# OS > Stability: 2 - Stable The `os` module provides operating system-related utility methods and properties. It can be accessed using: ```js 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_os_constants_1). ## `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. ```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()` * 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][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()` * Returns: {string} Returns the hostname 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`. ```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()` * 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()` * 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. ## `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 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
[`SystemError`]: errors.html#errors_class_systemerror [`process.arch`]: process.html#process_process_arch [`process.platform`]: process.html#process_process_platform [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 [uname(3)]: https://linux.die.net/man/3/uname