# Errno An error number used by system calls to communicate what kind of error occurred. ``` @frozen struct Errno ``` ## Topics ### File and Directory Errors [`static var attributeNotFound: Errno`](/documentation/System/Errno/attributeNotFound) Attribute not found. [`static var badFileDescriptor: Errno`](/documentation/System/Errno/badFileDescriptor) Bad file descriptor. [`static var fileExists: Errno`](/documentation/System/Errno/fileExists) File exists. [`static var fileTooLarge: Errno`](/documentation/System/Errno/fileTooLarge) The file is too large. [`static var improperLink: Errno`](/documentation/System/Errno/improperLink) Improper link. [`static var isDirectory: Errno`](/documentation/System/Errno/isDirectory) Is a directory. [`static var noLocks: Errno`](/documentation/System/Errno/noLocks) No locks available. [`static var noSuchFileOrDirectory: Errno`](/documentation/System/Errno/noSuchFileOrDirectory) No such file or directory. [`static var notDirectory: Errno`](/documentation/System/Errno/notDirectory) Not a directory. [`static var permissionDenied: Errno`](/documentation/System/Errno/permissionDenied) Permission denied. [`static var textFileBusy: Errno`](/documentation/System/Errno/textFileBusy) Text file busy. ### File System Errors [`static var badFileTypeOrFormat: Errno`](/documentation/System/Errno/badFileTypeOrFormat) Inappropriate file type or format. [`static var directoryNotEmpty: Errno`](/documentation/System/Errno/directoryNotEmpty) Directory not empty. [`static var diskQuotaExceeded: Errno`](/documentation/System/Errno/diskQuotaExceeded) Disk quota exceeded. [`static var noSpace: Errno`](/documentation/System/Errno/noSpace) Device out of space. [`static var readOnlyFileSystem: Errno`](/documentation/System/Errno/readOnlyFileSystem) Read-only file system. [`static var tooManyLinks: Errno`](/documentation/System/Errno/tooManyLinks) Too many links. [`static var tooManyOpenFilesInSystem: Errno`](/documentation/System/Errno/tooManyOpenFilesInSystem) The system has too many open files. [`static var tooManyOpenFiles: Errno`](/documentation/System/Errno/tooManyOpenFiles) This process has too many open files. ### NFS Errors [`static var authenticationError: Errno`](/documentation/System/Errno/authenticationError) Authentication error. [`static var needAuthenticator: Errno`](/documentation/System/Errno/needAuthenticator) Need authenticator. [`static var staleNFSFileHandle: Errno`](/documentation/System/Errno/staleNFSFileHandle) Stale NFS file handle. ### Device Errors [`static var deviceError: Errno`](/documentation/System/Errno/deviceError) Device error. [`static var devicePowerIsOff: Errno`](/documentation/System/Errno/devicePowerIsOff) Device power is off. [`static var inappropriateIOCTLForDevice: Errno`](/documentation/System/Errno/inappropriateIOCTLForDevice) Inappropriate control function. [`static var ioError: Errno`](/documentation/System/Errno/ioError) Input/output error. [`static var noSuchAddressOrDevice: Errno`](/documentation/System/Errno/noSuchAddressOrDevice) No such device or address. [`static var notBlockDevice: Errno`](/documentation/System/Errno/notBlockDevice) Not a block device. [`static var operationNotSupportedByDevice: Errno`](/documentation/System/Errno/operationNotSupportedByDevice) Operation not supported by device. ### Path Errors [`static var fileNameTooLong: Errno`](/documentation/System/Errno/fileNameTooLong) The file name is too long. [`static var tooManyRemoteLevels: Errno`](/documentation/System/Errno/tooManyRemoteLevels) Too many levels of remote in path. [`static var tooManySymbolicLinkLevels: Errno`](/documentation/System/Errno/tooManySymbolicLinkLevels) Too many levels of symbolic links. ### Pipe Errors [`static var brokenPipe: Errno`](/documentation/System/Errno/brokenPipe) Broken pipe. [`static var illegalSeek: Errno`](/documentation/System/Errno/illegalSeek) Illegal seek. ### Runtime Errors [`static var deadlock: Errno`](/documentation/System/Errno/deadlock) Resource deadlock avoided. [`static var noMemory: Errno`](/documentation/System/Errno/noMemory) Can’t allocate memory. [`static var wouldBlock: Errno`](/documentation/System/Errno/wouldBlock) Operation would block. ### Math Errors [`static var outOfDomain: Errno`](/documentation/System/Errno/outOfDomain) Numerical argument out of domain. [`static var outOfRange: Errno`](/documentation/System/Errno/outOfRange) Numerical result out of range. [`static var overflow: Errno`](/documentation/System/Errno/overflow) Value too large to be stored in data type. ### Executable File Errors [`static var badCPUType: Errno`](/documentation/System/Errno/badCPUType) Bad CPU type in executable. [`static var