makes the emulator print its version number. The same as erl +V.
510
512 erl invokes the code for the Erlang emulator (virtual machine), which
513 supports the following flags:
514 +a size:
516 Suggested stack size, in kilowords, for threads in the async thread
517 pool. Valid range is 16-8192 kilowords. The default suggested stack
518 size is 16 kilowords, that is, 64 kilobyte on 32-bit architectures.
519 This small default size has been chosen because the number of async
520 threads can be large. The default size is enough for drivers deliv‐
521 ered with Erlang/OTP, but might not be large enough for other dy‐
522 namically linked-in drivers that use the driver_async() functional‐
523 ity. Notice that the value passed is only a suggestion, and it can
524 even be ignored on some platforms.
525 +A size:
527 Sets the number of threads in async thread pool. Valid range is
528 1-1024. The async thread pool is used by linked-in drivers to han‐
529 dle work that may take a very long time. Since OTP 21 there are
530 very few linked-in drivers in the default Erlang/OTP distribution
531 that uses the async thread pool. Most of them have been migrated to
532 dirty IO schedulers. Defaults to 1.
533 +B [c | d | i]:
535 Option c makes Ctrl-C interrupt the current shell instead of invok‐
536 ing the emulator break handler. Option d (same as specifying +B
537 without an extra option) disables the break handler. Option i makes
538 the emulator ignore any break signal.
539 If option c is used with oldshell on Unix, Ctrl-C will restart the
541 shell process rather than interrupt it.
542 Notice that on Windows, this flag is only applicable for werl, not
544 erl (oldshell). Notice also that Ctrl-Break is used instead of
545 Ctrl-C on Windows.
546 +c true | false:
548 Enables or disables time correction:
549 true:
551 Enables time correction. This is the default if time correction
552 is supported on the specific platform.
553 false:
555 Disables time correction.
556 For backward compatibility, the boolean value can be omitted. This
558 is interpreted as +c false.
559 +C no_time_warp | single_time_warp | multi_time_warp:
561 Sets time warp mode:
562 no_time_warp:
564 No time warp mode (the default)
565 single_time_warp:
567 Single time warp mode
568 multi_time_warp:
570 Multi-time warp mode
571 +d:
573 If the emulator detects an internal error (or runs out of memory),
574 it, by default, generates both a crash dump and a core dump. The
575 core dump is, however, not very useful as the content of process
576 heaps is destroyed by the crash dump generation.
577 Option +d instructs the emulator to produce only a core dump and no
579 crash dump if an internal error is detected.
580 Calling erlang:halt/1 with a string argument still produces a crash
582 dump. On Unix systems, sending an emulator process a SIGUSR1 signal
583 also forces a crash dump.
584 +dcg DecentralizedCounterGroupsLimit:
586 Limits the number of decentralized counter groups used by decen‐
587 tralized counters optimized for update operations in the Erlang
588 runtime system. By default, the limit is 256.
589 When the number of schedulers is less than or equal to the limit,
591 each scheduler has its own group. When the number of schedulers is
592 larger than the groups limit, schedulers share groups. Shared
593 groups degrade the performance for updating counters while many
594 reader groups degrade the performance for reading counters. So, the
595 limit is a tradeoff between performance for update operations and
596 performance for read operations. Each group consumes 64 bytes in
597 each counter.
598 Notice that a runtime system using decentralized counter groups
600 benefits from binding schedulers to logical processors, as the
601 groups are distributed better between schedulers with this option.
602 This option only affects decentralized counters used for the coun‐
604 ters that are keeping track of the memory consumption and the num‐
605 ber of terms in ETS tables of type ordered_set with the write_con‐
606 currency option activated.
607 +e Number:
609 Sets the maximum number of ETS tables. This limit is partially ob‐
610 solete.
611 +ec:
613 Forces option compressed on all ETS tables. Only intended for test
614 and evaluation.
615 +fnl:
617 The virtual machine works with filenames as if they are encoded us‐
618 ing the ISO Latin-1 encoding, disallowing Unicode characters with
619 code points > 255.
620 For more information about Unicode filenames, see section Unicode
622 Filenames in the STDLIB User's Guide. Notice that this value also
623 applies to command-line parameters and environment variables (see
624 section Unicode in Environment and Parameters in the STDLIB User's
625 Guide).
626 +fnu[{w|i|e}]:
628 The virtual machine works with filenames as if they are encoded us‐
629 ing UTF-8 (or some other system-specific Unicode encoding). This is
630 the default on operating systems that enforce Unicode encoding,
631 that is, Windows MacOS X and Android.
632 The +fnu switch can be followed by w, i, or e to control how
634 wrongly encoded filenames are to be reported:
635 * w means that a warning is sent to the error_logger whenever a
637 wrongly encoded filename is "skipped" in directory listings. This
638 is the default.
639 * i means that those wrongly encoded filenames are silently ig‐
641 nored.
642 * e means that the API function returns an error whenever a wrongly
644 encoded filename (or directory name) is encountered.
645 Notice that file:read_link/1 always returns an error if the link
647 points to an invalid filename.
648 For more information about Unicode filenames, see section Unicode
650 Filenames in the STDLIB User's Guide. Notice that this value also
651 applies to command-line parameters and environment variables (see
652 section Unicode in Environment and Parameters in the STDLIB User's
653 Guide).
654 +fna[{w|i|e}]:
656 Selection between +fnl and +fnu is done based on the current locale
657 settings in the OS. This means that if you have set your terminal
658 for UTF-8 encoding, the filesystem is expected to use the same en‐
659 coding for filenames. This is the default on all operating systems,
660 except Android, MacOS X and Windows.
