errno - number of last error


   #include <errno.h>


   The  <errno.h> 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
   return value of the call indicated an error (i.e., -1 from most  system
   calls;  -1  or  NULL  from  most  library  functions);  a function that
   succeeds is allowed to change errno.

   Valid error numbers are all nonzero; errno is never set to zero by  any
   system call or library function.

   For  some system calls and library functions (e.g., getpriority(2)), -1
   is a valid return on success.  In such cases, a successful  return  can
   be  distinguished  from an error return by setting errno to zero before
   the call, and then, if the call returns a status that indicates that an
   error may have occurred, checking to see if errno has a nonzero value.

   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.

   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          Invalid  or  incomplete  multibyte  or  wide  character
                   (POSIX.1, C99).

                   The text shown here is the glibc error description;  in
                   POSIX.1,  this  error  is  described  as  "Illegal byte

   EINPROGRESS     Operation in progress (POSIX.1).

   EINTR           Interrupted function call (POSIX.1); see signal(7).

   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).   Commonly  caused  by
                   exceeding the RLIMIT_NOFILE resource limit described in

   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).   On  Linux,
                   this   is   probably   a  result  of  encountering  the
                   /proc/sys/fs/file-max limit (see proc(5)).

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

   ENODATA         No  message  is available on the STREAM head read queue

   ENODEV          No such device (POSIX.1).

   ENOENT          No such file or directory (POSIX.1).

                   Typically, this error results when a specified pathname
                   does  not  exist,  or  one  of  the  components  in the
                   directory prefix of a pathname does not exist,  or  the
                   specified pathname is a dangling symbolic link.

   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

   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 filesystem (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 filesystems.

   ESTRPIPE        Streams pipe error.

   ETIME           Timer expired.  (POSIX.1 (XSI STREAMS option))

                   (POSIX.1 says "STREAM ioctl(2) 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)

   EXDEV           Improper link (POSIX.1).

   EXFULL          Exchange full.


   A common mistake is to do

       if (somecall() == -1) {
           printf("somecall() failed\n");
           if (errno == ...) { ... }

   where errno no longer needs to have the value it had upon  return  from
   somecall()  (i.e.,  it may have been changed by the printf(3)).  If the
   value of errno should be preserved across a library call,  it  must  be

       if (somecall() == -1) {
           int errsv = errno;
           printf("somecall() failed\n");
           if (errsv == ...) { ... }

   It  was common in traditional C to declare errno manually (i.e., extern
   int errno) instead of including <errno.h>.  Do not do  this.   It  will
   not work with modern versions of the C library.  However, on (very) old
   UNIX systems, there may be no <errno.h> and the declaration is needed.


   errno(1), err(3), error(3), perror(3), strerror(3)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

                              2016-12-12                          ERRNO(3)


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