# OS

<!--introduced_in=v0.10.0-->

> Stability: 2 - Stable

<!-- source_link=lib/os.js -->

The `os` module provides operating system-related utility methods and
properties. It can be accessed using:

```js
const os = require('os');
```

## `os.EOL`
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* {string}

The operating system-specific end-of-line marker.

* `\n` on POSIX
* `\r\n` on Windows

## `os.arch()`
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* Returns: {string}

Returns the operating system CPU architecture for which the Node.js binary was
compiled. Possible values are `'arm'`, `'arm64'`, `'ia32'`, `'mips'`,
`'mipsel'`, `'ppc'`, `'ppc64'`, `'s390'`, `'s390x'`, `'x32'`, and `'x64'`.

The return value is equivalent to [`process.arch`][].

## `os.constants`
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* {Object}

Contains commonly used operating system-specific constants for error codes,
process signals, and so on. The specific constants defined are described in
[OS constants](#os_os_constants_1).

## `os.cpus()`
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* Returns: {Object[]}

Returns an array of objects containing information about each logical CPU core.

The properties included on each object include:

* `model` {string}
* `speed` {number} (in MHz)
* `times` {Object}
  * `user` {number} The number of milliseconds the CPU has spent in user mode.
  * `nice` {number} The number of milliseconds the CPU has spent in nice mode.
  * `sys` {number} The number of milliseconds the CPU has spent in sys mode.
  * `idle` {number} The number of milliseconds the CPU has spent in idle mode.
  * `irq` {number} The number of milliseconds the CPU has spent in irq mode.

<!-- eslint-disable semi -->
```js
[
  {
    model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times: {
      user: 252020,
      nice: 0,
      sys: 30340,
      idle: 1070356870,
      irq: 0
    }
  },
  {
    model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times: {
      user: 306960,
      nice: 0,
      sys: 26980,
      idle: 1071569080,
      irq: 0
    }
  },
  {
    model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times: {
      user: 248450,
      nice: 0,
      sys: 21750,
      idle: 1070919370,
      irq: 0
    }
  },
  {
    model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times: {
      user: 256880,
      nice: 0,
      sys: 19430,
      idle: 1070905480,
      irq: 20
    }
  }
]
```

`nice` values are POSIX-only. On Windows, the `nice` values of all processors
are always 0.

## `os.endianness()`
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* Returns: {string}

Returns a string identifying the endianness of the CPU for which the Node.js
binary was compiled.

Possible values are `'BE'` for big endian and `'LE'` for little endian.

## `os.freemem()`
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* Returns: {integer}

Returns the amount of free system memory in bytes as an integer.

## `os.getPriority([pid])`
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* `pid` {integer} The process ID to retrieve scheduling priority for.
  **Default** `0`.
* Returns: {integer}

Returns the scheduling priority for the process specified by `pid`. If `pid` is
not provided or is `0`, the priority of the current process is returned.

## `os.homedir()`
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* Returns: {string}

Returns the string path of the current user's home directory.

On POSIX, it uses the `$HOME` environment variable if defined. Otherwise it
uses the [effective UID][EUID] to look up the user's home directory.

On Windows, it uses the `USERPROFILE` environment variable if defined.
Otherwise it uses the path to the profile directory of the current user.

## `os.hostname()`
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* Returns: {string}

Returns the host name of the operating system as a string.

## `os.loadavg()`
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* Returns: {number[]}

Returns an array containing the 1, 5, and 15 minute load averages.

The load average is a measure of system activity calculated by the operating
system and expressed as a fractional number.

The load average is a Unix-specific concept. On Windows, the return value is
always `[0, 0, 0]`.

## `os.networkInterfaces()`
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* Returns: {Object}

Returns an object containing network interfaces that have been assigned a
network address.

Each key on the returned object identifies a network interface. The associated
value is an array of objects that each describe an assigned network address.

The properties available on the assigned network address object include:

* `address` {string} The assigned IPv4 or IPv6 address
* `netmask` {string} The IPv4 or IPv6 network mask
* `family` {string} Either `IPv4` or `IPv6`
* `mac` {string} The MAC address of the network interface
* `internal` {boolean} `true` if the network interface is a loopback or
  similar interface that is not remotely accessible; otherwise `false`
* `scopeid` {number} The numeric IPv6 scope ID (only specified when `family`
  is `IPv6`)
* `cidr` {string} The assigned IPv4 or IPv6 address with the routing prefix
  in CIDR notation. If the `netmask` is invalid, this property is set
  to `null`.

