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 flag '' on the resulting command line.

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

The flag is treated in special way. Its scope ends at the end of the file. Arguments following an flag are moved on the command line into the section, that is, 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/OTP 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 in SASL.

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, does 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. Implies .

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

Start an emulator of a different type. For example, to start the lock-counter emualator, use -emu_type lcnt. (The emulator must already be built. Use the configure option --enable-lock-counter to build the lock-counter 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 environment variable set to .

Configures the module responsible to communicate to epmd. Defaults to erl_epmd.

Makes evaluate the expression ; see init(3).

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

Starts heartbeat 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 any of the connected nodes, that is, none 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 flag is present.

The IP addresses must be specified 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 flag or .

Makes write some debug information while interpreting the boot script.

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 analyzed 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:

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.

Modules are auto loaded when they are first referenced if the runtime system runs in mode, which is the default. In mode modules are not auto loaded. The latter is recommended when the boot script preloads all modules, as conventionally happens in OTP releases. See code(3)

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).and the -start_epmd option.

The node name will be , where is the fully qualified host name of the current host. For short names, use 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/OTP 3.3. The old shell can still be used.

Adds the specified directories to the beginning of the code path, similar to . Note that the order of the given directories will be reversed in the resulting path.

As an alternative to -pa, if several directories are to be prepended to the code path and the directories have a common parent directory, that parent directory can be specified in environment variable ERL_LIBS; see code(3).

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

Replaces the path specified in the boot script; see script(4).

Starts Erlang with a remote shell connected to .

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

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).

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 atoms. See init(3).

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 milliseconds 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 Domain Name System (DNS) is not running. No communication can exist between nodes running with flag and those running with flag , as node names must be unique in distributed Erlang systems.

Specifies whether Erlang should start epmd on startup. By default this is true, but if you prefer to start epmd manually, set this to false.

This only applies if Erlang is started as a distributed node, i.e. if -name or -sname is specified. Otherwise, epmd is not started even if -start_epmd true is given.

Note that a distributed node will fail to start if epmd is not running.

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

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, that is, 64 kilobyte on 32-bit architectures. This small default size has been chosen because the number of async threads can be large. The default size is enough for drivers delivered with Erlang/OTP, but might not be large enough for other dynamically linked-in drivers that use the driver_async() functionality. Notice that the value passed is only a suggestion, and it can even be ignored on some platforms.

Sets the number of threads in async thread pool. Valid range is 0-1024. Defaults to 1.

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

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

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

Enables or disables time correction:

For backward compatibility, the boolean value can be omitted. This is interpreted as +c false.

Sets time warp mode:

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

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

Calling erlang:halt/1 with a string argument still produces a crash dump. On Unix systems, sending an emulator process a SIGUSR1 signal also forces a crash dump.

Sets the maximum number of ETS tables.

Forces option compressed on all ETS tables. Only intended for test and evaluation.

The virtual machine works with filenames as if they are encoded using the ISO Latin-1 encoding, disallowing Unicode characters with code points > 255.

For more information about Unicode filenames, see section Unicode Filenames in the STDLIB User's Guide. Notice that this value also applies to command-line parameters and environment variables (see section Unicode in Environment and Parameters in the STDLIB User's Guide).

The virtual machine works with filenames as if they are encoded using UTF-8 (or some other system-specific Unicode encoding). This is the default on operating systems that enforce Unicode encoding, that is, Windows and MacOS X.

The +fnu switch can be followed by w, i, or e to control how wrongly encoded filenames are to be reported:

Notice that file:read_link/1 always returns an error if the link points to an invalid filename.

For more information about Unicode filenames, see section Unicode Filenames in the STDLIB User's Guide. Notice that this value also applies to command-line parameters and environment variables (see section Unicode in Environment and Parameters in the STDLIB User's Guide).

Selection between +fnl and +fnu is done based on the current locale settings in the OS. This means that if you have set your terminal for UTF-8 encoding, the filesystem is expected to use the same encoding for filenames. This is default on all operating systems, except MacOS X and Windows.

The +fna switch can be followed by w, i, or e. This has effect if the locale settings cause the behavior of +fnu to be selected; see the description of +fnu above. If the locale settings cause the behavior of +fnl to be selected, then w, i, or e have no effect.

For more information about Unicode filenames, see section Unicode Filenames in the STDLIB User's Guide. Notice that this value also applies to command-line parameters and environment variables (see section Unicode in Environment and Parameters in the STDLIB User's Guide).

Sets the default heap size of processes to the size .

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

Sets the default maximum heap size of processes to the size . Defaults to 0, which means that no maximum heap size is used. For more information, see process_flag(max_heap_size, MaxHeapSize).

Sets whether to send an error logger message or not for processes reaching the maximum heap size. Defaults to true. For more information, see process_flag(max_heap_size, MaxHeapSize).

