setsockopt: Protocol not available [Solved]

Problem code:

if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) 

{ 

perror("setsockopt"); 

exit(EXIT_FAILURE); 

}

Solution:

if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) 

{ 

perror("setsockopt"); 

exit(EXIT_FAILURE); 

}

Ref.: https://stackoverflow.com/a/59807281/4064166

This error appears when a socket option is not supported on the current platform. Here the combination of SO_REUSEADDR and SO_REUSEPORT fails because SO_REUSEPORT is unavailable, so the call returns Protocol not available.

Setting SO_REUSEADDR on its own fixes it, which is widely supported and enough for the common case of rebinding a recently used address. SO_REUSEPORT behaves differently across operating systems and is not always present.