<!-- eslint-skip -->
```js
{
  lo: [
    {
      address: '127.0.0.1',
      netmask: '255.0.0.0',
      family: 'IPv4',
      mac: '00:00:00:00:00:00',
      internal: true,
      cidr: '127.0.0.1/8'
    },
    {
      address: '::1',
      netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
      family: 'IPv6',
      mac: '00:00:00:00:00:00',
      scopeid: 0,
      internal: true,
      cidr: '::1/128'
    }
  ],
  eth0: [
    {
      address: '192.168.1.108',
      netmask: '255.255.255.0',
      family: 'IPv4',
      mac: '01:02:03:0a:0b:0c',
      internal: false,
      cidr: '192.168.1.108/24'
    },
    {
      address: 'fe80::a00:27ff:fe4e:66a1',
      netmask: 'ffff:ffff:ffff:ffff::',
      family: 'IPv6',
      mac: '01:02:03:0a:0b:0c',
      scopeid: 1,
      internal: false,
      cidr: 'fe80::a00:27ff:fe4e:66a1/64'
    }
  ]
}
```

## `os.platform()`
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* Returns: {string}

Returns a string identifying the operating system platform. The value is set
at compile time. Possible values are `'aix'`, `'darwin'`, `'freebsd'`,
`'linux'`, `'openbsd'`, `'sunos'`, and `'win32'`.

The return value is equivalent to [`process.platform`][].

The value `'android'` may also be returned if Node.js is built on the Android
operating system. [Android support is experimental][Android building].

## `os.release()`
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* Returns: {string}

Returns the operating system as a string.

On POSIX systems, the operating system release is determined by calling
[`uname(3)`][]. On Windows, `GetVersionExW()` is used. See
<https://en.wikipedia.org/wiki/Uname#Examples> for more information.

## `os.setPriority([pid, ]priority)`
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* `pid` {integer} The process ID to set scheduling priority for.
  **Default** `0`.
* `priority` {integer} The scheduling priority to assign to the process.

Attempts to set the scheduling priority for the process specified by `pid`. If
`pid` is not provided or is `0`, the process ID of the current process is used.

The `priority` input must be an integer between `-20` (high priority) and `19`
(low priority). Due to differences between Unix priority levels and Windows
priority classes, `priority` is mapped to one of six priority constants in
`os.constants.priority`. When retrieving a process priority level, this range
mapping may cause the return value to be slightly different on Windows. To avoid
confusion, set `priority` to one of the priority constants.

On Windows, setting priority to `PRIORITY_HIGHEST` requires elevated user
privileges. Otherwise the set priority will be silently reduced to
`PRIORITY_HIGH`.

## `os.tmpdir()`
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    description: This function is now cross-platform consistent and no longer
                 returns a path with a trailing slash on any platform.
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* Returns: {string}

Returns the operating system's default directory for temporary files as a
string.

## `os.totalmem()`
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* Returns: {integer}

Returns the total amount of system memory in bytes as an integer.

## `os.type()`
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* Returns: {string}

Returns the operating system name as returned by [`uname(3)`][]. For example, it
returns `'Linux'` on Linux, `'Darwin'` on macOS, and `'Windows_NT'` on Windows.

See <https://en.wikipedia.org/wiki/Uname#Examples> for additional information
about the output of running [`uname(3)`][] on various operating systems.

## `os.uptime()`
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                 component on Windows.
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* Returns: {integer}

Returns the system uptime in number of seconds.

The value returned can be inaccurate in some
rare virtualization cases. The issue arises when the virtualized
guest instance shares the kernel with the host system.
Due to the fact that libuv uses a syscall that
provides host's uptime instead of guest's
uptime on OpenVZ, `os.uptime()` may also provide
erroneous result.

Please refer to <https://github.com/nodejs/node/issues/36244> and
<https://github.com/libuv/libuv/issues/3068> for an exploration of
this issue, until it is resolved by libuv.

## `os.userInfo([options])`
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* `options` {Object}
  * `encoding` {string} Character encoding used to interpret resulting strings.
    If `encoding` is set to `'buffer'`, the `username`, `shell`, and `homedir`
    values will be `Buffer` instances. **Default:** `'utf8'`.
* Returns: {Object}

Returns information about the currently effective user. On POSIX platforms,
this is typically a subset of the password file. The returned object includes
the `username`, `uid`, `gid`, `shell`, and `homedir`. On Windows, the `uid` and
`gid` fields are `-1`, and `shell` is `null`.

The value of `homedir` returned by `os.userInfo()` is provided by the operating
system. This differs from the result of `os.homedir()`, which queries
environment variables for the home directory before falling back to the
operating system response.

Throws a [`SystemError`][] if a user has no `username` or `homedir`.

## `os.version()`
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 - v12.17.0
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* Returns {string}

Returns a string identifying the kernel version.