badExecutable: Errno`](/documentation/System/Errno/badExecutable) Bad executable or shared library. [`static var execFormatError: Errno`](/documentation/System/Errno/execFormatError) Executable format error. [`static var malformedMachO: Errno`](/documentation/System/Errno/malformedMachO) Malformed Mach-O file. [`static var sharedLibraryVersionMismatch: Errno`](/documentation/System/Errno/sharedLibraryVersionMismatch) Shared library version mismatch. ### Network Errors [`static var connectionAbort: Errno`](/documentation/System/Errno/connectionAbort) Software caused a connection abort. [`static var connectionRefused: Errno`](/documentation/System/Errno/connectionRefused) Connection refused. [`static var connectionReset: Errno`](/documentation/System/Errno/connectionReset) Connection reset by peer. [`static var hostIsDown: Errno`](/documentation/System/Errno/hostIsDown) The host is down. [`static var messageTooLong: Errno`](/documentation/System/Errno/messageTooLong) Message too long. [`static var networkDown: Errno`](/documentation/System/Errno/networkDown) Network is down. [`static var networkReset: Errno`](/documentation/System/Errno/networkReset) Network dropped connection on reset. [`static var networkUnreachable: Errno`](/documentation/System/Errno/networkUnreachable) Network is unreachable. [`static var noBufferSpace: Errno`](/documentation/System/Errno/noBufferSpace) No buffer space available. [`static var noRouteToHost: Errno`](/documentation/System/Errno/noRouteToHost) No route to host. [`static var notSupported: Errno`](/documentation/System/Errno/notSupported) Not supported. [`static var timedOut: Errno`](/documentation/System/Errno/timedOut) Operation timed out. ### Network Protocol Errors [`static var protocolError: Errno`](/documentation/System/Errno/protocolError) Protocol error. [`static var protocolFamilyNotSupported: Errno`](/documentation/System/Errno/protocolFamilyNotSupported) Protocol family not supported. [`static var protocolNotAvailable: Errno`](/documentation/System/Errno/protocolNotAvailable) Protocol not available. [`static var protocolNotSupported: Errno`](/documentation/System/Errno/protocolNotSupported) Protocol not supported. [`static var protocolWrongTypeForSocket: Errno`](/documentation/System/Errno/protocolWrongTypeForSocket) Protocol wrong for socket type. ### Network Address Errors [`static var addressFamilyNotSupported: Errno`](/documentation/System/Errno/addressFamilyNotSupported) The address family isn’t supported by the protocol family. [`static var addressInUse: Errno`](/documentation/System/Errno/addressInUse) Address already in use. [`static var addressNotAvailable: Errno`](/documentation/System/Errno/addressNotAvailable) Can’t assign the requested address. [`static var addressRequired: Errno`](/documentation/System/Errno/addressRequired) Destination address required. ### Network Socket Errors [`static var notSocket: Errno`](/documentation/System/Errno/notSocket) A socket operation was performed on something that isn’t a socket. [`static var notSupportedOnSocket: Errno`](/documentation/System/Errno/notSupportedOnSocket) Operation not supported on socket. [`static var socketIsConnected: Errno`](/documentation/System/Errno/socketIsConnected) Socket is already connected. [`static var socketNotConnected: Errno`](/documentation/System/Errno/socketNotConnected) Socket is not connected. [`static var socketShutdown: Errno`](/documentation/System/Errno/socketShutdown) Can’t send after socket shutdown. [`static var socketTypeNotSupported: Errno`](/documentation/System/Errno/socketTypeNotSupported) Socket type not supported. ### RPC Errors [`static var rpcProcedureUnavailable: Errno`](/documentation/System/Errno/rpcProcedureUnavailable) Bad procedure for program. [`static var rpcProgramUnavailable: Errno`](/documentation/System/Errno/rpcProgramUnavailable) The remote procedure call (RPC) program isn’t available. [`static var rpcProgramVersionMismatch: Errno`](/documentation/System/Errno/rpcProgramVersionMismatch) The version of the remote procedure call (RPC) program is incorrect. [`static var rpcUnsuccessful: Errno`](/documentation/System/Errno/rpcUnsuccessful) The structure of the remote procedure call (RPC) is bad. [`static var rpcVersionMismatch: Errno`](/documentation/System/Errno/rpcVersionMismatch) The version of the remote procedure call (RPC) is incorrect. ### Process Errors [`static var argListTooLong: Errno`](/documentation/System/Errno/argListTooLong) The argument list is too long. [`static var identifierRemoved: Errno`](/documentation/System/Errno/identifierRemoved) Identifier removed. [`static var noChildProcess: Errno`](/documentation/System/Errno/noChildProcess) No