---
title: Errno
framework: system
role: symbol
role_heading: Structure
path: system/errno
---

# Errno

An error number used by system calls to communicate what kind of error occurred.

## Declaration

```swift
@frozen struct Errno
```

## Topics

### File and Directory Errors

- [attributeNotFound](system/errno/attributenotfound.md)
- [badFileDescriptor](system/errno/badfiledescriptor.md)
- [fileExists](system/errno/fileexists.md)
- [fileTooLarge](system/errno/filetoolarge.md)
- [improperLink](system/errno/improperlink.md)
- [isDirectory](system/errno/isdirectory.md)
- [noLocks](system/errno/nolocks.md)
- [noSuchFileOrDirectory](system/errno/nosuchfileordirectory.md)
- [notDirectory](system/errno/notdirectory.md)
- [permissionDenied](system/errno/permissiondenied.md)
- [textFileBusy](system/errno/textfilebusy.md)

### File System Errors

- [badFileTypeOrFormat](system/errno/badfiletypeorformat.md)
- [directoryNotEmpty](system/errno/directorynotempty.md)
- [diskQuotaExceeded](system/errno/diskquotaexceeded.md)
- [noSpace](system/errno/nospace.md)
- [readOnlyFileSystem](system/errno/readonlyfilesystem.md)
- [tooManyLinks](system/errno/toomanylinks.md)
- [tooManyOpenFilesInSystem](system/errno/toomanyopenfilesinsystem.md)
- [tooManyOpenFiles](system/errno/toomanyopenfiles.md)

### NFS Errors

- [authenticationError](system/errno/authenticationerror.md)
- [needAuthenticator](system/errno/needauthenticator.md)
- [staleNFSFileHandle](system/errno/stalenfsfilehandle.md)

### Device Errors

- [deviceError](system/errno/deviceerror.md)
- [devicePowerIsOff](system/errno/devicepowerisoff.md)
- [inappropriateIOCTLForDevice](system/errno/inappropriateioctlfordevice.md)
- [ioError](system/errno/ioerror.md)
- [noSuchAddressOrDevice](system/errno/nosuchaddressordevice.md)
- [notBlockDevice](system/errno/notblockdevice.md)
- [operationNotSupportedByDevice](system/errno/operationnotsupportedbydevice.md)

### Path Errors

- [fileNameTooLong](system/errno/filenametoolong.md)
- [tooManyRemoteLevels](system/errno/toomanyremotelevels.md)
- [tooManySymbolicLinkLevels](system/errno/toomanysymboliclinklevels.md)

### Pipe Errors

- [brokenPipe](system/errno/brokenpipe.md)
- [illegalSeek](system/errno/illegalseek.md)

### Runtime Errors

- [deadlock](system/errno/deadlock.md)
- [noMemory](system/errno/nomemory.md)
- [wouldBlock](system/errno/wouldblock.md)

### Math Errors

- [outOfDomain](system/errno/outofdomain.md)
- [outOfRange](system/errno/outofrange.md)
- [overflow](system/errno/overflow.md)

### Executable File Errors

- [badCPUType](system/errno/badcputype.md)
- [badExecutable](system/errno/badexecutable.md)
- [execFormatError](system/errno/execformaterror.md)
- [malformedMachO](system/errno/malformedmacho.md)
- [sharedLibraryVersionMismatch](system/errno/sharedlibraryversionmismatch.md)

### Network Errors

- [connectionAbort](system/errno/connectionabort.md)
- [connectionRefused](system/errno/connectionrefused.md)
- [connectionReset](system/errno/connectionreset.md)
- [hostIsDown](system/errno/hostisdown.md)
- [messageTooLong](system/errno/messagetoolong.md)
- [networkDown](system/errno/networkdown.md)
- [networkReset](system/errno/networkreset.md)
- [networkUnreachable](system/errno/networkunreachable.md)
- [noBufferSpace](system/errno/nobufferspace.md)
- [noRouteToHost](system/errno/noroutetohost.md)
- [notSupported](system/errno/notsupported.md)
- [timedOut](system/errno/timedout.md)

### Network Protocol Errors

- [protocolError](system/errno/protocolerror.md)
- [protocolFamilyNotSupported](system/errno/protocolfamilynotsupported.md)
- [protocolNotAvailable](system/errno/protocolnotavailable.md)
- [protocolNotSupported](system/errno/protocolnotsupported.md)
- [protocolWrongTypeForSocket](system/errno/protocolwrongtypeforsocket.md)