661 The +fna switch can be followed by w, i, or e. This has effect if
663 the locale settings cause the behavior of +fnu to be selected; see
664 the description of +fnu above. If the locale settings cause the be‐
665 havior of +fnl to be selected, then w, i, or e have no effect.
666 For more information about Unicode filenames, see section Unicode
668 Filenames in the STDLIB User's Guide. Notice that this value also
669 applies to command-line parameters and environment variables (see
670 section Unicode in Environment and Parameters in the STDLIB User's
671 Guide).
672 +hms Size:
674 Sets the default heap size of processes to the size Size.
675 +hmbs Size:
677 Sets the default binary virtual heap size of processes to the size
678 Size.
679 +hmax Size:
681 Sets the default maximum heap size of processes to the size Size
682 words. Defaults to 0, which means that no maximum heap size is
683 used. For more information, see process_flag(max_heap_size, Max‐
684 HeapSize).
685 +hmaxel true|false:
687 Sets whether to send an error logger message or not for processes
688 reaching the maximum heap size. Defaults to true. For more informa‐
689 tion, see process_flag(max_heap_size, MaxHeapSize).
690 +hmaxib true|false:
692 Sets whether to include the size of shared off-heap binaries in the
693 sum compared against the maximum heap size. Defaults to false. For
694 more information, see process_flag(max_heap_size, MaxHeapSize).
695 +hmaxk true|false:
697 Sets whether to kill processes reaching the maximum heap size or
698 not. Default to true. For more information, see
699 process_flag(max_heap_size, MaxHeapSize).
700 +hpds Size:
702 Sets the initial process dictionary size of processes to the size
703 Size.
704 +hmqd off_heap|on_heap:
706 Sets the default value of the message_queue_data process flag. De‐
707 faults to on_heap. If +hmqd is not passed, on_heap will be the de‐
708 fault. For more information, see process_flag(message_queue_data,
709 MQD).
710 +IOp PollSets:
712 Sets the number of IO pollsets to use when polling for I/O. This
713 option is only used on platforms that support concurrent updates of
714 a pollset, otherwise the same number of pollsets are used as IO
715 poll threads. The default is 1.
716 +IOt PollThreads:
718 Sets the number of IO poll threads to use when polling for I/O. The
719 maximum number of poll threads allowed is 1024. The default is 1.
720 A good way to check if more IO poll threads are needed is to use
722 microstate accounting and see what the load of the IO poll thread
723 is. If it is high it could be a good idea to add more threads.
724 +IOPp PollSetsPercentage:
726 Similar to +IOp but uses percentages to set the number of IO
727 pollsets to create, based on the number of poll threads configured.
728 If both +IOPp and +IOp are used, +IOPp is ignored.
729 +IOPt PollThreadsPercentage:
731 Similar to +IOt but uses percentages to set the number of IO poll
732 threads to create, based on the number of schedulers configured. If
733 both +IOPt and +IOt are used, +IOPt is ignored.
734 +IOs true|false:
736 Enable or disable scheduler thread poll optimization. Default is
737 true.
738 If enabled, file descriptors that are frequently read may be moved
740 to a special pollset used by scheduler threads. The objective is to
741 reduce the number of system calls and thereby CPU load, but it can
742 in some cases increase scheduling latency for individual file de‐
743 scriptor input events.
744 +JPperf true|false|dump|map|fp|no_fp:
746 Enables or disables support for the perf profiler when running with
747 the JIT on Linux. Defaults to false.
748 This option can be combined multiple times to enable several op‐
750 tions:
751 dump:
753 Gives perf detailed line information, so that the perf annotate
754 feature works.
755 map:
757 Gives perf a map over all module code, letting it translate ma‐
758 chine code addresses to Erlang source code locations. This also
759 enables frame pointers for Erlang code so that perf can walk the
760 call stacks of Erlang processes, which costs one extra word per
761 stack frame.
762 fp:
764 Enables frame pointers independently of the map option.
765 no_fp:
767 Disables the frame pointers added by the map option.
768 true:
770 Enables map and dump.
771 false:
773 Disables all other options.
774 For more details about how to run perf see the perf support section
776 in the BeamAsm internal documentation.
777 +JMsingle true|false:
779 Enables or disables the use of single-mapped RWX memory for JIT
780 code. The default is to map JIT:ed machine code into two regions
781 sharing the same physical pages, where one region is executable but
782 not writable, and the other writable but not executable. As some
783 tools, such as QEMU user mode emulation, cannot deal with the dual
784 mapping, this flags allows it to be disabled. This flag is automat‐
785 ically enabled by the +JPperf flag.
786 +L:
788 Prevents loading information about source filenames and line num‐
789 bers. This saves some memory, but exceptions do not contain infor‐
790 mation about the filenames and line numbers.
791 +MFlag Value:
793 Memory allocator-specific flags. For more information, see erts_al‐
794 loc(3).
795 +pad true|false:
797 Since: OTP 25.3
798 The boolean value used with the +pad parameter determines the de‐
800 fault value of the async_dist process flag of newly spawned pro‐
801 cesses. By default, if no +pad command line option is passed, the
802 async_dist flag will be set to false.
803 The value used in runtime can be inspected by calling erlang:sys‐
805 tem_info(async_dist).
806 +pc Range:
808 Sets the range of characters that the system considers printable in
809 heuristic detection of strings. This typically affects the shell,
810 debugger, and io:format functions (when ~tp is used in the format
811 string).
