NAME

       epoll_create, epoll_create1 - open an epoll file descriptor

SYNOPSIS

       #include <sys/epoll.h>

       int epoll_create(int size);
       int epoll_create1(int flags);

DESCRIPTION

       epoll_create()  creates  a  new  epoll(7) instance.  Since Linux 2.6.8, the size argument is ignored, but
       must be greater than zero; see NOTES below.

       epoll_create() returns a file descriptor referring to the new epoll instance.  This  file  descriptor  is
       used  for  all the subsequent calls to the epoll interface.  When no longer required, the file descriptor
       returned by epoll_create() should be closed by using close(2).  When all file descriptors referring to an
       epoll instance have been closed, the kernel destroys the instance and releases the  associated  resources
       for reuse.

   epoll_create1()
       If  flags  is 0, then, other than the fact that the obsolete size argument is dropped, epoll_create1() is
       the same as epoll_create().  The following value can be included in flags to obtain different behavior:

       EPOLL_CLOEXEC
              Set the close-on-exec (FD_CLOEXEC) flag on the new file descriptor.  See the  description  of  the
              O_CLOEXEC flag in open(2) for reasons why this may be useful.

RETURN VALUE

       On success, these system calls return a nonnegative file descriptor.  On error, -1 is returned, and errno
       is set to indicate the error.

ERRORS

       EINVAL size is not positive.

       EINVAL (epoll_create1()) Invalid value specified in flags.

       EMFILE The     per-user     limit     on     the     number     of    epoll    instances    imposed    by
              /proc/sys/fs/epoll/max_user_instances was encountered.  See epoll(7) for further details.

       EMFILE The per-process limit on the number of open file descriptors has been reached.

       ENFILE The system-wide limit on the total number of open files has been reached.

       ENOMEM There was insufficient memory to create the kernel object.

VERSIONS

       epoll_create() was added to the kernel in version 2.6.  Library support is  provided  in  glibc  starting
       with version 2.3.2.

       epoll_create1() was added to the kernel in version 2.6.27.  Library support is provided in glibc starting
       with version 2.9.

CONFORMING TO

       epoll_create() is Linux-specific.

NOTES

       In the initial epoll_create() implementation, the size argument informed the kernel of the number of file
       descriptors that the caller expected to add to the epoll instance.  The kernel used this information as a
       hint  for  the  amount of space to initially allocate in internal data structures describing events.  (If
       necessary, the kernel would allocate more space if the caller's usage exceeded the hint given  in  size.)
       Nowadays,  this  hint  is  no  longer required (the kernel dynamically sizes the required data structures
       without needing the hint), but size must still  be  greater  than  zero,  in  order  to  ensure  backward
       compatibility when new epoll applications are run on older kernels.

SEE ALSO

       close(2), epoll_ctl(2), epoll_wait(2), epoll(7)

COLOPHON

       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
       https://www.kernel.org/doc/man-pages/.

Linux                                              2017-09-15                                    EPOLL_CREATE(2)