node/doc/api/cli.md

# Command-line API

<!--introduced_in=v5.9.1-->

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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] [<program-entry-point> | -e "script" | -] [--] [arguments]`

`node inspect [<program-entry-point> | -e "script" | <host>:<port>] …`

`node --v8-options`

Execute without arguments to start the [REPL][].

For more info about `node inspect`, see the [debugger][] documentation.

## Program entry point

The program entry point is a specifier-like string. If the string is not an
absolute path, it's resolved as a relative path from the current working
directory. That path is then resolved by [CommonJS][] module loader. If no
corresponding file is found, an error is thrown.

If a file is found, its path will be passed to the [ECMAScript module loader][]
under any of the following conditions:

* The program was started with a command-line flag that forces the entry
  point to be loaded with ECMAScript module loader.
* The file has an `.mjs` extension.
* The file does not have a `.cjs` extension, and the nearest parent
  `package.json` file contains a top-level [`"type"`][] field with a value of
  `"module"`.

Otherwise, the file is loaded using the CommonJS module loader. See
[Modules loaders][] for more details.

### ECMAScript modules loader entry point caveat

When loading [ECMAScript module loader][] loads the program entry point, the `node`
command will only accept as input only files with `.js`, `.mjs`, or `.cjs`
extensions; and with `.wasm` extensions when
[`--experimental-wasm-modules`][] is enabled.

## Options

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                 Node.js options as well, in addition to V8 options.
-->

All options, including V8 options, allow words to be separated by both
dashes (`-`) or underscores (`_`). For example, `--pending-deprecation` is
equivalent to `--pending_deprecation`.

If an option that takes a single value (such as `--max-http-header-size`) is
passed more than once, then the last passed value is used. Options from the
command line take precedence over options passed through the [`NODE_OPTIONS`][]
environment variable.

### `-`

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

### `--`

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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 is used as a script filename.

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

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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
`node:domain` module that uses it).

### `--build-snapshot`

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> Stability: 1 - Experimental

Generates a snapshot blob when the process exits and writes it to
disk, which can be loaded later with `--snapshot-blob`.

When building the snapshot, if `--snapshot-blob` is not specified,
the generated blob will be written, by default, to `snapshot.blob`
in the current working directory. Otherwise it will be written to
the path specified by `--snapshot-blob`.

```console
$ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js

# Run snapshot.js to intialize the application and snapshot the
# state of it into snapshot.blob.
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js

$ echo "console.log(globalThis.foo)" > index.js

# Load the generated snapshot and start the application from index.js.
$ node --snapshot-blob snapshot.blob index.js
I am from the snapshot
```

The [`v8.startupSnapshot` API][] can be used to specify an entry point at
snapshot building time, thus avoiding the need of an additional entry
script at deserialization time:

```console
$ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
$ node --snapshot-blob snapshot.blob
I am from the snapshot
```

For more information, check out the [`v8.startupSnapshot` API][] documentation.

Currently the support for run-time snapshot is experimental in that:

1. User-land modules are not yet supported in the snapshot, so only
   one single file can be snapshotted. Users can bundle their applications
   into a single script with their bundler of choice before building
   a snapshot, however.
2. Only a subset of the built-in modules work in the snapshot, though the
   Node.js core test suite checks that a few fairly complex applications
   can be snapshotted. Support for more modules are being added. If any
   crashes or buggy behaviors occur when building a snapshot, please file
   a report in the [Node.js issue tracker][] and link to it in the
   [tracking issue for user-land snapshots][].

### `--completion-bash`

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Print source-able bash completion script for Node.js.

```console
$ node --completion-bash > node_bash_completion
$ source node_bash_completion
```

### `-C=condition`, `--conditions=condition`

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> Stability: 1 - Experimental

Enable experimental support for custom [conditional exports][] resolution
conditions.

Any number of custom string condition names are permitted.

The default Node.js conditions of `"node"`, `"default"`, `"import"`, and
`"require"` will always apply as defined.

For example, to run a module with "development" resolutions:

```console
$ node -C=development app.js
```

### `--cpu-prof`

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> Stability: 1 - Experimental

Starts the V8 CPU profiler on start up, and writes the CPU profile to disk
before exit.

If `--cpu-prof-dir` is not specified, the generated profile is placed
in the current working directory.

If `--cpu-prof-name` is not specified, the generated profile is
named `CPU.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.cpuprofile`.

```console
$ node --cpu-prof index.js
$ ls *.cpuprofile
CPU.20190409.202950.15293.0.0.cpuprofile
```

### `--cpu-prof-dir`

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> Stability: 1 - Experimental

Specify the directory where the CPU profiles generated by `--cpu-prof` will
be placed.

The default value is controlled by the
[`--diagnostic-dir`][] command-line option.

### `--cpu-prof-interval`

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-->

> Stability: 1 - Experimental

Specify the sampling interval in microseconds for the CPU profiles generated
by `--cpu-prof`. The default is 1000 microseconds.

### `--cpu-prof-name`

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> Stability: 1 - Experimental

Specify the file name of the CPU profile generated by `--cpu-prof`.

### `--diagnostic-dir=directory`

Set the directory to which all diagnostic output files are written.
Defaults to current working directory.

Affects the default output directory of:

* [`--cpu-prof-dir`][]
* [`--heap-prof-dir`][]
* [`--redirect-warnings`][]

### `--disable-proto=mode`

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Disable the `Object.prototype.__proto__` property. If `mode` is `delete`, the
property is removed entirely. If `mode` is `throw`, accesses to the
property throw an exception with the code `ERR_PROTO_ACCESS`.