child processes. [`static var noSuchProcess: Errno`](/documentation/System/Errno/noSuchProcess) No such process. [`static var previousOwnerDied: Errno`](/documentation/System/Errno/previousOwnerDied) Previous pthread mutex owner died. [`static var tooManyProcesses: Errno`](/documentation/System/Errno/tooManyProcesses) Too many processes. ### System Call Errors [`static var alreadyInProcess: Errno`](/documentation/System/Errno/alreadyInProcess) Operation already in progress. [`static var badAddress: Errno`](/documentation/System/Errno/badAddress) Bad address. [`static var interrupted: Errno`](/documentation/System/Errno/interrupted) Interrupted function call. [`static var invalidArgument: Errno`](/documentation/System/Errno/invalidArgument) Invalid argument. [`static var noFunction: Errno`](/documentation/System/Errno/noFunction) Function not implemented. [`static var nowInProgress: Errno`](/documentation/System/Errno/nowInProgress) Operation now in progress. [`static var resourceBusy: Errno`](/documentation/System/Errno/resourceBusy) Resource busy. [`static var resourceTemporarilyUnavailable: Errno`](/documentation/System/Errno/resourceTemporarilyUnavailable) Resource temporarily unavailable. ### General Errors [`static var badMessage: Errno`](/documentation/System/Errno/badMessage) Bad message. [`static var canceled: Errno`](/documentation/System/Errno/canceled) Operation canceled. [`static var illegalByteSequence: Errno`](/documentation/System/Errno/illegalByteSequence) Illegal byte sequence. [`static var noData: Errno`](/documentation/System/Errno/noData) No message available. [`static var noMessage: Errno`](/documentation/System/Errno/noMessage) No message of desired type. [`static var noSuchPolicy: Errno`](/documentation/System/Errno/noSuchPolicy) No such policy registered. [`static var notPermitted: Errno`](/documentation/System/Errno/notPermitted) Operation not permitted. [`static var notRecoverable: Errno`](/documentation/System/Errno/notRecoverable) State not recoverable. [`static var outputQueueFull: Errno`](/documentation/System/Errno/outputQueueFull) Interface output queue is full. [`static var tooManyReferences: Errno`](/documentation/System/Errno/tooManyReferences) Too many references: can’t splice. [`static var tooManyUsers: Errno`](/documentation/System/Errno/tooManyUsers) Too many users. ### Reserved [`static var lastErrnoValue: Errno`](/documentation/System/Errno/lastErrnoValue) The largest valid error. [`static var multiHop: Errno`](/documentation/System/Errno/multiHop) Reserved. [`static var noLink: Errno`](/documentation/System/Errno/noLink) Reserved. [`static var noStreamResources: Errno`](/documentation/System/Errno/noStreamResources) Reserved. [`static var notStream: Errno`](/documentation/System/Errno/notStream) Reserved. [`static var notUsed: Errno`](/documentation/System/Errno/notUsed) Error. Not used. [`static var timeout: Errno`](/documentation/System/Errno/timeout) Reserved. ### Interacting with C APIs [`init(rawValue: CInt)`](/documentation/System/Errno/init(rawValue:)) Creates a strongly typed error number from a raw C error number. [`let rawValue: CInt`](/documentation/System/Errno/rawValue) The raw C error number. ### Debugging [`var description: String`](/documentation/System/Errno/description) A textual representation of the most recent error returned by a system call. [`var debugDescription: String`](/documentation/System/Errno/debugDescription) A textual representation, suitable for debugging, of the most recent error returned by a system call. ### Encoding Errors ### Comparing Errors [`static func ~= (Errno, any Error) -> Bool`](/documentation/System/Errno/~=(_:_:)) ### Default Implementations [CustomDebugStringConvertible Implementations](/documentation/System/Errno/CustomDebugStringConvertible-Implementations) [CustomStringConvertible Implementations](/documentation/System/Errno/CustomStringConvertible-Implementations) ## Relationships ### Conforms To [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Copyable`](/documentation/Swift/Copyable) [`Decodable`](/documentation/Swift/Decodable) [`Escapable`](/documentation/Swift/Escapable) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`Equatable`](/documentation/Swift/Equatable) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`BitwiseCopyable`](/documentation/Swift/BitwiseCopyable) [`Hashable`](/documentation/Swift/Hashable) [`RawRepresentable`](/documentation/Swift/RawRepresentable) [`Encodable`](/documentation/Swift/Encodable) [`Error`](/documentation/Swift/Error) [`Sendable`](/documentation/Swift/Sendable) --- Copyright © 2026 Apple Inc. 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