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

NAME         top

       errno - number of last error

SYNOPSIS         top

       #include <errno.h>

DESCRIPTION         top

       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 getrlimit(2).

       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

       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.

NOTES         top

       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.

SEE ALSO         top

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

COLOPHON         top

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       latest version of this page, can be found at

                                 2016-12-12                         ERRNO(3)