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
56 occur 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
110 accepted by erl are allowed, also flag -args_file FileName. Be
111 careful 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
136 installed 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:
150 Specifies the name of a configuration file, Config.config, which is
151 used to configure applications; see app(4) and application(3).
152 -connect_all false:
154 If this flag is present, global does not maintain a fully connected
155 network of distributed Erlang nodes, and then global name registra‐
156 tion cannot be used; see global(3).
157 -cookie Cookie:
159 Obsolete flag without any effect and common misspelling for -set‐
160 cookie. Use -setcookie instead.
161 -detached:
163 Starts the Erlang runtime system detached from the system console.
164 Useful for running daemons and backgrounds processes. Implies
165 -noinput.
166 -emu_args:
168 Useful for debugging. Prints the arguments sent to the emulator.
169 -emu_type Type:
171 Start an emulator of a different type. For example, to start the
172 lock-counter emualator, use -emu_type lcnt. (The emulator must
173 already be built. Use the configure option --enable-lock-counter to
174 build the lock-counter emulator.)
175 -env Variable Value:
177 Sets the host OS environment variable Variable to the value Value
178 for the Erlang runtime system. Example:
179 % erl -env DISPLAY gin:0
181 In this example, an Erlang runtime system is started with environ‐
183 ment variable DISPLAY set to gin:0.
184 -epmd_module Module (init flag):
186 Configures the module responsible to communicate to epmd. Defaults
187 to erl_epmd.
188 -eval Expr (init flag):
190 Makes init evaluate the expression Expr; see init(3).
191 -extra (init flag):
193 Everything following -extra is considered plain arguments and can
194 be retrieved using init:get_plain_arguments/0.
195 -heart:
197 Starts heartbeat monitoring of the Erlang runtime system; see
198 heart(3).
199 -hidden:
201 Starts the Erlang runtime system as a hidden node, if it is run as
202 a distributed node. Hidden nodes always establish hidden connec‐
203 tions to all other nodes except for nodes in the same global group.
204 Hidden connections are not published on any of the connected nodes,
205 that is, none of the connected nodes are part of the result from
206 nodes/0 on the other node. See also hidden global groups;
207 global_group(3).
208 -hosts Hosts:
210 Specifies the IP addresses for the hosts on which Erlang boot
211 servers are running, see erl_boot_server(3). This flag is mandatory
212 if flag -loader inet is present.
213 The IP addresses must be specified in the standard form (four deci‐
215 mal numbers separated by periods, for example, "150.236.20.74".
216 Hosts names are not acceptable, but a broadcast address (preferably
217 limited to the local network) is.
218 -id Id:
220 Specifies the identity of the Erlang runtime system. If it is run
221 as a distributed node, Id must be identical to the name supplied
222 together with flag -sname or -name.
223 -init_debug:
225 Makes init write some debug information while interpreting the boot
226 script.
227 -instr (emulator flag):
229 Selects an instrumented Erlang runtime system (virtual machine) to
230 run, instead of the ordinary one. When running an instrumented run‐
231 time system, some resource usage data can be obtained and analyzed
232 using the instrument module. Functionally, it behaves exactly like
233 an ordinary Erlang runtime system.
234 -loader Loader:
236 Specifies the method used by erl_prim_loader to load Erlang modules
237 into the system; see erl_prim_loader(3). Two Loader methods are
238 supported:
239 * efile, which means use the local file system, this is the
241 default.
242 * inet, which means use a boot server on another machine. The flags
244 -id, -hosts and -setcookie must also be specified.
245 If Loader is something else, the user-supplied Loader port program
247 is started.
248 -make:
250 Makes the Erlang runtime system invoke make:all() in the current
251 working directory and then terminate; see make(3). Implies -noin‐
252 put.
253 -man Module:
255 Displays the manual page for the Erlang module Module. Only sup‐
256 ported on Unix.
257 -mode interactive | embedded:
259 Modules are auto loaded when they are first referenced if the run‐
260 time system runs in interactive mode, which is the default. In
261 embedded mode modules are not auto loaded. The latter is recom‐
262 mended when the boot script preloads all modules, as conventionally
263 happens in OTP releases. See code(3).
264 -name Name:
266 Makes the Erlang runtime system into a distributed node. This flag
267 invokes all network servers necessary for a node to become distrib‐
268 uted; see net_kernel(3). It is also ensured that epmd runs on the
269 current host before Erlang is started; see epmd(1).and the
270 -start_epmd option.
271 The node name will be Name@Host, where Host is the fully qualified
273 host name of the current host. For short names, use flag -sname
274 instead.
275 Warning:
277 Starting a distributed node without also specifying -proto_dist
278 inet_tls will expose the node to attacks that may give the attacker
279 complete access to the node and in extension the cluster. When using
280 un-secure distributed nodes, make sure that the network is configured
281 to keep potential attackers out.
282 -noinput:
285 Ensures that the Erlang runtime system never tries to read any
286 input. Implies -noshell.
287 -noshell:
289 Starts an Erlang runtime system with no shell. This flag makes it
290 possible to have the Erlang runtime system as a component in a
291 series of Unix pipes.
292 -nostick:
294 Disables the sticky directory facility of the Erlang code server;
295 see code(3).
296 -oldshell:
298 Invokes the old Erlang shell from Erlang/OTP 3.3. The old shell can
299 still be used.
300 -pa Dir1 Dir2 ...:
302 Adds the specified directories to the beginning of the code path,
303 similar to code:add_pathsa/1. Note that the order of the given
304 directories will be reversed in the resulting path.
305 As an alternative to -pa, if several directories are to be
307 prepended to the code path and the directories have a common parent
308 directory, that parent directory can be specified in environment
309 variable ERL_LIBS; see code(3).
310 -pz Dir1 Dir2 ...:
312 Adds the specified directories to the end of the code path, similar
313 to code:add_pathsz/1; see code(3).
314 -path Dir1 Dir2 ...:
316 Replaces the path specified in the boot script; see script(4).
317 -proto_dist Proto:
319 Specifies a protocol for Erlang distribution:
322 inet_tcp:
324 TCP over IPv4 (the default)
325 inet_tls:
327 Distribution over TLS/SSL, See the Using SSL for Erlang Distri‐
328 bution User's Guide for details on how to setup a secure distrib‐
329 uted node.