On POSIX systems, the operating system release is determined by calling
[`uname(3)`][]. On Windows, `RtlGetVersion()` is used, and if it is not
available, `GetVersionExW()` will be used. See
<https://en.wikipedia.org/wiki/Uname#Examples> for more information.

## OS constants

The following constants are exported by `os.constants`.

Not all constants will be available on every operating system.

### Signal constants
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The following signal constants are exported by `os.constants.signals`.

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>SIGHUP</code></td>
    <td>Sent to indicate when a controlling terminal is closed or a parent
    process exits.</td>
  </tr>
  <tr>
    <td><code>SIGINT</code></td>
    <td>Sent to indicate when a user wishes to interrupt a process
    (<kbd>Ctrl</kbd>+<kbd>C</kbd>).</td>
  </tr>
  <tr>
    <td><code>SIGQUIT</code></td>
    <td>Sent to indicate when a user wishes to terminate a process and perform a
    core dump.</td>
  </tr>
  <tr>
    <td><code>SIGILL</code></td>
    <td>Sent to a process to notify that it has attempted to perform an illegal,
    malformed, unknown, or privileged instruction.</td>
  </tr>
  <tr>
    <td><code>SIGTRAP</code></td>
    <td>Sent to a process when an exception has occurred.</td>
  </tr>
  <tr>
    <td><code>SIGABRT</code></td>
    <td>Sent to a process to request that it abort.</td>
  </tr>
  <tr>
    <td><code>SIGIOT</code></td>
    <td>Synonym for <code>SIGABRT</code></td>
  </tr>
  <tr>
    <td><code>SIGBUS</code></td>
    <td>Sent to a process to notify that it has caused a bus error.</td>
  </tr>
  <tr>
    <td><code>SIGFPE</code></td>
    <td>Sent to a process to notify that it has performed an illegal arithmetic
    operation.</td>
  </tr>
  <tr>
    <td><code>SIGKILL</code></td>
    <td>Sent to a process to terminate it immediately.</td>
  </tr>
  <tr>
    <td><code>SIGUSR1</code> <code>SIGUSR2</code></td>
    <td>Sent to a process to identify user-defined conditions.</td>
  </tr>
  <tr>
    <td><code>SIGSEGV</code></td>
    <td>Sent to a process to notify of a segmentation fault.</td>
  </tr>
  <tr>
    <td><code>SIGPIPE</code></td>
    <td>Sent to a process when it has attempted to write to a disconnected
    pipe.</td>
  </tr>
  <tr>
    <td><code>SIGALRM</code></td>
    <td>Sent to a process when a system timer elapses.</td>
  </tr>
  <tr>
    <td><code>SIGTERM</code></td>
    <td>Sent to a process to request termination.</td>
  </tr>
  <tr>
    <td><code>SIGCHLD</code></td>
    <td>Sent to a process when a child process terminates.</td>
  </tr>
  <tr>
    <td><code>SIGSTKFLT</code></td>
    <td>Sent to a process to indicate a stack fault on a coprocessor.</td>
  </tr>
  <tr>
    <td><code>SIGCONT</code></td>
    <td>Sent to instruct the operating system to continue a paused process.</td>
  </tr>
  <tr>
    <td><code>SIGSTOP</code></td>
    <td>Sent to instruct the operating system to halt a process.</td>
  </tr>
  <tr>
    <td><code>SIGTSTP</code></td>
    <td>Sent to a process to request it to stop.</td>
  </tr>
  <tr>
    <td><code>SIGBREAK</code></td>
    <td>Sent to indicate when a user wishes to interrupt a process.</td>
  </tr>
  <tr>
    <td><code>SIGTTIN</code></td>
    <td>Sent to a process when it reads from the TTY while in the
    background.</td>
  </tr>
  <tr>
    <td><code>SIGTTOU</code></td>
    <td>Sent to a process when it writes to the TTY while in the
    background.</td>
  </tr>
  <tr>
    <td><code>SIGURG</code></td>
    <td>Sent to a process when a socket has urgent data to read.</td>
  </tr>
  <tr>
    <td><code>SIGXCPU</code></td>
    <td>Sent to a process when it has exceeded its limit on CPU usage.</td>
  </tr>
  <tr>
    <td><code>SIGXFSZ</code></td>
    <td>Sent to a process when it grows a file larger than the maximum
    allowed.</td>
  </tr>
  <tr>
    <td><code>SIGVTALRM</code></td>
    <td>Sent to a process when a virtual timer has elapsed.</td>
  </tr>
  <tr>
    <td><code>SIGPROF</code></td>
    <td>Sent to a process when a system timer has elapsed.</td>
  </tr>
  <tr>
    <td><code>SIGWINCH</code></td>
    <td>Sent to a process when the controlling terminal has changed its
    size.</td>
  </tr>
  <tr>
    <td><code>SIGIO</code></td>
    <td>Sent to a process when I/O is available.</td>
  </tr>
  <tr>
    <td><code>SIGPOLL</code></td>
    <td>Synonym for <code>SIGIO</code></td>
  </tr>
  <tr>
    <td><code>SIGLOST</code></td>
    <td>Sent to a process when a file lock has been lost.</td>
  </tr>
  <tr>
    <td><code>SIGPWR</code></td>
    <td>Sent to a process to notify of a power failure.</td>
  </tr>
  <tr>
    <td><code>SIGINFO</code></td>
    <td>Synonym for <code>SIGPWR</code></td>
  </tr>
  <tr>
    <td><code>SIGSYS</code></td>
    <td>Sent to a process to notify of a bad argument.</td>
  </tr>
  <tr>
    <td><code>SIGUNUSED</code></td>
    <td>Synonym for <code>SIGSYS</code></td>
  </tr>
</table>

