---
name: "poll.h"
section: "0p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/poll.h"
---

# poll.h(0p)

definitions for the poll() function

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

## NAME

poll.h — definitions for the poll() function

## SYNOPSIS

```
#include <poll.h>
```

## DESCRIPTION

The *\<poll.h\>* header shall define the **pollfd** structure, which shall include at least the following members:

```
int    fd       The following descriptor being polled.
short  events   The input event flags (see below).
short  revents  The output event flags (see below).
```

The *\<poll.h\>* header shall define the following type through **typedef**:

- **nfds\_t**

  An unsigned integer type used for the number of file descriptors.

The implementation shall support one or more programming environments in which the width of **nfds\_t** is no greater than the width of type **long**. The names of these programming environments can be obtained using the *confstr*() function or the *getconf* utility.

The *\<poll.h\>* header shall define the following symbolic constants, zero or more of which may be OR'ed together to form the *events* or *revents* members in the **pollfd** structure:

- POLLIN

  Data other than high-priority data may be read without blocking.

- POLLRDNORM

  Normal data may be read without blocking.

- POLLRDBAND

  Priority data may be read without blocking.

- POLLPRI

  High priority data may be read without blocking.

- POLLOUT

  Normal data may be written without blocking.

- POLLWRNORM

  Equivalent to POLLOUT.

- POLLWRBAND

  Priority data may be written.

- POLLERR

  An error has occurred (*revents* only).

- POLLHUP

  Device has been disconnected (*revents* only).

- POLLNVAL

  Invalid *fd* member (*revents* only).

The significance and semantics of normal, priority, and high-priority data are file and device-specific.

The following shall be declared as a function and may also be defined as a macro. A function prototype shall be provided.

```
int   poll(struct pollfd [], nfds_t, int);
```

*The following sections are informative.*

## APPLICATION USAGE

None.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

The System Interfaces volume of POSIX.1‐2017, *confstr()*, *poll()*

The Shell and Utilities volume of POSIX.1‐2017, *getconf*

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .