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.

       The  value  in  errno  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.  The value of 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.

   Error numbers and names
       Valid error numbers are all positive  numbers.   The  <errno.h>  header
       file defines symbolic names for each of the possible error numbers that
       may appear in errno.

       All the error names specified by POSIX.1  must  have  distinct  values,
       with  the  exception  of EAGAIN and EWOULDBLOCK, which may be the same.
       On Linux, these two have the same value on all architectures.

       The error numbers that correspond to each  symbolic  name  vary  across
       UNIX systems, and even across different architectures on Linux.  There-
       fore, numeric values are not included as part  of  the  list  of  error
       names  below.   The  perror(3) and strerror(3) functions can be used to
       convert these names to corresponding textual error messages.

       On any particular Linux system, one can obtain a list of  all  symbolic
       error names and the corresponding error numbers using the errno(1) com-
       mand (part of the moreutils package):

           $ errno -l
           EPERM 1 Operation not permitted
           ENOENT 2 No such file or directory
           ESRCH 3 No such process
           EINTR 4 Interrupted system call
           EIO 5 Input/output error

       The errno(1) command can also be used to look up individual error  num-
       bers  and  names, and to search for errors using strings from the error
       description, as in the following examples:

           $ errno 2
           ENOENT 2 No such file or directory
           $ errno ESRCH
           ESRCH 3 No such process
           $ errno -s permission
           EACCES 13 Permission denied

   List of error names
       In the list of the symbolic error names below, various names are marked
       as follows:

       *  POSIX.1-2001: The name is defined by POSIX.1-2001, and is defined in
          later POSIX.1 versions, unless otherwise indicated.

       *  POSIX.1-2008: The name is  defined  in  POSIX.1-2008,  but  was  not
          present in earlier POSIX.1 standards.

       *  C99:  The  name  is defined by C99.  Below is a list of the symbolic
          error names that are defined on Linux:

       E2BIG           Argument list too long (POSIX.1-2001).

       EACCES          Permission denied (POSIX.1-2001).

       EADDRINUSE      Address already in use (POSIX.1-2001).

       EADDRNOTAVAIL   Address not available (POSIX.1-2001).

       EAFNOSUPPORT    Address family not supported (POSIX.1-2001).

       EAGAIN          Resource temporarily unavailable (may be the same value
                       as EWOULDBLOCK) (POSIX.1-2001).

       EALREADY        Connection already in progress (POSIX.1-2001).

       EBADE           Invalid exchange.

       EBADF           Bad file descriptor (POSIX.1-2001).

       EBADFD          File descriptor in bad state.

       EBADMSG         Bad message (POSIX.1-2001).

       EBADR           Invalid request descriptor.

       EBADRQC         Invalid request code.

       EBADSLT         Invalid slot.

       EBUSY           Device or resource busy (POSIX.1-2001).

       ECANCELED       Operation canceled (POSIX.1-2001).

       ECHILD          No child processes (POSIX.1-2001).

       ECHRNG          Channel number out of range.

       ECOMM           Communication error on send.

       ECONNABORTED    Connection aborted (POSIX.1-2001).

       ECONNREFUSED    Connection refused (POSIX.1-2001).

       ECONNRESET      Connection reset (POSIX.1-2001).

       EDEADLK         Resource deadlock avoided (POSIX.1-2001).

       EDEADLOCK       On  most architectures, a synonym for EDEADLK.  On some
                       architectures (e.g., Linux MIPS, PowerPC, SPARC), it is
                       a separate error code "File locking deadlock error".

       EDESTADDRREQ    Destination address required (POSIX.1-2001).

       EDOM            Mathematics   argument   out   of  domain  of  function
                       (POSIX.1, C99).

       EDQUOT          Disk quota exceeded (POSIX.1-2001).

       EEXIST          File exists (POSIX.1-2001).

       EFAULT          Bad address (POSIX.1-2001).

       EFBIG           File too large (POSIX.1-2001).

       EHOSTDOWN       Host is down.

       EHOSTUNREACH    Host is unreachable (POSIX.1-2001).

       EHWPOISON       Memory page has hardware error.

       EIDRM           Identifier removed (POSIX.1-2001).

       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  se-

       EINPROGRESS     Operation in progress (POSIX.1-2001).

       EINTR           Interrupted  function  call  (POSIX.1-2001);  see  sig-

       EINVAL          Invalid argument (POSIX.1-2001).

       EIO             Input/output error (POSIX.1-2001).

