---
name: "bindresvport"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/bindresvport"
---

# bindresvport(3)

bind a socket to a privileged IP port

## NAME

bindresvport - bind a socket to a privileged IP port

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <sys/types.h>
#include <netinet/in.h>
```

**int bindresvport(int** *sockfd***, struct sockaddr\_in \****sin***);**

## DESCRIPTION

**bindresvport**() is used to bind the socket referred to by the file descriptor *sockfd* to a privileged anonymous IP port, that is, a port number arbitrarily selected from the range 512 to 1023.

If the [**bind**(2)](/bind/2.md) performed by **bindresvport**() is successful, and *sin* is not NULL, then *sin-\>sin\_port* returns the port number actually allocated.

*sin* can be NULL, in which case *sin-\>sin\_family* is implicitly taken to be **AF\_INET**. However, in this case, **bindresvport**() has no way to return the port number actually allocated. (This information can later be obtained using [**getsockname**(2)](/getsockname/2.md).)

## RETURN VALUE

**bindresvport**() returns 0 on success; otherwise -1 is returned and *errno* is set to indicate the error.

## ERRORS

**bindresvport**() can fail for any of the same reasons as [**bind**(2)](/bind/2.md). In addition, the following errors may occur:

- **EACCES**

  The calling process was not privileged (on Linux: the calling process did not have the **CAP\_NET\_BIND\_SERVICE** capability in the user namespace governing its network namespace).

- **EADDRINUSE**

  All privileged ports are in use.

- **EAFNOSUPPORT** (**EPFNOSUPPORT** in glibc 2.7 and earlier)

  *sin* is not NULL and *sin-\>sin\_family* is not **AF\_INET**.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **bindresvport**() | Thread safety | glibc \>= 2.17: MT-Safe; glibc \< 2.17: MT-Unsafe |

The **bindresvport**() function uses a static variable that was not protected by a lock before glibc 2.17, rendering the function MT-Unsafe.

## VERSIONS

Present on the BSDs, Solaris, and many other systems.

## NOTES

Unlike some **bindresvport**() implementations, the glibc implementation ignores any value that the caller supplies in *sin-\>sin\_port*.

## STANDARDS

BSD.

## SEE ALSO

[**bind**(2)](/bind/2.md), [**getsockname**(2)](/getsockname/2.md)