### `--disallow-code-generation-from-strings`

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Make built-in language features like `eval` and `new Function` that generate
code from strings throw an exception instead. This does not affect the Node.js
`node:vm` module.

### `--dns-result-order=order`

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Set the default value of `verbatim` in [`dns.lookup()`][] and
[`dnsPromises.lookup()`][]. The value could be:

* `ipv4first`: sets default `verbatim` `false`.
* `verbatim`: sets default `verbatim` `true`.

The default is `verbatim` and [`dns.setDefaultResultOrder()`][] have higher
priority than `--dns-result-order`.

### `--enable-fips`

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Enable FIPS-compliant crypto at startup. (Requires Node.js to be built
against FIPS-compatible OpenSSL.)

### `--enable-source-maps`

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-->

Enable [Source Map v3][Source Map] support for stack traces.

When using a transpiler, such as TypeScript, stack traces thrown by an
application reference the transpiled code, not the original source position.
`--enable-source-maps` enables caching of Source Maps and makes a best
effort to report stack traces relative to the original source file.

Overriding `Error.prepareStackTrace` prevents `--enable-source-maps` from
modifying the stack trace.

Note, enabling source maps can introduce latency to your application
when `Error.stack` is accessed. If you access `Error.stack` frequently
in your application, take into account the performance implications
of `--enable-source-maps`.

### `--experimental-global-customevent`

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Expose the [CustomEvent Web API][] on the global scope.

### `--experimental-global-webcrypto`

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Expose the [Web Crypto API][] on the global scope.

### `--experimental-import-meta-resolve`

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Enable experimental `import.meta.resolve()` support.

### `--experimental-loader=module`

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                 `--experimental-loader`.
-->

Specify the `module` of a custom experimental [ECMAScript module loader][].
`module` may be any string accepted as an [`import` specifier][].

### `--experimental-network-imports`

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> Stability: 1 - Experimental

Enable experimental support for the `https:` protocol in `import` specifiers.

### `--experimental-policy`

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Use the specified file as a security policy.

### `--no-experimental-fetch`

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Disable experimental support for the [Fetch API][].

### `--no-experimental-repl-await`

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Use this flag to disable top-level await in REPL.

### `--experimental-shadow-realm`

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Use this flag to enable [ShadowRealm][] support.

### `--experimental-specifier-resolution=mode`

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Sets the resolution algorithm for resolving ES module specifiers. Valid options
are `explicit` and `node`.

The default is `explicit`, which requires providing the full path to a
module. The `node` mode enables support for optional file extensions and
the ability to import a directory that has an index file.

See [customizing ESM specifier resolution][] for example usage.

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

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

### `--experimental-wasi-unstable-preview1`

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                 `--experimental-wasi-unstable-preview1`.
-->

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-wasm-modules`

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Enable experimental WebAssembly module support.

### `--force-context-aware`

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Disable loading native addons that are not [context-aware][].

### `--force-fips`

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

### `--frozen-intrinsics`

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> Stability: 1 - Experimental

Enable experimental frozen intrinsics like `Array` and `Object`.

Only the root context is supported. There is no guarantee that
`globalThis.Array` is indeed the default intrinsic reference. Code may break
under this flag.

To allow polyfills to be added,
[`--require`][] and [`--import`][] both run before freezing intrinsics.

### `--force-node-api-uncaught-exceptions-policy`

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Enforces `uncaughtException` event on Node-API asynchronous callbacks.

To prevent from an existing add-on from crashing the process, this flag is not
enabled by default. In the future, this flag will be enabled by default to
enforce the correct behavior.

### `--heapsnapshot-near-heap-limit=max_count`

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> Stability: 1 - Experimental

Writes a V8 heap snapshot to disk when the V8 heap usage is approaching the
heap limit. `count` should be a non-negative integer (in which case
Node.js will write no more than `max_count` snapshots to disk).

When generating snapshots, garbage collection may be triggered and bring
the heap usage down. Therefore multiple snapshots may be written to disk
before the Node.js instance finally runs out of memory. These heap snapshots
can be compared to determine what objects are being allocated during the
time consecutive snapshots are taken. It's not guaranteed that Node.js will
write exactly `max_count` snapshots to disk, but it will try
its best to generate at least one and up to `max_count` snapshots before the
Node.js instance runs out of memory when `max_count` is greater than `0`.

Generating V8 snapshots takes time and memory (both memory managed by the
V8 heap and native memory outside the V8 heap). The bigger the heap is,
the more resources it needs. Node.js will adjust the V8 heap to accommodate
the additional V8 heap memory overhead, and try its best to avoid using up
all the memory available to the process. When the process uses
more memory than the system deems appropriate, the process may be terminated
abruptly by the system, depending on the system configuration.

```console
$ node --max-old-space-size=100 --heapsnapshot-near-heap-limit=3 index.js
Wrote snapshot to Heap.20200430.100036.49580.0.001.heapsnapshot
Wrote snapshot to Heap.20200430.100037.49580.0.002.heapsnapshot
Wrote snapshot to Heap.20200430.100038.49580.0.003.heapsnapshot

<--- Last few GCs --->

[49580:0x110000000]     4826 ms: Mark-sweep 130.6 (147.8) -> 130.5 (147.8) MB, 27.4 / 0.0 ms  (average mu = 0.126, current mu = 0.034) allocation failure scavenge might not succeed
[49580:0x110000000]     4845 ms: Mark-sweep 130.6 (147.8) -> 130.6 (147.8) MB, 18.8 / 0.0 ms  (average mu = 0.088, current mu = 0.031) allocation failure scavenge might not succeed


<--- JS stacktrace --->

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
....
```

### `--heapsnapshot-signal=signal`

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Enables a signal handler that causes the Node.js process to write a heap dump
when the specified signal is received. `signal` must be a valid signal name.
Disabled by default.

```console
$ node --heapsnapshot-signal=SIGUSR2 index.js &
$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
node         1  5.5  6.1 787252 247004 ?       Ssl  16:43   0:02 node --heapsnapshot-signal=SIGUSR2 index.js
$ kill -USR2 1
$ ls
Heap.20190718.133405.15554.0.001.heapsnapshot
```

### `--heap-prof`

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> Stability: 1 - Experimental

Starts the V8 heap profiler on start up, and writes the heap profile to disk
before exit.

