doc/api/report.md

# Diagnostic report

<!--introduced_in=v11.8.0-->

<!-- type=misc -->

> Stability: 2 - Stable

<!-- name=report -->

Delivers a JSON-formatted diagnostic summary, written to a file.

The report is intended for development, test, and production use, to capture
and preserve information for problem determination. It includes JavaScript
and native stack traces, heap statistics, platform information, resource
usage etc. With the report option enabled, diagnostic reports can be triggered
on unhandled exceptions, fatal errors and user signals, in addition to
triggering programmatically through API calls.

A complete example report that was generated on an uncaught exception
is provided below for reference.

```json
{
  "header": {
    "reportVersion": 3,
    "event": "exception",
    "trigger": "Exception",
    "filename": "report.20181221.005011.8974.0.001.json",
    "dumpEventTime": "2018-12-21T00:50:11Z",
    "dumpEventTimeStamp": "1545371411331",
    "processId": 8974,
    "cwd": "/home/nodeuser/project/node",
    "commandLine": [
      "/home/nodeuser/project/node/out/Release/node",
      "--report-uncaught-exception",
      "/home/nodeuser/project/node/test/report/test-exception.js",
      "child"
    ],
    "nodejsVersion": "v12.0.0-pre",
    "glibcVersionRuntime": "2.17",
    "glibcVersionCompiler": "2.17",
    "wordSize": "64 bit",
    "arch": "x64",
    "platform": "linux",
    "componentVersions": {
      "node": "12.0.0-pre",
      "v8": "7.1.302.28-node.5",
      "uv": "1.24.1",
      "zlib": "1.2.11",
      "ares": "1.15.0",
      "modules": "68",
      "nghttp2": "1.34.0",
      "napi": "3",
      "llhttp": "1.0.1",
      "openssl": "1.1.0j"
    },
    "release": {
      "name": "node"
    },
    "osName": "Linux",
    "osRelease": "3.10.0-862.el7.x86_64",
    "osVersion": "#1 SMP Wed Mar 21 18:14:51 EDT 2018",
    "osMachine": "x86_64",
    "cpus": [
      {
        "model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz",
        "speed": 2700,
        "user": 88902660,
        "nice": 0,
        "sys": 50902570,
        "idle": 241732220,
        "irq": 0
      },
      {
        "model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz",
        "speed": 2700,
        "user": 88902660,
        "nice": 0,
        "sys": 50902570,
        "idle": 241732220,
        "irq": 0
      }
    ],
    "networkInterfaces": [
      {
        "name": "en0",
        "internal": false,
        "mac": "13:10:de:ad:be:ef",
        "address": "10.0.0.37",
        "netmask": "255.255.255.0",
        "family": "IPv4"
      }
    ],
    "host": "test_machine"
  },
  "javascriptStack": {
    "message": "Error: *** test-exception.js: throwing uncaught Error",
    "stack": [
      "at myException (/home/nodeuser/project/node/test/report/test-exception.js:9:11)",
      "at Object.<anonymous> (/home/nodeuser/project/node/test/report/test-exception.js:12:3)",
      "at Module._compile (internal/modules/cjs/loader.js:718:30)",
      "at Object.Module._extensions..js (internal/modules/cjs/loader.js:729:10)",
      "at Module.load (internal/modules/cjs/loader.js:617:32)",
      "at tryModuleLoad (internal/modules/cjs/loader.js:560:12)",
      "at Function.Module._load (internal/modules/cjs/loader.js:552:3)",
      "at Function.Module.runMain (internal/modules/cjs/loader.js:771:12)",
      "at executeUserCode (internal/bootstrap/node.js:332:15)"
    ]
  },
  "nativeStack": [
    {
      "pc": "0x000055b57f07a9ef",
      "symbol": "report::GetNodeReport(v8::Isolate*, node::Environment*, char const*, char const*, v8::Local<v8::String>, std::ostream&) [./node]"
    },
    {
      "pc": "0x000055b57f07cf03",
      "symbol": "report::GetReport(v8::FunctionCallbackInfo<v8::Value> const&) [./node]"
    },
    {