Sets whether to kill processes reaching the maximum heap size or not. Default to true. For more information, see process_flag(max_heap_size, MaxHeapSize).

Sets the initial process dictionary size of processes to the size .

Sets the default value for process flag message_queue_data. Defaults to on_heap. If +hmqd is not passed, on_heap will be the default. For more information, see process_flag(message_queue_data, MQD).

Sets the number of IO pollsets to use when polling for I/O. This option is only used on platforms that support concurrent updates of a pollset, otherwise the same number of pollsets are used as IO poll threads. The default is 1.

Sets the number of IO poll threads to use when polling for I/O. The maximum number of poll threads allowed is 1024. The default is 1.

A good way to check if more IO poll threads are needed is to use microstate accounting and see what the load of the IO poll thread is. If it is high it could be a good idea to add more threads.

Similar to +IOp but uses percentages to set the number of IO pollsets to create, based on the number of poll threads configured. If both +IOPp and +IOp are used, +IOPp is ignored.

Similar to +IOt but uses percentages to set the number of IO poll threads to create, based on the number of schedulers configured. If both +IOPt and +IOt are used, +IOPt is ignored.

Enables autoload tracing, displaying information while loading code.

Prevents loading information about source filenames and line numbers. This saves some memory, but exceptions do not contain information about the filenames and line numbers.

Memory allocator-specific flags. For more information, see erts_alloc(3).

Sets the range of characters that the system considers printable in heuristic detection of strings. This typically affects the shell, debugger, and io:format functions (when ~tp is used in the format string).

Two values are supported for Range:

See also io:printable_range/0 in STDLIB.

Sets the maximum number of simultaneously existing processes for this system if a Number is passed as value. Valid range for Number is [1024-134217727]

NOTE: The actual maximum chosen may be much larger than the Number passed. Currently the runtime system often, but not always, chooses a value that is a power of 2. This might, however, be changed in the future. The actual value chosen can be checked by calling erlang:system_info(process_limit).

The default value is 262144

Sets the maximum number of simultaneously existing ports for this system if a Number is passed as value. Valid range for Number is [1024-134217727]

NOTE: The actual maximum chosen may be much larger than the actual Number passed. Currently the runtime system often, but not always, chooses a value that is a power of 2. This might, however, be changed in the future. The actual value chosen can be checked by calling erlang:system_info(port_limit).

The default value used is normally 65536. However, if the runtime system is able to determine maximum amount of file descriptors that it is allowed to open and this value is larger than 65536, the chosen value will increased to a value larger or equal to the maximum amount of file descriptors that can be opened.

On Windows the default value is set to 8196 because the normal OS limitations are set higher than most machines can handle.

Sets the compatibility mode.

The distribution mechanism is not backward compatible by default. This flag sets the emulator in compatibility mode with an earlier Erlang/OTP release . The release number must be in the range -2..]]>. 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.

Forces ETS memory block to be moved on realloc.

Limits the number of reader groups used by read/write locks optimized for read operations in the Erlang runtime system. By default the reader groups limit is 64.

When the number of schedulers is less than or equal to the reader groups limit, each scheduler has its own reader group. When the number of schedulers is larger than the reader groups limit, schedulers share reader groups. Shared reader groups degrade read lock and read unlock performance while many reader groups degrade write lock performance. So, the limit is a tradeoff between performance for read operations and performance for write operations. Each reader group consumes 64 byte in each read/write lock.

Notice that a runtime system using shared reader groups benefits from binding schedulers to logical processors, as the reader groups are distributed better between schedulers.

Sets the number of scheduler threads to create and scheduler threads to set online. The maximum for both values is 1024. If the Erlang runtime system is able to determine the number of logical processors configured and logical processors available, Schedulers defaults to logical processors configured, and SchedulersOnline defaults to logical processors available; otherwise the default values are 1. Schedulers can be omitted if :SchedulerOnline is not and conversely. The number of schedulers online can be changed at runtime through erlang:system_flag(schedulers_online, SchedulersOnline).

If Schedulers or SchedulersOnline is specified as a negative number, the value is subtracted from the default number of logical processors configured or logical processors available, respectively.

Specifying value 0 for Schedulers or SchedulersOnline resets the number of scheduler threads or scheduler threads online, respectively, to its default value.

Similar to +S but uses percentages to set the number of scheduler threads to create, based on logical processors configured, and scheduler threads to set online, based on logical processors available. Specified values must be > 0. For example, +SP 50:25 sets the number of scheduler threads to 50% of the logical processors configured, and the number of scheduler threads online to 25% of the logical processors available. SchedulersPercentage can be omitted if :SchedulersOnlinePercentage is not and conversely. The number of schedulers online can be changed at runtime through erlang:system_flag(schedulers_online, SchedulersOnline).

This option interacts with +S settings. For example, on a system with 8 logical cores configured and 8 logical cores available, the combination of the options +S 4:4 +SP 50:25 (in either order) results in 2 scheduler threads (50% of 4) and 1 scheduler thread online (25% of 4).