If `--heap-prof-dir` is not specified, the generated profile is placed
in the current working directory.

If `--heap-prof-name` is not specified, the generated profile is
named `Heap.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.heapprofile`.

```console
$ node --heap-prof index.js
$ ls *.heapprofile
Heap.20190409.202950.15293.0.001.heapprofile
```

### `--heap-prof-dir`

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> Stability: 1 - Experimental

Specify the directory where the heap profiles generated by `--heap-prof` will
be placed.

The default value is controlled by the
[`--diagnostic-dir`][] command-line option.

### `--heap-prof-interval`

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> Stability: 1 - Experimental

Specify the average sampling interval in bytes for the heap profiles generated
by `--heap-prof`. The default is 512 \* 1024 bytes.

### `--heap-prof-name`

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> Stability: 1 - Experimental

Specify the file name of the heap profile generated by `--heap-prof`.

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

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

### `--import=module`

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> Stability: 1 - Experimental

Preload the specified module at startup.

Follows [ECMAScript module][] resolution rules.
Use [`--require`][] to load a [CommonJS module][].
Modules preloaded with `--require` will run before modules preloaded with `--import`.

### `--input-type=type`

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This configures Node.js to interpret string input as CommonJS or as an ES
module. String input is input via `--eval`, `--print`, or `STDIN`.

Valid values are `"commonjs"` and `"module"`. The default is `"commonjs"`.

The REPL does not support this option.

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

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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`

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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`.

See the [security warning][] below regarding the `host`
parameter usage.

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

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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][].

<!-- Anchor to make sure old links find a target -->

<a id="inspector_security"></a>

#### Warning: binding inspector to a public IP:port combination is insecure

Binding the inspector to a public IP (including `0.0.0.0`) with an open port is
insecure, as it allows external hosts to connect to the inspector and perform
a [remote code execution][] attack.

If specifying a host, make sure that either:

* The host is not accessible from public networks.
* A firewall disallows unwanted connections on the port.

**More specifically, `--inspect=0.0.0.0` is insecure if the port (`9229` by
default) is not firewall-protected.**

See the [debugging security implications][] section for more information.

### `--inspect-publish-uid=stderr,http`

Specify ways of the inspector web socket url exposure.

By default inspector websocket url is available in stderr and under `/json/list`
endpoint on `http://host:port/json/list`.

### `--insecure-http-parser`

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Use an insecure HTTP parser that accepts invalid HTTP headers. This may allow
interoperability with non-conformant HTTP implementations. It may also allow
request smuggling and other HTTP attacks that rely on invalid headers being
accepted. Avoid using this option.

### `--jitless`

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Disable [runtime allocation of executable memory][jitless]. This may be
required on some platforms for security reasons. It can also reduce attack
surface on other platforms, but the performance impact may be severe.

This flag is inherited from V8 and is subject to change upstream. It may
disappear in a non-semver-major release.

### `--max-http-header-size=size`

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    description: Change maximum default size of HTTP headers from 8 KiB to 16 KiB.
-->

Specify the maximum size, in bytes, of HTTP headers. Defaults to 16 KiB.

### `--napi-modules`

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

### `--no-addons`

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  - v14.19.0
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Disable the `node-addons` exports condition as well as disable loading
native addons. When `--no-addons` is specified, calling `process.dlopen` or
requiring a native C++ addon will fail and throw an exception.

### `--no-deprecation`

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Silence deprecation warnings.

### `--no-extra-info-on-fatal-exception`

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Hide extra information on fatal exception that causes exit.

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

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

### `--no-global-search-paths`

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Do not search modules from global paths like `$HOME/.node_modules` and
`$NODE_PATH`.

### `--no-warnings`

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Silence all process warnings (including deprecations).

### `--node-memory-debug`

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Enable extra debug checks for memory leaks in Node.js internals. This is
usually only useful for developers debugging Node.js itself.

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

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Load an OpenSSL configuration file on startup. Among other uses, this can be
used to enable FIPS-compliant crypto if Node.js is built
against FIPS-enabled OpenSSL.

### `--openssl-shared-config`

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Enable OpenSSL default configuration section, `openssl_conf` to be read from
the OpenSSL configuration file. The default configuration file is named
`openssl.cnf` but this can be changed using the environment variable
`OPENSSL_CONF`, or by using the command line option `--openssl-config`.
The location of the default OpenSSL configuration file depends on how OpenSSL
is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted
implications and it is recommended to use a configuration section specific to
Node.js which is `nodejs_conf` and is default when this option is not used.

### `--openssl-legacy-provider`

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Enable OpenSSL 3.0 legacy provider. For more information please see
[OSSL\_PROVIDER-legacy][OSSL_PROVIDER-legacy].

### `--pending-deprecation`

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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.

### `--policy-integrity=sri`

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> Stability: 1 - Experimental

Instructs Node.js to error prior to running any code if the policy does not have
the specified integrity. It expects a [Subresource Integrity][] string as a
parameter.

