OS

Stability: 2 - Stable

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

import os from 'node:os';

const os = require('node:os');

`os.EOL`

{string}

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

\n on POSIX
\r\n on Windows

`os.availableParallelism()`

Returns: {integer}

Returns an estimate of the default amount of parallelism a program should use. Always returns a value greater than zero.

This function is a small wrapper about libuv's uv_available_parallelism().

`os.arch()`

Returns: {string}

Returns the operating system CPU architecture for which the Node.js binary was compiled. Possible values are 'arm', 'arm64', 'ia32', 'loong64', 'mips', 'mipsel', 'ppc64', 'riscv64', 's390', 's390x', and 'x64'.

The return value is equivalent to process.arch.

`os.constants`

{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.cpus()`

Returns: {Object[]}

Returns an array of objects containing information about each logical CPU core. The array will be empty if no CPU information is available, such as if the /proc file system is unavailable.

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.

[
  {
    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.cpus().length should not be used to calculate the amount of parallelism available to an application. Use os.availableParallelism() for this purpose.

`os.devNull`

{string}

The platform-specific file path of the null device.

\\.\nul on Windows
/dev/null on POSIX

`os.endianness()`

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()`

Returns: {integer}

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

`os.getPriority([pid])`

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()`

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 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()`

Returns: {string}

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

`os.loadavg()`

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.machine()`

Returns: {string}

Returns the machine type as a string, such as arm, arm64, aarch64, mips, mips64, ppc64, ppc64le, s390, s390x, i386, i686, x86_64.

On POSIX systems, the machine type 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.networkInterfaces()`

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.

{
  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()`

Returns: {string}

Returns a string identifying the operating system platform for which the Node.js binary was compiled. 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.

`os.release()`

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)`

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()`

Returns: {string}

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

On Windows, the result can be overridden by TEMP and TMP environment variables, and TEMP takes precedence over TMP. If neither is set, it defaults to %SystemRoot%\temp or %windir%\temp.

On non-Windows platforms, TMPDIR, TMP and TEMP environment variables will be checked to override the result of this method, in the described order. If none of them is set, it defaults to /tmp.

Some operating system distributions would either configure TMPDIR (non-Windows) or TEMP and TMP (Windows) by default without additional configurations by the system administrators. The result of os.tmpdir() typically reflects the system preference unless it's explicitly overridden by the users.

`os.totalmem()`

Returns: {integer}

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

`os.type()`

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()`

Returns: {integer}

Returns the system uptime in number of seconds.

`os.userInfo([options])`

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()`

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

The following signal constants are exported by os.constants.signals.

Error constants

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

POSIX error constants

Windows-specific error constants

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

dlopen constants

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

Priority constants

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

OS

os.EOL

os.availableParallelism()

os.arch()

os.constants

os.cpus()

os.devNull

os.endianness()

os.freemem()

os.getPriority([pid])

os.homedir()

os.hostname()

os.loadavg()

os.machine()

os.networkInterfaces()

os.platform()

os.release()

os.setPriority([pid, ]priority)

os.tmpdir()

os.totalmem()

os.type()

os.uptime()

os.userInfo([options])

os.version()