330 inet6_tcp:
332 TCP over IPv6
333 For example, to start up IPv6 distributed nodes:
335 % erl -name test@ipv6node.example.com -proto_dist inet6_tcp
337 -remsh Node:
339 Starts Erlang with a remote shell connected to Node. Requires
340 either -name or -sname to be given. If Node does not contain a
341 hostname, one is automatically taken from -name or -sname
342 -rsh Program:
344 Specifies an alternative to ssh for starting a slave node on a
345 remote host; see slave(3).
346 -run Mod [Func [Arg1, Arg2, ...]] (init flag):
348 Makes init call the specified function. Func defaults to start. If
349 no arguments are provided, the function is assumed to be of arity
350 0. Otherwise it is assumed to be of arity 1, taking the list
351 [Arg1,Arg2,...] as argument. All arguments are passed as strings.
352 See init(3).
353 -s Mod [Func [Arg1, Arg2, ...]] (init flag):
355 Makes init call the specified function. Func defaults to start. If
356 no arguments are provided, the function is assumed to be of arity
357 0. Otherwise it is assumed to be of arity 1, taking the list
358 [Arg1,Arg2,...] as argument. All arguments are passed as atoms. See
359 init(3).
360 -setcookie Cookie:
362 Sets the magic cookie of the node to Cookie; see
363 erlang:set_cookie/2.
364 -shutdown_time Time:
366 Specifies how long time (in milliseconds) the init process is
367 allowed to spend shutting down the system. If Time milliseconds
368 have elapsed, all processes still existing are killed. Defaults to
369 infinity.
370 -sname Name:
372 Makes the Erlang runtime system into a distributed node, similar to
373 -name, but the host name portion of the node name Name@Host will be
374 the short name, not fully qualified.
375 This is sometimes the only way to run distributed Erlang if the
377 Domain Name System (DNS) is not running. No communication can exist
378 between nodes running with flag -sname and those running with flag
379 -name, as node names must be unique in distributed Erlang systems.
380 Warning:
382 Starting a distributed node without also specifying -proto_dist
383 inet_tls will expose the node to attacks that may give the attacker
384 complete access to the node and in extension the cluster. When using
385 un-secure distributed nodes, make sure that the network is configured
386 to keep potential attackers out.
387 -start_epmd true | false:
390 Specifies whether Erlang should start epmd on startup. By default
391 this is true, but if you prefer to start epmd manually, set this to
392 false.
393 This only applies if Erlang is started as a distributed node, i.e.
395 if -name or -sname is specified. Otherwise, epmd is not started
396 even if -start_epmd true is given.
397 Note that a distributed node will fail to start if epmd is not run‐
399 ning.
400 -version (emulator flag):
402 Makes the emulator print its version number. The same as erl +V.
403
405 erl invokes the code for the Erlang emulator (virtual machine), which
406 supports the following flags:
407 +a size:
409 Suggested stack size, in kilowords, for threads in the async thread
410 pool. Valid range is 16-8192 kilowords. The default suggested stack
411 size is 16 kilowords, that is, 64 kilobyte on 32-bit architectures.
412 This small default size has been chosen because the number of async
413 threads can be large. The default size is enough for drivers deliv‐
414 ered with Erlang/OTP, but might not be large enough for other
415 dynamically linked-in drivers that use the driver_async() function‐
416 ality. Notice that the value passed is only a suggestion, and it
417 can even be ignored on some platforms.
418 +A size:
420 Sets the number of threads in async thread pool. Valid range is
421 0-1024. The async thread pool is used by linked-in drivers to han‐
422 dle work that may take a very long time. Since OTP-21 there are
423 very few linked-in drivers in the default Erlang/OTP distribution
424 that uses the async thread pool. Most of them have been migrated to
425 dirty IO schedulers. Defaults to 1.
426 +B [c | d | i]:
428 Option c makes Ctrl-C interrupt the current shell instead of invok‐
429 ing the emulator break handler. Option d (same as specifying +B
430 without an extra option) disables the break handler. Option i makes
431 the emulator ignore any break signal.
432 If option c is used with oldshell on Unix, Ctrl-C will restart the
434 shell process rather than interrupt it.
435 Notice that on Windows, this flag is only applicable for werl, not
437 erl (oldshell). Notice also that Ctrl-Break is used instead of
438 Ctrl-C on Windows.
439 +c true | false:
441 Enables or disables time correction:
442 true:
444 Enables time correction. This is the default if time correction
445 is supported on the specific platform.
446 false:
448 Disables time correction.
449 For backward compatibility, the boolean value can be omitted. This
451 is interpreted as +c false.
452 +C no_time_warp | single_time_warp | multi_time_warp:
454 Sets time warp mode:
455 no_time_warp:
457 No time warp mode (the default)
458 single_time_warp:
460 Single time warp mode
461 multi_time_warp:
463 Multi-time warp mode
464 +d:
466 If the emulator detects an internal error (or runs out of memory),
467 it, by default, generates both a crash dump and a core dump. The
468 core dump is, however, not very useful as the content of process
469 heaps is destroyed by the crash dump generation.
470 Option +d instructs the emulator to produce only a core dump and no
472 crash dump if an internal error is detected.
473 Calling erlang:halt/1 with a string argument still produces a crash
475 dump. On Unix systems, sending an emulator process a SIGUSR1 signal
476 also forces a crash dump.
477 +rg DecentralizedCounterGroupsLimit:
479 Limits the number of decentralized counter groups used by decen‐
480 tralized counters optimized for update operations in the Erlang
481 runtime system. By default, the limit is 256.
482 When the number of schedulers is less than or equal to the limit,
484 each scheduler has its own group. When the number of schedulers is
485 larger than the groups limit, schedulers share groups. Shared
486 groups degrade the performance for updating counters while many
487 reader groups degrade the performance for reading counters. So, the
488 limit is a tradeoff between performance for update operations and
489 performance for read operations. Each group consumes 64 bytes in
490 each counter.
