epoll_create, epoll_create1 - open an epoll file descriptor


#include <sys/epoll.h>

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


epoll_create() creates an epoll "instance", requesting the kernel to allocate an event backing store dimensioned for size descriptors. The size is not the maximum size of the backing store but just a hint to the kernel about how to dimension internal structures. (Nowadays, size is ignored; see NOTES below.)

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 re-use.

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:
 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 non-negative file descriptor. 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-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.
ENFILE The system limit on the total number of open files has been reached.
ENOMEM There was insufficient memory to create the kernel object.


epoll_create() is Linux-specific, and was introduced in kernel 2.5.44.


Since Linux 2.6.8, the size argument is unused. (The kernel dynamically sizes the required data structures without needing this initial hint.)


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


This page is part of release 3.23 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at

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