      "pc": "0x000055b57f1bccfd",
      "symbol": " [./node]"
    },
    {
      "pc": "0x000055b57f1be048",
      "symbol": "v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) [./node]"
    },
    {
      "pc": "0x000055b57feeda0e",
      "symbol": " [./node]"
    }
  ],
  "javascriptHeap": {
    "totalMemory": 5660672,
    "executableMemory": 524288,
    "totalCommittedMemory": 5488640,
    "availableMemory": 4341379928,
    "totalGlobalHandlesMemory": 8192,
    "usedGlobalHandlesMemory": 3136,
    "usedMemory": 4816432,
    "memoryLimit": 4345298944,
    "mallocedMemory": 254128,
    "externalMemory": 315644,
    "peakMallocedMemory": 98752,
    "nativeContextCount": 1,
    "detachedContextCount": 0,
    "doesZapGarbage": 0,
    "heapSpaces": {
      "read_only_space": {
        "memorySize": 524288,
        "committedMemory": 39208,
        "capacity": 515584,
        "used": 30504,
        "available": 485080
      },
      "new_space": {
        "memorySize": 2097152,
        "committedMemory": 2019312,
        "capacity": 1031168,
        "used": 985496,
        "available": 45672
      },
      "old_space": {
        "memorySize": 2273280,
        "committedMemory": 1769008,
        "capacity": 1974640,
        "used": 1725488,
        "available": 249152
      },
      "code_space": {
        "memorySize": 696320,
        "committedMemory": 184896,
        "capacity": 152128,
        "used": 152128,
        "available": 0
      },
      "map_space": {
        "memorySize": 536576,
        "committedMemory": 344928,
        "capacity": 327520,
        "used": 327520,
        "available": 0
      },
      "large_object_space": {
        "memorySize": 0,
        "committedMemory": 0,
        "capacity": 1520590336,
        "used": 0,
        "available": 1520590336
      },
      "new_large_object_space": {
        "memorySize": 0,
        "committedMemory": 0,
        "capacity": 0,
        "used": 0,
        "available": 0
      }
    }
  },
  "resourceUsage": {
    "rss": "35766272",
    "free_memory": "1598337024",
    "total_memory": "17179869184",
    "available_memory": "1598337024",
    "maxRss": "36624662528",
    "constrained_memory": "36624662528",
    "userCpuSeconds": 0.040072,
    "kernelCpuSeconds": 0.016029,
    "cpuConsumptionPercent": 5.6101,
    "userCpuConsumptionPercent": 4.0072,
    "kernelCpuConsumptionPercent": 1.6029,
    "pageFaults": {
      "IORequired": 0,
      "IONotRequired": 4610
    },
    "fsActivity": {
      "reads": 0,
      "writes": 0
    }
  },
  "uvthreadResourceUsage": {
    "userCpuSeconds": 0.039843,
    "kernelCpuSeconds": 0.015937,
    "cpuConsumptionPercent": 5.578,
    "userCpuConsumptionPercent": 3.9843,
    "kernelCpuConsumptionPercent": 1.5937,
    "fsActivity": {
      "reads": 0,
      "writes": 0
    }
  },
  "libuv": [
    {
      "type": "async",
      "is_active": true,
      "is_referenced": false,
      "address": "0x0000000102910900",
      "details": ""
    },
    {
      "type": "timer",
      "is_active": false,
      "is_referenced": false,
      "address": "0x00007fff5fbfeab0",
      "repeat": 0,
      "firesInMsFromNow": 94403548320796,
      "expired": true
    },
    {
      "type": "check",
      "is_active": true,
      "is_referenced": false,
      "address": "0x00007fff5fbfeb48"
    },
    {
      "type": "idle",
      "is_active": false,
      "is_referenced": true,
      "address": "0x00007fff5fbfebc0"
    },
    {
      "type": "prepare",
      "is_active": false,
      "is_referenced": false,
      "address": "0x00007fff5fbfec38"
    },
    {
      "type": "check",
      "is_active": false,
      "is_referenced": false,
      "address": "0x00007fff5fbfecb0"
    },
    {
      "type": "async",
      "is_active": true,
