epoll_create(2) - Linux manual page (original) (raw)

epollcreate(2) System Calls Manual epollcreate(2)

NAME top

   epoll_create, epoll_create1 - open an epoll file descriptor

LIBRARY top

   Standard C library (_libc_, _-lc_)

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)](../man7/epoll.7.html) 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)](../man2/close.2.html).  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)](../man2/open.2.html) 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](../man3/errno.3.html)_ is set
   to indicate the error.

ERRORS top

   **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 top

   Linux.

HISTORY top

   **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/maxuserinstances_
   kernel parameter limited live epolls for each real user ID, and
   caused **epoll_create**() to fail with **EMFILE** on overrun.

SEE ALSO top

   [close(2)](../man2/close.2.html), [epoll_ctl(2)](../man2/epoll%5Fctl.2.html), [epoll_wait(2)](../man2/epoll%5Fwait.2.html), [ioctl_eventpoll(2)](../man2/ioctl%5Feventpoll.2.html),
   [epoll(7)](../man7/epoll.7.html)

COLOPHON top

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   man-pages@man7.org

Linux man-pages 6.10 2024-07-23 epollcreate(2)

Pages that refer to this page:epoll_ctl(2), epoll_wait(2), ioctl_eventpoll(2), kcmp(2), syscalls(2), proc_pid_fd(5), epoll(7)