NAME

       epoll_create, epoll_create1 - open an epoll file descriptor

LIBRARY

       Standard C library (libc, -lc)

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 HISTORY.

       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-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.

STANDARDS

       Linux.

HISTORY

       epoll_create()
              Linux 2.6, glibc 2.3.2.

       epoll_create1()
              Linux 2.6.27, glibc 2.9.

       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.

       Prior to Linux 2.6.29, a /proc/sys/fs/epoll/max_user_instances kernel parameter limited live  epolls  for
       each real user ID, and caused epoll_create() to fail with EMFILE on overrun.

SEE ALSO

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

Linux man-pages 6.7                                2023-10-31                                    epoll_create(2)