### `--preserve-symlinks`

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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:

```text
{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`

<!-- YAML
added: 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.

`--preserve-symlinks-main` does not imply `--preserve-symlinks`; use
`--preserve-symlinks-main` in addition to
`--preserve-symlinks` when it is not desirable to follow symlinks before
resolving relative paths.

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

### `--prof`

<!-- YAML
added: v2.0.0
-->

Generate V8 profiler output.

### `--prof-process`

<!-- YAML
added: v5.2.0
-->

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

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

<!-- YAML
added: 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.

The `file` name may be an absolute path. If it is not, the default directory it
will be written to is controlled by the
[`--diagnostic-dir`][] command-line option.

### `--report-compact`

<!-- YAML
added:
 - v13.12.0
 - v12.17.0
-->

Write reports in a compact format, single-line JSON, more easily consumable
by log processing systems than the default multi-line format designed for
human consumption.

### `--report-dir=directory`, `report-directory=directory`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: Changed from `--diagnostic-report-directory` to
                 `--report-directory`.
-->

Location at which the report will be generated.

### `--report-filename=filename`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-filename` to
                 `--report-filename`.
-->

Name of the file to which the report will be written.

### `--report-on-fatalerror`

<!-- YAML
added: v11.8.0
changes:
  - version:
    - v14.0.0
    - v13.14.0
    - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32496
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-on-fatalerror` to
                 `--report-on-fatalerror`.
-->

Enables the report to be triggered on fatal errors (internal errors within
the Node.js runtime such as out of memory) that lead to termination of the
application. Useful to inspect various diagnostic data elements such as heap,
stack, event loop state, resource consumption etc. to reason about the fatal
error.

### `--report-on-signal`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-on-signal` to
                 `--report-on-signal`.
-->

Enables report to be generated upon receiving the specified (or predefined)
signal to the running Node.js process. The signal to trigger the report is
specified through `--report-signal`.

### `--report-signal=signal`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-signal` to
                 `--report-signal`.
-->

Sets or resets the signal for report generation (not supported on Windows).
Default signal is `SIGUSR2`.

### `--report-uncaught-exception`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-uncaught-exception` to
                 `--report-uncaught-exception`.
-->

Enables report to be generated on uncaught exceptions. Useful when inspecting
the JavaScript stack in conjunction with native stack and other runtime
environment data.

### `--secure-heap=n`

<!-- YAML
added: v15.6.0
-->

Initializes an OpenSSL secure heap of `n` bytes. When initialized, the
secure heap is used for selected types of allocations within OpenSSL
during key generation and other operations. This is useful, for instance,
to prevent sensitive information from leaking due to pointer overruns
or underruns.

The secure heap is a fixed size and cannot be resized at runtime so,
if used, it is important to select a large enough heap to cover all
application uses.

The heap size given must be a power of two. Any value less than 2
will disable the secure heap.

The secure heap is disabled by default.

The secure heap is not available on Windows.

See [`CRYPTO_secure_malloc_init`][] for more details.

### `--secure-heap-min=n`

<!-- YAML
added: v15.6.0
-->

When using `--secure-heap`, the `--secure-heap-min` flag specifies the
minimum allocation from the secure heap. The minimum value is `2`.
The maximum value is the lesser of `--secure-heap` or `2147483647`.
The value given must be a power of two.

### `--snapshot-blob=path`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental

When used with `--build-snapshot`, `--snapshot-blob` specifies the path
where the generated snapshot blob will be written to. If not specified,
the generated blob will be written, by default, to `snapshot.blob`
in the current working directory.

When used without `--build-snapshot`, `--snapshot-blob` specifies the
path to the blob that will be used to restore the application state.

When loading a snapshot, Node.js checks that:

1. The version, architecture and platform of the running Node.js binary
   are exactly the same as that of the binary that generates the snapshot.
2. The V8 flags and CPU features are compatible with that of the binary
   that generates the snapshot.

If they don't match, Node.js would refuse to load the snapshot and exit with 1.

### `--test`

<!-- YAML
added: v18.1.0
-->

Starts the Node.js command line test runner. This flag cannot be combined with
`--check`, `--eval`, `--interactive`, or the inspector. See the documentation
on [running tests from the command line][] for more details.

### `--test-only`

<!-- YAML
added: v18.0.0
-->

Configures the test runner to only execute top level tests that have the `only`
option set.

### `--throw-deprecation`

<!-- YAML
added: v0.11.14
-->

Throw errors for deprecations.

### `--title=title`

<!-- YAML
added: v10.7.0
-->

Set `process.title` on startup.

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

<!-- YAML
added: v4.0.0
-->

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

### `--tls-keylog=file`

<!-- YAML
added:
 - v13.2.0
 - v12.16.0
-->

Log TLS key material to a file. The key material is in NSS `SSLKEYLOGFILE`
format and can be used by software (such as Wireshark) to decrypt the TLS
traffic.

### `--tls-max-v1.2`

<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

Set [`tls.DEFAULT_MAX_VERSION`][] to 'TLSv1.2'. Use to disable support for
TLSv1.3.

### `--tls-max-v1.3`

<!-- YAML
added: v12.0.0
-->

Set default [`tls.DEFAULT_MAX_VERSION`][] to 'TLSv1.3'. Use to enable support
for TLSv1.3.

### `--tls-min-v1.0`

<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

Set default [`tls.DEFAULT_MIN_VERSION`][] to 'TLSv1'. Use for compatibility with
old TLS clients or servers.

### `--tls-min-v1.1`

<!-- YAML
added:
 - v12.0.0
 - v10.20.0
-->

Set default [`tls.DEFAULT_MIN_VERSION`][] to 'TLSv1.1'. Use for compatibility
with old TLS clients or servers.

### `--tls-min-v1.2`

<!-- YAML
added:
 - v12.2.0
 - v10.20.0
-->

Set default [`tls.DEFAULT_MIN_VERSION`][] to 'TLSv1.2'. This is the default for
12.x and later, but the option is supported for compatibility with older Node.js
versions.

### `--tls-min-v1.3`

<!-- YAML
added: v12.0.0
-->

Set default [`tls.DEFAULT_MIN_VERSION`][] to 'TLSv1.3'. Use to disable support
for TLSv1.2, which is not as secure as TLSv1.3.

### `--trace-atomics-wait`

<!-- YAML
added: v14.3.0
deprecated: REPLACEME
-->

> Stability: 0 - Deprecated

Print short summaries of calls to [`Atomics.wait()`][] to stderr.
The output could look like this:

