epoll_create(2)

1EPOLL_CREATE(2)            Linux Programmer's Manual           EPOLL_CREATE(2)
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NAME

6       epoll_create, epoll_create1 - open an epoll file descriptor
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SYNOPSIS

9       #include <sys/epoll.h>
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11       int epoll_create(int size);
12       int epoll_create1(int flags);
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DESCRIPTION

15       epoll_create() creates a new epoll(7) instance.  Since Linux 2.6.8, the
16       size argument is ignored, but must be greater than zero; see NOTES.
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18       epoll_create() returns a file descriptor referring to the new epoll in‐
19       stance.   This  file descriptor is used for all the subsequent calls to
20       the epoll interface.  When no longer required, the file descriptor  re‐
21       turned  by epoll_create() should be closed by using close(2).  When all
22       file descriptors referring to an epoll instance have been  closed,  the
23       kernel  destroys the instance and releases the associated resources for
24       reuse.
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26   epoll_create1()
27       If flags is 0, then, other than the fact that the obsolete  size  argu‐
28       ment  is  dropped,  epoll_create1() is the same as epoll_create().  The
29       following value can be included in flags to obtain different behavior:
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31       EPOLL_CLOEXEC
32              Set the close-on-exec (FD_CLOEXEC) flag on the new file descrip‐
33              tor.   See  the description of the O_CLOEXEC flag in open(2) for
34              reasons why this may be useful.
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RETURN VALUE

37       On success, these system calls return a file descriptor (a  nonnegative
38       integer).   On  error, -1 is returned, and errno is set to indicate the
39       error.
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ERRORS

42       EINVAL size is not positive.
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44       EINVAL (epoll_create1()) Invalid value specified in flags.
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46       EMFILE The per-user limit on the number of epoll instances  imposed  by
47              /proc/sys/fs/epoll/max_user_instances   was   encountered.   See
48              epoll(7) for further details.
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50       EMFILE The per-process limit on the number of open file descriptors has
51              been reached.
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53       ENFILE The system-wide limit on the total number of open files has been
54              reached.
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56       ENOMEM There was insufficient memory to create the kernel object.
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VERSIONS

59       epoll_create() was added to the kernel in version 2.6.  Library support
60       is provided in glibc starting with version 2.3.2.
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62       epoll_create1()  was  added  to  the kernel in version 2.6.27.  Library
63       support is provided in glibc starting with version 2.9.
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CONFORMING TO

66       epoll_create() and epoll_create1() are Linux-specific.
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NOTES

69       In the initial epoll_create() implementation,  the  size  argument  in‐
70       formed the kernel of the number of file descriptors that the caller ex‐
71       pected to add to the epoll instance.  The kernel used this  information
72       as  a  hint  for  the amount of space to initially allocate in internal
73       data structures describing events.  (If necessary, the kernel would al‐
74       locate  more  space  if  the  caller's usage exceeded the hint given in
75       size.)  Nowadays, this hint is no longer required (the  kernel  dynami‐
76       cally sizes the required data structures without needing the hint), but
77       size must still be greater than zero, in order to ensure backward  com‐
78       patibility when new epoll applications are run on older kernels.
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COLOPHON

84       This  page  is  part of release 5.13 of the Linux man-pages project.  A
85       description of the project, information about reporting bugs,  and  the
86       latest     version     of     this    page,    can    be    found    at
87       https://www.kernel.org/doc/man-pages/.
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91Linux                             2021-03-22                   EPOLL_CREATE(2)