491 Notice that a runtime system using decentralized counter groups
493 benefits from binding schedulers to logical processors, as the
494 groups are distributed better between schedulers with this option.
495 This option only affects decentralized counters used for the coun‐
497 ters that are keeping track of the memory consumption and the num‐
498 ber of terms in ETS tables of type ordered_set with the write_con‐
499 currency option activated.
500 +e Number:
502 Sets the maximum number of ETS tables. This limit is partially
503 obsolete.
504 +ec:
506 Forces option compressed on all ETS tables. Only intended for test
507 and evaluation.
508 +fnl:
510 The virtual machine works with filenames as if they are encoded
511 using the ISO Latin-1 encoding, disallowing Unicode characters with
512 code points > 255.
513 For more information about Unicode filenames, see section Unicode
515 Filenames in the STDLIB User's Guide. Notice that this value also
516 applies to command-line parameters and environment variables (see
517 section Unicode in Environment and Parameters in the STDLIB User's
518 Guide).
519 +fnu[{w|i|e}]:
521 The virtual machine works with filenames as if they are encoded
522 using UTF-8 (or some other system-specific Unicode encoding). This
523 is the default on operating systems that enforce Unicode encoding,
524 that is, Windows and MacOS X.
525 The +fnu switch can be followed by w, i, or e to control how
527 wrongly encoded filenames are to be reported:
528 * w means that a warning is sent to the error_logger whenever a
530 wrongly encoded filename is "skipped" in directory listings. This
531 is the default.
532 * i means that those wrongly encoded filenames are silently
534 ignored.
535 * e means that the API function returns an error whenever a wrongly
537 encoded filename (or directory name) is encountered.
538 Notice that file:read_link/1 always returns an error if the link
540 points to an invalid filename.
541 For more information about Unicode filenames, see section Unicode
543 Filenames in the STDLIB User's Guide. Notice that this value also
544 applies to command-line parameters and environment variables (see
545 section Unicode in Environment and Parameters in the STDLIB User's
546 Guide).
547 +fna[{w|i|e}]:
549 Selection between +fnl and +fnu is done based on the current locale
550 settings in the OS. This means that if you have set your terminal
551 for UTF-8 encoding, the filesystem is expected to use the same
552 encoding for filenames. This is default on all operating systems,
553 except MacOS X and Windows.
554 The +fna switch can be followed by w, i, or e. This has effect if
556 the locale settings cause the behavior of +fnu to be selected; see
557 the description of +fnu above. If the locale settings cause the
558 behavior of +fnl to be selected, then w, i, or e have no effect.
559 For more information about Unicode filenames, see section Unicode
561 Filenames in the STDLIB User's Guide. Notice that this value also
562 applies to command-line parameters and environment variables (see
563 section Unicode in Environment and Parameters in the STDLIB User's
564 Guide).
565 +hms Size:
567 Sets the default heap size of processes to the size Size.
568 +hmbs Size:
570 Sets the default binary virtual heap size of processes to the size
571 Size.
572 +hmax Size:
574 Sets the default maximum heap size of processes to the size Size.
575 Defaults to 0, which means that no maximum heap size is used. For
576 more information, see process_flag(max_heap_size, MaxHeapSize).
577 +hmaxel true|false:
579 Sets whether to send an error logger message or not for processes
580 reaching the maximum heap size. Defaults to true. For more informa‐
581 tion, see process_flag(max_heap_size, MaxHeapSize).
582 +hmaxk true|false:
584 Sets whether to kill processes reaching the maximum heap size or
585 not. Default to true. For more information, see
586 process_flag(max_heap_size, MaxHeapSize).
587 +hpds Size:
589 Sets the initial process dictionary size of processes to the size
590 Size.
591 +hmqd off_heap|on_heap:
593 Sets the default value for process flag message_queue_data.
594 Defaults to on_heap. If +hmqd is not passed, on_heap will be the
595 default. For more information, see process_flag(message_queue_data,
596 MQD).
597 +IOp PollSets:
599 Sets the number of IO pollsets to use when polling for I/O. This
600 option is only used on platforms that support concurrent updates of
601 a pollset, otherwise the same number of pollsets are used as IO
602 poll threads. The default is 1.
603 +IOt PollThreads:
605 Sets the number of IO poll threads to use when polling for I/O. The
606 maximum number of poll threads allowed is 1024. The default is 1.
607 A good way to check if more IO poll threads are needed is to use
609 microstate accounting and see what the load of the IO poll thread
610 is. If it is high it could be a good idea to add more threads.
611 +IOPp PollSetsPercentage:
613 Similar to +IOp but uses percentages to set the number of IO
614 pollsets to create, based on the number of poll threads configured.
615 If both +IOPp and +IOp are used, +IOPp is ignored.
616 +IOPt PollThreadsPercentage:
618 Similar to +IOt but uses percentages to set the number of IO poll
619 threads to create, based on the number of schedulers configured. If
620 both +IOPt and +IOt are used, +IOPt is ignored.
621 +l:
623 Enables autoload tracing, displaying information while loading
624 code.
625 +L:
627 Prevents loading information about source filenames and line num‐
628 bers. This saves some memory, but exceptions do not contain infor‐
629 mation about the filenames and line numbers.
630 +MFlag Value:
632 Memory allocator-specific flags. For more information, see
633 erts_alloc(3).
634 +pc Range:
636 Sets the range of characters that the system considers printable in
637 heuristic detection of strings. This typically affects the shell,
638 debugger, and io:format functions (when ~tp is used in the format
639 string).
640 Two values are supported for Range:
642 latin1:
644 The default. Only characters in the ISO Latin-1 range can be con‐
645 sidered printable. This means that a character with a code point
646 > 255 is never considered printable and that lists containing
647 such characters are displayed as lists of integers rather than
648 text strings by tools.
649 unicode:
651 All printable Unicode characters are considered when determining
652 if a list of integers is to be displayed in string syntax. This
653 can give unexpected results if, for example, your font does not
654 cover all Unicode characters.
