EPOLL_CREATE(2)             Linux Programmer's Manual            EPOLL_CREATE(2)

       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 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

       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 file descriptor (a nonnegative
       integer).  On error, -1 is returned, and errno is set to indicate the

       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.

       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

       ENOMEM There was insufficient memory to create the kernel object.

       epoll_create() was added to the kernel in version 2.6.  Library support
       is provided in glibc starting with version 2.3.2.

       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() and epoll_create1() are 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.

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

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       latest version of this page, can be found at

Linux                              2021-03-22                    EPOLL_CREATE(2)