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 #include 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 6.9.1 2024-05-02 bindresvport(3)