---
name: "libressl-SSL_set_fd"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-SSL_set_fd"
---

# libressl-SSL\_set\_fd(3)

connect the SSL object with a file descriptor

## NAME

**SSL\_set\_fd**, **SSL\_set\_rfd**, **SSL\_set\_wfd** – connect the SSL object with a file descriptor

## SYNOPSIS

SSL Library (libssl, -lssl) libcrypto

**#include \<openssl/ssl.h\>**

*int*\

**SSL\_set\_fd**(*SSL \*ssl*, *int fd*);

*int*\

**SSL\_set\_rfd**(*SSL \*ssl*, *int fd*);

*int*\

**SSL\_set\_wfd**(*SSL \*ssl*, *int fd*);

## DESCRIPTION

**SSL\_set\_fd**() sets the file descriptor *fd* as the input/output facility for the TLS/SSL (encrypted) side of *ssl*. *fd* will typically be the socket file descriptor of a network connection.

When performing the operation, a socket *BIO* is automatically created to interface between the *ssl* and *fd*. The *BIO* and hence the SSL engine inherit the behaviour of *fd*. If *fd* is non-blocking, the *ssl* will also have non-blocking behaviour.

If there was already a *BIO* connected to *ssl*, BIO\_free(3) will be called (for both the reading and writing side, if different).

**SSL\_set\_rfd**() and **SSL\_set\_wfd**() perform the respective action, but only for the read channel or the write channel, which can be set independently.

## RETURN VALUES

The following return values can occur:

- 0

  The operation failed. Check the error stack to find out why.

- 1

  The operation succeeded.

## SEE ALSO

BIO\_new(3), [ssl(3)](/ssl/3.md), SSL\_accept(3), SSL\_connect(3), SSL\_get\_fd(3), SSL\_set\_bio(3), SSL\_shutdown(3)

## HISTORY

**SSL\_set\_fd**() appeared in SSLeay 0.4 or earlier. **SSL\_set\_rfd**() and **SSL\_set\_wfd**() first appeared in SSLeay 0.6.0. These functions have been available since OpenBSD 2.4.