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BINDRESVPORT(3) Linux Programmer's Manual BINDRESVPORT(3)
NAME
bindresvport - bind a socket to a privileged IP port
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 se‐
lected 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 ac‐
tually 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.
CONFORMING TO
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)
2021-03-22 BINDRESVPORT(3)