epoll_create1(2) — Linux manual page


EPOLL_CREATE(2)           Linux Programmer's Manual          EPOLL_CREATE(2)

NAME         top

       epoll_create, epoll_create1 - open an epoll file descriptor

SYNOPSIS         top

       #include <sys/epoll.h>

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

DESCRIPTION         top

       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

       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.

       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

              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         top

       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         top

       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         top

       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         top

       epoll_create() is Linux-specific.

NOTES         top

       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         top

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

COLOPHON         top

       This page is part of release 5.09 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

Linux                            2020-04-11                  EPOLL_CREATE(2)

Pages that refer to this page: syscalls(2)epoll(7)