812 Two values are supported for Range:
814 latin1:
816 The default. Only characters in the ISO Latin-1 range can be con‐
817 sidered printable. This means that a character with a code point
818 > 255 is never considered printable and that lists containing
819 such characters are displayed as lists of integers rather than
820 text strings by tools.
821 unicode:
823 All printable Unicode characters are considered when determining
824 if a list of integers is to be displayed in string syntax. This
825 can give unexpected results if, for example, your font does not
826 cover all Unicode characters.
827 See also io:printable_range/0 in STDLIB.
829 +P Number:
831 Sets the maximum number of simultaneously existing processes for
832 this system if a Number is passed as value. Valid range for Number
833 is [1024-134217727]
834 NOTE: The actual maximum chosen may be much larger than the Number
836 passed. Currently the runtime system often, but not always, chooses
837 a value that is a power of 2. This might, however, be changed in
838 the future. The actual value chosen can be checked by calling er‐
839 lang:system_info(process_limit).
840 The default value is 262144
842 +Q Number:
844 Sets the maximum number of simultaneously existing ports for this
845 system if a Number is passed as value. Valid range for Number is
846 [1024-134217727]
847 NOTE: The actual maximum chosen may be much larger than the actual
849 Number passed. Currently the runtime system often, but not always,
850 chooses a value that is a power of 2. This might, however, be
851 changed in the future. The actual value chosen can be checked by
852 calling erlang:system_info(port_limit).
853 The default value used is normally 65536. However, if the runtime
855 system is able to determine maximum amount of file descriptors that
856 it is allowed to open and this value is larger than 65536, the cho‐
857 sen value will increased to a value larger or equal to the maximum
858 amount of file descriptors that can be opened.
859 On Windows the default value is set to 8196 because the normal OS
861 limitations are set higher than most machines can handle.
862 +R ReleaseNumber:
864 Sets the compatibility mode.
865 The distribution mechanism is not backward compatible by default.
867 This flag sets the emulator in compatibility mode with an earlier
868 Erlang/OTP release ReleaseNumber. The release number must be in the
869 range <current release>-2..<current release>. This limits the emu‐
870 lator, making it possible for it to communicate with Erlang nodes
871 (as well as C- and Java nodes) running that earlier release.
872 Note:
874 Ensure that all nodes (Erlang-, C-, and Java nodes) of a distributed
875 Erlang system is of the same Erlang/OTP release, or from two differ‐
876 ent Erlang/OTP releases X and Y, where all Y nodes have compatibility
877 mode X.
878 +r:
881 Forces ETS memory block to be moved on realloc.
882 +rg ReaderGroupsLimit:
884 Limits the number of reader groups used by read/write locks opti‐
885 mized for read operations in the Erlang runtime system. By default
886 the reader groups limit is 64.
887 When the number of schedulers is less than or equal to the reader
889 groups limit, each scheduler has its own reader group. When the
890 number of schedulers is larger than the reader groups limit, sched‐
891 ulers share reader groups. Shared reader groups degrade read lock
892 and read unlock performance while many reader groups degrade write
893 lock performance. So, the limit is a tradeoff between performance
894 for read operations and performance for write operations. Each
895 reader group consumes 64 byte in each read/write lock.
896 Notice that a runtime system using shared reader groups benefits
898 from binding schedulers to logical processors, as the reader groups
899 are distributed better between schedulers.
900 +S Schedulers:SchedulerOnline:
902 Sets the number of scheduler threads to create and scheduler
903 threads to set online. The maximum for both values is 1024. If the
904 Erlang runtime system is able to determine the number of logical
905 processors configured and logical processors available, Schedulers
906 defaults to logical processors configured, and SchedulersOnline de‐
907 faults to logical processors available; otherwise the default val‐
908 ues are 1. If the emulator detects that it is subject to a CPU
909 quota, the default value for SchedulersOnline will be limited ac‐
910 cordingly.
911 Schedulers can be omitted if :SchedulerOnline is not and con‐
913 versely. The number of schedulers online can be changed at runtime
914 through erlang:system_flag(schedulers_online, SchedulersOnline).
915 If Schedulers or SchedulersOnline is specified as a negative num‐
917 ber, the value is subtracted from the default number of logical
918 processors configured or logical processors available, respec‐
919 tively.
920 Specifying value 0 for Schedulers or SchedulersOnline resets the
922 number of scheduler threads or scheduler threads online, respec‐
923 tively, to its default value.
924 +SP SchedulersPercentage:SchedulersOnlinePercentage:
926 Similar to +S but uses percentages to set the number of scheduler
927 threads to create, based on logical processors configured, and
928 scheduler threads to set online, based on logical processors avail‐
929 able. Specified values must be > 0. For example, +SP 50:25 sets the
930 number of scheduler threads to 50% of the logical processors con‐
931 figured, and the number of scheduler threads online to 25% of the
932 logical processors available. SchedulersPercentage can be omitted
933 if :SchedulersOnlinePercentage is not and conversely. The number of
934 schedulers online can be changed at runtime through erlang:sys‐
935 tem_flag(schedulers_online, SchedulersOnline).
936 This option interacts with +S settings. For example, on a system
938 with 8 logical cores configured and 8 logical cores available, the
939 combination of the options +S 4:4 +SP 50:25 (in either order) re‐
940 sults in 2 scheduler threads (50% of 4) and 1 scheduler thread on‐
941 line (25% of 4).
