[Socket programming] bind: Address already in use

Aquarius_Girl · 09-19-2011, 02:55 AM

From Beej's socket programming book, page 13:

Quote:

Sometimes, you might notice, you try to rerun a server and bind() fails, claiming “Address already in use.” What does that mean? Well, a little bit of a socket that was connected is still hanging around in the kernel, and it's hogging the port.

What EXACTLY is the meaning of the bold words above, in technical terms?

vadiml · 09-19-2011, 05:50 AM

Following is form here: http://www.unixguide.net/network/socketfaq/4.1.shtml

Quote:

How come I get "address already in use" from bind()?

You get this when the address is already in use. (Oh, you figured
that much out?) The most common reason for this is that you have
stopped your server, and then re-started it right away. The sockets
that were used by the first incarnation of the server are still
active. This is further explained in ``2.7 Please explain the
TIME_WAIT state.'', and ``2.5 How do I properly close a socket?''.

Aquarius_Girl · 09-19-2011, 06:02 AM

Thanks, that was somewhat helpful, beej should be
told to write serious stuff after jokes, I think.

ta0kira · 09-19-2011, 08:39 AM

In case you're wondering, you can overcome that with this before bind:

Code:

//(#include <sys/socket.h> somewhere earlier)

    #if defined(SOL_SOCKET) && defined(SO_REUSEADDR)
        int value = 1;
        setsockopt(new_socket, SOL_SOCKET, SO_REUSEADDR, (void*) &value, sizeof value);
    #endif

Kevin Barry

Aquarius_Girl · 09-19-2011, 09:36 AM

Yeah, that is mentioned in that beej's guide too, but I just
wanted to understand the reason for the error.

vadiml · 09-19-2011, 12:16 PM

Quote:

Originally Posted by Anisha Kaul

Yeah, that is mentioned in that beej's guide too, but I just
wanted to understand the reason for the error.

The reason is that in order to insure that all packets pertaining to the given tcp connection which were in transit
at the moment you've called 'close' on the socket, are off the wire, the socket is put in a state which causes it to throw all incoming packets.
This state has a timeout and during this timeout you can't recreate the socket with the same combinaton of address,port.
You can read detailed explanation here:
http://www.isi.edu/touch/pubs/infocomm99/infocomm99-web