```text
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 1, inf) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 1, inf) did not wait because the values mismatched
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 0, 10) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 0, 10) timed out
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 4, 0, inf) started
(node:15701) [Thread 1] Atomics.wait(&lt;address> + 4, -1, inf) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 4, 0, inf) was woken up by another thread
(node:15701) [Thread 1] Atomics.wait(&lt;address> + 4, -1, inf) was woken up by another thread
```

The fields here correspond to:

* The thread id as given by [`worker_threads.threadId`][]
* The base address of the `SharedArrayBuffer` in question, as well as the
  byte offset corresponding to the index passed to `Atomics.wait()`
* The expected value that was passed to `Atomics.wait()`
* The timeout passed to `Atomics.wait`

### `--trace-deprecation`

<!-- YAML
added: v0.8.0
-->

Print stack traces for deprecations.

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

<!-- YAML
added: 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`

<!-- YAML
added: v9.8.0
-->

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

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

<!-- YAML
added: v7.7.0
-->

Enables the collection of trace event tracing information.

### `--trace-exit`

<!-- YAML
added:
 - v13.5.0
 - v12.16.0
-->

Prints a stack trace whenever an environment is exited proactively,
i.e. invoking `process.exit()`.

### `--trace-sigint`

<!-- YAML
added:
 - v13.9.0
 - v12.17.0
-->

Prints a stack trace on SIGINT.

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

<!-- YAML
added: v2.1.0
-->

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

### `--trace-tls`

<!-- YAML
added: v12.2.0
-->

Prints TLS packet trace information to `stderr`. This can be used to debug TLS
connection problems.

### `--trace-uncaught`

<!-- YAML
added: v13.1.0
-->

Print stack traces for uncaught exceptions; usually, the stack trace associated
with the creation of an `Error` is printed, whereas this makes Node.js also
print the stack trace associated with throwing the value (which does not need
to be an `Error` instance).

Enabling this option may affect garbage collection behavior negatively.

### `--trace-warnings`

<!-- YAML
added: v6.0.0
-->

Print stack traces for process warnings (including deprecations).

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

<!-- YAML
added: v2.4.0
-->

Track heap object allocations for heap snapshots.

### `--unhandled-rejections=mode`

<!-- YAML
added:
  - v12.0.0
  - v10.17.0
changes:
  - version: v15.0.0
    pr-url: https://github.com/nodejs/node/pull/33021
    description: Changed default mode to `throw`. Previously, a warning was
                 emitted.
-->

Using this flag allows to change what should happen when an unhandled rejection
occurs. One of the following modes can be chosen:

* `throw`: Emit [`unhandledRejection`][]. If this hook is not set, raise the
  unhandled rejection as an uncaught exception. This is the default.
* `strict`: Raise the unhandled rejection as an uncaught exception. If the
  exception is handled, [`unhandledRejection`][] is emitted.
* `warn`: Always trigger a warning, no matter if the [`unhandledRejection`][]
  hook is set or not but do not print the deprecation warning.
* `warn-with-error-code`: Emit [`unhandledRejection`][]. If this hook is not
  set, trigger a warning, and set the process exit code to 1.
* `none`: Silence all warnings.

If a rejection happens during the command line entry point's ES module static
loading phase, it will always raise it as an uncaught exception.

### `--update-assert-snapshot`

<!-- YAML
added: REPLACEME
-->

Force updating snapshot files for [`assert.snapshot()`][]

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

<!-- YAML
added: 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`.

### `--use-largepages=mode`

<!-- YAML
added:
 - v13.6.0
 - v12.17.0
-->

Re-map the Node.js static code to large memory pages at startup. If supported on
the target system, this will cause the Node.js static code to be moved onto 2
MiB pages instead of 4 KiB pages.

The following values are valid for `mode`:

* `off`: No mapping will be attempted. This is the default.
* `on`: If supported by the OS, mapping will be attempted. Failure to map will
  be ignored and a message will be printed to standard error.
* `silent`: If supported by the OS, mapping will be attempted. Failure to map
  will be ignored and will not be reported.

### `--v8-options`

<!-- YAML
added: v0.1.3
-->

Print V8 command-line options.

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

<!-- YAML
added: 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`

<!-- YAML
added: v6.0.0
-->

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

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

<!-- YAML
added:
  - v5.0.0
  - v4.2.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19600
    description: The `--require` option is now supported when checking a file.
-->

Syntax check the script without executing.

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

<!-- YAML
added: v0.5.2
changes:
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5348
    description: Built-in libraries are now available as predefined variables.
-->

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`

<!-- YAML
added: v0.1.3
-->

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

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

<!-- YAML
added: v0.7.7
-->

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

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

<!-- YAML
added: v0.6.4
changes:
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5348
    description: Built-in libraries are now available as predefined variables.
-->

Identical to `-e` but prints the result.

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

<!-- YAML
added: 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.

Only CommonJS modules are supported.
Use [`--import`][] to preload an [ECMAScript module][].
Modules preloaded with `--require` will run before modules preloaded with `--import`.

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

<!-- YAML
added: v0.1.3
-->

Print node's version.

## Environment variables

### `FORCE_COLOR=[1, 2, 3]`

The `FORCE_COLOR` environment variable is used to
enable ANSI colorized output. The value may be:

* `1`, `true`, or the empty string `''` indicate 16-color support,
* `2` to indicate 256-color support, or
* `3` to indicate 16 million-color support.

When `FORCE_COLOR` is used and set to a supported value, both the `NO_COLOR`,
and `NODE_DISABLE_COLORS` environment variables are ignored.

Any other value will result in colorized output being disabled.

### `NODE_DEBUG=module[,…]`

<!-- YAML
added: v0.1.32
-->

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

### `NODE_DEBUG_NATIVE=module[,…]`

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

### `NODE_DISABLE_COLORS=1`

<!-- YAML
added: v0.3.0
-->

When set, colors will not be used in the REPL.

### `NODE_EXTRA_CA_CERTS=file`

<!-- YAML
added: 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()`][emit_warning] if the file is missing or
malformed, but any errors are otherwise ignored.

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.

This environment variable is ignored when `node` runs as setuid root or
has Linux file capabilities set.

The `NODE_EXTRA_CA_CERTS` environment variable is only read when the Node.js
process is first launched. Changing the value at runtime using
`process.env.NODE_EXTRA_CA_CERTS` has no effect on the current process.

### `NODE_ICU_DATA=file`

<!-- YAML
added: 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`

<!-- YAML
added: v6.11.0
-->

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

### `NODE_OPTIONS=options...`

<!-- YAML
added: v8.0.0
-->

A space-separated list of command-line options. `options...` are interpreted
before command-line options, so command-line options will override or
compound after anything in `options...`. 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.

If an option value contains a space, it can be escaped using double quotes:

