erl

19962010 Ericsson AB. All Rights Reserved. The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. erl erl.xml

erl The Erlang Emulator

The program starts an Erlang runtime system. The exact details (for example, whether is a script or a program and which other programs it calls) are system-dependent.

Windows users probably wants to use the program instead, which runs in its own window with scrollbars and supports command-line editing. The program on Windows provides no line editing in its shell, and on Windows 95 there is no way to scroll back to text which has scrolled off the screen. The program must be used, however, in pipelines or if you want to redirect standard input or output.

As of ERTS version 5.8 (OTP-R14A) the runtime system will by default bind schedulers to logical processors using the default_bind bind type if the amount of schedulers are at least equal to the amount of logical processors configured, binding of schedulers is supported, and a CPU topology is available at startup.

If the Erlang runtime system is the only operating system process that binds threads to logical processors, this improves the performance of the runtime system. However, if other operating system processes (as for example another Erlang runtime system) also bind threads to logical processors, there might be a performance penalty instead. If this is the case you, are are advised to unbind the schedulers using the +sbtu command line argument, or by invoking erlang:system_flag(scheduler_bind_type, unbound).

erl <arguments> Start an Erlang runtime system

Starts an Erlang runtime system.

The arguments can be divided into emulator flags, flags and plain arguments:

Any argument starting with the character is interpreted as an emulator flag.

As indicated by the name, emulator flags controls the behavior of the emulator.

Any argument starting with the character (hyphen) is interpreted as a flag which should be passed to the Erlang part of the runtime system, more specifically to the system process, see init(3).

The process itself interprets some of these flags, the init flags. It also stores any remaining flags, the user flags. The latter can be retrieved by calling .

It can be noted that there are a small number of "-" flags which now actually are emulator flags, see the description below.

Plain arguments are not interpreted in any way. They are also stored by the process and can be retrieved by calling . Plain arguments can occur before the first flag, or after a flag. Additionally, the flag causes everything that follows to become plain arguments.

Example:

% erl +W w -sname arnie +R 9 -s my_init -extra +bertie
(arnie@host)1> init:get_argument(sname).
{ok,[["arnie"]]}
(arnie@host)2> init:get_plain_arguments().
["+bertie"]

Here and are emulator flags. is an init flag, interpreted by . is a user flag, stored by . It is read by Kernel and will cause the Erlang runtime system to become distributed. Finally, everything after (that is, ) is considered as plain arguments.

% erl -myflag 1
1> init:get_argument(myflag).
{ok,[["1"]]}
2> init:get_plain_arguments().
[]

Here the user flag is passed to and stored by the process. It is a user defined flag, presumably used by some user defined application.

Flags

In the following list, init flags are marked (init flag). Unless otherwise specified, all other flags are user flags, for which the values can be retrieved by calling . Note that the list of user flags is not exhaustive, there may be additional, application specific flags which instead are documented in the corresponding application documentation.

(init flag)

Everything following up to the next flag ( or ) is considered plain arguments and can be retrieved using .

Sets the application configuration parameter to the value for the application , see app(4) and application(3).

Command line arguments are read from the file . The arguments read from the file replace the '' flag on the resulting command line.

The file should be a plain text file and may contain comments and command line arguments. A comment begins with a # character and continues until next end of line character. Backslash (\\) is used as quoting character. All command line arguments accepted by are allowed, also the flag. Be careful not to cause circular dependencies between files containing the flag, though.

The flag is treated specially. Its scope ends at the end of the file. Arguments following an flag are moved on the command line into the section, i.e. the end of the command line following after an flag.

The initial Erlang shell does not read user input until the system boot procedure has been completed (Erlang 5.4 and later). This flag disables the start synchronization feature and lets the shell start in parallel with the rest of the system.

Specifies the name of the boot file, , which is used to start the system. See init(3). Unless contains an absolute path, the system searches for in the current and directories.

Defaults to .

If the boot script contains a path variable other than , this variable is expanded to . Used when applications are installed in another directory than , see systools:make_script/1,2.

Enables the code path cache of the code server, see code(3).

Compiles the specified modules and then terminates (with non-zero exit code if the compilation of some file did not succeed). Implies . Not recommended - use erlc instead.

Specifies the name of a configuration file, , which is used to configure applications. See app(4) and application(3).

