BINDRESVPORT(3) Linux Programmer's Manual BINDRESVPORT(3)
bindresvport - bind a socket to a privileged IP port
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. How-
ever, in this case, bindresvport() has no way to return the port number actually allo-
cated. (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 follow-
ing errors may occur:
EACCES The caller did not have superuser privilege (to be precise: the CAP_NET_BIND_SER-
VICE capability is required).
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 pro-
tected, so it is not thread-safe.
Since glibc 2.17, the bindresvport() function uses a lock to protect 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.
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