Errno.h

Synopsis

 * 1) include 

Description
The  header file defines the integer variable errno, which is set by system calls and some library functions in the event of an error to indicate what went wrong. Its value is significant only when the call returned an error (usually -1), and a function that does succeed is allowed to change errno.

Sometimes, when -1 is also a valid successful return value one has to zero errno before the call in order to detect possible errors.

errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno may be a macro. errno is thread-local; setting it in one thread does not affect its value in any other thread.

Valid error numbers are all non-zero; errno is never set to zero by any library function. All the error names specified by POSIX.1 must have distinct values, with the exception of EAGAIN and EWOULDBLOCK, which may be the same.

Below is a list of the symbolic error names that are defined on Linux. Some of these are marked POSIX.1, indicating that the name is defined by POSIX.1-2001, or C99, indicating that the name is defined by C99.

E2BIG
Argument list too long (POSIX.1)

EACCES
Permission denied (POSIX.1)

EADDRINUSE
Address already in use (POSIX.1)

EADDRNOTAVAIL
Address not available (POSIX.1)

EAFNOSUPPORT
Address family not supported (POSIX.1)

EAGAIN
Resource temporarily unavailable (may be the same value as EWOULDBLOCK) (POSIX.1)

EALREADY
Connection already in progress (POSIX.1)

EBADE
Invalid exchange

EBADF
Bad file descriptor (POSIX.1)

EBADFD
File descriptor in bad state

EBADMSG
Bad message (POSIX.1)

EBADR
Invalid request descriptor

EBADRQC
Invalid request code

EBADSLT
Invalid slot

EBUSY
Device or resource busy (POSIX.1)

ECANCELED
Operation canceled (POSIX.1)

ECHILD
No child processes (POSIX.1)

ECHRNG
Channel number out of range

ECOMM
Communication error on send

ECONNABORTED
Connection aborted (POSIX.1)

ECONNREFUSED
Connection refused (POSIX.1)

ECONNRESET
Connection reset (POSIX.1)

EDEADLK
Resource deadlock avoided (POSIX.1)

EDEADLOCK
Synonym for EDEADLK

EDESTADDRREQ
Destination address required (POSIX.1)

EDOM
Mathematics argument out of domain of function (POSIX.1, C99)

EDQUOT
Disk quota exceeded (POSIX.1)

EEXIST
File exists (POSIX.1)

EFAULT
Bad address (POSIX.1)

EFBIG
File too large (POSIX.1)

EHOSTDOWN
Host is down

EHOSTUNREACH
Host is unreachable (POSIX.1)

EIDRM
Identifier removed (POSIX.1)

EILSEQ
Illegal byte sequence (POSIX.1, C99)

EINPROGRESS
Operation in progress (POSIX.1)

EINTR
Interrupted function call (POSIX.1)

EINVAL
Invalid argument (POSIX.1)

EIO
Input/output error (POSIX.1)

EISCONN
Socket is connected (POSIX.1)

EISDIR
Is a directory (POSIX.1)

EISNAM
Is a named type file

EKEYEXPIRED
Key has expired

EKEYREJECTED
Key was rejected by service

EKEYREVOKED
Key has been revoked

EL2HLT
Level 2 halted

EL2NSYNC
Level 2 not synchronized

EL3HLT
Level 3 halted

EL3RST
Level 3 halted

ELIBACC
Cannot access a needed shared library

ELIBBAD
Accessing a corrupted shared library

ELIBMAX
Attempting to link in too many shared libraries

ELIBSCN
lib section in a.out corrupted

ELIBEXEC
Cannot exec a shared library directly

ELOOP
Too many levels of symbolic links (POSIX.1)

EMEDIUMTYPE
Wrong medium type

EMFILE
Too many open files (POSIX.1)

EMLINK
Too many links (POSIX.1)

EMSGSIZE
Message too long (POSIX.1)

EMULTIHOP
Multihop attempted (POSIX.1)

ENAMETOOLONG
Filename too long (POSIX.1)

ENETDOWN
Network is down (POSIX.1)

ENETRESET
Connection aborted by network (POSIX.1)

ENETUNREACH
Network unreachable (POSIX.1)

ENFILE
Too many open files in system (POSIX.1)

ENOBUFS
No buffer space available (POSIX.1 (XSI STREAMS option))

ENODATA
No message is available on the STREAM head read queue (POSIX.1)

ENODEV
No such device (POSIX.1)

ENOENT
No such file or directory (POSIX.1)

ENOEXEC
Exec format error (POSIX.1)

ENOKEY
Required key not available

ENOLCK
No locks available (POSIX.1)

ENOLINK
Link has been severed (POSIX.1)

ENOMEDIUM
No medium found

ENOMEM
Not enough space (POSIX.1)

ENOMSG
No message of the desired type (POSIX.1)

ENONET
Machine is not on the network

ENOPKG
Package not installed

ENOPROTOOPT
Protocol not available (POSIX.1)

ENOSPC
No space left on device (POSIX.1)

ENOSR
No STREAM resources (POSIX.1 (XSI STREAMS option))

ENOSTR
Not a STREAM (POSIX.1 (XSI STREAMS option))

ENOSYS
Function not implemented (POSIX.1)

ENOTBLK
Block device required

ENOTCONN
The socket is not connected (POSIX.1)

ENOTDIR
Not a directory (POSIX.1)

ENOTEMPTY
Directory not empty (POSIX.1)

ENOTSOCK
Not a socket (POSIX.1)

ENOTSUP
Operation not supported (POSIX.1)

ENOTTY
Inappropriate I/O control operation (POSIX.1)

ENOTUNIQ
Name not unique on network

ENXIO
No such device or address (POSIX.1)

EOPNOTSUPP
Operation not supported on socket (POSIX.1)

(ENOTSUP and EOPNOTSUPP have the same value on Linux, but according to POSIX.1 these error values should be distinct.)

EOVERFLOW
Value too large to be stored in data type (POSIX.1)

EPERM
Operation not permitted (POSIX.1)

EPFNOSUPPORT
Protocol family not supported

EPIPE
Broken pipe (POSIX.1)

EPROTO
Protocol error (POSIX.1)

EPROTONOSUPPORT
Protocol not supported (POSIX.1)

EPROTOTYPE
Protocol wrong type for socket (POSIX.1)

ERANGE
Result too large (POSIX.1, C99)

EREMCHG
Remote address changed

EREMOTE
Object is remote

EREMOTEIO
Remote I/O error

ERESTART
Interrupted system call should be restarted

EROFS
Read-only file system (POSIX.1)

ESHUTDOWN
Cannot send after transport endpoint shutdown

ESPIPE
Invalid seek (POSIX.1)

ESOCKTNOSUPPORT
Socket type not supported

ESRCH
No such process (POSIX.1)

ESTALE
Stale file handle (POSIX.1)) This error can occur for NFS and for other file systems

ESTRPIPE
Streams pipe error

ETIME
Timer expired (POSIX.1 (XSI STREAMS option)) (POSIX.1 says "STREAM ioctl timeout")

ETIMEDOUT
Connection timed out (POSIX.1)

ETXTBSY
Text file busy (POSIX.1)

EUCLEAN
Structure needs cleaning

EUNATCH
Protocol driver not attached

EUSERS
Too many users

EWOULDBLOCK
Operation would block (may be same value as EAGAIN) (POSIX.1)

EXDEV
Improper link (POSIX.1)

EXFULL
Exchange full