If this flag is present, will not maintain a fully connected network of distributed Erlang nodes, and then global name registration cannot be used. See global(3).

Obsolete flag without any effect and common misspelling for . Use instead.

Starts the Erlang runtime system detached from the system console. Useful for running daemons and backgrounds processes.

Useful for debugging. Prints out the actual arguments sent to the emulator.

Sets the host OS environment variable to the value for the Erlang runtime system. Example:

% erl -env DISPLAY gin:0

In this example, an Erlang runtime system is started with the environment variable set to .

(init flag)

Makes evaluate the expression , see init(3).

(init flag)

Everything following is considered plain arguments and can be retrieved using .

Starts heart beat monitoring of the Erlang runtime system. See heart(3).

Starts the Erlang runtime system as a hidden node, if it is run as a distributed node. Hidden nodes always establish hidden connections to all other nodes except for nodes in the same global group. Hidden connections are not published on either of the connected nodes, i.e. neither of the connected nodes are part of the result from on the other node. See also hidden global groups, global_group(3).

Specifies the IP addresses for the hosts on which Erlang boot servers are running, see erl_boot_server(3). This flag is mandatory if the flag is present.

The IP addresses must be given in the standard form (four decimal numbers separated by periods, for example . Hosts names are not acceptable, but a broadcast address (preferably limited to the local network) is.

Specifies the identity of the Erlang runtime system. If it is run as a distributed node, must be identical to the name supplied together with the or flag.

Makes write some debug information while interpreting the boot script.

(emulator flag)

Selects an instrumented Erlang runtime system (virtual machine) to run, instead of the ordinary one. When running an instrumented runtime system, some resource usage data can be obtained and analysed using the module . Functionally, it behaves exactly like an ordinary Erlang runtime system.

Specifies the method used by to load Erlang modules into the system. See erl_prim_loader(3). Two methods are supported, and . means use the local file system, this is the default. means use a boot server on another machine, and the , and flags must be specified as well. If is something else, the user supplied port program is started.

Makes the Erlang runtime system invoke in the current working directory and then terminate. See make(3). Implies .

Displays the manual page for the Erlang module . Only supported on Unix.

Indicates if the system should load code dynamically (), or if all code should be loaded during system initialization (), see code(3). Defaults to .

Makes the Erlang runtime system into a distributed node. This flag invokes all network servers necessary for a node to become distributed. See net_kernel(3). It is also ensured that runs on the current host before Erlang is started. See epmd(1).

The name of the node will be , where is the fully qualified host name of the current host. For short names, use the flag instead.

Ensures that the Erlang runtime system never tries to read any input. Implies .

Starts an Erlang runtime system with no shell. This flag makes it possible to have the Erlang runtime system as a component in a series of UNIX pipes.

Disables the sticky directory facility of the Erlang code server, see code(3).

Invokes the old Erlang shell from Erlang 3.3. The old shell can still be used.

Adds the specified directories to the beginning of the code path, similar to . See code(3). As an alternative to -pa, if several directories are to be prepended to the code and the directories have a common parent directory, that parent directory could be specified in the ERL_LIBS environment variable. See code(3).

Adds the specified directories to the end of the code path, similar to . See code(3).

Starts Erlang with a remote shell connected to .

Specifies an alternative to for starting a slave node on a remote host. See slave(3).

(init flag)

Makes call the specified function. defaults to . If no arguments are provided, the function is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list as argument. All arguments are passed as strings. See init(3).

(init flag)

Sets the magic cookie of the node to , see erlang:set_cookie/2.

Specifies how long time (in milliseconds) the process is allowed to spend shutting down the system. If ms have elapsed, all processes still existing are killed. Defaults to .

Makes the Erlang runtime system into a distributed node, similar to , but the host name portion of the node name will be the short name, not fully qualified.

This is sometimes the only way to run distributed Erlang if the DNS (Domain Name System) is not running. There can be no communication between nodes running with the flag and those running with the flag, as node names must be unique in distributed Erlang systems.

-smp enable and -smp starts the Erlang runtime system with SMP support enabled. This may fail if no runtime system with SMP support is available. -smp auto starts the Erlang runtime system with SMP support enabled if it is available and more than one logical processor are detected. -smp disable starts a runtime system without SMP support. By default -smp auto will be used unless a conflicting parameter has been passed, then -smp disable will be used. Currently only the -hybrid parameter conflicts with -smp auto.

