.\"  Copyright (C) 2003  Davide Libenzi

.\"  Davide Libenzi <davidel@xmailserver.org>

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.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>

.\" Modified 2005-04-04 by Marko Kohtala <marko.kohtala@gmail.com>

.\" 2008-10-10, mtk: add description of epoll_create1()

.\"

.TH EPOLL_CREATE 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

epoll_create, epoll_create1 \- open an epoll file descriptor

.SH SYNOPSIS

.nf

.B #include <sys/epoll.h>

.PP

.BI "int epoll_create(int " size );

.BI "int epoll_create1(int " flags );

.fi

.SH DESCRIPTION

.BR epoll_create ()

creates a new

.BR epoll (7)

instance.

Since Linux 2.6.8, the

.I size

argument is ignored, but must be greater than zero; see NOTES below.

.PP

.BR epoll_create ()

returns a file descriptor referring to the new epoll instance.

This file descriptor is used for all the subsequent calls to the

.B epoll

interface.

When no longer required, the file descriptor returned by

.BR epoll_create ()

should be closed by using

.BR 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.

.SS epoll_create1()

If

.I flags

is 0, then, other than the fact that the obsolete

.I size

argument is dropped,

.BR epoll_create1 ()

is the same as

.BR epoll_create ().

The following value can be included in

.IR flags

to obtain different behavior:

.TP

.B EPOLL_CLOEXEC

Set the close-on-exec

.RB ( FD_CLOEXEC )

flag on the new file descriptor.

See the description of the

.B O_CLOEXEC

flag in

.BR open (2)

for reasons why this may be useful.

.SH RETURN VALUE

On success,

these system calls

return a nonnegative file descriptor.

On error, \-1 is returned, and

.I errno

is set to indicate the error.

.SH ERRORS

.TP

.B EINVAL

.I size

is not positive.

.TP

.B EINVAL

.RB ( epoll_create1 ())

Invalid value specified in

.IR flags .

.TP

.B EMFILE

The per-user limit on the number of epoll instances imposed by

.I /proc/sys/fs/epoll/max_user_instances

was encountered.

See

.BR epoll (7)

for further details.

.TP

.B EMFILE

The per-process limit on the number of open file descriptors has been reached.

.TP

.B ENFILE

The system-wide limit on the total number of open files has been reached.

.TP

.B ENOMEM

There was insufficient memory to create the kernel object.

.SH VERSIONS

.BR epoll_create ()

was added to the kernel in version 2.6.

Library support is provided in glibc starting with version 2.3.2.

.PP

.\" To be precise: kernel 2.5.44.

.\" The interface should be finalized by Linux kernel 2.5.66.

.BR epoll_create1 ()

was added to the kernel in version 2.6.27.

Library support is provided in glibc starting with version 2.9.

.SH CONFORMING TO

.BR epoll_create ()

is Linux-specific.

.SH NOTES

In the initial

.BR epoll_create ()

implementation, the

.I size

argument informed the kernel of the number of file descriptors

that the caller expected to add to the

.B 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

.IR size .)

Nowadays,

this hint is no longer required

(the kernel dynamically sizes the required data structures

without needing the hint), but

.I size

must still be greater than zero,

in order to ensure backward compatibility when new

.B epoll

applications are run on older kernels.

.SH SEE ALSO

.BR close (2),

.BR epoll_ctl (2),

.BR epoll_wait (2),

.BR epoll (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.