Node.js

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# Command Line Options#

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.

To view this documentation as a manual page in a terminal, run `man node`.

## Synopsis#

`node [options] [V8 options] [script.js | -e "script" | -] [--] [arguments]`

`node debug [script.js | -e "script" | <host>:<port>] …`

`node --v8-options`

Execute without arguments to start the REPL.

For more info about `node debug`, please see the debugger documentation.

## Options#

### `-`#

Added in: v8.0.0

Alias for stdin, analogous to the use of - in other command line utilities, meaning that the script will be read from stdin, and the rest of the options are passed to that script.

### `--`#

Added in: v6.11.0

Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument will be used as a script filename.

### `--abort-on-uncaught-exception`#

Added in: v0.10

Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as `lldb`, `gdb`, and `mdb`).

If this flag is passed, the behavior can still be set to not abort through `process.setUncaughtExceptionCaptureCallback()` (and through usage of the `domain` module that uses it).

### `--enable-fips`#

Added in: v6.0.0

Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with `./configure --openssl-fips`.)

### `--experimental-modules`#

Added in: v8.5.0

Enable experimental ES module support and caching modules.

### `--experimental-repl-await`#

Added in: v10.0.0

Enable experimental top-level `await` keyword support in REPL.

### `--experimental-vm-modules`#

Added in: v9.6.0

Enable experimental ES Module support in the `vm` module.

### `--experimental-worker`#

Added in: v10.5.0

Enable experimental worker threads using the `worker_threads` module.

### `--force-fips`#

Added in: v6.0.0

Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as `--enable-fips`.)

### `--icu-data-dir=file`#

Added in: v0.11.15

Specify ICU data load path. (Overrides `NODE_ICU_DATA`.)

### `--inspect-brk[=[host:]port]`#

Added in: v7.6.0

Activate inspector on `host:port` and break at start of user script. Default `host:port` is `127.0.0.1:9229`.

### `--inspect-port=[host:]port`#

Added in: v7.6.0

Set the `host:port` to be used when the inspector is activated. Useful when activating the inspector by sending the `SIGUSR1` signal.

Default host is `127.0.0.1`.

### `--inspect[=[host:]port]`#

Added in: v6.3.0

Activate inspector on `host:port`. Default is `127.0.0.1:9229`.

V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome DevTools Protocol.

### `--napi-modules`#

Added in: v7.10.0

This option is a no-op. It is kept for compatibility.

### `--no-deprecation`#

Added in: v0.8.0

Silence deprecation warnings.

### `--no-force-async-hooks-checks`#

Added in: v9.0.0

Disables runtime checks for `async_hooks`. These will still be enabled dynamically when `async_hooks` is enabled.

### `--no-warnings`#

Added in: v6.0.0

Silence all process warnings (including deprecations).

### `--openssl-config=file`#

Added in: v6.9.0

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with `./configure --openssl-fips`.

### `--pending-deprecation`#

Added in: v8.0.0

Emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

### `--preserve-symlinks`#

Added in: v6.3.0

Instructs the module loader to preserve symbolic links when resolving and caching modules.

By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if `moduleA` attempts to require `moduleB` as a peer dependency:

    {appDir}
     ├── app
     │   ├── index.js
     │   └── node_modules
     │       ├── moduleA -> {appDir}/moduleA
     │       └── moduleB
     │           ├── index.js
     │           └── package.json
     └── moduleA
         ├── index.js
         └── package.json

The `--preserve-symlinks` command line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found.

Note, however, that using `--preserve-symlinks` can have other side effects. Specifically, symbolically linked native modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown).

The `--preserve-symlinks` flag does not apply to the main module, which allows `node --preserve-symlinks node_module/.bin/<foo>` to work. To apply the same behavior for the main module, also use `--preserve-symlinks-main`.

### `--preserve-symlinks-main`#

Added in: v10.2.0

Instructs the module loader to preserve symbolic links when resolving and caching the main module (`require.main`).

This flag exists so that the main module can be opted-in to the same behavior that `--preserve-symlinks` gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions.