      "is_referenced": false,
      "address": "0x000000010188f2e0"
    },
    {
      "type": "tty",
      "is_active": false,
      "is_referenced": true,
      "address": "0x000055b581db0e18",
      "width": 204,
      "height": 55,
      "fd": 17,
      "writeQueueSize": 0,
      "readable": true,
      "writable": true
    },
    {
      "type": "signal",
      "is_active": true,
      "is_referenced": false,
      "address": "0x000055b581d80010",
      "signum": 28,
      "signal": "SIGWINCH"
    },
    {
      "type": "tty",
      "is_active": true,
      "is_referenced": true,
      "address": "0x000055b581df59f8",
      "width": 204,
      "height": 55,
      "fd": 19,
      "writeQueueSize": 0,
      "readable": true,
      "writable": true
    },
    {
      "type": "loop",
      "is_active": true,
      "address": "0x000055fc7b2cb180",
      "loopIdleTimeSeconds": 22644.8
    }
  ],
  "workers": [],
  "environmentVariables": {
    "REMOTEHOST": "REMOVED",
    "MANPATH": "/opt/rh/devtoolset-3/root/usr/share/man:",
    "XDG_SESSION_ID": "66126",
    "HOSTNAME": "test_machine",
    "HOST": "test_machine",
    "TERM": "xterm-256color",
    "SHELL": "/bin/csh",
    "SSH_CLIENT": "REMOVED",
    "PERL5LIB": "/opt/rh/devtoolset-3/root//usr/lib64/perl5/vendor_perl:/opt/rh/devtoolset-3/root/usr/lib/perl5:/opt/rh/devtoolset-3/root//usr/share/perl5/vendor_perl",
    "OLDPWD": "/home/nodeuser/project/node/src",
    "JAVACONFDIRS": "/opt/rh/devtoolset-3/root/etc/java:/etc/java",
    "SSH_TTY": "/dev/pts/0",
    "PCP_DIR": "/opt/rh/devtoolset-3/root",
    "GROUP": "normaluser",
    "USER": "nodeuser",
    "LD_LIBRARY_PATH": "/opt/rh/devtoolset-3/root/usr/lib64:/opt/rh/devtoolset-3/root/usr/lib",
    "HOSTTYPE": "x86_64-linux",
    "XDG_CONFIG_DIRS": "/opt/rh/devtoolset-3/root/etc/xdg:/etc/xdg",
    "MAIL": "/var/spool/mail/nodeuser",
    "PATH": "/home/nodeuser/project/node:/opt/rh/devtoolset-3/root/usr/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin",
    "PWD": "/home/nodeuser/project/node",
    "LANG": "en_US.UTF-8",
    "PS1": "\\u@\\h : \\[\\e[31m\\]\\w\\[\\e[m\\] >  ",
    "SHLVL": "2",
    "HOME": "/home/nodeuser",
    "OSTYPE": "linux",
    "VENDOR": "unknown",
    "PYTHONPATH": "/opt/rh/devtoolset-3/root/usr/lib64/python2.7/site-packages:/opt/rh/devtoolset-3/root/usr/lib/python2.7/site-packages",
    "MACHTYPE": "x86_64",
    "LOGNAME": "nodeuser",
    "XDG_DATA_DIRS": "/opt/rh/devtoolset-3/root/usr/share:/usr/local/share:/usr/share",
    "LESSOPEN": "||/usr/bin/lesspipe.sh %s",
    "INFOPATH": "/opt/rh/devtoolset-3/root/usr/share/info",
    "XDG_RUNTIME_DIR": "/run/user/50141",
    "_": "./node"
  },
  "userLimits": {
    "core_file_size_blocks": {
      "soft": "",
      "hard": "unlimited"
    },
    "data_seg_size_kbytes": {
      "soft": "unlimited",
      "hard": "unlimited"
    },
    "file_size_blocks": {
      "soft": "unlimited",
      "hard": "unlimited"
    },
    "max_locked_memory_bytes": {
      "soft": "unlimited",
      "hard": 65536
    },
    "max_memory_size_kbytes": {
      "soft": "unlimited",
      "hard": "unlimited"
    },
    "open_files": {
      "soft": "unlimited",
      "hard": 4096
    },
    "stack_size_bytes": {
      "soft": "unlimited",
      "hard": "unlimited"
    },
    "cpu_time_seconds": {
      "soft": "unlimited",
      "hard": "unlimited"
    },
    "max_user_processes": {
      "soft": "unlimited",
      "hard": 4127290
    },
    "virtual_memory_kbytes": {
      "soft": "unlimited",
      "hard": "unlimited"
    }
  },
  "sharedObjects": [
    "/lib64/libdl.so.2",
    "/lib64/librt.so.1",
    "/lib64/libstdc++.so.6",
    "/lib64/libm.so.6",
    "/lib64/libgcc_s.so.1",
    "/lib64/libpthread.so.0",
    "/lib64/libc.so.6",
    "/lib64/ld-linux-x86-64.so.2"
  ]
}
```