Sets the number of dirty CPU scheduler threads to create and dirty CPU scheduler threads to set online. The maximum for both values is 1024, and each value is further limited by the settings for normal schedulers:

For details, see the +S and +SP. By default, the number of dirty CPU scheduler threads created equals the number of normal scheduler threads created, and the number of dirty CPU scheduler threads online equals the number of normal scheduler threads online. DirtyCPUSchedulers can be omitted if :DirtyCPUSchedulersOnline is not and conversely. The number of dirty CPU schedulers online can be changed at runtime through erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

The amount of dirty CPU schedulers is limited by the amount of normal schedulers in order to limit the effect on processes executing on ordinary schedulers. If the amount of dirty CPU schedulers was allowed to be unlimited, dirty CPU bound jobs would potentially starve normal jobs.

Similar to +SDcpu but uses percentages to set the number of dirty CPU scheduler threads to create and the number of dirty CPU scheduler threads to set online. Specified values must be > 0. For example, +SDPcpu 50:25 sets the number of dirty CPU scheduler threads to 50% of the logical processors configured and the number of dirty CPU scheduler threads online to 25% of the logical processors available. DirtyCPUSchedulersPercentage can be omitted if :DirtyCPUSchedulersOnlinePercentage is not and conversely. The number of dirty CPU schedulers online can be changed at runtime through erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

This option interacts with +SDcpu settings. For example, on a system with 8 logical cores configured and 8 logical cores available, the combination of the options +SDcpu 4:4 +SDPcpu 50:25 (in either order) results in 2 dirty CPU scheduler threads (50% of 4) and 1 dirty CPU scheduler thread online (25% of 4).

Sets the number of dirty I/O scheduler threads to create. Valid range is 0-1024. By default, the number of dirty I/O scheduler threads created is 10, same as the default number of threads in the async thread pool.

The amount of dirty IO schedulers is not limited by the amount of normal schedulers like the amount of dirty CPU schedulers. This since only I/O bound work is expected to execute on dirty I/O schedulers. If the user should schedule CPU bound jobs on dirty I/O schedulers, these jobs might starve ordinary jobs executing on ordinary schedulers.

Scheduling specific flags.

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

% 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}}]}]}]

% 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

Sets the maximum number of atoms the virtual machine can handle. Defaults to 1,048,576.

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

Modified timing affects the following:

Verbose.

Makes the emulator print its version number.

Sets the mapping of warning messages for . Messages sent to the error logger using one of the warning routines can be mapped to errors (), warnings (), or information reports (). Defaults to warnings. The current mapping can be retrieved using . For more information, see error_logger:warning_map/0 in Kernel.

Miscellaneous flags:

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

Unix systems: If the emulator needs to write a crash dump, it uses the value of this variable to set the nice value for the process, thus lowering its priority. Valid range is 1-39 (higher values are replaced with 39). The highest value, 39, gives the process the lowest priority.

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

See also heart(3).

This variable sets the maximum size of a crash dump file in bytes. The crash dump will be truncated if this limit is exceeded. If the variable is not set, no size limit is enforced by default. If the variable is set to 0, the runtime system does not even attempt to write a crash dump file.

Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).

The content of this variable is added to the beginning of the command line for .

Flag is treated in a special way. Its scope ends at the end of the environment variable content. Arguments following an flag are moved on the command line into section , that is, the end of the command line following an flag.

The content of these variables are added to the end of the command line for .

Flag is treated in a special way. Its scope ends at the end of the environment variable content. Arguments following an flag are moved on the command line into section , that is, the end of the command line following an flag.

Contains a list of additional library directories that the code server searches for applications and adds to the code path; see code(3).

Can be set to a comma-separated list of IP addresses, in which case the epmd daemon listens only on the specified address(es) and on the loopback address (which is implicitly added to the list if it has not been specified).

Can contain the port number to use when communicating with epmd. The default port works 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.

A SIGUSR1 signal forces a crash dump.

A SIGTERM will produce a stop message to the init process. This is equivalent to a init:stop/0 call.

Introduced in ERTS 8.3 (Erlang/OTP 19.3)

When Erlang/OTP is started, the system searches for a file named .erlang in the user's home directory.

If an .erlang file is found, it is assumed to contain valid Erlang expressions. These expressions are evaluated as if they were input to the shell.

A typical .erlang file contains a set of search paths, for example:

Functions in the shell that are not prefixed by a module name are assumed to be functional objects (funs), built-in functions (BIFs), or belong to the module user_default or shell_default.

To include private shell commands, define them in a module user_default and add the following argument as the first line in the .erlang file:

If the contents of .erlang are changed and a private version of user_default is defined, the Erlang/OTP environment can be customized. More powerful changes can be made by supplying command-line arguments in the startup script erl. For more information, see init(3).