942 +SDcpu DirtyCPUSchedulers:DirtyCPUSchedulersOnline:
944 Sets the number of dirty CPU scheduler threads to create and dirty
945 CPU scheduler threads to set online. The maximum for both values is
946 1024, and each value is further limited by the settings for normal
947 schedulers:
948 * The number of dirty CPU scheduler threads created cannot exceed
950 the number of normal scheduler threads created.
951 * The number of dirty CPU scheduler threads online cannot exceed
953 the number of normal scheduler threads online.
954 For details, see the +S and +SP. By default, the number of dirty
956 CPU scheduler threads created equals the number of normal scheduler
957 threads created, and the number of dirty CPU scheduler threads on‐
958 line equals the number of normal scheduler threads online. DirtyC‐
959 PUSchedulers can be omitted if :DirtyCPUSchedulersOnline is not and
960 conversely. The number of dirty CPU schedulers online can be
961 changed at runtime through erlang:system_flag(dirty_cpu_sched‐
962 ulers_online, DirtyCPUSchedulersOnline).
963 The amount of dirty CPU schedulers is limited by the amount of nor‐
965 mal schedulers in order to limit the effect on processes executing
966 on ordinary schedulers. If the amount of dirty CPU schedulers was
967 allowed to be unlimited, dirty CPU bound jobs would potentially
968 starve normal jobs.
969 Typical users of the dirty CPU schedulers are large garbage collec‐
971 tions, json protocol encode/decoders written as nifs and matrix ma‐
972 nipulation libraries.
973 You can use msacc(3) in order to see the current load of the dirty
975 CPU schedulers threads and adjust the number used accordingly.
976 +SDPcpu DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercent‐
978 age:
979 Similar to +SDcpu but uses percentages to set the number of dirty
980 CPU scheduler threads to create and the number of dirty CPU sched‐
981 uler threads to set online. Specified values must be > 0. For exam‐
982 ple, +SDPcpu 50:25 sets the number of dirty CPU scheduler threads
983 to 50% of the logical processors configured and the number of dirty
984 CPU scheduler threads online to 25% of the logical processors
985 available. DirtyCPUSchedulersPercentage can be omitted if :DirtyC‐
986 PUSchedulersOnlinePercentage is not and conversely. The number of
987 dirty CPU schedulers online can be changed at runtime through er‐
988 lang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOn‐
989 line).
990 This option interacts with +SDcpu settings. For example, on a sys‐
992 tem with 8 logical cores configured and 8 logical cores available,
993 the combination of the options +SDcpu 4:4 +SDPcpu 50:25 (in either
994 order) results in 2 dirty CPU scheduler threads (50% of 4) and 1
995 dirty CPU scheduler thread online (25% of 4).
996 +SDio DirtyIOSchedulers:
998 Sets the number of dirty I/O scheduler threads to create. Valid
999 range is 1-1024. By default, the number of dirty I/O scheduler
1000 threads created is 10.
1001 The amount of dirty IO schedulers is not limited by the amount of
1003 normal schedulers like the amount of dirty CPU schedulers. This
1004 since only I/O bound work is expected to execute on dirty I/O
1005 schedulers. If the user should schedule CPU bound jobs on dirty I/O
1006 schedulers, these jobs might starve ordinary jobs executing on or‐
1007 dinary schedulers.
1008 Typical users of the dirty IO schedulers are reading and writing to
1010 files.
1011 You can use msacc(3) in order to see the current load of the dirty
1013 IO schedulers threads and adjust the number used accordingly.
1014 +sFlag Value:
1016 Scheduling specific flags.
1017 +sbt BindType:
1019 Sets scheduler bind type.
1020 Schedulers can also be bound using flag +stbt. The only differ‐
1022 ence between these two flags is how the following errors are han‐
1023 dled:
1024 * Binding of schedulers is not supported on the specific plat‐
1026 form.
1027 * No available CPU topology. That is, the runtime system was not
1029 able to detect the CPU topology automatically, and no user-de‐
1030 fined CPU topology was set.
1031 If any of these errors occur when +sbt has been passed, the run‐
1033 time system prints an error message, and refuses to start. If any
1034 of these errors occur when +stbt has been passed, the runtime
1035 system silently ignores the error, and start up using unbound
1036 schedulers.
1037 Valid BindTypes:
1039 u:
1041 unbound - Schedulers are not bound to logical processors, that
1042 is, the operating system decides where the scheduler threads
1043 execute, and when to migrate them. This is the default.
1044 ns:
1046 no_spread - Schedulers with close scheduler identifiers are
1047 bound as close as possible in hardware.
1048 ts:
1050 thread_spread - Thread refers to hardware threads (such as In‐
1051 tel's hyper-threads). Schedulers with low scheduler identi‐
1052 fiers, are bound to the first hardware thread of each core,
1053 then schedulers with higher scheduler identifiers are bound to
1054 the second hardware thread of each core,and so on.
1055 ps:
1057 processor_spread - Schedulers are spread like thread_spread,
1058 but also over physical processor chips.
1059 s:
1061 spread - Schedulers are spread as much as possible.
1062 nnts:
1064 no_node_thread_spread - Like thread_spread, but if multiple
1065 Non-Uniform Memory Access (NUMA) nodes exist, schedulers are
1066 spread over one NUMA node at a time, that is, all logical pro‐
1067 cessors of one NUMA node are bound to schedulers in sequence.
1068 nnps:
1070 no_node_processor_spread - Like processor_spread, but if multi‐
1071 ple NUMA nodes exist, schedulers are spread over one NUMA node
1072 at a time, that is, all logical processors of one NUMA node are
1073 bound to schedulers in sequence.