NOTE: The runtime system with SMP support will not be available on all supported platforms. See also the +S flag.

(emulator flag)

Makes the emulator print out its version number. The same as .

Emulator Flags

invokes the code for the Erlang emulator (virtual machine), which supports the following flags:

Suggested stack size, in kilowords, for threads in the async-thread pool. Valid range is 16-8192 kilowords. The default suggested stack size is 16 kilowords, i.e, 64 kilobyte on 32-bit architectures. This small default size has been chosen since the amount of async-threads might be quite large. The default size is enough for drivers delivered with Erlang/OTP, but might not be sufficiently large for other dynamically linked in drivers that use the driver_async() functionality. Note that the value passed is only a suggestion, and it might even be ignored on some platforms.

Sets the number of threads in async thread pool, valid range is 0-1024. Default is 0.

The option makes interrupt the current shell instead of invoking the emulator break handler. The option (same as specifying without an extra option) disables the break handler. The option makes the emulator ignore any break signal.

If the option is used with on Unix, will restart the shell process rather than interrupt it.

Note that on Windows, this flag is only applicable for , not (). Note also that is used instead of on Windows.

Disable compensation for sudden changes of system time.

Normally, will not immediately reflect sudden changes in the system time, in order to keep timers (including ) working. Instead, the time maintained by is slowly adjusted towards the new system time. (Slowly means in one percent adjustments; if the time is off by one minute, the time will be adjusted in 100 minutes.)

When the option is given, this slow adjustment will not take place. Instead will always reflect the current system time. Note that timers are based on . If the system time jumps, timers then time out at the wrong time.

If the emulator detects an internal error (or runs out of memory), it will by default generate both a crash dump and a core dump. The core dump will, however, not be very useful since the content of process heaps is destroyed by the crash dump generation.

The +d option instructs the emulator to only produce a core dump and no crash dump if an internal error is detected.

Calling erlang:halt/1 with a string argument will still produce a crash dump.

Sets the default heap size of processes to the size .

Sets the default binary virtual heap size of processes to the size .

Enables or disables the kernel poll functionality if the emulator supports it. Default is (disabled). If the emulator does not support kernel poll, and the flag is passed to the emulator, a warning is issued at startup.

Enables auto load tracing, displaying info while loading code.

Memory allocator specific flags, see erts_alloc(3) for further information.

Sets the maximum number of concurrent processes for this system. must be in the range 16..134217727. Default is 32768.

Sets the compatibility mode.

The distribution mechanism is not backwards compatible by default. This flags sets the emulator in compatibility mode with an earlier Erlang/OTP release . The release number must be in the range ]]>. This limits the emulator, making it possible for it to communicate with Erlang nodes (as well as C- and Java nodes) running that earlier release.

For example, an R10 node is not automatically compatible with an R9 node, but R10 nodes started with the flag can co-exist with R9 nodes in the same distributed Erlang system, they are R9-compatible.

Note: Make sure all nodes (Erlang-, C-, and Java nodes) of a distributed Erlang system is of the same Erlang/OTP release, or from two different Erlang/OTP releases X and Y, where all Y nodes have compatibility mode X.

For example: A distributed Erlang system can consist of R10 nodes, or of R9 nodes and R9-compatible R10 nodes, but not of R9 nodes, R9-compatible R10 nodes and "regular" R10 nodes, as R9 and "regular" R10 nodes are not compatible.

Force ets memory block to be moved on realloc.

Limits the amount of reader groups used by read/write locks optimized for read operations in the Erlang runtime system. By default the reader groups limit equals 8.

When the amount of schedulers is less than or equal to the reader groups limit, each scheduler has its own reader group. When the amount of schedulers is larger than the reader groups limit, schedulers share reader groups. Shared reader groups degrades read lock and read unlock performance while a large amount of reader groups degrades write lock performance, so the limit is a tradeoff between performance for read operations and performance for write operations. Each reader group currently consumes 64 byte in each read/write lock. Also note that a runtime system using shared reader groups benefits from binding schedulers to logical processors, since the reader groups are distributed better between schedulers.