655 See also io:printable_range/0 in STDLIB.
657 +P Number:
659 Sets the maximum number of simultaneously existing processes for
660 this system if a Number is passed as value. Valid range for Number
661 is [1024-134217727]
662 NOTE: The actual maximum chosen may be much larger than the Number
664 passed. Currently the runtime system often, but not always, chooses
665 a value that is a power of 2. This might, however, be changed in
666 the future. The actual value chosen can be checked by calling
667 erlang:system_info(process_limit).
668 The default value is 262144
670 +Q Number:
672 Sets the maximum number of simultaneously existing ports for this
673 system if a Number is passed as value. Valid range for Number is
674 [1024-134217727]
675 NOTE: The actual maximum chosen may be much larger than the actual
677 Number passed. Currently the runtime system often, but not always,
678 chooses a value that is a power of 2. This might, however, be
679 changed in the future. The actual value chosen can be checked by
680 calling erlang:system_info(port_limit).
681 The default value used is normally 65536. However, if the runtime
683 system is able to determine maximum amount of file descriptors that
684 it is allowed to open and this value is larger than 65536, the cho‐
685 sen value will increased to a value larger or equal to the maximum
686 amount of file descriptors that can be opened.
687 On Windows the default value is set to 8196 because the normal OS
689 limitations are set higher than most machines can handle.
690 +R ReleaseNumber:
692 Sets the compatibility mode.
693 The distribution mechanism is not backward compatible by default.
695 This flag sets the emulator in compatibility mode with an earlier
696 Erlang/OTP release ReleaseNumber. The release number must be in the
697 range <current release>-2..<current release>. This limits the emu‐
698 lator, making it possible for it to communicate with Erlang nodes
699 (as well as C- and Java nodes) running that earlier release.
700 Note:
702 Ensure that all nodes (Erlang-, C-, and Java nodes) of a distributed
703 Erlang system is of the same Erlang/OTP release, or from two differ‐
704 ent Erlang/OTP releases X and Y, where all Y nodes have compatibility
705 mode X.
706 +r:
709 Forces ETS memory block to be moved on realloc.
710 +rg ReaderGroupsLimit:
712 Limits the number of reader groups used by read/write locks opti‐
713 mized for read operations in the Erlang runtime system. By default
714 the reader groups limit is 64.
715 When the number of schedulers is less than or equal to the reader
717 groups limit, each scheduler has its own reader group. When the
718 number of schedulers is larger than the reader groups limit, sched‐
719 ulers share reader groups. Shared reader groups degrade read lock
720 and read unlock performance while many reader groups degrade write
721 lock performance. So, the limit is a tradeoff between performance
722 for read operations and performance for write operations. Each
723 reader group consumes 64 byte in each read/write lock.
724 Notice that a runtime system using shared reader groups benefits
726 from binding schedulers to logical processors, as the reader groups
727 are distributed better between schedulers.
728 +S Schedulers:SchedulerOnline:
730 Sets the number of scheduler threads to create and scheduler
731 threads to set online. The maximum for both values is 1024. If the
732 Erlang runtime system is able to determine the number of logical
733 processors configured and logical processors available, Schedulers
734 defaults to logical processors configured, and SchedulersOnline
735 defaults to logical processors available; otherwise the default
736 values are 1. Schedulers can be omitted if :SchedulerOnline is not
737 and conversely. The number of schedulers online can be changed at
738 runtime through erlang:system_flag(schedulers_online, SchedulersOn‐
739 line).
740 If Schedulers or SchedulersOnline is specified as a negative num‐
742 ber, the value is subtracted from the default number of logical
743 processors configured or logical processors available, respec‐
744 tively.
745 Specifying value 0 for Schedulers or SchedulersOnline resets the
747 number of scheduler threads or scheduler threads online, respec‐
748 tively, to its default value.
749 +SP SchedulersPercentage:SchedulersOnlinePercentage:
751 Similar to +S but uses percentages to set the number of scheduler
752 threads to create, based on logical processors configured, and
753 scheduler threads to set online, based on logical processors avail‐
754 able. Specified values must be > 0. For example, +SP 50:25 sets the
755 number of scheduler threads to 50% of the logical processors con‐
756 figured, and the number of scheduler threads online to 25% of the
757 logical processors available. SchedulersPercentage can be omitted
758 if :SchedulersOnlinePercentage is not and conversely. The number of
759 schedulers online can be changed at runtime through erlang:sys‐
760 tem_flag(schedulers_online, SchedulersOnline).
761 This option interacts with +S settings. For example, on a system
763 with 8 logical cores configured and 8 logical cores available, the
764 combination of the options +S 4:4 +SP 50:25 (in either order)
765 results in 2 scheduler threads (50% of 4) and 1 scheduler thread
766 online (25% of 4).
767 +SDcpu DirtyCPUSchedulers:DirtyCPUSchedulersOnline:
769 Sets the number of dirty CPU scheduler threads to create and dirty
770 CPU scheduler threads to set online. The maximum for both values is
771 1024, and each value is further limited by the settings for normal
772 schedulers:
773 * The number of dirty CPU scheduler threads created cannot exceed
775 the number of normal scheduler threads created.
776 * The number of dirty CPU scheduler threads online cannot exceed
778 the number of normal scheduler threads online.
779 For details, see the +S and +SP. By default, the number of dirty
781 CPU scheduler threads created equals the number of normal scheduler
782 threads created, and the number of dirty CPU scheduler threads
783 online equals the number of normal scheduler threads online. Dirty‐
784 CPUSchedulers can be omitted if :DirtyCPUSchedulersOnline is not
785 and conversely. The number of dirty CPU schedulers online can be
786 changed at runtime through erlang:system_flag(dirty_cpu_sched‐
787 ulers_online, DirtyCPUSchedulersOnline).
788 The amount of dirty CPU schedulers is limited by the amount of nor‐
790 mal schedulers in order to limit the effect on processes executing
791 on ordinary schedulers. If the amount of dirty CPU schedulers was
792 allowed to be unlimited, dirty CPU bound jobs would potentially
793 starve normal jobs.
794 Typical users of the dirty CPU schedulers are large garbage collec‐
796 tions, json protocol encode/decoders written as nifs and matrix
797 manipulation libraries.