1074 tnnps:
1076 thread_no_node_processor_spread - A combination of
1077 thread_spread, and no_node_processor_spread. Schedulers are
1078 spread over hardware threads across NUMA nodes, but schedulers
1079 are only spread over processors internally in one NUMA node at
1080 a time.
1081 db:
1083 default_bind - Binds schedulers the default way. Defaults to
1084 thread_no_node_processor_spread (which can change in the fu‐
1085 ture).
1086 Binding of schedulers is only supported on newer Linux, Solaris,
1088 FreeBSD, and Windows systems.
1089 If no CPU topology is available when flag +sbt is processed and
1091 BindType is any other type than u, the runtime system fails to
1092 start. CPU topology can be defined using flag +sct. Notice that
1093 flag +sct can have to be passed before flag +sbt on the command
1094 line (if no CPU topology has been automatically detected).
1095 The runtime system does by default not bind schedulers to logical
1097 processors.
1098 Note:
1100 If the Erlang runtime system is the only operating system process
1101 that binds threads to logical processors, this improves the perfor‐
1102 mance of the runtime system. However, if other operating system
1103 processes (for example another Erlang runtime system) also bind
1104 threads to logical processors, there can be a performance penalty
1105 instead. This performance penalty can sometimes be severe. If so,
1106 you are advised not to bind the schedulers.
1107 How schedulers are bound matters. For example, in situations when
1110 there are fewer running processes than schedulers online, the
1111 runtime system tries to migrate processes to schedulers with low
1112 scheduler identifiers. The more the schedulers are spread over
1113 the hardware, the more resources are available to the runtime
1114 system in such situations.
1115 Note:
1117 If a scheduler fails to bind, this is often silently ignored, as it
1118 is not always possible to verify valid logical processor identi‐
1119 fiers. If an error is reported, it is reported to the error_logger.
1120 If you want to verify that the schedulers have bound as requested,
1121 call erlang:system_info(scheduler_bindings).
1122 +sbwt none|very_short|short|medium|long|very_long:
1125 Sets scheduler busy wait threshold. Defaults to medium. The
1126 threshold determines how long schedulers are to busy wait when
1127 running out of work before going to sleep.
1128 Note:
1130 This flag can be removed or changed at any time without prior no‐
1131 tice.
1132 +sbwtdcpu none|very_short|short|medium|long|very_long:
1135 As +sbwt but affects dirty CPU schedulers. Defaults to short.
1136 Note:
1138 This flag can be removed or changed at any time without prior no‐
1139 tice.
1140 +sbwtdio none|very_short|short|medium|long|very_long:
1143 As +sbwt but affects dirty IO schedulers. Defaults to short.
1144 Note:
1146 This flag can be removed or changed at any time without prior no‐
1147 tice.
1148 +scl true|false:
1151 Enables or disables scheduler compaction of load. By default
1152 scheduler compaction of load is enabled. When enabled, load bal‐
1153 ancing strives for a load distribution, which causes as many
1154 scheduler threads as possible to be fully loaded (that is, not
1155 run out of work). This is accomplished by migrating load (for ex‐
1156 ample, runnable processes) into a smaller set of schedulers when
1157 schedulers frequently run out of work. When disabled, the fre‐
1158 quency with which schedulers run out of work is not taken into
1159 account by the load balancing logic.
1160 +scl false is similar to +sub true, but +sub true also balances
1162 scheduler utilization between schedulers.
1163 +sct CpuTopology:
1165 * <Id> = integer(); when 0 =< <Id> =< 65535
1168 * <IdRange> = <Id>-<Id>
1170 * <IdOrIdRange> = <Id> | <IdRange>
1172 * <IdList> = <IdOrIdRange>,<IdOrIdRange> | <IdOrIdRange>
1174 * <LogicalIds> = L<IdList>
1176 * <ThreadIds> = T<IdList> | t<IdList>
1178 * <CoreIds> = C<IdList> | c<IdList>
1180 * <ProcessorIds> = P<IdList> | p<IdList>
1182 * <NodeIds> = N<IdList> | n<IdList>
1184 * <IdDefs> = <LogicalIds><ThreadIds><CoreIds><Proces‐
1186 sorIds><NodeIds> | <LogicalIds><ThreadIds><Cor‐
1187 eIds><NodeIds><ProcessorIds>
1188 * CpuTopology = <IdDefs>:<IdDefs> | <IdDefs>
1190 Sets a user-defined CPU topology. The user-defined CPU topology
1192 overrides any automatically detected CPU topology. The CPU topol‐
1193 ogy is used when binding schedulers to logical processors.
1194 Uppercase letters signify real identifiers and lowercase letters
1196 signify fake identifiers only used for description of the topol‐
1197 ogy. Identifiers passed as real identifiers can be used by the
1198 runtime system when trying to access specific hardware; if they
1199 are incorrect the behavior is undefined. Faked logical CPU iden‐
1200 tifiers are not accepted, as there is no point in defining the
1201 CPU topology without real logical CPU identifiers. Thread, core,
1202 processor, and node identifiers can be omitted. If omitted, the
1203 thread ID defaults to t0, the core ID defaults to c0, the proces‐
1204 sor ID defaults to p0, and the node ID is left undefined. Either
1205 each logical processor must belong to only one NUMA node, or no
1206 logical processors must belong to any NUMA nodes.