### Error constants

The following error constants are exported by `os.constants.errno`.

#### POSIX error constants

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>E2BIG</code></td>
    <td>Indicates that the list of arguments is longer than expected.</td>
  </tr>
  <tr>
    <td><code>EACCES</code></td>
    <td>Indicates that the operation did not have sufficient permissions.</td>
  </tr>
  <tr>
    <td><code>EADDRINUSE</code></td>
    <td>Indicates that the network address is already in use.</td>
  </tr>
  <tr>
    <td><code>EADDRNOTAVAIL</code></td>
    <td>Indicates that the network address is currently unavailable for
    use.</td>
  </tr>
  <tr>
    <td><code>EAFNOSUPPORT</code></td>
    <td>Indicates that the network address family is not supported.</td>
  </tr>
  <tr>
    <td><code>EAGAIN</code></td>
    <td>Indicates that there is no data available and to try the
    operation again later.</td>
  </tr>
  <tr>
    <td><code>EALREADY</code></td>
    <td>Indicates that the socket already has a pending connection in
    progress.</td>
  </tr>
  <tr>
    <td><code>EBADF</code></td>
    <td>Indicates that a file descriptor is not valid.</td>
  </tr>
  <tr>
    <td><code>EBADMSG</code></td>
    <td>Indicates an invalid data message.</td>
  </tr>
  <tr>
    <td><code>EBUSY</code></td>
    <td>Indicates that a device or resource is busy.</td>
  </tr>
  <tr>
    <td><code>ECANCELED</code></td>
    <td>Indicates that an operation was canceled.</td>
  </tr>
  <tr>
    <td><code>ECHILD</code></td>
    <td>Indicates that there are no child processes.</td>
  </tr>
  <tr>
    <td><code>ECONNABORTED</code></td>
    <td>Indicates that the network connection has been aborted.</td>
  </tr>
  <tr>
    <td><code>ECONNREFUSED</code></td>
    <td>Indicates that the network connection has been refused.</td>
  </tr>
  <tr>
    <td><code>ECONNRESET</code></td>
    <td>Indicates that the network connection has been reset.</td>
  </tr>
  <tr>
    <td><code>EDEADLK</code></td>
    <td>Indicates that a resource deadlock has been avoided.</td>
  </tr>
  <tr>
    <td><code>EDESTADDRREQ</code></td>
    <td>Indicates that a destination address is required.</td>
  </tr>
  <tr>
    <td><code>EDOM</code></td>
    <td>Indicates that an argument is out of the domain of the function.</td>
  </tr>
  <tr>
    <td><code>EDQUOT</code></td>
    <td>Indicates that the disk quota has been exceeded.</td>
  </tr>
  <tr>
    <td><code>EEXIST</code></td>
    <td>Indicates that the file already exists.</td>
  </tr>
  <tr>
    <td><code>EFAULT</code></td>
    <td>Indicates an invalid pointer address.</td>
  </tr>
  <tr>
    <td><code>EFBIG</code></td>
    <td>Indicates that the file is too large.</td>
  </tr>
  <tr>
    <td><code>EHOSTUNREACH</code></td>
    <td>Indicates that the host is unreachable.</td>
  </tr>
  <tr>
    <td><code>EIDRM</code></td>
    <td>Indicates that the identifier has been removed.</td>
  </tr>
  <tr>
    <td><code>EILSEQ</code></td>
    <td>Indicates an illegal byte sequence.</td>
  </tr>
  <tr>
    <td><code>EINPROGRESS</code></td>
    <td>Indicates that an operation is already in progress.</td>
  </tr>
  <tr>
    <td><code>EINTR</code></td>
    <td>Indicates that a function call was interrupted.</td>
  </tr>
  <tr>
    <td><code>EINVAL</code></td>
    <td>Indicates that an invalid argument was provided.</td>
  </tr>
  <tr>
    <td><code>EIO</code></td>
    <td>Indicates an otherwise unspecified I/O error.</td>
  </tr>
  <tr>
    <td><code>EISCONN</code></td>
    <td>Indicates that the socket is connected.</td>
  </tr>
  <tr>
    <td><code>EISDIR</code></td>
    <td>Indicates that the path is a directory.</td>
  </tr>
  <tr>
    <td><code>ELOOP</code></td>
    <td>Indicates too many levels of symbolic links in a path.</td>
  </tr>
  <tr>
    <td><code>EMFILE</code></td>
    <td>Indicates that there are too many open files.</td>
  </tr>
  <tr>
    <td><code>EMLINK</code></td>
    <td>Indicates that there are too many hard links to a file.</td>
  </tr>
  <tr>
    <td><code>EMSGSIZE</code></td>
    <td>Indicates that the provided message is too long.</td>
  </tr>
  <tr>
    <td><code>EMULTIHOP</code></td>
    <td>Indicates that a multihop was attempted.</td>
  </tr>
  <tr>
    <td><code>ENAMETOOLONG</code></td>
    <td>Indicates that the filename is too long.</td>
  </tr>
  <tr>
    <td><code>ENETDOWN</code></td>
    <td>Indicates that the network is down.</td>
  </tr>
  <tr>
    <td><code>ENETRESET</code></td>
