bindresvport man page
bindresvport ā bind a socket to a privileged IP port 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).) bindresvport() returns 0 on success; otherwise -1 is returned and errno set to indicate the cause of the error. bindresvport() can fail for any of the same reasons as bind(2). In addition, the following errors may occur: 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). All privileged ports are in use. sin is not NULL and sin->sin_family is not AF_INET. For an explanation of the terms used in this section, see attributes(7). The bindresvport() function uses a static variable that was not protected by a lock before glibc 2.17, rendering the function MT-Unsafe. Not in POSIX.1. Present on the BSDs, Solaris, and many other systems. Unlike some bindresvport() implementations, the glibc implementation ignores any value that the caller supplies in sin->sin_port. This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.Synopsis
#include <sys/types.h>
#include <netinet/in.h>
int bindresvport(int sockfd, struct sockaddr_in *sin);
Description
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Attributes
Interface Attribute Value bindresvport() Thread safety glibc >= 2.17: MT-Safe
glibc < 2.17: MT-UnsafeConforming to
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