epoll_create(2) — Linux manual page


epoll_create(2)            System Calls Manual           epoll_create(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) 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.

       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.

RETURN VALUE         top

       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.

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


HISTORY         top

              Linux 2.6, glibc 2.3.2.

              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.

SEE ALSO         top

       close(2), epoll_ctl(2), epoll_wait(2), ioctl_eventpoll(2),

COLOPHON         top

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Linux man-pages 6.9.1          2024-06-12                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)