    <td>Indicates that the connection has been aborted by the network.</td>
  </tr>
  <tr>
    <td><code>ENETUNREACH</code></td>
    <td>Indicates that the network is unreachable.</td>
  </tr>
  <tr>
    <td><code>ENFILE</code></td>
    <td>Indicates too many open files in the system.</td>
  </tr>
  <tr>
    <td><code>ENOBUFS</code></td>
    <td>Indicates that no buffer space is available.</td>
  </tr>
  <tr>
    <td><code>ENODATA</code></td>
    <td>Indicates that no message is available on the stream head read
    queue.</td>
  </tr>
  <tr>
    <td><code>ENODEV</code></td>
    <td>Indicates that there is no such device.</td>
  </tr>
  <tr>
    <td><code>ENOENT</code></td>
    <td>Indicates that there is no such file or directory.</td>
  </tr>
  <tr>
    <td><code>ENOEXEC</code></td>
    <td>Indicates an exec format error.</td>
  </tr>
  <tr>
    <td><code>ENOLCK</code></td>
    <td>Indicates that there are no locks available.</td>
  </tr>
  <tr>
    <td><code>ENOLINK</code></td>
    <td>Indications that a link has been severed.</td>
  </tr>
  <tr>
    <td><code>ENOMEM</code></td>
    <td>Indicates that there is not enough space.</td>
  </tr>
  <tr>
    <td><code>ENOMSG</code></td>
    <td>Indicates that there is no message of the desired type.</td>
  </tr>
  <tr>
    <td><code>ENOPROTOOPT</code></td>
    <td>Indicates that a given protocol is not available.</td>
  </tr>
  <tr>
    <td><code>ENOSPC</code></td>
    <td>Indicates that there is no space available on the device.</td>
  </tr>
  <tr>
    <td><code>ENOSR</code></td>
    <td>Indicates that there are no stream resources available.</td>
  </tr>
  <tr>
    <td><code>ENOSTR</code></td>
    <td>Indicates that a given resource is not a stream.</td>
  </tr>
  <tr>
    <td><code>ENOSYS</code></td>
    <td>Indicates that a function has not been implemented.</td>
  </tr>
  <tr>
    <td><code>ENOTCONN</code></td>
    <td>Indicates that the socket is not connected.</td>
  </tr>
  <tr>
    <td><code>ENOTDIR</code></td>
    <td>Indicates that the path is not a directory.</td>
  </tr>
  <tr>
    <td><code>ENOTEMPTY</code></td>
    <td>Indicates that the directory is not empty.</td>
  </tr>
  <tr>
    <td><code>ENOTSOCK</code></td>
    <td>Indicates that the given item is not a socket.</td>
  </tr>
  <tr>
    <td><code>ENOTSUP</code></td>
    <td>Indicates that a given operation is not supported.</td>
  </tr>
  <tr>
    <td><code>ENOTTY</code></td>
    <td>Indicates an inappropriate I/O control operation.</td>
  </tr>
  <tr>
    <td><code>ENXIO</code></td>
    <td>Indicates no such device or address.</td>
  </tr>
  <tr>
    <td><code>EOPNOTSUPP</code></td>
    <td>Indicates that an operation is not supported on the socket. Although
    <code>ENOTSUP</code> and <code>EOPNOTSUPP</code> have the same value
    on Linux, according to POSIX.1 these error values should be distinct.)</td>
  </tr>
  <tr>
    <td><code>EOVERFLOW</code></td>
    <td>Indicates that a value is too large to be stored in a given data
    type.</td>
  </tr>
  <tr>
    <td><code>EPERM</code></td>
    <td>Indicates that the operation is not permitted.</td>
  </tr>
  <tr>
    <td><code>EPIPE</code></td>
    <td>Indicates a broken pipe.</td>
  </tr>
  <tr>
    <td><code>EPROTO</code></td>
    <td>Indicates a protocol error.</td>
  </tr>
  <tr>
    <td><code>EPROTONOSUPPORT</code></td>
    <td>Indicates that a protocol is not supported.</td>
  </tr>
  <tr>
    <td><code>EPROTOTYPE</code></td>
    <td>Indicates the wrong type of protocol for a socket.</td>
  </tr>
  <tr>
    <td><code>ERANGE</code></td>
    <td>Indicates that the results are too large.</td>
  </tr>
  <tr>
    <td><code>EROFS</code></td>
    <td>Indicates that the file system is read only.</td>
  </tr>
  <tr>
    <td><code>ESPIPE</code></td>
    <td>Indicates an invalid seek operation.</td>
  </tr>
  <tr>
    <td><code>ESRCH</code></td>
    <td>Indicates that there is no such process.</td>
  </tr>
  <tr>
    <td><code>ESTALE</code></td>
    <td>Indicates that the file handle is stale.</td>
  </tr>
  <tr>
    <td><code>ETIME</code></td>
    <td>Indicates an expired timer.</td>
  </tr>
  <tr>
    <td><code>ETIMEDOUT</code></td>
    <td>Indicates that the connection timed out.</td>
  </tr>
  <tr>
    <td><code>ETXTBSY</code></td>
    <td>Indicates that a text file is busy.</td>
  </tr>
  <tr>
    <td><code>EWOULDBLOCK</code></td>
    <td>Indicates that the operation would block.</td>
  </tr>
  <tr>
    <td><code>EXDEV</code></td>
    <td>Indicates an improper link.
  </tr>
</table>