798 You can use msacc(3) in order to see the current load of the dirty
800 CPU schedulers threads and adjust the number used accordingly.
801 +SDPcpu DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercent‐
803 age:
804 Similar to +SDcpu but uses percentages to set the number of dirty
805 CPU scheduler threads to create and the number of dirty CPU sched‐
806 uler threads to set online. Specified values must be > 0. For exam‐
807 ple, +SDPcpu 50:25 sets the number of dirty CPU scheduler threads
808 to 50% of the logical processors configured and the number of dirty
809 CPU scheduler threads online to 25% of the logical processors
810 available. DirtyCPUSchedulersPercentage can be omitted if :DirtyC‐
811 PUSchedulersOnlinePercentage is not and conversely. The number of
812 dirty CPU schedulers online can be changed at runtime through
813 erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUScheduler‐
814 sOnline).
815 This option interacts with +SDcpu settings. For example, on a sys‐
817 tem with 8 logical cores configured and 8 logical cores available,
818 the combination of the options +SDcpu 4:4 +SDPcpu 50:25 (in either
819 order) results in 2 dirty CPU scheduler threads (50% of 4) and 1
820 dirty CPU scheduler thread online (25% of 4).
821 +SDio DirtyIOSchedulers:
823 Sets the number of dirty I/O scheduler threads to create. Valid
824 range is 1-1024. By default, the number of dirty I/O scheduler
825 threads created is 10.
826 The amount of dirty IO schedulers is not limited by the amount of
828 normal schedulers like the amount of dirty CPU schedulers. This
829 since only I/O bound work is expected to execute on dirty I/O
830 schedulers. If the user should schedule CPU bound jobs on dirty I/O
831 schedulers, these jobs might starve ordinary jobs executing on
832 ordinary schedulers.
833 Typical users of the dirty IO schedulers are reading and writing to
835 files.
836 You can use msacc(3) in order to see the current load of the dirty
838 IO schedulers threads and adjust the number used accordingly.
839 +sFlag Value:
841 Scheduling specific flags.
842 +sbt BindType:
844 Sets scheduler bind type.
845 Schedulers can also be bound using flag +stbt. The only differ‐
847 ence between these two flags is how the following errors are han‐
848 dled:
849 * Binding of schedulers is not supported on the specific plat‐
851 form.
852 * No available CPU topology. That is, the runtime system was not
854 able to detect the CPU topology automatically, and no user-
855 defined CPU topology was set.
856 If any of these errors occur when +sbt has been passed, the run‐
858 time system prints an error message, and refuses to start. If any
859 of these errors occur when +stbt has been passed, the runtime
860 system silently ignores the error, and start up using unbound
861 schedulers.
862 Valid BindTypes:
864 u:
866 unbound - Schedulers are not bound to logical processors, that
867 is, the operating system decides where the scheduler threads
868 execute, and when to migrate them. This is the default.
869 ns:
871 no_spread - Schedulers with close scheduler identifiers are
872 bound as close as possible in hardware.
873 ts:
875 thread_spread - Thread refers to hardware threads (such as
876 Intel's hyper-threads). Schedulers with low scheduler identi‐
877 fiers, are bound to the first hardware thread of each core,
878 then schedulers with higher scheduler identifiers are bound to
879 the second hardware thread of each core,and so on.
880 ps:
882 processor_spread - Schedulers are spread like thread_spread,
883 but also over physical processor chips.
884 s:
886 spread - Schedulers are spread as much as possible.
887 nnts:
889 no_node_thread_spread - Like thread_spread, but if multiple
890 Non-Uniform Memory Access (NUMA) nodes exist, schedulers are
891 spread over one NUMA node at a time, that is, all logical pro‐
892 cessors of one NUMA node are bound to schedulers in sequence.
893 nnps:
895 no_node_processor_spread - Like processor_spread, but if multi‐
896 ple NUMA nodes exist, schedulers are spread over one NUMA node
897 at a time, that is, all logical processors of one NUMA node are
898 bound to schedulers in sequence.
899 tnnps:
901 thread_no_node_processor_spread - A combination of
902 thread_spread, and no_node_processor_spread. Schedulers are
903 spread over hardware threads across NUMA nodes, but schedulers
904 are only spread over processors internally in one NUMA node at
905 a time.
906 db:
908 default_bind - Binds schedulers the default way. Defaults to
909 thread_no_node_processor_spread (which can change in the
910 future).
911 Binding of schedulers is only supported on newer Linux, Solaris,
913 FreeBSD, and Windows systems.
914 If no CPU topology is available when flag +sbt is processed and
916 BindType is any other type than u, the runtime system fails to
917 start. CPU topology can be defined using flag +sct. Notice that
918 flag +sct can have to be passed before flag +sbt on the command
919 line (if no CPU topology has been automatically detected).
920 The runtime system does by default not bind schedulers to logical
922 processors.
923 Note:
925 If the Erlang runtime system is the only operating system process
926 that binds threads to logical processors, this improves the perfor‐
927 mance of the runtime system. However, if other operating system
928 processes (for example another Erlang runtime system) also bind
929 threads to logical processors, there can be a performance penalty
930 instead. This performance penalty can sometimes be severe. If so,
931 you are advised not to bind the schedulers.
932 How schedulers are bound matters. For example, in situations when
935 there are fewer running processes than schedulers online, the
936 runtime system tries to migrate processes to schedulers with low
937 scheduler identifiers. The more the schedulers are spread over
938 the hardware, the more resources are available to the runtime
939 system in such situations.
940 Note:
942 If a scheduler fails to bind, this is often silently ignored, as it
943 is not always possible to verify valid logical processor identi‐
944 fiers. If an error is reported, it is reported to the error_logger.
945 If you want to verify that the schedulers have bound as requested,
946 call erlang:system_info(scheduler_bindings).
947 +sbwt none|very_short|short|medium|long|very_long:
950 Sets scheduler busy wait threshold. Defaults to medium. The
951 threshold determines how long schedulers are to busy wait when
952 running out of work before going to sleep.
953 Note:
955 This flag can be removed or changed at any time without prior
956 notice.
957 +sbwtdcpu none|very_short|short|medium|long|very_long:
960 As +sbwt but affects dirty CPU schedulers. Defaults to short.
961 Note:
963 This flag can be removed or changed at any time without prior
964 notice.
