errno(top10.html) - phpMan

ERRNO(3)                   Linux Programmer's Manual                  ERRNO(3)

NAME
       errno - number of last error
SYNOPSIS
       #include <errno.h>
DESCRIPTION
       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 suc-
       ceeds 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          Illegal byte sequence (POSIX.1, C99)
       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)
       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(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)
                       (POSIX.1)
       EXDEV           Improper link (POSIX.1)
       EXFULL          Exchange full
NOTES
       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
       saved:
           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.
SEE ALSO
       err(3), error(3), perror(3), strerror(3)
COLOPHON
       This page is part of release 3.53 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2008-07-09                          ERRNO(3)