### Network Address Errors

- [addressFamilyNotSupported](system/errno/addressfamilynotsupported.md)
- [addressInUse](system/errno/addressinuse.md)
- [addressNotAvailable](system/errno/addressnotavailable.md)
- [addressRequired](system/errno/addressrequired.md)

### Network Socket Errors

- [notSocket](system/errno/notsocket.md)
- [notSupportedOnSocket](system/errno/notsupportedonsocket.md)
- [socketIsConnected](system/errno/socketisconnected.md)
- [socketNotConnected](system/errno/socketnotconnected.md)
- [socketShutdown](system/errno/socketshutdown.md)
- [socketTypeNotSupported](system/errno/sockettypenotsupported.md)

### RPC Errors

- [rpcProcedureUnavailable](system/errno/rpcprocedureunavailable.md)
- [rpcProgramUnavailable](system/errno/rpcprogramunavailable.md)
- [rpcProgramVersionMismatch](system/errno/rpcprogramversionmismatch.md)
- [rpcUnsuccessful](system/errno/rpcunsuccessful.md)
- [rpcVersionMismatch](system/errno/rpcversionmismatch.md)

### Process Errors

- [argListTooLong](system/errno/arglisttoolong.md)
- [identifierRemoved](system/errno/identifierremoved.md)
- [noChildProcess](system/errno/nochildprocess.md)
- [noSuchProcess](system/errno/nosuchprocess.md)
- [previousOwnerDied](system/errno/previousownerdied.md)
- [tooManyProcesses](system/errno/toomanyprocesses.md)

### System Call Errors

- [alreadyInProcess](system/errno/alreadyinprocess.md)
- [badAddress](system/errno/badaddress.md)
- [interrupted](system/errno/interrupted.md)
- [invalidArgument](system/errno/invalidargument.md)
- [noFunction](system/errno/nofunction.md)
- [nowInProgress](system/errno/nowinprogress.md)
- [resourceBusy](system/errno/resourcebusy.md)
- [resourceTemporarilyUnavailable](system/errno/resourcetemporarilyunavailable.md)

### General Errors

- [badMessage](system/errno/badmessage.md)
- [canceled](system/errno/canceled.md)
- [illegalByteSequence](system/errno/illegalbytesequence.md)
- [noData](system/errno/nodata.md)
- [noMessage](system/errno/nomessage.md)
- [noSuchPolicy](system/errno/nosuchpolicy.md)
- [notPermitted](system/errno/notpermitted.md)
- [notRecoverable](system/errno/notrecoverable.md)
- [outputQueueFull](system/errno/outputqueuefull.md)
- [tooManyReferences](system/errno/toomanyreferences.md)
- [tooManyUsers](system/errno/toomanyusers.md)

### Reserved

- [lastErrnoValue](system/errno/lasterrnovalue.md)
- [multiHop](system/errno/multihop.md)
- [noLink](system/errno/nolink.md)
- [noStreamResources](system/errno/nostreamresources.md)
- [notStream](system/errno/notstream.md)
- [notUsed](system/errno/notused.md)
- [timeout](system/errno/timeout.md)

### Interacting with C APIs

- [init(rawValue:)](system/errno/init(rawvalue:).md)
- [rawValue](system/errno/rawvalue.md)

### Debugging

- [description](system/errno/description.md)
- [debugDescription](system/errno/debugdescription.md)

### Comparing Errors

- [~=(_:_:)](system/errno/~=(_:_:).md)

### Default Implementations

- [CustomDebugStringConvertible Implementations](system/errno/customdebugstringconvertible-implementations.md)
- [CustomStringConvertible Implementations](system/errno/customstringconvertible-implementations.md)

## Relationships

### Conforms To

- [BitwiseCopyable](swift/bitwisecopyable.md)
- [Copyable](swift/copyable.md)
- [CustomDebugStringConvertible](swift/customdebugstringconvertible.md)
- [CustomStringConvertible](swift/customstringconvertible.md)
- [Decodable](swift/decodable.md)
- [Encodable](swift/encodable.md)
- [Equatable](swift/equatable.md)
- [Error](swift/error.md)
- [Escapable](swift/escapable.md)
- [Hashable](swift/hashable.md)
- [RawRepresentable](swift/rawrepresentable.md)
- [Sendable](swift/sendable.md)
- [SendableMetatype](swift/sendablemetatype.md)