965 +sbwtdio none|very_short|short|medium|long|very_long:
968 As +sbwt but affects dirty IO schedulers. Defaults to short.
969 Note:
971 This flag can be removed or changed at any time without prior
972 notice.
973 +scl true|false:
976 Enables or disables scheduler compaction of load. By default
977 scheduler compaction of load is enabled. When enabled, load bal‐
978 ancing strives for a load distribution, which causes as many
979 scheduler threads as possible to be fully loaded (that is, not
980 run out of work). This is accomplished by migrating load (for
981 example, runnable processes) into a smaller set of schedulers
982 when schedulers frequently run out of work. When disabled, the
983 frequency with which schedulers run out of work is not taken into
984 account by the load balancing logic.
985 +scl false is similar to +sub true, but +sub true also balances
987 scheduler utilization between schedulers.
988 +sct CpuTopology:
990 * <Id> = integer(); when 0 =< <Id> =< 65535
993 * <IdRange> = <Id>-<Id>
995 * <IdOrIdRange> = <Id> | <IdRange>
997 * <IdList> = <IdOrIdRange>,<IdOrIdRange> | <IdOrIdRange>
999 * <LogicalIds> = L<IdList>
1001 * <ThreadIds> = T<IdList> | t<IdList>
1003 * <CoreIds> = C<IdList> | c<IdList>
1005 * <ProcessorIds> = P<IdList> | p<IdList>
1007 * <NodeIds> = N<IdList> | n<IdList>
1009 * <IdDefs> = <LogicalIds><ThreadIds><CoreIds><Proces‐
1011 sorIds><NodeIds> | <LogicalIds><ThreadIds><Cor‐
1012 eIds><NodeIds><ProcessorIds>
1013 * CpuTopology = <IdDefs>:<IdDefs> | <IdDefs>
1015 Sets a user-defined CPU topology. The user-defined CPU topology
1017 overrides any automatically detected CPU topology. The CPU topol‐
1018 ogy is used when binding schedulers to logical processors.
1019 Uppercase letters signify real identifiers and lowercase letters
1021 signify fake identifiers only used for description of the topol‐
1022 ogy. Identifiers passed as real identifiers can be used by the
1023 runtime system when trying to access specific hardware; if they
1024 are incorrect the behavior is undefined. Faked logical CPU iden‐
1025 tifiers are not accepted, as there is no point in defining the
1026 CPU topology without real logical CPU identifiers. Thread, core,
1027 processor, and node identifiers can be omitted. If omitted, the
1028 thread ID defaults to t0, the core ID defaults to c0, the proces‐
1029 sor ID defaults to p0, and the node ID is left undefined. Either
1030 each logical processor must belong to only one NUMA node, or no
1031 logical processors must belong to any NUMA nodes.
1032 Both increasing and decreasing <IdRange>s are allowed.
1034 NUMA node identifiers are system wide. That is, each NUMA node on
1036 the system must have a unique identifier. Processor identifiers
1037 are also system wide. Core identifiers are processor wide. Thread
1038 identifiers are core wide.
1039 The order of the identifier types implies the hierarchy of the
1041 CPU topology. The valid orders are as follows:
1042 * <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>, that
1044 is, thread is part of a core that is part of a processor, which
1045 is part of a NUMA node.
1046 * <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>, that
1048 is, thread is part of a core that is part of a NUMA node, which
1049 is part of a processor.
1050 A CPU topology can consist of both processor external, and pro‐
1052 cessor internal NUMA nodes as long as each logical processor
1053 belongs to only one NUMA node. If <ProcessorIds> is omitted, its
1054 default position is before <NodeIds>. That is, the default is
1055 processor external NUMA nodes.
1056 If a list of identifiers is used in an <IdDefs>:
1058 * <LogicalIds> must be a list of identifiers.
1060 * At least one other identifier type besides <LogicalIds> must
1062 also have a list of identifiers.
1063 * All lists of identifiers must produce the same number of iden‐
1065 tifiers.
1066 A simple example. A single quad core processor can be described
1068 as follows:
1069 % erl +sct L0-3c0-3
1071 1> erlang:system_info(cpu_topology).
1072 [{processor,[{core,{logical,0}},
1073 {core,{logical,1}},
1074 {core,{logical,2}},
1075 {core,{logical,3}}]}]
1076 A more complicated example with two quad core processors, each
1078 processor in its own NUMA node. The ordering of logical proces‐
1079 sors is a bit weird. This to give a better example of identifier
1080 lists:
1081 % erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1
1083 1> erlang:system_info(cpu_topology).
1084 [{node,[{processor,[{core,{logical,0}},
1085 {core,{logical,1}},
1086 {core,{logical,3}},
1087 {core,{logical,2}}]}]},
1088 {node,[{processor,[{core,{logical,7}},
1089 {core,{logical,4}},
1090 {core,{logical,6}},
1091 {core,{logical,5}}]}]}]
1092 As long as real identifiers are correct, it is OK to pass a CPU
1094 topology that is not a correct description of the CPU topology.
1095 When used with care this can be very useful. This to trick the
1096 emulator to bind its schedulers as you want. For example, if you
1097 want to run multiple Erlang runtime systems on the same machine,
1098 you want to reduce the number of schedulers used and manipulate
1099 the CPU topology so that they bind to different logical CPUs. An
1100 example, with two Erlang runtime systems on a quad core machine:
1101 % erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
1103 % erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two
1104 In this example, each runtime system have two schedulers each
1106 online, and all schedulers online will run on different cores. If
1107 we change to one scheduler online on one runtime system, and
1108 three schedulers online on the other, all schedulers online will
1109 still run on different cores.
1110 Notice that a faked CPU topology that does not reflect how the
1112 real CPU topology looks like is likely to decrease the perfor‐
1113 mance of the runtime system.
1114 For more information, see erlang:system_info(cpu_topology).
1116 +sfwi Interval:
1118 Sets scheduler-forced wakeup interval. All run queues are scanned
1119 each Interval milliseconds. While there are sleeping schedulers
1120 in the system, one scheduler is woken for each non-empty run
1121 queue found. Interval default to 0, meaning this feature is dis‐
1122 abled.
