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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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epoll_create(2) System Calls Manual epoll_create(2)
epoll_create, epoll_create1 - open an epoll file descriptor
Standard C library (libc, -lc)
#include <sys/epoll.h>
int epoll_create(int size);
int epoll_create1(int flags);
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.
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.
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.
Linux.
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.
close(2), epoll_ctl(2), epoll_wait(2), ioctl_eventpoll(2),
epoll(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 epoll_create(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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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