## Usage

```bash
node --report-uncaught-exception --report-on-signal \
--report-on-fatalerror app.js
```

* `--report-uncaught-exception` Enables report to be generated on
  un-caught exceptions. Useful when inspecting JavaScript stack in conjunction
  with native stack and other runtime environment data.

* `--report-on-signal` Enables report to be generated upon receiving
  the specified (or predefined) signal to the running Node.js process. (See
  below on how to modify the signal that triggers the report.) Default signal is
  `SIGUSR2`. Useful when a report needs to be triggered from another program.
  Application monitors may leverage this feature to collect report at regular
  intervals and plot rich set of internal runtime data to their views.

Signal based report generation is not supported in Windows.

Under normal circumstances, there is no need to modify the report triggering
signal. However, if `SIGUSR2` is already used for other purposes, then this
flag helps to change the signal for report generation and preserve the original
meaning of `SIGUSR2` for the said purposes.

* `--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 leads 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-compact` 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-directory` Location at which the report will be
  generated.

* `--report-filename` Name of the file to which the report will be
  written.

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

A report can also be triggered via an API call from a JavaScript application:

```js
process.report.writeReport();
```

This function takes an optional additional argument `filename`, which is
the name of a file into which the report is written.

```js
process.report.writeReport('./foo.json');
```

This function takes an optional additional argument `err` which is an `Error`
object that will be used as the context for the JavaScript stack printed in the
report. When using report to handle errors in a callback or an exception
handler, this allows the report to include the location of the original error as
well as where it was handled.

```js
try {
  process.chdir('/non-existent-path');
} catch (err) {
  process.report.writeReport(err);
}
// Any other code
```

If both filename and error object are passed to `writeReport()` the
error object must be the second parameter.

```js
try {
  process.chdir('/non-existent-path');
} catch (err) {
  process.report.writeReport(filename, err);
}
// Any other code
```

The content of the diagnostic report can be returned as a JavaScript Object
via an API call from a JavaScript application:

```js
const report = process.report.getReport();
console.log(typeof report === 'object'); // true

// Similar to process.report.writeReport() output
console.log(JSON.stringify(report, null, 2));
```

This function takes an optional additional argument `err`, which is an `Error`
object that will be used as the context for the JavaScript stack printed in the
report.

```js
const report = process.report.getReport(new Error('custom error'));
console.log(typeof report === 'object'); // true
```

The API versions are useful when inspecting the runtime state from within
the application, in expectation of self-adjusting the resource consumption,
load balancing, monitoring etc.

The content of the report consists of a header section containing the event
type, date, time, PID, and Node.js version, sections containing JavaScript and
native stack traces, a section containing V8 heap information, a section
containing `libuv` handle information, and an OS platform information section
showing CPU and memory usage and system limits. An example report can be
triggered using the Node.js REPL:

```console
$ node
> process.report.writeReport();
Writing Node.js report to file: report.20181126.091102.8480.0.001.json
Node.js report completed
>
```

When a report is written, start and end messages are issued to stderr
and the filename of the report is returned to the caller. The default filename
includes the date, time, PID, and a sequence number. The sequence number helps
in associating the report dump with the runtime state if generated multiple
times for the same Node.js process.

Diagnostic report has an associated single-digit version number (`report.header.reportVersion`),
uniquely representing the report format. The version number is bumped
when new key is added or removed, or the data type of a value is changed.
Report version definitions are consistent across LTS releases.

## Configuration

Additional runtime configuration of report generation is available via
the following properties of `process.report`:

`reportOnFatalError` triggers diagnostic reporting on fatal errors when `true`.
Defaults to `false`.

`reportOnSignal` triggers diagnostic reporting on signal when `true`. This is
not supported on Windows. Defaults to `false`.

`reportOnUncaughtException` triggers diagnostic reporting on uncaught exception
when `true`. Defaults to `false`.

`signal` specifies the POSIX signal identifier that will be used
to intercept external triggers for report generation. Defaults to
`'SIGUSR2'`.

`filename` specifies the name of the output file in the file system.
Special meaning is attached to `stdout` and `stderr`. Usage of these
will result in report being written to the associated standard streams.
In cases where standard streams are used, the value in `directory` is ignored.
URLs are not supported. Defaults to a composite filename that contains
timestamp, PID, and sequence number.

`directory` specifies the file system directory where the report will be
written. URLs are not supported. Defaults to the current working directory of
the Node.js process.

```js
// Trigger report only on uncaught exceptions.
process.report.reportOnFatalError = false;
process.report.reportOnSignal = false;
process.report.reportOnUncaughtException = true;

// Trigger report for both internal errors as well as external signal.
process.report.reportOnFatalError = true;
process.report.reportOnSignal = true;
process.report.reportOnUncaughtException = false;

// Change the default signal to 'SIGQUIT' and enable it.
process.report.reportOnFatalError = false;
process.report.reportOnUncaughtException = false;
process.report.reportOnSignal = true;
process.report.signal = 'SIGQUIT';
```

Configuration on module initialization is also available via
environment variables:

```bash
NODE_OPTIONS="--report-uncaught-exception \
  --report-on-fatalerror --report-on-signal \
  --report-signal=SIGUSR2  --report-filename=./report.json \
  --report-directory=/home/nodeuser"
```

Specific API documentation can be found under
[`process API documentation`][] section.

## Interaction with workers

<!-- YAML
changes:
  - version:
      - v13.9.0
      - v12.16.2
    pr-url: https://github.com/nodejs/node/pull/31386
    description: Workers are now included in the report.
-->

[`Worker`][] threads can create reports in the same way that the main thread
does.

Reports will include information on any Workers that are children of the current
thread as part of the `workers` section, with each Worker generating a report
in the standard report format.

The thread which is generating the report will wait for the reports from Worker
threads to finish. However, the latency for this will usually be low, as both
running JavaScript and the event loop are interrupted to generate the report.

[`Worker`]: worker_threads.md
[`process API documentation`]: process.md