1123 Note:
1125 This feature has been introduced as a temporary workaround for
1126 long-executing native code, and native code that does not bump
1127 reductions properly in OTP. When these bugs have be fixed, this
1128 flag will be removed.
1129 +spp Bool:
1132 Sets default scheduler hint for port parallelism. If set to true,
1133 the virtual machine schedules port tasks when it improves paral‐
1134 lelism in the system. If set to false, the virtual machine tries
1135 to perform port tasks immediately, improving latency at the
1136 expense of parallelism. Default to false. The default used can be
1137 inspected in runtime by calling erlang:system_info(port_parallel‐
1138 ism). The default can be overridden on port creation by passing
1139 option parallelism to erlang:open_port/2.
1140 +sss size:
1142 Suggested stack size, in kilowords, for scheduler threads. Valid
1143 range is 20-8192 kilowords. The default suggested stack size is
1144 128 kilowords.
1145 +sssdcpu size:
1147 Suggested stack size, in kilowords, for dirty CPU scheduler
1148 threads. Valid range is 20-8192 kilowords. The default suggested
1149 stack size is 40 kilowords.
1150 +sssdio size:
1152 Suggested stack size, in kilowords, for dirty IO scheduler
1153 threads. Valid range is 20-8192 kilowords. The default suggested
1154 stack size is 40 kilowords.
1155 +stbt BindType:
1157 Tries to set the scheduler bind type. The same as flag +sbt
1158 except how some errors are handled. For more information, see
1159 +sbt.
1160 +sub true|false:
1162 Enables or disables scheduler utilization balancing of load. By
1163 default scheduler utilization balancing is disabled and instead
1164 scheduler compaction of load is enabled, which strives for a load
1165 distribution that causes as many scheduler threads as possible to
1166 be fully loaded (that is, not run out of work). When scheduler
1167 utilization balancing is enabled, the system instead tries to
1168 balance scheduler utilization between schedulers. That is, strive
1169 for equal scheduler utilization on all schedulers.
1170 +sub true is only supported on systems where the runtime system
1172 detects and uses a monotonically increasing high-resolution
1173 clock. On other systems, the runtime system fails to start.
1174 +sub true implies +scl false. The difference between +sub true
1176 and +scl false is that +scl false does not try to balance the
1177 scheduler utilization.
1178 +swct very_eager|eager|medium|lazy|very_lazy:
1180 Sets scheduler wake cleanup threshold. Defaults to medium. Con‐
1181 trols how eager schedulers are to be requesting wakeup because of
1182 certain cleanup operations. When a lazy setting is used, more
1183 outstanding cleanup operations can be left undone while a sched‐
1184 uler is idling. When an eager setting is used, schedulers are
1185 more frequently woken, potentially increasing CPU-utilization.
1186 Note:
1188 This flag can be removed or changed at any time without prior
1189 notice.
1190 +sws default|legacy:
1193 Sets scheduler wakeup strategy. Default strategy changed in ERTS
1194 5.10 (Erlang/OTP R16A). This strategy was known as proposal in
1195 Erlang/OTP R15. The legacy strategy was used as default from R13
1196 up to and including R15.
1197 Note:
1199 This flag can be removed or changed at any time without prior
1200 notice.
1201 +swt very_low|low|medium|high|very_high:
1204 Sets scheduler wakeup threshold. Defaults to medium. The thresh‐
1205 old determines when to wake up sleeping schedulers when more work
1206 than can be handled by currently awake schedulers exists. A low
1207 threshold causes earlier wakeups, and a high threshold causes
1208 later wakeups. Early wakeups distribute work over multiple sched‐
1209 ulers faster, but work does more easily bounce between sched‐
1210 ulers.
1211 Note:
1213 This flag can be removed or changed at any time without prior
1214 notice.
1215 +swtdcpu very_low|low|medium|high|very_high:
1218 As +swt but affects dirty CPU schedulers. Defaults to medium.
1219 Note:
1221 This flag can be removed or changed at any time without prior
1222 notice.
1223 +swtdio very_low|low|medium|high|very_high:
1226 As +swt but affects dirty IO schedulers. Defaults to medium.
1227 Note:
1229 This flag can be removed or changed at any time without prior
1230 notice.
1231 +t size:
1234 Sets the maximum number of atoms the virtual machine can handle.
1235 Defaults to 1,048,576.
1236 +T Level:
1238 Enables modified timing and sets the modified timing level. Valid
1239 range is 0-9. The timing of the runtime system is changed. A high
1240 level usually means a greater change than a low level. Changing the
1241 timing can be very useful for finding timing-related bugs.
1242 Modified timing affects the following:
1244 Process spawning:
1246 A process calling spawn, spawn_link, spawn_monitor, or spawn_opt
1247 is scheduled out immediately after completing the call. When
1248 higher modified timing levels are used, the caller also sleeps
1249 for a while after it is scheduled out.
1250 Context reductions:
1252 The number of reductions a process is allowed to use before it is
1253 scheduled out is increased or reduced.
1254 Input reductions:
1256 The number of reductions performed before checking I/O is
1257 increased or reduced.
1258 Note:
1260 Performance suffers when modified timing is enabled. This flag is
1261 only intended for testing and debugging.
1262 return_to and return_from trace messages are lost when tracing on the
1264 spawn BIFs.
1265 This flag can be removed or changed at any time without prior notice.
1267 +v:
1270 Verbose.
1271 +V:
1273 Makes the emulator print its version number.
1274 +W w | i | e:
1276 Sets the mapping of warning messages for error_logger. Messages
1277 sent to the error logger using one of the warning routines can be
1278 mapped to errors (+W e), warnings (+W w), or information reports
1279 (+W i). Defaults to warnings. The current mapping can be retrieved
1280 using error_logger:warning_map/0. For more information, see
1281 error_logger:warning_map/0 in Kernel.
1282 +zFlag Value:
1284 Miscellaneous flags:
1285 +zdbbl size:
1287 Sets the distribution buffer busy limit (dist_buf_busy_limit) in
1288 kilobytes. Valid range is 1-2097151. Defaults to 1024.
