PollEvents

There is data to read.

Writing is now possible, though a write larger that the available space in a socket or pipe will still block (unless O_NONBLOCK is set).

There is some exceptional condition on the file descriptor. Possibilities include:

* There is out-of-band data on a TCP socket (see tcp(7)). * A pseudoterminal master in packet mode has seen a state change on the slave (see ioctl_tty(2)). * A cgroup.events file has been modified (see cgroups(7)).

Error condition (only returned in revents; ignored in events). * This bit is also set for a file descriptor referring to the * write end of a pipe when the read end has been closed.

Invalid request: fd not open (only returned in revents; ignored in events).

Equivalent to POLLIN.

Priority band data can be read (generally unused on Linux).

Equivalent to POLLOUT.

Priority data may be written.

Hang up (only returned in revents; ignored in events). Note that when reading from a channel such as a pipe or a stream socket, this event merely indicates that the peer closed its end of the channel. Subsequent reads from the channel will return 0 (end of file) only after all outstanding data in the channel has been consumed.

(since Linux 2.6.17) Stream socket peer closed connection, or shut down writing half of connection.

(since Linux 4.5) Sets an exclusive wakeup mode for the epoll file descriptor that is being attached to the target file descriptor, fd. When a wakeup event occurs and multiple epoll file descriptors are attached to the same target file using EPOLLEXCLUSIVE, one or more of the epoll file descriptors will receive an event with epoll_wait(2). The default in this scenario (when EPOLLEXCLUSIVE is not set) is for all epoll file descriptors to receive an event. EPOLLEXCLUSIVE is thus useful for avoiding thundering herd problems in certain scenarios.