#### Windows-specific error constants

The following error codes are specific to the Windows operating system.

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>WSAEINTR</code></td>
    <td>Indicates an interrupted function call.</td>
  </tr>
  <tr>
    <td><code>WSAEBADF</code></td>
    <td>Indicates an invalid file handle.</td>
  </tr>
  <tr>
    <td><code>WSAEACCES</code></td>
    <td>Indicates insufficient permissions to complete the operation.</td>
  </tr>
  <tr>
    <td><code>WSAEFAULT</code></td>
    <td>Indicates an invalid pointer address.</td>
  </tr>
  <tr>
    <td><code>WSAEINVAL</code></td>
    <td>Indicates that an invalid argument was passed.</td>
  </tr>
  <tr>
    <td><code>WSAEMFILE</code></td>
    <td>Indicates that there are too many open files.</td>
  </tr>
  <tr>
    <td><code>WSAEWOULDBLOCK</code></td>
    <td>Indicates that a resource is temporarily unavailable.</td>
  </tr>
  <tr>
    <td><code>WSAEINPROGRESS</code></td>
    <td>Indicates that an operation is currently in progress.</td>
  </tr>
  <tr>
    <td><code>WSAEALREADY</code></td>
    <td>Indicates that an operation is already in progress.</td>
  </tr>
  <tr>
    <td><code>WSAENOTSOCK</code></td>
    <td>Indicates that the resource is not a socket.</td>
  </tr>
  <tr>
    <td><code>WSAEDESTADDRREQ</code></td>
    <td>Indicates that a destination address is required.</td>
  </tr>
  <tr>
    <td><code>WSAEMSGSIZE</code></td>
    <td>Indicates that the message size is too long.</td>
  </tr>
  <tr>
    <td><code>WSAEPROTOTYPE</code></td>
    <td>Indicates the wrong protocol type for the socket.</td>
  </tr>
  <tr>
    <td><code>WSAENOPROTOOPT</code></td>
    <td>Indicates a bad protocol option.</td>
  </tr>
  <tr>
    <td><code>WSAEPROTONOSUPPORT</code></td>
    <td>Indicates that the protocol is not supported.</td>
  </tr>
  <tr>
    <td><code>WSAESOCKTNOSUPPORT</code></td>
    <td>Indicates that the socket type is not supported.</td>
  </tr>
  <tr>
    <td><code>WSAEOPNOTSUPP</code></td>
    <td>Indicates that the operation is not supported.</td>
  </tr>
  <tr>
    <td><code>WSAEPFNOSUPPORT</code></td>
    <td>Indicates that the protocol family is not supported.</td>
  </tr>
  <tr>
    <td><code>WSAEAFNOSUPPORT</code></td>
    <td>Indicates that the address family is not supported.</td>
  </tr>
  <tr>
    <td><code>WSAEADDRINUSE</code></td>
    <td>Indicates that the network address is already in use.</td>
  </tr>
  <tr>
    <td><code>WSAEADDRNOTAVAIL</code></td>
    <td>Indicates that the network address is not available.</td>
  </tr>
  <tr>
    <td><code>WSAENETDOWN</code></td>
    <td>Indicates that the network is down.</td>
  </tr>
  <tr>
    <td><code>WSAENETUNREACH</code></td>
    <td>Indicates that the network is unreachable.</td>
  </tr>
  <tr>
    <td><code>WSAENETRESET</code></td>
    <td>Indicates that the network connection has been reset.</td>
  </tr>
  <tr>
    <td><code>WSAECONNABORTED</code></td>
    <td>Indicates that the connection has been aborted.</td>
  </tr>
  <tr>
    <td><code>WSAECONNRESET</code></td>
    <td>Indicates that the connection has been reset by the peer.</td>
  </tr>
  <tr>
    <td><code>WSAENOBUFS</code></td>
    <td>Indicates that there is no buffer space available.</td>
  </tr>
  <tr>
    <td><code>WSAEISCONN</code></td>
    <td>Indicates that the socket is already connected.</td>
  </tr>
  <tr>
    <td><code>WSAENOTCONN</code></td>
