bindresvport(3)            Library Functions Manual            bindresvport(3)

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) 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).)

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).  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).

       +----------------+---------------+-------------------------------------+
       |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), getsockname(2)

Linux man-pages 6.7               2023-10-31                   bindresvport(3)