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BINDRESVPORT(3) Library Functions Manual BINDRESVPORT(3)

bindresvport, bindresvport_sa
bind a socket to a privileged IP port

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

bindresvport(int sd, struct sockaddr_in *sin);

bindresvport_sa(int sd, struct sockaddr *sa);

The bindresvport() and bindresvport_sa() functions are used to bind a socket descriptor to a privileged IP port, that is, a port number in the range 0-1023. The bindresvport() function operates solely on AF_INET sockets, whereas the bindresvport_sa() function is capable of binding both AF_INET and AF_INET6 sockets.

Only the superuser may bind to a privileged port; these functions will fail for any other user.

sd should be a socket descriptor that was returned by a call to socket(2).

If sin is not the NULL pointer, sin->sin_family must be initialized to the address family of the socket sd. If the value of sin->sin_port is non-zero, bindresvport() will attempt to use the specified port. Otherwise, a free port in the range 600-1023 will be chosen and, if the bind(2) succeeds, sin->sin_port will be updated with the port that was assigned.

If sin is the NULL pointer, a free port in the range 600-1023 will be chosen (as above), but in this case there is no way for bindresvport() to communicate to the caller which port was assigned.

bindresvport() returns 0 if it is successful, otherwise -1 is returned and errno set to reflect the cause of the error.

The bindresvport() function fails if:
sd is not a valid descriptor.
sd is not a socket.
The specified address is not available from the local machine.
The specified address is already in use.
The socket is already bound to an address.
The family of the socket and that requested in sa->sa_family are not equivalent.
The requested address is protected, and the current user has inadequate permission to access it.
The name parameter is not in a valid part of the user address space.
Insufficient resources were available in the system to perform the operation.
The protocol family has not been configured into the system, no implementation for it exists, or address family did not match between arguments.

bind(2), socket(2), rresvport(3), rresvport_af(3)
June 5, 2013 OpenBSD-current