epoll_create(2)                                         System Calls Manual                                         epoll_create(2)

NAME
       epoll_create, epoll_create1 - open an epoll file descriptor

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <sys/epoll.h>

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

DESCRIPTION
       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 sub‐
       sequent  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 file descriptor (a nonnegative integer).  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.

       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.

VERSIONS
       epoll_create() was added in Linux 2.6.  Library support is provided in glibc 2.3.2.

       epoll_create1() was added in Linux 2.6.27.  Library support is provided in glibc 2.9.

STANDARDS
       epoll_create() and epoll_create1() are 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)

Linux man-pages 6.03                                         2022-12-04                                             epoll_create(2)