```bash
NODE_OPTIONS='--require "./my path/file.js"'
```

A singleton flag passed as a command-line option will override the same flag
passed into `NODE_OPTIONS`:

```bash
# The inspector will be available on port 5555
NODE_OPTIONS='--inspect=localhost:4444' node --inspect=localhost:5555
```

A flag that can be passed multiple times will be treated as if its
`NODE_OPTIONS` instances were passed first, and then its command-line
instances afterwards:

```bash
NODE_OPTIONS='--require "./a.js"' node --require "./b.js"
# is equivalent to:
node --require "./a.js" --require "./b.js"
```

Node.js options that are allowed are:

<!-- node-options-node start -->

* `--conditions`, `-C`
* `--diagnostic-dir`
* `--disable-proto`
* `--dns-result-order`
* `--enable-fips`
* `--enable-source-maps`
* `--experimental-abortcontroller`
* `--experimental-global-customevent`
* `--experimental-global-webcrypto`
* `--experimental-import-meta-resolve`
* `--experimental-json-modules`
* `--experimental-loader`
* `--experimental-modules`
* `--experimental-network-imports`
* `--experimental-policy`
* `--experimental-shadow-realm`
* `--experimental-specifier-resolution`
* `--experimental-top-level-await`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-wasm-modules`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
* `--frozen-intrinsics`
* `--heapsnapshot-near-heap-limit`
* `--heapsnapshot-signal`
* `--http-parser`
* `--icu-data-dir`
* `--import`
* `--input-type`
* `--insecure-http-parser`
* `--inspect-brk`
* `--inspect-port`, `--debug-port`
* `--inspect-publish-uid`
* `--inspect`
* `--max-http-header-size`
* `--napi-modules`
* `--no-addons`
* `--no-deprecation`
* `--no-experimental-fetch`
* `--no-experimental-repl-await`
* `--no-extra-info-on-fatal-exception`
* `--no-force-async-hooks-checks`
* `--no-global-search-paths`
* `--no-warnings`
* `--node-memory-debug`
* `--openssl-config`
* `--openssl-legacy-provider`
* `--openssl-shared-config`
* `--pending-deprecation`
* `--policy-integrity`
* `--preserve-symlinks-main`
* `--preserve-symlinks`
* `--prof-process`
* `--redirect-warnings`
* `--report-compact`
* `--report-dir`, `--report-directory`
* `--report-filename`
* `--report-on-fatalerror`
* `--report-on-signal`
* `--report-signal`
* `--report-uncaught-exception`
* `--require`, `-r`
* `--secure-heap-min`
* `--secure-heap`
* `--snapshot-blob`
* `--test-only`
* `--throw-deprecation`
* `--title`
* `--tls-cipher-list`
* `--tls-keylog`
* `--tls-max-v1.2`
* `--tls-max-v1.3`
* `--tls-min-v1.0`
* `--tls-min-v1.1`
* `--tls-min-v1.2`
* `--tls-min-v1.3`
* `--trace-atomics-wait`
* `--trace-deprecation`
* `--trace-event-categories`
* `--trace-event-file-pattern`
* `--trace-events-enabled`
* `--trace-exit`
* `--trace-sigint`
* `--trace-sync-io`
* `--trace-tls`
* `--trace-uncaught`
* `--trace-warnings`
* `--track-heap-objects`
* `--unhandled-rejections`
* `--update-assert-snapshot`
* `--use-bundled-ca`
* `--use-largepages`
* `--use-openssl-ca`
* `--v8-pool-size`
* `--zero-fill-buffers`

<!-- node-options-node end -->

V8 options that are allowed are:

<!-- node-options-v8 start -->

* `--abort-on-uncaught-exception`
* `--disallow-code-generation-from-strings`
* `--huge-max-old-generation-size`
* `--interpreted-frames-native-stack`
* `--jitless`
* `--max-old-space-size`
* `--perf-basic-prof-only-functions`
* `--perf-basic-prof`
* `--perf-prof-unwinding-info`
* `--perf-prof`
* `--stack-trace-limit`

<!-- node-options-v8 end -->

`--perf-basic-prof-only-functions`, `--perf-basic-prof`,
`--perf-prof-unwinding-info`, and `--perf-prof` are only available on Linux.

### `NODE_PATH=path[:…]`

<!-- YAML
added: 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`

<!-- YAML
added: 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_PENDING_PIPE_INSTANCES=instances`

Set the number of pending pipe instance handles when the pipe server is waiting
for connections. This setting applies to Windows only.

### `NODE_PRESERVE_SYMLINKS=1`

<!-- YAML
added: v7.1.0
-->

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

### `NODE_REDIRECT_WARNINGS=file`

<!-- YAML
added: 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`

<!-- YAML
added: 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.

### `NODE_REPL_EXTERNAL_MODULE=file`

<!-- YAML
added:
 - v13.0.0
 - v12.16.0
-->

Path to a Node.js module which will be loaded in place of the built-in REPL.
Overriding this value to an empty string (`''`) will use the built-in REPL.

### `NODE_SKIP_PLATFORM_CHECK=value`

<!-- YAML
added: v14.5.0
-->

If `value` equals `'1'`, the check for a supported platform is skipped during
Node.js startup. Node.js might not execute correctly. Any issues encountered
on unsupported platforms will not be fixed.

### `NODE_TLS_REJECT_UNAUTHORIZED=value`

If `value` equals `'0'`, certificate validation is disabled for TLS connections.
This makes TLS, and HTTPS by extension, insecure. The use of this environment
variable is strongly discouraged.

### `NODE_V8_COVERAGE=dir`

When set, Node.js will begin outputting [V8 JavaScript code coverage][] and
[Source Map][] data to the directory provided as an argument (coverage
information is written as JSON to files with a `coverage` prefix).

`NODE_V8_COVERAGE` will automatically propagate to subprocesses, making it
easier to instrument applications that call the `child_process.spawn()` family
of functions. `NODE_V8_COVERAGE` can be set to an empty string, to prevent
propagation.

#### Coverage output

Coverage is output as an array of [ScriptCoverage][] objects on the top-level
key `result`:

