bindresvport(3) Library Functions Manual bindresvport(3)
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 de-
scriptor sockfd to a privileged anonymous IP port, that is, a port num-
ber 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 allo-
cated.
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 ob-
tained 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 ad-
dition, 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 at-
tributes(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 pro-
tected 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)
Linux man-pages 6.03 2023-02-05 bindresvport(3)
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