OS

Stability: 2 - Stable

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

const os = require('os');

`os.EOL`

{string}

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

\n on POSIX
\r\n on Windows

`os.arch()`

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`

{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 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.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.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. 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.

`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.

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 nodejs#36244 and libuv/libuv#3068 for an exploration of this issue, until it is resolved by libuv.

`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.

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

Error constants

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

POSIX error constants

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

Windows-specific error constants

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

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

dlopen constants

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

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

Priority constants

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

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

libuv constants

Constant	Description
`UV_UDP_REUSEADDR`

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os.md

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OS

`os.EOL`

`os.arch()`

`os.constants`

`os.cpus()`

`os.endianness()`

`os.freemem()`

`os.getPriority([pid])`

`os.homedir()`

`os.hostname()`

`os.loadavg()`

`os.networkInterfaces()`

`os.platform()`

`os.release()`

`os.setPriority([pid, ]priority)`

`os.tmpdir()`

`os.totalmem()`

`os.type()`

`os.uptime()`

`os.userInfo([options])`

`os.version()`

OS constants

Signal constants

Error constants

POSIX error constants

Windows-specific error constants

dlopen constants

Priority constants

libuv constants

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OS

os.EOL

os.arch()

os.constants

os.cpus()

os.endianness()

os.freemem()

os.getPriority([pid])

os.homedir()

os.hostname()

os.loadavg()

os.networkInterfaces()

os.platform()

os.release()

os.setPriority([pid, ]priority)

os.tmpdir()

os.totalmem()

os.type()

os.uptime()

os.userInfo([options])

os.version()

OS constants

Signal constants

Error constants

POSIX error constants

Windows-specific error constants

dlopen constants

Priority constants

libuv constants

`os.EOL`

`os.arch()`

`os.constants`

`os.cpus()`

`os.endianness()`

`os.freemem()`

`os.getPriority([pid])`

`os.homedir()`

`os.hostname()`

`os.loadavg()`

`os.networkInterfaces()`

`os.platform()`

`os.release()`

`os.setPriority([pid, ]priority)`

`os.tmpdir()`

`os.totalmem()`

`os.type()`

`os.uptime()`

`os.userInfo([options])`

`os.version()`