Getting "Address already in use" error using Unix socket

Question

Writing the C source below using Unix local sockets I got an error about the address already in use. After having checked man 7 Unix for further informations I tried to create a sub-folder where executing my program (obviously modifying the sun_path field on the current folder) but the error was ever the same.

Is there someone able to help me?

Source code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <unistd.h>
#include <errno.h>

#define MAXLEN  128

int main (int argc, char *argv[]){

        struct sockaddr_un      server;
        int                                     serverfd, clientfd;
        socklen_t                       addrsize = sizeof(struct sockaddr_un);
        char                            buff[MAXLEN], *path;

        if (argc < 2){
                printf("Error: %s [MESSAGE]\n", argv[0]);
                return 1;
        }

        if ((serverfd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0){
                printf("Error \"%s\" in socket()\n", strerror(errno));
                exit(1);
        }
        puts("socket()");

        server.sun_family = AF_UNIX;
        path = strcpy(server.sun_path, "/home/myhome/Dropbox/Sources/C/sub");

        printf("[DEBUG]Address bound at %s\n", path);

        if ((bind(serverfd, (struct sockaddr*)&server, addrsize)) < 0){
                printf("Error \"%s\" in bind()\n", strerror(errno));
                exit(1);
        }
        puts("bind()");


        if ((listen(serverfd, 1)) < 0){
                printf("Error \"%s\" in listen()\n", strerror(errno));
                exit(1);
        }

        if ((clientfd = accept(serverfd, NULL, &addrsize)) < 0){
                printf("Error \"%s\" in accept()\n", strerror(errno));
                exit(1);
        }

        write(clientfd, argv[1], strlen(argv[1]));
        read(clientfd, buff, sizeof(buff));

        puts(buff);

        close(clientfd);
        close(serverfd);
        return 0;
}

The error displayed is this: "Error "Address already in use" in bind()" — Acsor, Jul 03 '13 at 15:31
hey, DO NOT use a dropbox filesystem for AF_UNIX. It really needs to be a local filesystem. You can google around for why. Here there be dragons, so until you try it on a local filesystem and reproduce it, I don't think anyone can help you. — xaxxon, Jul 03 '13 at 15:32
It sounds pretty strange, since the Dropbox folder is located on my filesystem. Anyway I'm gonna try it. — Acsor, Jul 03 '13 at 15:36
is DropBox associated with the file sharing service DropBox? https://www.dropbox.com/ or just a coincidental name? — xaxxon, Jul 03 '13 at 15:37
also, are you making sure to unlink the file if it exists? http://beej.us/guide/bgipc/output/html/multipage/unixsock.html — xaxxon, Jul 03 '13 at 15:40
Just tried it moving the program on my home, and it doesn't even work. I'm going to read that page. — Acsor, Jul 03 '13 at 15:43

VoidPointer · Accepted Answer · 2013-11-18T09:54:29.577

25

You should unlink() the path file before bind call. You will get this error when file exists during the bind. Either you should ensure to unlink/remove the file before exiting the application or you could always unlink it before bind.

Check man page of bind. Also, note the example given in the man page at the end.

edited Nov 18 '13 at 09:54

answered Jul 03 '13 at 15:39

VoidPointer

3,037
21
25

1

yeah, I just saw this, too – xaxxon Jul 03 '13 at 15:41
Yes, just tried and it works. Anyway, thanks to both and +1 to xaxxon. – Acsor Jul 03 '13 at 15:49

score -4 · Answer 2 · answered Jul 03 '13 at 15:43

-4

You can try to use the SO_REUSEADDR flag like so:

int yes = 1;
if (setsockopt(socketfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
    // error handling
    exit(1);
}

answered Jul 03 '13 at 15:43

Thire

437
4
10

I read some stuff that while it's not strongly defined that this isn't meaningful for non network protocols. – xaxxon Jul 03 '13 at 16:45

Getting "Address already in use" error using Unix socket

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