```json
{
  "result": [
    {
      "scriptId": "67",
      "url": "internal/tty.js",
      "functions": []
    }
  ]
}
```

#### Source map cache

> Stability: 1 - Experimental

If found, source map data is appended to the top-level key `source-map-cache`
on the JSON coverage object.

`source-map-cache` is an object with keys representing the files source maps
were extracted from, and values which include the raw source-map URL
(in the key `url`), the parsed Source Map v3 information (in the key `data`),
and the line lengths of the source file (in the key `lineLengths`).

```json
{
  "result": [
    {
      "scriptId": "68",
      "url": "file:///absolute/path/to/source.js",
      "functions": []
    }
  ],
  "source-map-cache": {
    "file:///absolute/path/to/source.js": {
      "url": "./path-to-map.json",
      "data": {
        "version": 3,
        "sources": [
          "file:///absolute/path/to/original.js"
        ],
        "names": [
          "Foo",
          "console",
          "info"
        ],
        "mappings": "MAAMA,IACJC,YAAaC",
        "sourceRoot": "./"
      },
      "lineLengths": [
        13,
        62,
        38,
        27
      ]
    }
  }
}
```

### `NO_COLOR=<any>`

[`NO_COLOR`][]  is an alias for `NODE_DISABLE_COLORS`. The value of the
environment variable is arbitrary.

### `OPENSSL_CONF=file`

<!-- YAML
added: 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`

<!-- YAML
added: 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`

<!-- YAML
added: 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.

### `TZ`

<!-- YAML
added: v0.0.1
changes:
  - version:
     - v16.2.0
    pr-url: https://github.com/nodejs/node/pull/38642
    description:
      Changing the TZ variable using process.env.TZ = changes the timezone
      on Windows as well.
  - version:
     - v13.0.0
    pr-url: https://github.com/nodejs/node/pull/20026
    description:
      Changing the TZ variable using process.env.TZ = changes the timezone
      on POSIX systems.
-->

The `TZ` environment variable is used to specify the timezone configuration.

While Node.js does not support all of the various [ways that `TZ` is handled in
other environments][], it does support basic [timezone IDs][] (such as
`'Etc/UTC'`, `'Europe/Paris'`, or `'America/New_York'`).
It may support a few other abbreviations or aliases, but these are strongly
discouraged and not guaranteed.

```console
$ TZ=Europe/Dublin node -pe "new Date().toString()"
Wed May 12 2021 20:30:48 GMT+0100 (Irish Standard Time)
```

### `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
* asynchronous crypto APIs such as `crypto.pbkdf2()`, `crypto.scrypt()`,
  `crypto.randomBytes()`, `crypto.randomFill()`, `crypto.generateKeyPair()`
* `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][].

## Useful V8 options

V8 has its own set of CLI options. Any V8 CLI option that is provided to `node`
will be passed on to V8 to handle. V8's options have _no stability guarantee_.
The V8 team themselves don't consider them to be part of their formal API,
and reserve the right to change them at any time. Likewise, they are not
covered by the Node.js stability guarantees. Many of the V8
options are of interest only to V8 developers. Despite this, there is a small
set of V8 options that are widely applicable to Node.js, and they are
documented here:

### `--max-old-space-size=SIZE` (in megabytes)

Sets the max memory size of V8's old memory section. As memory
consumption approaches the limit, V8 will spend more time on
garbage collection in an effort to free unused memory.

On a machine with 2 GiB of memory, consider setting this to
1536 (1.5 GiB) to leave some memory for other uses and avoid swapping.