1289 A larger buffer limit allows processes to buffer more outgoing
1291 messages over the distribution. When the buffer limit has been
1292 reached, sending processes will be suspended until the buffer
1293 size has shrunk. The buffer limit is per distribution channel. A
1294 higher limit gives lower latency and higher throughput at the
1295 expense of higher memory use.
1296 +zdntgc time:
1298 Sets the delayed node table garbage collection time
1299 (delayed_node_table_gc) in seconds. Valid values are either
1300 infinity or an integer in the range 0-100000000. Defaults to 60.
1301 Node table entries that are not referred linger in the table for
1303 at least the amount of time that this parameter determines. The
1304 lingering prevents repeated deletions and insertions in the
1305 tables from occurring.
1306
1308 ERL_CRASH_DUMP:
1309 If the emulator needs to write a crash dump, the value of this
1310 variable is the filename of the crash dump file. If the variable is
1311 not set, the name of the crash dump file is erl_crash.dump in the
1312 current directory.
1313 ERL_CRASH_DUMP_NICE:
1315 Unix systems: If the emulator needs to write a crash dump, it uses
1316 the value of this variable to set the nice value for the process,
1317 thus lowering its priority. Valid range is 1-39 (higher values are
1318 replaced with 39). The highest value, 39, gives the process the
1319 lowest priority.
1320 ERL_CRASH_DUMP_SECONDS:
1322 Unix systems: This variable gives the number of seconds that the
1323 emulator is allowed to spend writing a crash dump. When the given
1324 number of seconds have elapsed, the emulator is terminated.
1325 ERL_CRASH_DUMP_SECONDS=0:
1327 If the variable is set to 0 seconds, the runtime system does not
1328 even attempt to write the crash dump file. It only terminates.
1329 This is the default if option -heart is passed to erl and
1330 ERL_CRASH_DUMP_SECONDS is not set.
1331 ERL_CRASH_DUMP_SECONDS=S:
1333 If the variable is set to a positive value S, wait for S seconds
1334 to complete the crash dump file and then terminates the runtime
1335 system with a SIGALRM signal.
1336 ERL_CRASH_DUMP_SECONDS=-1:
1338 A negative value causes the termination of the runtime system to
1339 wait indefinitely until the crash dump file has been completly
1340 written. This is the default if option -heart is not passed to
1341 erl and ERL_CRASH_DUMP_SECONDS is not set.
1342 See also heart(3).
1344 ERL_CRASH_DUMP_BYTES:
1346 This variable sets the maximum size of a crash dump file in bytes.
1347 The crash dump will be truncated if this limit is exceeded. If the
1348 variable is not set, no size limit is enforced by default. If the
1349 variable is set to 0, the runtime system does not even attempt to
1350 write a crash dump file.
1351 Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).
1353 ERL_AFLAGS:
1355 The content of this variable is added to the beginning of the com‐
1356 mand line for erl.
1357 Flag -extra is treated in a special way. Its scope ends at the end
1359 of the environment variable content. Arguments following an -extra
1360 flag are moved on the command line into section -extra, that is,
1361 the end of the command line following an -extra flag.
1362 ERL_ZFLAGS and ERL_FLAGS:
1364 The content of these variables are added to the end of the command
1365 line for erl.
1366 Flag -extra is treated in a special way. Its scope ends at the end
1368 of the environment variable content. Arguments following an -extra
1369 flag are moved on the command line into section -extra, that is,
1370 the end of the command line following an -extra flag.
1371 ERL_LIBS:
1373 Contains a list of additional library directories that the code
1374 server searches for applications and adds to the code path; see
1375 code(3).
1376 ERL_EPMD_ADDRESS:
1378 Can be set to a comma-separated list of IP addresses, in which case
1379 the epmd daemon listens only on the specified address(es) and on
1380 the loopback address (which is implicitly added to the list if it
1381 has not been specified).
1382 ERL_EPMD_PORT:
1384 Can contain the port number to use when communicating with epmd.
1385 The default port works fine in most cases. A different port can be
1386 specified to allow nodes of independent clusters to co-exist on the
1387 same host. All nodes in a cluster must use the same epmd port num‐
1388 ber.
1389
1391 On Unix systems, the Erlang runtime will interpret two types of sig‐
1392 nals.
1393 SIGUSR1:
1395 A SIGUSR1 signal forces a crash dump.
1396 SIGTERM:
1398 A SIGTERM will produce a stop message to the init process. This is
1399 equivalent to a init:stop/0 call.
1400 Introduced in ERTS 8.3 (Erlang/OTP 19.3)
1402 The signal SIGUSR2 is reserved for internal usage. No other signals are
1404 handled.
1405
1407 The standard Erlang/OTP system can be reconfigured to change the
1408 default behavior on startup.
1409 The .erlang startup file:
1411 When Erlang/OTP is started, the system searches for a file named
1412 .erlang in the user's home directory.
1413 If an .erlang file is found, it is assumed to contain valid Erlang
1415 expressions. These expressions are evaluated as if they were input
1416 to the shell.
1417 A typical .erlang file contains a set of search paths, for example:
1419 io:format("executing user profile in HOME/.erlang\n",[]).
1421 code:add_path("/home/calvin/test/ebin").
1422 code:add_path("/home/hobbes/bigappl-1.2/ebin").
1423 io:format(".erlang rc finished\n",[]).
1424 user_default and shell_default:
1426 Functions in the shell that are not prefixed by a module name are
1427 assumed to be functional objects (funs), built-in functions (BIFs),
1428 or belong to the module user_default or shell_default.
1429 To include private shell commands, define them in a module
1431 user_default and add the following argument as the first line in
1432 the .erlang file:
1433 code:load_abs("..../user_default").
1435 erl:
1437 If the contents of .erlang are changed and a private version of
1438 user_default is defined, the Erlang/OTP environment can be custom‐
1439 ized. More powerful changes can be made by supplying command-line
1440 arguments in the startup script erl. For more information, see
1441 init(3).
1442
1444 epmd(1), erl_prim_loader(3), erts_alloc(3), init(3), application(3),
1445 auth(3), code(3), erl_boot_server(3), heart(3), net_kernel(3), make(3)
1446Ericsson AB erts 10.7.1 erl(1)