    <td>Indicates that the socket is not connected.</td>
  </tr>
  <tr>
    <td><code>WSAESHUTDOWN</code></td>
    <td>Indicates that data cannot be sent after the socket has been
    shutdown.</td>
  </tr>
  <tr>
    <td><code>WSAETOOMANYREFS</code></td>
    <td>Indicates that there are too many references.</td>
  </tr>
  <tr>
    <td><code>WSAETIMEDOUT</code></td>
    <td>Indicates that the connection has timed out.</td>
  </tr>
  <tr>
    <td><code>WSAECONNREFUSED</code></td>
    <td>Indicates that the connection has been refused.</td>
  </tr>
  <tr>
    <td><code>WSAELOOP</code></td>
    <td>Indicates that a name cannot be translated.</td>
  </tr>
  <tr>
    <td><code>WSAENAMETOOLONG</code></td>
    <td>Indicates that a name was too long.</td>
  </tr>
  <tr>
    <td><code>WSAEHOSTDOWN</code></td>
    <td>Indicates that a network host is down.</td>
  </tr>
  <tr>
    <td><code>WSAEHOSTUNREACH</code></td>
    <td>Indicates that there is no route to a network host.</td>
  </tr>
  <tr>
    <td><code>WSAENOTEMPTY</code></td>
    <td>Indicates that the directory is not empty.</td>
  </tr>
  <tr>
    <td><code>WSAEPROCLIM</code></td>
    <td>Indicates that there are too many processes.</td>
  </tr>
  <tr>
    <td><code>WSAEUSERS</code></td>
    <td>Indicates that the user quota has been exceeded.</td>
  </tr>
  <tr>
    <td><code>WSAEDQUOT</code></td>
    <td>Indicates that the disk quota has been exceeded.</td>
  </tr>
  <tr>
    <td><code>WSAESTALE</code></td>
    <td>Indicates a stale file handle reference.</td>
  </tr>
  <tr>
    <td><code>WSAEREMOTE</code></td>
    <td>Indicates that the item is remote.</td>
  </tr>
  <tr>
    <td><code>WSASYSNOTREADY</code></td>
    <td>Indicates that the network subsystem is not ready.</td>
  </tr>
  <tr>
    <td><code>WSAVERNOTSUPPORTED</code></td>
    <td>Indicates that the <code>winsock.dll</code> version is out of
    range.</td>
  </tr>
  <tr>
    <td><code>WSANOTINITIALISED</code></td>
    <td>Indicates that successful WSAStartup has not yet been performed.</td>
  </tr>
  <tr>
    <td><code>WSAEDISCON</code></td>
    <td>Indicates that a graceful shutdown is in progress.</td>
  </tr>
  <tr>
    <td><code>WSAENOMORE</code></td>
    <td>Indicates that there are no more results.</td>
  </tr>
  <tr>
    <td><code>WSAECANCELLED</code></td>
    <td>Indicates that an operation has been canceled.</td>
  </tr>
  <tr>
    <td><code>WSAEINVALIDPROCTABLE</code></td>
    <td>Indicates that the procedure call table is invalid.</td>
  </tr>
  <tr>
    <td><code>WSAEINVALIDPROVIDER</code></td>
    <td>Indicates an invalid service provider.</td>
  </tr>
  <tr>
    <td><code>WSAEPROVIDERFAILEDINIT</code></td>
    <td>Indicates that the service provider failed to initialized.</td>
  </tr>
  <tr>
    <td><code>WSASYSCALLFAILURE</code></td>
    <td>Indicates a system call failure.</td>
  </tr>
  <tr>
    <td><code>WSASERVICE_NOT_FOUND</code></td>
    <td>Indicates that a service was not found.</td>
  </tr>
  <tr>
    <td><code>WSATYPE_NOT_FOUND</code></td>
    <td>Indicates that a class type was not found.</td>
  </tr>
  <tr>
    <td><code>WSA_E_NO_MORE</code></td>
    <td>Indicates that there are no more results.</td>
  </tr>
  <tr>
    <td><code>WSA_E_CANCELLED</code></td>
    <td>Indicates that the call was canceled.</td>
  </tr>
  <tr>
    <td><code>WSAEREFUSED</code></td>
    <td>Indicates that a database query was refused.</td>
  </tr>
</table>