Sets the amount of scheduler threads to create and scheduler threads to set online when SMP support has been enabled. Valid range for both values are 1-1024. If the Erlang runtime system is able to determine the amount of logical processors configured and logical processors available, Schedulers will default to logical processors configured, and SchedulersOnline will default to logical processors available; otherwise, the default values will be 1. Schedulers may be omitted if :SchedulerOnline is not and vice versa. The amount of schedulers online can be changed at run time via erlang:system_flag(schedulers_online, SchedulersOnline).

This flag will be ignored if the emulator doesn't have SMP support enabled (see the -smp flag).

Scheduling specific flags.

+sbt BindType

Set scheduler bind type. Currently valid BindTypes:

Same as erlang:system_flag(scheduler_bind_type, unbound).

Same as erlang:system_flag(scheduler_bind_type, no_spread).

Same as erlang:system_flag(scheduler_bind_type, thread_spread).

Same as erlang:system_flag(scheduler_bind_type, processor_spread).

Same as erlang:system_flag(scheduler_bind_type, spread).

nnts

Same as erlang:system_flag(scheduler_bind_type, no_node_thread_spread).

nnps

Same as erlang:system_flag(scheduler_bind_type, no_node_processor_spread).

tnnps

Same as erlang:system_flag(scheduler_bind_type, thread_no_node_processor_spread).

Same as erlang:system_flag(scheduler_bind_type, default_bind).

Binding of schedulers is currently only supported on newer Linux, Solaris, FreeBSD, and Windows systems.

If no CPU topology is available when the +sbt flag is processed and BindType is any other type than u, the runtime system will fail to start. CPU topology can be defined using the +sct flag. Note that the +sct flag may have to be passed before the +sbt flag on the command line (in case no CPU topology has been automatically detected).

The runtime system will by default bind schedulers to logical processors using the default_bind bind type if the amount of schedulers are at least equal to the amount of logical processors configured, binding of schedulers is supported, and a CPU topology is available at startup.

NOTE: If the Erlang runtime system is the only operating system process that binds threads to logical processors, this improves the performance of the runtime system. However, if other operating system processes (as for example another Erlang runtime system) also bind threads to logical processors, there might be a performance penalty instead. If this is the case you, are advised to unbind the schedulers using the +sbtu command line argument, or by invoking erlang:system_flag(scheduler_bind_type, unbound).

For more information, see erlang:system_flag(scheduler_bind_type, SchedulerBindType).

+sct CpuTopology = integer(); when 0 =< =< 65535]]> = -]]> = | ]]> = , | ]]> = L]]> = T | t]]> = C | c]]> = P | p]]> = N | n]]> = | ]]> : | ]]>

Upper-case letters signify real identifiers and lower-case letters signify fake identifiers only used for description of the topology. Identifiers passed as real identifiers may be used by the runtime system when trying to access specific hardware and if they are not correct the behavior is undefined. Faked logical CPU identifiers are not accepted since there is no point in defining the CPU topology without real logical CPU identifiers. Thread, core, processor, and node identifiers may be left out. If left out, thread id defaults to t0, core id defaults to c0, processor id defaults to p0, and node id will be left undefined. Either each logical processor must belong to one and only one NUMA node, or no logical processors must belong to any NUMA nodes.

Both increasing and decreasing ]]>s are allowed.

NUMA node identifiers are system wide. That is, each NUMA node on the system have to have a unique identifier. Processor identifiers are also system wide. Core identifiers are processor wide. Thread identifiers are core wide.

The order of the identifier types imply the hierarchy of the CPU topology. Valid orders are either ]]>, or ]]>. That is, thread is part of a core which is part of a processor which is part of a NUMA node, or thread is part of a core which is part of a NUMA node which is part of a processor. A cpu topology can consist of both processor external, and processor internal NUMA nodes as long as each logical processor belongs to one and only one NUMA node. If ]]> is left out, its default position will be before ]]>. That is, the default is processor external NUMA nodes.

If a list of identifiers is used in an ]]>:

]]> have to be a list of identifiers. At least one other identifier type apart from ]]> also have to have a list of identifiers. All lists of identifiers have to produce the same amount of identifiers.