1207 Both increasing and decreasing <IdRange>s are allowed.
1209 NUMA node identifiers are system wide. That is, each NUMA node on
1211 the system must have a unique identifier. Processor identifiers
1212 are also system wide. Core identifiers are processor wide. Thread
1213 identifiers are core wide.
1214 The order of the identifier types implies the hierarchy of the
1216 CPU topology. The valid orders are as follows:
1217 * <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>, that
1219 is, thread is part of a core that is part of a processor, which
1220 is part of a NUMA node.
1221 * <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>, that
1223 is, thread is part of a core that is part of a NUMA node, which
1224 is part of a processor.
1225 A CPU topology can consist of both processor external, and pro‐
1227 cessor internal NUMA nodes as long as each logical processor be‐
1228 longs to only one NUMA node. If <ProcessorIds> is omitted, its
1229 default position is before <NodeIds>. That is, the default is
1230 processor external NUMA nodes.
1231 If a list of identifiers is used in an <IdDefs>:
1233 * <LogicalIds> must be a list of identifiers.
1235 * At least one other identifier type besides <LogicalIds> must
1237 also have a list of identifiers.
1238 * All lists of identifiers must produce the same number of iden‐
1240 tifiers.
1241 A simple example. A single quad core processor can be described
1243 as follows:
1244 % erl +sct L0-3c0-3
1246 1> erlang:system_info(cpu_topology).
1247 [{processor,[{core,{logical,0}},
1248 {core,{logical,1}},
1249 {core,{logical,2}},
1250 {core,{logical,3}}]}]
1251 A more complicated example with two quad core processors, each
1253 processor in its own NUMA node. The ordering of logical proces‐
1254 sors is a bit weird. This to give a better example of identifier
1255 lists:
1256 % erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1
1258 1> erlang:system_info(cpu_topology).
1259 [{node,[{processor,[{core,{logical,0}},
1260 {core,{logical,1}},
1261 {core,{logical,3}},
1262 {core,{logical,2}}]}]},
1263 {node,[{processor,[{core,{logical,7}},
1264 {core,{logical,4}},
1265 {core,{logical,6}},
1266 {core,{logical,5}}]}]}]
1267 As long as real identifiers are correct, it is OK to pass a CPU
1269 topology that is not a correct description of the CPU topology.
1270 When used with care this can be very useful. This to trick the
1271 emulator to bind its schedulers as you want. For example, if you
1272 want to run multiple Erlang runtime systems on the same machine,
1273 you want to reduce the number of schedulers used and manipulate
1274 the CPU topology so that they bind to different logical CPUs. An
1275 example, with two Erlang runtime systems on a quad core machine:
1276 % erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
1278 % erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two
1279 In this example, each runtime system have two schedulers each on‐
1281 line, and all schedulers online will run on different cores. If
1282 we change to one scheduler online on one runtime system, and
1283 three schedulers online on the other, all schedulers online will
1284 still run on different cores.
1285 Notice that a faked CPU topology that does not reflect how the
1287 real CPU topology looks like is likely to decrease the perfor‐
1288 mance of the runtime system.
1289 For more information, see erlang:system_info(cpu_topology).
1291 +ssrct:
1293 Skips reading CPU topology.
1294 Note:
1296 Reading CPU topology slows down startup when starting many parallel
1297 instances of ERTS on systems with large amount of cores, using this
1298 flag might speed up execution in such scenarios.
1299 +sfwi Interval:
1302 Sets scheduler-forced wakeup interval. All run queues are scanned
1303 each Interval milliseconds. While there are sleeping schedulers
1304 in the system, one scheduler is woken for each non-empty run
1305 queue found. Interval default to 0, meaning this feature is dis‐
1306 abled.
1307 Note:
1309 This feature has been introduced as a temporary workaround for
1310 long-executing native code, and native code that does not bump re‐
1311 ductions properly in OTP. When these bugs have been fixed, this
1312 flag will be removed.
1313 +spp Bool:
1316 Sets default scheduler hint for port parallelism. If set to true,
1317 the virtual machine schedules port tasks when it improves paral‐
1318 lelism in the system. If set to false, the virtual machine tries
1319 to perform port tasks immediately, improving latency at the ex‐
1320 pense of parallelism. Default to false. The default used can be
1321 inspected in runtime by calling erlang:system_info(port_parallel‐
1322 ism). The default can be overridden on port creation by passing
1323 option parallelism to erlang:open_port/2.
1324 +sss size:
1326 Suggested stack size, in kilowords, for scheduler threads. Valid
1327 range is 20-8192 kilowords. The default suggested stack size is
1328 128 kilowords.
1329 +sssdcpu size:
1331 Suggested stack size, in kilowords, for dirty CPU scheduler
1332 threads. Valid range is 20-8192 kilowords. The default suggested
1333 stack size is 40 kilowords.
1334 +sssdio size:
1336 Suggested stack size, in kilowords, for dirty IO scheduler
1337 threads. Valid range is 20-8192 kilowords. The default suggested
1338 stack size is 40 kilowords.
1339 +stbt BindType:
1341 Tries to set the scheduler bind type. The same as flag +sbt ex‐
1342 cept how some errors are handled. For more information, see +sbt.
1343 +sub true|false:
1345 Enables or disables scheduler utilization balancing of load. By
1346 default scheduler utilization balancing is disabled and instead
1347 scheduler compaction of load is enabled, which strives for a load
1348 distribution that causes as many scheduler threads as possible to
1349 be fully loaded (that is, not run out of work). When scheduler
1350 utilization balancing is enabled, the system instead tries to
1351 balance scheduler utilization between schedulers. That is, strive
1352 for equal scheduler utilization on all schedulers.
