NAME

       bindresvport - bind a socket to a privileged IP port

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

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

       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.

STANDARDS

       Not in POSIX.1.  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.

SEE ALSO

       bind(2), getsockname(2)