Node.js os.constants

The os.constants is an inbuilt application programming interface of the os module which is used to get operating system specified constants for error code, signal constants, priority constants, dlopen constants, etc.

Syntax:

os.constants

Return Value: It returns an object that contains operating system-specified constants. 

Examples: error codes, signal constants, priority constants, dlopen constants, etc.

Signal constants can be accessed by using os.constants.signals and priority constants can be accessed by using os.constants.priority. 

Some of the constants are listed below:

Signal Constants:

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

Error constants:

1. POSIX error constant

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

2. Windows specific error

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

dlopen Constants:

Constant Code	Constant Description
RTLD_LAZY	It performs lazy binding. Node.js sets this flag by default.
RTLD_NOW	It solve all undefined symbols in the library before dlopen(3) returns.
RTLD_GLOBAL	These 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	this make a self-contained library use its own symbols in preference to symbols from previously loaded libraries.

Priority constants:

Constant Codes	Constant Description
PRIORITY_LOW	The minimum process scheduling priority.
PRIORITY_BELOW_NORMAL	The process scheduling priority is below PRIORITY_NORMAL and above PRIORITY_LOW.
PRIORITY_NORMAL	The process scheduling priority is normal or default.
PRIORITY_ABOVE_NORMAL	The process scheduling priority is below PRIORITY_HIGH and above PRIORITY_NORMAL.
PRIORITY_HIGH	The process scheduling priority below PRIORITY_HIGHEST and above PRIORITY_ABOVE_NORMAL.
PRIORITY_HIGHEST	Process scheduling priority is maximum.

libuv Constants:

Constant Codes	Constant Description
UV_UDP_REUSEADDR

The below examples illustrate the use of os.constants in Node.js:

Example 1:

javascript

// Import os module
const os = require('os');

constants = os.constants;

// Printing all os.constants
console.log(constants);

Output:

[Object: null prototype] {
  UV_UDP_REUSEADDR: 4,
  dlopen: [Object: null prototype] {},
  errno:
   [Object: null prototype] {
     E2BIG: 7,
     EACCES: 13,
     EADDRINUSE: 100,
     . . .
     PRIORITY_HIGH: -14,
     PRIORITY_HIGHEST: -20 } }

Example 2:

javascript

// Import os module
const os = require('os');

constants = os.constants;

// Printing os.constants

// Signals constants
if(constants.signals != undefined){
    console.log("Signals:");
    console.log(constants.signals);
}

// Priority constants
if(constants.priority!=undefined){
    console.log("priority:");
    console.log(constants.priority);
}

Output:

Signals:
[Object: null prototype] {
  SIGHUP: 1,
  SIGINT: 2,
  . . .
  PRIORITY_HIGH: -14,
  PRIORITY_HIGHEST: -20 }

Note: The above program will compile and run by using the node index.js command.

Reference: https://nodejs.org/api/os.html#os_os_constants