1353 +sub true is only supported on systems where the runtime system
1355 detects and uses a monotonically increasing high-resolution
1356 clock. On other systems, the runtime system fails to start.
1357 +sub true implies +scl false. The difference between +sub true
1359 and +scl false is that +scl false does not try to balance the
1360 scheduler utilization.
1361 +swct very_eager|eager|medium|lazy|very_lazy:
1363 Sets scheduler wake cleanup threshold. Defaults to medium. Con‐
1364 trols how eager schedulers are to be requesting wakeup because of
1365 certain cleanup operations. When a lazy setting is used, more
1366 outstanding cleanup operations can be left undone while a sched‐
1367 uler is idling. When an eager setting is used, schedulers are
1368 more frequently woken, potentially increasing CPU-utilization.
1369 Note:
1371 This flag can be removed or changed at any time without prior no‐
1372 tice.
1373 +sws default|legacy:
1376 Sets scheduler wakeup strategy. Default strategy changed in ERTS
1377 5.10 (Erlang/OTP R16A). This strategy was known as proposal in
1378 Erlang/OTP R15. The legacy strategy was used as default from R13
1379 up to and including R15.
1380 Note:
1382 This flag can be removed or changed at any time without prior no‐
1383 tice.
1384 +swt very_low|low|medium|high|very_high:
1387 Sets scheduler wakeup threshold. Defaults to medium. The thresh‐
1388 old determines when to wake up sleeping schedulers when more work
1389 than can be handled by currently awake schedulers exists. A low
1390 threshold causes earlier wakeups, and a high threshold causes
1391 later wakeups. Early wakeups distribute work over multiple sched‐
1392 ulers faster, but work does more easily bounce between sched‐
1393 ulers.
1394 Note:
1396 This flag can be removed or changed at any time without prior no‐
1397 tice.
1398 +swtdcpu very_low|low|medium|high|very_high:
1401 As +swt but affects dirty CPU schedulers. Defaults to medium.
1402 Note:
1404 This flag can be removed or changed at any time without prior no‐
1405 tice.
1406 +swtdio very_low|low|medium|high|very_high:
1409 As +swt but affects dirty IO schedulers. Defaults to medium.
1410 Note:
1412 This flag can be removed or changed at any time without prior no‐
1413 tice.
1414 +t size:
1417 Sets the maximum number of atoms the virtual machine can handle.
1418 Defaults to 1,048,576.
1419 +T Level:
1421 Enables modified timing and sets the modified timing level. Valid
1422 range is 0-9. The timing of the runtime system is changed. A high
1423 level usually means a greater change than a low level. Changing the
1424 timing can be very useful for finding timing-related bugs.
1425 Modified timing affects the following:
1427 Process spawning:
1429 A process calling spawn, spawn_link, spawn_monitor, or spawn_opt
1430 is scheduled out immediately after completing the call. When
1431 higher modified timing levels are used, the caller also sleeps
1432 for a while after it is scheduled out.
1433 Context reductions:
1435 The number of reductions a process is allowed to use before it is
1436 scheduled out is increased or reduced.
1437 Input reductions:
1439 The number of reductions performed before checking I/O is in‐
1440 creased or reduced.
1441 Note:
1443 Performance suffers when modified timing is enabled. This flag is
1444 only intended for testing and debugging.
1445 return_to and return_from trace messages are lost when tracing on the
1447 spawn BIFs.
1448 This flag can be removed or changed at any time without prior notice.
1450 +v:
1453 Verbose.
1454 +V:
1456 Makes the emulator print its version number.
1457 +W w | i | e:
1459 Sets the mapping of warning messages for error_logger. Messages
1460 sent to the error logger using one of the warning routines can be
1461 mapped to errors (+W e), warnings (+W w), or information reports
1462 (+W i). Defaults to warnings. The current mapping can be retrieved
1463 using error_logger:warning_map/0. For more information, see er‐
1464 ror_logger:warning_map/0 in Kernel.
1465 +zFlag Value:
1467 Miscellaneous flags:
1468 +zdbbl size:
1470 Sets the distribution buffer busy limit (dist_buf_busy_limit) in
1471 kilobytes. Valid range is 1-2097151. Defaults to 1024.
1472 A larger buffer limit allows processes to buffer more outgoing
1474 messages over the distribution. When the buffer limit has been
1475 reached, sending processes will be suspended until the buffer
1476 size has shrunk. The buffer limit is per distribution channel. A
1477 higher limit gives lower latency and higher throughput at the ex‐
1478 pense of higher memory use.
1479 This limit only affects processes that have disabled fully asyn‐
1481 chronous distributed signaling .
1482 +zdntgc time:
1484 Sets the delayed node table garbage collection time (de‐
1485 layed_node_table_gc) in seconds. Valid values are either infinity
1486 or an integer in the range 0-100000000. Defaults to 60.
1487 Node table entries that are not referred linger in the table for
1489 at least the amount of time that this parameter determines. The
1490 lingering prevents repeated deletions and insertions in the ta‐
1491 bles from occurring.
1492 +zosrl limit:
1494 Sets a limit on the amount of outstanding requests made by a sys‐
1495 tem process orchestrating system wide changes. Valid range of
1496 this limit is [1, 134217727]. See erlang:system_flag(outstand‐
1497 ing_system_requests_limit, Limit) for more information.
