.\" $OpenBSD: bindresvport.3,v 1.4 1996/10/21 03:49:53 deraadt Exp $ .\" .Dd November 22, 1987 .Dt BINDRESVPORT 3 .Os .Sh NAME .Nm bindresvport .Nd bind a socket to a privileged IP port .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd include <netinet/in.h> .Ft int .Fn bindresvport "int sd" "struct sockaddr_in **sin" .Sh DESCRIPTION .Fn bindresvport is used to bind a socket descriptor to a privileged .Tn IP port, that is, a port number in the range 0-1023. The routine returns 0 if it is successful, otherwise -1 is returned and .Va errno set to reflect the cause of the error. .Pp Only root can bind to a privileged port; this call will fail for any other users. .Pp If the value of sin->sin_port is non-zero .Fn bindresvport otherwise it attempts to use the specified port. If that fails, it chooses another privileged port number automatically.