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# OS <!--introduced_in=v0.10.0--> > Stability: 2 - Stable <!-- source_link=lib/os.js --> The `node:os` module provides operating system-related utility methods and properties. It can be accessed using: ```mjs import os from 'node:os'; ``` ```cjs const os = require('node:os'); ``` ## `os.EOL` <!-- YAML added: v0.7.8 --> * Type: {string} The operating system-specific end-of-line marker. * `\n` on POSIX * `\r\n` on Windows ## `os.availableParallelism()` <!-- YAML added: - v19.4.0 - v18.14.0 --> * 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()` <!-- YAML added: v0.5.0 --> * 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'`, `'ppc'`, `'ppc64'`, `'riscv64'`, `'s390'`, `'s390x'`, and `'x64'`. The return value is equivalent to [`process.arch`][]. ## `os.constants` <!-- YAML added: v6.3.0 --> * Type: {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-constants). ## `os.cpus()` <!-- YAML added: v0.3.3 --> * 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. <!-- eslint-disable @stylistic/js/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.cpus().length` should not be used to calculate the amount of parallelism available to an application. Use [`os.availableParallelism()`](#osavailableparallelism) for this purpose. ## `os.devNull` <!-- YAML added: - v16.3.0 - v14.18.0 --> * Type: {string} The platform-specific file path of the null device. * `\\.\nul` on Windows * `/dev/null` on POSIX ## `os.endianness()` <!-- YAML added: v0.9.4 --> * 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()` <!-- YAML added: v0.3.3 --> * Returns: {integer} Returns the amount of free system memory in bytes as an integer. ## `os.getPriority([pid])` <!-- YAML added: v10.10.0 --> * `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()` <!-- YAML added: v2.3.0 --> * 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()` <!-- YAML added: v0.3.3 --> * Returns: {string} Returns the host name of the operating system as a string. ## `os.loadavg()` <!-- YAML added: v0.3.3 --> * 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()` <!-- YAML added: - v18.9.0 - v16.18.0 --> * 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()` <!-- YAML added: v0.6.0 changes: - version: v18.4.0 pr-url: https://github.com/nodejs/node/pull/43054 description: The `family` property now returns a string instead of a number. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41431 description: The `family` property now returns a number instead of a string. --> * 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()` <!-- YAML added: v0.5.0 --> * 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][Android building]. ## `os.release()` <!-- YAML added: v0.3.3 --> * 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)` <!-- YAML added: v10.10.0 --> * `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()` <!-- YAML added: v0.9.9 changes: - version: v2.0.0 pr-url: https://github.com/nodejs/node/pull/747 description: This function is now cross-platform consistent and no longer returns a path with a trailing slash on any platform. --> * 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()` <!-- YAML added: v0.3.3 --> * Returns: {integer} Returns the total amount of system memory in bytes as an integer. ## `os.type()` <!-- YAML added: v0.3.3 --> * 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()` <!-- YAML added: v0.3.3 changes: - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/20129 description: The result of this function no longer contains a fraction component on Windows. --> * Returns: {integer} Returns the system uptime in number of seconds. ## `os.userInfo([options])` <!-- YAML added: v6.0.0 --> * `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()` <!-- YAML added: - v13.11.0 - v12.17.0 --> * 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 <!-- YAML changes: - version: v5.11.0 pr-url: https://github.com/nodejs/node/pull/6093 description: Added support for `SIGINFO`. --> 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.</td> </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/HEAD/BUILDING.md#android [EUID]: https://en.wikipedia.org/wiki/User_identifier#Effective_user_ID [`SystemError`]: errors.md#class-systemerror [`process.arch`]: process.md#processarch [`process.platform`]: process.md#processplatform [`uname(3)`]: https://linux.die.net/man/3/uname [`uv_available_parallelism()`]: https://docs.libuv.org/en/v1.x/misc.html#c.uv_available_parallelism