Ubuntu Manpage: This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

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PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       errno.h — system error numbers

SYNOPSIS

       #include <errno.h>

DESCRIPTION

Some of the functionality described on this reference page extends the ISO C standard. Any conflict
between the requirements described here and the ISO C standard is unintentional. This volume of
POSIX.1‐2017 defers to the ISO C standard.

The ISO C standard only requires the symbols [EDOM], [EILSEQ], and [ERANGE] to be defined.

The <errno.h> header shall provide a declaration or definition for errno. The symbol errno shall expand
to a modifiable lvalue of type int. It is unspecified whether errno is a macro or an identifier declared
with external linkage. If a macro definition is suppressed in order to access an actual object, or a
program defines an identifier with the name errno, the behavior is undefined.

The <errno.h> header shall define the following macros which shall expand to integer constant expressions
with type int, distinct positive values (except as noted below), and which shall be suitable for use in
#if preprocessing directives:

E2BIG Argument list too long.

EACCES Permission denied.

EADDRINUSE
Address in use.

EADDRNOTAVAIL
Address not available.

EAFNOSUPPORT
Address family not supported.

EAGAIN Resource unavailable, try again (may be the same value as [EWOULDBLOCK]).

EALREADY
Connection already in progress.

EBADF Bad file descriptor.

EBADMSG
Bad message.

EBUSY Device or resource busy.

ECANCELED
Operation canceled.

ECHILD No child processes.

ECONNABORTED
Connection aborted.

ECONNREFUSED
Connection refused.

ECONNRESET
Connection reset.

EDEADLK
Resource deadlock would occur.

EDESTADDRREQ
Destination address required.

EDOM Mathematics argument out of domain of function.

EDQUOT Reserved.

EEXIST File exists.

EFAULT Bad address.

EFBIG File too large.

EHOSTUNREACH
Host is unreachable.

EIDRM Identifier removed.

EILSEQ Illegal byte sequence.

EINPROGRESS
Operation in progress.

EINTR Interrupted function.

EINVAL Invalid argument.

EIO I/O error.

EISCONN
Socket is connected.

EISDIR Is a directory.

ELOOP Too many levels of symbolic links.

EMFILE File descriptor value too large.

EMLINK Too many links.

EMSGSIZE
Message too large.

EMULTIHOP
Reserved.

ENAMETOOLONG
Filename too long.

ENETDOWN
Network is down.

ENETRESET
Connection aborted by network.

ENETUNREACH
Network unreachable.

ENFILE Too many files open in system.

ENOBUFS
No buffer space available.

ENODATA
No message is available on the STREAM head read queue.

ENODEV No such device.

ENOENT No such file or directory.

ENOEXEC
Executable file format error.

ENOLCK No locks available.

ENOLINK
Reserved.

ENOMEM Not enough space.

ENOMSG No message of the desired type.

ENOPROTOOPT
Protocol not available.

ENOSPC No space left on device.

ENOSR No STREAM resources.

ENOSTR Not a STREAM.

ENOSYS Functionality not supported.

ENOTCONN
The socket is not connected.

ENOTDIR
Not a directory or a symbolic link to a directory.

ENOTEMPTY
Directory not empty.

ENOTRECOVERABLE
State not recoverable.

ENOTSOCK
Not a socket.

ENOTSUP
Not supported (may be the same value as [EOPNOTSUPP]).

ENOTTY Inappropriate I/O control operation.

ENXIO No such device or address.

EOPNOTSUPP
Operation not supported on socket (may be the same value as [ENOTSUP]).

EOVERFLOW
Value too large to be stored in data type.

EOWNERDEAD
Previous owner died.

EPERM Operation not permitted.

EPIPE Broken pipe.

EPROTO Protocol error.

EPROTONOSUPPORT
Protocol not supported.

EPROTOTYPE
Protocol wrong type for socket.

ERANGE Result too large.

EROFS Read-only file system.

ESPIPE Invalid seek.

ESRCH No such process.

ESTALE Reserved.

ETIME Stream ioctl() timeout.

ETIMEDOUT
Connection timed out.

ETXTBSY
Text file busy.

EWOULDBLOCK
Operation would block (may be the same value as [EAGAIN]).

EXDEV Cross-device link.

The following sections are informative.

APPLICATION USAGE

       Additional error numbers may be defined on conforming  systems;  see  the  System  Interfaces  volume  of
       POSIX.1‐2017.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                       errno.h(7POSIX)