Note that `--preserve-symlinks-main` does not imply `--preserve-symlinks`; it is expected that `--preserve-symlinks-main` will be used in addition to `--preserve-symlinks` when it is not desirable to follow symlinks before resolving relative paths.

See `--preserve-symlinks` for more information.

### `--prof`#

Added in: v2.0.0

Generate V8 profiler output.

### `--prof-process`#

Added in: v5.2.0

Process V8 profiler output generated using the V8 option `--prof`.

### `--redirect-warnings=file`#

Added in: v8.0.0

Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.

### `--throw-deprecation`#

Added in: v0.11.14

Throw errors for deprecations.

### `--tls-cipher-list=list`#

Added in: v4.0.0

Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default).

### `--trace-deprecation`#

Added in: v0.8.0

Print stack traces for deprecations.

### `--trace-event-categories`#

Added in: v7.7.0

A comma separated list of categories that should be traced when trace event tracing is enabled using `--trace-events-enabled`.

### `--trace-event-file-pattern`#

Added in: v9.8.0

Template string specifying the filepath for the trace event data, it supports `${rotation}` and `${pid}`.

### `--trace-events-enabled`#

Added in: v7.7.0

Enables the collection of trace event tracing information.

### `--trace-sync-io`#

Added in: v2.1.0

Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.

### `--trace-warnings`#

Added in: v6.0.0

Print stack traces for process warnings (including deprecations).

### `--track-heap-objects`#

Added in: v2.4.0

Track heap object allocations for heap snapshots.

### `--use-bundled-ca`, `--use-openssl-ca`#

Added in: v6.11.0

Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store. The default store is selectable at build-time.

The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.

Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.

See `SSL_CERT_DIR` and `SSL_CERT_FILE`.

### `--v8-options`#

Added in: v0.1.3

Print V8 command line options.

V8 options allow words to be separated by both dashes (`-`) or underscores (`_`).

For example, `--stack-trace-limit` is equivalent to `--stack_trace_limit`.

### `--v8-pool-size=num`#

Added in: v5.10.0

Set V8's thread pool size which will be used to allocate background jobs.

If set to `0` then V8 will choose an appropriate size of the thread pool based on the number of online processors.

If the value provided is larger than V8's maximum, then the largest value will be chosen.

### `--zero-fill-buffers`#

Added in: v6.0.0

Automatically zero-fills all newly allocated `Buffer` and `SlowBuffer` instances.

### `-c`, `--check`#

History

Version | Changes
--- | ---
v10.0.0 | The `--require` option is now supported when checking a file.
v5.0.0, v4.2.0 | Added in: v5.0.0, v4.2.0

Syntax check the script without executing.

### `-e`, `--eval "script"`#

History

Version | Changes
--- | ---
v5.11.0 | Built-in libraries are now available as predefined variables.
v0.5.2 | Added in: v0.5.2

Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in `script`.

On Windows, using `cmd.exe` a single quote will not work correctly because it only recognizes double `"` for quoting. In Powershell or Git bash, both `'` and `"` are usable.

### `-h`, `--help`#

Added in: v0.1.3

Print node command line options. The output of this option is less detailed than this document.

### `-i`, `--interactive`#

Added in: v0.7.7

Opens the REPL even if stdin does not appear to be a terminal.

### `-p`, `--print "script"`#

History

Version | Changes
--- | ---
v5.11.0 | Built-in libraries are now available as predefined variables.
v0.6.4 | Added in: v0.6.4

Identical to `-e` but prints the result.

### `-r`, `--require module`#

Added in: v1.6.0

Preload the specified module at startup.

Follows `require()`'s module resolution rules. `module` may be either a path to a file, or a node module name.

### `-v`, `--version`#

Added in: v0.1.3

Print node's version.

## Environment Variables#

### `NODE_DEBUG=module[,…]`#

Added in: v0.1.32

`','`-separated list of core modules that should print debug information.

### `NODE_DISABLE_COLORS=1`#

Added in: v0.3.0

When set to `1` colors will not be used in the REPL.