A simple example. A single quad core processor may be described this way:

% erl +sct L0-3c0-3
1> erlang:system_info(cpu_topology).
[{processor,[{core,{logical,0}},
             {core,{logical,1}},
             {core,{logical,2}},
             {core,{logical,3}}]}]

A little more complicated example. Two quad core processors. Each processor in its own NUMA node. The ordering of logical processors is a little weird. This in order to give a better example of identifier lists:

% erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1
1> erlang:system_info(cpu_topology).
[{node,[{processor,[{core,{logical,0}},
                    {core,{logical,1}},
                    {core,{logical,3}},
                    {core,{logical,2}}]}]},
 {node,[{processor,[{core,{logical,7}},
                    {core,{logical,4}},
                    {core,{logical,6}},
                    {core,{logical,5}}]}]}]

As long as real identifiers are correct it is okay to pass a CPU topology that is not a correct description of the CPU topology. When used with care this can actually be very useful. This in order to trick the emulator to bind its schedulers as you want. For example, if you want to run multiple Erlang runtime systems on the same machine, you want to reduce the amount of schedulers used and manipulate the CPU topology so that they bind to different logical CPUs. An example, with two Erlang runtime systems on a quad core machine:

% erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
% erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two

In this example each runtime system have two schedulers each online, and all schedulers online will run on different cores. If we change to one scheduler online on one runtime system, and three schedulers online on the other, all schedulers online will still run on different cores.

Note that a faked CPU topology that does not reflect how the real CPU topology looks like is likely to decrease the performance of the runtime system.

For more information, see erlang:system_flag(cpu_topology, CpuTopology).

+swt very_low|low|medium|high|very_high

Set scheduler wakeup threshold. Default is medium. The threshold determines when to wake up sleeping schedulers when more work than can be handled by currently awake schedulers exist. A low threshold will cause earlier wakeups, and a high threshold will cause later wakeups. Early wakeups will distribute work over multiple schedulers faster, but work will more easily bounce between schedulers.

NOTE: This flag may be removed or changed at any time without prior notice.

Suggested stack size, in kilowords, for scheduler threads. Valid range is 4-8192 kilowords. The default stack size is OS dependent.

Set the maximum number of atoms the VM can handle. Default is 1048576.

Enables modified timing and sets the modified timing level. Currently valid range is 0-9. The timing of the runtime system will change. A high level usually means a greater change than a low level. Changing the timing can be very useful for finding timing related bugs.

Currently, modified timing affects the following:

Process spawning

A process calling , , , or will be scheduled out immediately after completing the call. When higher modified timing levels are used, the caller will also sleep for a while after being scheduled out.

Context reductions The amount of reductions a process is a allowed to use before being scheduled out is increased or reduced. Input reductions The amount of reductions performed before checking I/O is increased or reduced.

NOTE: Performance will suffer when modified timing is enabled. This flag is only intended for testing and debugging. Also note that and trace messages will be lost when tracing on the spawn BIFs. This flag may be removed or changed at any time without prior notice.

Makes the emulator print out its version number.

Verbose.

Sets the mapping of warning messages for . Messages sent to the error logger using one of the warning routines can be mapped either to errors (default), warnings (), or info reports (). The current mapping can be retrieved using . See error_logger(3) for further information.

Environment variables

If the emulator needs to write a crash dump, the value of this variable will be the file name of the crash dump file. If the variable is not set, the name of the crash dump file will be in the current directory.

Unix systems: If the emulator needs to write a crash dump, it will use the value of this variable to set the nice value for the process, thus lowering its priority. The allowable range is 1 through 39 (higher values will be replaced with 39). The highest value, 39, will give the process the lowest priority.

Unix systems: This variable gives the number of seconds that the emulator will be allowed to spend writing a crash dump. When the given number of seconds have elapsed, the emulator will be terminated by a SIGALRM signal.

The content of this environment variable will be added to the beginning of the command line for .

The flag is treated specially. Its scope ends at the end of the environment variable content. Arguments following an flag are moved on the command line into the section, i.e. the end of the command line following after an flag.

and

The content of these environment variables will be added to the end of the command line for .

This environment variable contains a list of additional library directories that the code server will search for applications and add to the code path. See code(3).

This environment variable can contain the port number to use when communicating with epmd. The default port will work fine in most cases. A different port can be specified to allow nodes of independent clusters to co-exist on the same host. All nodes in a cluster must use the same epmd port number.