simple UDP server can't accept packets

Question

I have a simple UDP server program

    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <stdio.h>
    #include <string.h>


    int main(int argc, char**argv)
    {
       int sockfd,n;
       struct sockaddr_in servaddr,cliaddr;
       socklen_t len;
       char mesg[1000];

       sockfd=socket(AF_INET,SOCK_DGRAM,0);

       bzero(&servaddr,sizeof(servaddr));
       servaddr.sin_family = AF_INET;
       servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
       servaddr.sin_port=htons(54000);
       bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));

       for (;;)
       {
          len = sizeof(cliaddr);
          n = recvfrom(sockfd,mesg,1000,0,(struct sockaddr *)&cliaddr,&len);
          sendto(sockfd,mesg,n,0,(struct sockaddr *)&cliaddr,sizeof(cliaddr));
          printf("-------------------------------------------------------\n");
          mesg[n] = 0;
          printf("Received the following:\n");
          printf("%s",mesg);
          printf("-------------------------------------------------------\n");
       }
    }
    ~

I compile it

  gcc -m32 -o udp_server udp_server.c

and run it(./udp_server) on several linux machines, it works fine and I use a udp client client to send packets to the UDP server on these machines, they are accepted

but I have a new machine(let me call it A), it is relatively strange compared to other linux machines, as shown in https://superuser.com/questions/581442/ifconfig-command-not-found anyway it has no "eth0" and the interfaces are:

    [root@kitch proxy]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: em1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT qlen 1000
    link/ether 00:1a:a0:23:86:6c brd ff:ff:ff:ff:ff:ff

First, I run the 32-bit-version of the program on it and I got

-bash: ./udp_server: /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory

Then, second, I compile the UDP program without '-m32' and run it on the machine A, it runs normally Then I use UDP client to send packets to the UDP server on A I can capture the sent packets on this machine, but the UDP server doesn't accept those packets,

are there any potential reasons for this? maybe the binding doesn't work here because this machine is special? thanks!

Davide Berra Davide Berra · Accepted Answer · 2013-04-11T14:48:42

Some recent Linux distros (e.g. Fedora) have changed the name of the interface from ethX to emX, so, nothing wrong with it.

You got problem with that machine because the server is not running at all as this line claims:

-bash: ./udp_server: /lib/ld-linux.so.2: bad ELF interpreter: No such file or directory

I guess you've compiled the program in a 32bit mode ( look at the -m32 gcc parameter ) in a 64bit machine with no 32bit library support installed.

Recompile it without -m32 options.

simple UDP server can't accept packets

1 Answers