### `NODE_EXTRA_CA_CERTS=file`#

Added in: v7.3.0

When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in `file`. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with `process.emitWarning()` if the file is missing or malformed, but any errors are otherwise ignored.

Note that neither the well known nor extra certificates are used when the `ca` options property is explicitly specified for a TLS or HTTPS client or server.

### `NODE_ICU_DATA=file`#

Added in: v0.11.15

Data path for ICU (`Intl` object) data. Will extend linked-in data when compiled with small-icu support.

### `NODE_NO_WARNINGS=1`#

Added in: v6.11.0

When set to `1`, process warnings are silenced.

### `NODE_OPTIONS=options...`#

Added in: v8.0.0

A space-separated list of command line options. `options...` are interpreted as if they had been specified on the command line before the actual command line (so they can be overridden). Node.js will exit with an error if an option that is not allowed in the environment is used, such as `-p` or a script file.

Node options that are allowed are:

- `--enable-fips`
- `--experimental-modules`
- `--experimental-repl-await`
- `--experimental-vm-modules`
- `--experimental-worker`
- `--force-fips`
- `--icu-data-dir`
- `--inspect`
- `--inspect-brk`
- `--inspect-port`
- `--loader`
- `--napi-modules`
- `--no-deprecation`
- `--no-force-async-hooks-checks`
- `--no-warnings`
- `--openssl-config`
- `--pending-deprecation`
- `--redirect-warnings`
- `--require`, `-r`
- `--throw-deprecation`
- `--tls-cipher-list`
- `--trace-deprecation`
- `--trace-event-categories`
- `--trace-event-file-pattern`
- `--trace-events-enabled`
- `--trace-sync-io`
- `--trace-warnings`
- `--track-heap-objects`
- `--use-bundled-ca`
- `--use-openssl-ca`
- `--v8-pool-size`
- `--zero-fill-buffers`

V8 options that are allowed are:

- `--abort-on-uncaught-exception`
- `--max-old-space-size`
- `--perf-basic-prof`
- `--perf-prof`
- `--stack-trace-limit`

### `NODE_PATH=path[:…]`#

Added in: v0.1.32

`':'`-separated list of directories prefixed to the module search path.

On Windows, this is a `';'`-separated list instead.

### `NODE_PENDING_DEPRECATION=1`#

Added in: v8.0.0

When set to `1`, emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

### `NODE_PRESERVE_SYMLINKS=1`#

Added in: v7.1.0

When set to `1`, instructs the module loader to preserve symbolic links when resolving and caching modules.

### `NODE_REDIRECT_WARNINGS=file`#

Added in: v8.0.0

When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the `--redirect-warnings=file` command-line flag.

### `NODE_REPL_HISTORY=file`#

Added in: v3.0.0

Path to the file used to store the persistent REPL history. The default path is `~/.node_repl_history`, which is overridden by this variable. Setting the value to an empty string (`''` or `' '`) disables persistent REPL history.

### `OPENSSL_CONF=file`#

Added in: v6.11.0

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with `./configure --openssl-fips`.

If the `--openssl-config` command line option is used, the environment variable is ignored.

### `SSL_CERT_DIR=dir`#

Added in: v7.7.0

If `--use-openssl-ca` is enabled, this overrides and sets OpenSSL's directory containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

### `SSL_CERT_FILE=file`#

Added in: v7.7.0

If `--use-openssl-ca` is enabled, this overrides and sets OpenSSL's file containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

### `UV_THREADPOOL_SIZE=size`#

Set the number of threads used in libuv's threadpool to `size` threads.

Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

- all `fs` APIs, other than the file watcher APIs and those that are explicitly synchronous
- `crypto.pbkdf2()`
- `crypto.randomBytes()`, unless it is used without a callback
- `crypto.randomFill()`
- `dns.lookup()`
- all `zlib` APIs, other than those that are explicitly synchronous

Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the `'UV_THREADPOOL_SIZE'` environment variable to a value greater than `4` (its current default value). For more information, see the libuv threadpool documentation.