### dlopen constants

If available on the operating system, the following constants
are exported in `os.constants.dlopen`. See dlopen(3) for detailed
information.

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>RTLD_LAZY</code></td>
    <td>Perform lazy binding. Node.js sets this flag by default.</td>
  </tr>
  <tr>
    <td><code>RTLD_NOW</code></td>
    <td>Resolve all undefined symbols in the library before dlopen(3)
    returns.</td>
  </tr>
  <tr>
    <td><code>RTLD_GLOBAL</code></td>
    <td>Symbols defined by the library will be made available for symbol
    resolution of subsequently loaded libraries.</td>
  </tr>
  <tr>
    <td><code>RTLD_LOCAL</code></td>
    <td>The converse of <code>RTLD_GLOBAL</code>. This is the default behavior
    if neither flag is specified.</td>
  </tr>
  <tr>
    <td><code>RTLD_DEEPBIND</code></td>
    <td>Make a self-contained library use its own symbols in preference to
    symbols from previously loaded libraries.</td>
  </tr>
</table>

### Priority constants
<!-- YAML
added: v10.10.0
-->

The following process scheduling constants are exported by
`os.constants.priority`.

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>PRIORITY_LOW</code></td>
    <td>The lowest process scheduling priority. This corresponds to
    <code>IDLE_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>19</code> on all other platforms.</td>
  </tr>
  <tr>
    <td><code>PRIORITY_BELOW_NORMAL</code></td>
    <td>The process scheduling priority above <code>PRIORITY_LOW</code> and
    below <code>PRIORITY_NORMAL</code>. This corresponds to
    <code>BELOW_NORMAL_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>10</code> on all other platforms.</td>
  </tr>
  <tr>
    <td><code>PRIORITY_NORMAL</code></td>
    <td>The default process scheduling priority. This corresponds to
    <code>NORMAL_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>0</code> on all other platforms.</td>
  </tr>
  <tr>
    <td><code>PRIORITY_ABOVE_NORMAL</code></td>
    <td>The process scheduling priority above <code>PRIORITY_NORMAL</code> and
    below <code>PRIORITY_HIGH</code>. This corresponds to
    <code>ABOVE_NORMAL_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>-7</code> on all other platforms.</td>
  </tr>
  <tr>
    <td><code>PRIORITY_HIGH</code></td>
    <td>The process scheduling priority above <code>PRIORITY_ABOVE_NORMAL</code>
    and below <code>PRIORITY_HIGHEST</code>. This corresponds to
    <code>HIGH_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>-14</code> on all other platforms.</td>
  </tr>
  <tr>
    <td><code>PRIORITY_HIGHEST</code></td>
    <td>The highest process scheduling priority. This corresponds to
    <code>REALTIME_PRIORITY_CLASS</code> on Windows, and a nice value of
    <code>-20</code> on all other platforms.</td>
  </tr>
</table>

### libuv constants

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>UV_UDP_REUSEADDR</code></td>
    <td></td>
  </tr>
</table>

[Android building]: https://github.com/nodejs/node/blob/master/BUILDING.md#androidandroid-based-devices-eg-firefox-os
[EUID]: https://en.wikipedia.org/wiki/User_identifier#Effective_user_ID
[`SystemError`]: errors.md#errors_class_systemerror
[`process.arch`]: process.md#process_process_arch
[`process.platform`]: process.md#process_process_platform
[`uname(3)`]: https://linux.die.net/man/3/uname
