bindresvport (3)

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

int bindresvport(int sockfd, struct sockaddr_in *sin);

bindresvport() is used to bind a socket descriptor 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:

EACCES

The caller did not have superuser privilege (to be precise: the CAP_NET_BIND_SERVICE capability is required).

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.

Multithreading (see pthreads(7))

Before glibc 2.17, the bindresvport() function uses a static variable that is not protected, so it is not thread-safe.

Since glibc 2.17, the bindresvport() function uses a lock to protect the static variable, so it is thread-safe.

Not in POSIX.1-2001. 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.

bind(2), getsockname(2)

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