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NAME

       epoll_create, epoll_create1 - open an epoll file descriptor

SYNOPSIS

       #include <sys/epoll.h>

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

DESCRIPTION

       epoll_create()  creates  an  epoll(7) instance.  Since Linux 2.6.8, the
       size argument is ignored, but must be  greater  than  zero;  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 reuse.

   epoll_create1()
       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:

       EPOLL_CLOEXEC
              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

       On success, these system calls return a  nonnegative  file  descriptor.
       On error, -1 is returned, and errno is set to indicate the error.

ERRORS

       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.

VERSIONS

       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.

CONFORMING TO

       epoll_create() is Linux-specific.

NOTES

       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.

SEE ALSO

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

COLOPHON

       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



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