```console
$ node --max-old-space-size=1536 index.js
```

### `--max-semi-space-size=SIZE` (in megabytes)

Sets the maximum [semi-space][] size for V8's [scavenge garbage collector][] in
MiB (megabytes).
Increasing the max size of a semi-space may improve throughput for Node.js at
the cost of more memory consumption.

Since the young generation size of the V8 heap is three times (see
[`YoungGenerationSizeFromSemiSpaceSize`][] in V8) the size of the semi-space,
an increase of 1 MiB to semi-space applies to each of the three individual
semi-spaces and causes the heap size to increase by 3 MiB. The throughput
improvement depends on your workload (see [#42511][]).

The default value is 16 MiB for 64-bit systems and 8 MiB for 32-bit systems. To
get the best configuration for your application, you should try different
max-semi-space-size values when running benchmarks for your application.

For example, benchmark on a 64-bit systems:

```bash
for MiB in 16 32 64 128; do
    node --max-semi-space-size=$MiB index.js
done
```

[#42511]: https://github.com/nodejs/node/issues/42511
[Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
[CommonJS]: modules.md
[CommonJS module]: modules.md
[CustomEvent Web API]: https://dom.spec.whatwg.org/#customevent
[ECMAScript module]: esm.md#modules-ecmascript-modules
[ECMAScript module loader]: esm.md#loaders
[Fetch API]: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
[Modules loaders]: packages.md#modules-loaders
[Node.js issue tracker]: https://github.com/nodejs/node/issues
[OSSL_PROVIDER-legacy]: https://www.openssl.org/docs/man3.0/man7/OSSL_PROVIDER-legacy.html
[REPL]: repl.md
[ScriptCoverage]: https://chromedevtools.github.io/devtools-protocol/tot/Profiler#type-ScriptCoverage
[ShadowRealm]: https://github.com/tc39/proposal-shadowrealm
[Source Map]: https://sourcemaps.info/spec.html
[Subresource Integrity]: https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
[V8 JavaScript code coverage]: https://v8project.blogspot.com/2017/12/javascript-code-coverage.html
[Web Crypto API]: webcrypto.md
[`"type"`]: packages.md#type
[`--cpu-prof-dir`]: #--cpu-prof-dir
[`--diagnostic-dir`]: #--diagnostic-dirdirectory
[`--experimental-wasm-modules`]: #--experimental-wasm-modules
[`--heap-prof-dir`]: #--heap-prof-dir
[`--import`]: #--importmodule
[`--openssl-config`]: #--openssl-configfile
[`--redirect-warnings`]: #--redirect-warningsfile
[`--require`]: #-r---require-module
[`Atomics.wait()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait
[`Buffer`]: buffer.md#class-buffer
[`CRYPTO_secure_malloc_init`]: https://www.openssl.org/docs/man1.1.0/man3/CRYPTO_secure_malloc_init.html
[`NODE_OPTIONS`]: #node_optionsoptions
[`NO_COLOR`]: https://no-color.org
[`SlowBuffer`]: buffer.md#class-slowbuffer
[`YoungGenerationSizeFromSemiSpaceSize`]: https://chromium.googlesource.com/v8/v8.git/+/refs/tags/10.3.129/src/heap/heap.cc#328
[`assert.snapshot()`]: assert.md#assertsnapshotvalue-name
[`dns.lookup()`]: dns.md#dnslookuphostname-options-callback
[`dns.setDefaultResultOrder()`]: dns.md#dnssetdefaultresultorderorder
[`dnsPromises.lookup()`]: dns.md#dnspromiseslookuphostname-options
[`import` specifier]: esm.md#import-specifiers
[`process.setUncaughtExceptionCaptureCallback()`]: process.md#processsetuncaughtexceptioncapturecallbackfn
[`tls.DEFAULT_MAX_VERSION`]: tls.md#tlsdefault_max_version
[`tls.DEFAULT_MIN_VERSION`]: tls.md#tlsdefault_min_version
[`unhandledRejection`]: process.md#event-unhandledrejection
[`v8.startupSnapshot` API]: v8.md#startup-snapshot-api
[`worker_threads.threadId`]: worker_threads.md#workerthreadid
[conditional exports]: packages.md#conditional-exports
[context-aware]: addons.md#context-aware-addons
[customizing ESM specifier resolution]: esm.md#customizing-esm-specifier-resolution-algorithm
[debugger]: debugger.md
[debugging security implications]: https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications
[emit_warning]: process.md#processemitwarningwarning-options
[jitless]: https://v8.dev/blog/jitless
[libuv threadpool documentation]: https://docs.libuv.org/en/latest/threadpool.html
[remote code execution]: https://www.owasp.org/index.php/Code_Injection
[running tests from the command line]: test.md#running-tests-from-the-command-line
[scavenge garbage collector]: https://v8.dev/blog/orinoco-parallel-scavenger
[security warning]: #warning-binding-inspector-to-a-public-ipport-combination-is-insecure
[semi-space]: https://www.memorymanagement.org/glossary/s.html#semi.space
[timezone IDs]: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
[tracking issue for user-land snapshots]: https://github.com/nodejs/node/issues/44014
[ways that `TZ` is handled in other environments]: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html