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.

       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  file  descriptor (a nonnegative integer).  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 5.10 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                                              2020-04-11                                    EPOLL_CREATE(2)