1498
1500 ERL_CRASH_DUMP:
1501 If the emulator needs to write a crash dump, the value of this
1502 variable is the filename of the crash dump file. If the variable is
1503 not set, the name of the crash dump file is erl_crash.dump in the
1504 current directory.
1505 ERL_CRASH_DUMP_NICE:
1507 Unix systems: If the emulator needs to write a crash dump, it uses
1508 the value of this variable to set the nice value for the process,
1509 thus lowering its priority. Valid range is 1-39 (higher values are
1510 replaced with 39). The highest value, 39, gives the process the
1511 lowest priority.
1512 ERL_CRASH_DUMP_SECONDS:
1514 Unix systems: This variable gives the number of seconds that the
1515 emulator is allowed to spend writing a crash dump. When the given
1516 number of seconds have elapsed, the emulator is terminated.
1517 ERL_CRASH_DUMP_SECONDS=0:
1519 If the variable is set to 0 seconds, the runtime system does not
1520 even attempt to write the crash dump file. It only terminates.
1521 This is the default if option -heart is passed to erl and
1522 ERL_CRASH_DUMP_SECONDS is not set.
1523 ERL_CRASH_DUMP_SECONDS=S:
1525 If the variable is set to a positive value S, wait for S seconds
1526 to complete the crash dump file and then terminates the runtime
1527 system with a SIGALRM signal.
1528 ERL_CRASH_DUMP_SECONDS=-1:
1530 A negative value causes the termination of the runtime system to
1531 wait indefinitely until the crash dump file has been completely
1532 written. This is the default if option -heart is not passed to
1533 erl and ERL_CRASH_DUMP_SECONDS is not set.
1534 See also heart(3).
1536 ERL_CRASH_DUMP_BYTES:
1538 This variable sets the maximum size of a crash dump file in bytes.
1539 The crash dump will be truncated if this limit is exceeded. If the
1540 variable is not set, no size limit is enforced by default. If the
1541 variable is set to 0, the runtime system does not even attempt to
1542 write a crash dump file.
1543 Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).
1545 ERL_AFLAGS:
1547 The content of this variable is added to the beginning of the com‐
1548 mand line for erl.
1549 Flag -extra is treated in a special way. Its scope ends at the end
1551 of the environment variable content. Arguments following an -extra
1552 flag are moved on the command line into section -extra, that is,
1553 the end of the command line following an -extra flag.
1554 ERL_ZFLAGS and ERL_FLAGS:
1556 The content of these variables are added to the end of the command
1557 line for erl.
1558 Flag -extra is treated in a special way. Its scope ends at the end
1560 of the environment variable content. Arguments following an -extra
1561 flag are moved on the command line into section -extra, that is,
1562 the end of the command line following an -extra flag.
1563 ERL_LIBS:
1565 Contains a list of additional library directories that the code
1566 server searches for applications and adds to the code path; see
1567 code(3).
1568 ERL_EPMD_ADDRESS:
1570 Can be set to a comma-separated list of IP addresses, in which case
1571 the epmd daemon listens only on the specified address(es) and on
1572 the loopback address (which is implicitly added to the list if it
1573 has not been specified).
1574 ERL_EPMD_PORT:
1576 Can contain the port number to use when communicating with epmd.
1577 The default port works fine in most cases. A different port can be
1578 specified to allow nodes of independent clusters to co-exist on the
1579 same host. All nodes in a cluster must use the same epmd port num‐
1580 ber.
1581
1583 On Unix systems, the Erlang runtime will interpret two types of sig‐
1584 nals.
1585 SIGUSR1:
1587 A SIGUSR1 signal forces a crash dump.
1588 SIGTERM:
1590 A SIGTERM will produce a stop message to the init process. This is
1591 equivalent to a init:stop/0 call.
1592 Introduced in ERTS 8.3 (Erlang/OTP 19.3)
1594 The signal SIGUSR2 is reserved for internal usage. No other signals are
1596 handled.
1597
1599 The standard Erlang/OTP system can be reconfigured to change the de‐
1600 fault behavior on startup.
1601 The .erlang startup file:
1603 When Erlang/OTP is started, the system searches for a file named
1604 .erlang in the user's home directory and then file‐
1605 name:basedir(user_config, "erlang").
1606 If an .erlang file is found, it is assumed to contain valid Erlang
1608 expressions. These expressions are evaluated as if they were input
1609 to the shell.
1610 A typical .erlang file contains a set of search paths, for example:
1612 io:format("executing user profile in $HOME/.erlang\n",[]).
1614 code:add_path("/home/calvin/test/ebin").
1615 code:add_path("/home/hobbes/bigappl-1.2/ebin").
1616 io:format(".erlang rc finished\n",[]).
1617 user_default and shell_default:
1619 Functions in the shell that are not prefixed by a module name are
1620 assumed to be functional objects (funs), built-in functions (BIFs),
1621 or belong to the module user_default or shell_default.
1622 To include private shell commands, define them in a module user_de‐
1624 fault and add the following argument as the first line in the .er‐
1625 lang file:
1626 code:load_abs("..../user_default").
1628 erl:
1630 If the contents of .erlang are changed and a private version of
1631 user_default is defined, the Erlang/OTP environment can be custom‐
1632 ized. More powerful changes can be made by supplying command-line
1633 arguments in the startup script erl. For more information, see
1634 init(3).
1635
1637 epmd(1), erl_prim_loader(3), erts_alloc(3), init(3), application(3),
1638 auth(3), code(3), erl_boot_server(3), heart(3), net_kernel(3), make(3)
1639Ericsson AB erts 14.1.1 erl(1)