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

       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 non-zero; 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 non-zero 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 EWOULD-
       BLOCK, 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, indi-
       cating 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 val-
                       ues 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

       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.

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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

                                  2008-07-09                          ERRNO(3)