epoll_create, epoll_create1 - open an epoll file descriptor
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 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.
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:
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.
- 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.
epoll_create() was added to the kernel in version 2.6. Library support is
provided in glibc starting with version 2.3.2.
- size is not positive.
- (epoll_create1()) Invalid value specified in flags.
- 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.
- The per-process limit on the number of open file descriptors has been
- The system-wide limit on the total number of open files has been
- There was insufficient memory to create the kernel object.
epoll_create1() was added to the kernel in version 2.6.27.
Library support is provided in glibc starting with version 2.9.
epoll_create() is Linux-specific.
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.
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/.