       EISCONN         Socket is connected (POSIX.1-2001).

       EISDIR          Is a directory (POSIX.1-2001).

       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 reset.

       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.

       ELNRANGE        Link number out of range.

       ELOOP           Too many levels of symbolic links (POSIX.1-2001).

       EMEDIUMTYPE     Wrong medium type.

       EMFILE          Too many open files (POSIX.1-2001).  Commonly caused by
                       exceeding the RLIMIT_NOFILE resource limit described in

       EMLINK          Too many links (POSIX.1-2001).

       EMSGSIZE        Message too long (POSIX.1-2001).

       EMULTIHOP       Multihop attempted (POSIX.1-2001).

       ENAMETOOLONG    Filename too long (POSIX.1-2001).

       ENETDOWN        Network is down (POSIX.1-2001).

       ENETRESET       Connection aborted by network (POSIX.1-2001).

       ENETUNREACH     Network unreachable (POSIX.1-2001).

       ENFILE          Too many  open  files  in  system  (POSIX.1-2001).   On
                       Linux,  this  is  probably a result of encountering the
                       /proc/sys/fs/file-max limit (see proc(5)).

       ENOANO          No anode.

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

       ENODATA         No  message  is available on the STREAM head read queue

       ENODEV          No such device (POSIX.1-2001).

       ENOENT          No such file or directory (POSIX.1-2001).

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

       ENOEXEC         Exec format error (POSIX.1-2001).

       ENOKEY          Required key not available.

       ENOLCK          No locks available (POSIX.1-2001).

       ENOLINK         Link has been severed (POSIX.1-2001).

       ENOMEDIUM       No medium found.

       ENOMEM          Not enough space/cannot allocate memory (POSIX.1-2001).

       ENOMSG          No message of the desired type (POSIX.1-2001).

       ENONET          Machine is not on the network.

       ENOPKG          Package not installed.

       ENOPROTOOPT     Protocol not available (POSIX.1-2001).

       ENOSPC          No space left on device (POSIX.1-2001).

       ENOSR           No STREAM resources (POSIX.1 (XSI STREAMS option)).

       ENOSTR          Not a STREAM (POSIX.1 (XSI STREAMS option)).

       ENOSYS          Function not implemented (POSIX.1-2001).

       ENOTBLK         Block device required.

       ENOTCONN        The socket is not connected (POSIX.1-2001).

       ENOTDIR         Not a directory (POSIX.1-2001).

       ENOTEMPTY       Directory not empty (POSIX.1-2001).

       ENOTRECOVERABLE State not recoverable (POSIX.1-2008).

       ENOTSOCK        Not a socket (POSIX.1-2001).

       ENOTSUP         Operation not supported (POSIX.1-2001).

       ENOTTY          Inappropriate I/O control operation (POSIX.1-2001).

       ENOTUNIQ        Name not unique on network.

       ENXIO           No such device or address (POSIX.1-2001).

       EOPNOTSUPP      Operation not supported on socket (POSIX.1-2001).

                       (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

       EOWNERDEAD      Owner died (POSIX.1-2008).

       EPERM           Operation not permitted (POSIX.1-2001).

       EPFNOSUPPORT    Protocol family not supported.

       EPIPE           Broken pipe (POSIX.1-2001).

       EPROTO          Protocol error (POSIX.1-2001).

       EPROTONOSUPPORT Protocol not supported (POSIX.1-2001).

       EPROTOTYPE      Protocol wrong type for socket (POSIX.1-2001).

       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.

       ERFKILL         Operation not possible due to RF-kill.

       EROFS           Read-only filesystem (POSIX.1-2001).

       ESHUTDOWN       Cannot send after transport endpoint shutdown.

       ESPIPE          Invalid seek (POSIX.1-2001).

       ESOCKTNOSUPPORT Socket type not supported.

       ESRCH           No such process (POSIX.1-2001).

       ESTALE          Stale file handle (POSIX.1-2001).

                       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.1-2001).

       ETOOMANYREFS    Too many references: cannot splice.

       ETXTBSY         Text file busy (POSIX.1-2001).

       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.1-2001).

       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 == ...) { ... }

       On some ancient systems, <errno.h> was not present or did  not  declare
       errno, so that it was necessary to declare errno manually (i.e., extern
       int errno).  Do not do this.  It long ago ceased to be  necessary,  and
       it will cause problems with modern versions of the C library.

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

       This  page  is  part of release 5.05 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

                                  2019-10-10                          ERRNO(3)
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