Simple UDP server taken from https://www.cs.cmu.edu/afs/cs/academic/class/15213-f99/www/class26/udpserver.c and modified a little.

upd_server_recv.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <net/if.h>

#define BUFSIZE 1024

/*
 * error - wrapper for perror
 */
void error(char *msg) {
	perror(msg);
	exit(1);
}

int main(int argc, char **argv)
{
	int sockfd;
	int portno;
	int clientlen;
	struct sockaddr_in serveraddr;
	struct sockaddr_in clientaddr;
	struct hostent *hostp;
	char buf[BUFSIZE];
	char *hostaddrp;
	int optval;
	int n;

	if (argc != 2) {
		fprintf(stderr, "usage: %s <port>\n", argv[0]);
		exit(1);
	}

	portno = atoi(argv[1]);

	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	if (sockfd < 0)
		error("ERROR opening socket");

	/* setsockopt: Handy debugging trick that lets
	 * us rerun the server immediately after we kill it;
	 * otherwise we have to wait about 20 secs.
	 * Eliminates "ERROR on binding: Address already in use" error.
	 */

	optval = 1;
	setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
			(const void *)&optval , sizeof(int));

	/*
	 * build the server's Internet address
	 */
	bzero((char *) &serveraddr, sizeof(serveraddr));
	serveraddr.sin_family = AF_INET;
	serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
	serveraddr.sin_port = htons((unsigned short)portno);

	/*
	 * bind: associate the parent socket with a port
	 */
	if (bind(sockfd, (struct sockaddr *) &serveraddr,
				sizeof(serveraddr)) < 0)
		error("ERROR on binding");

	/*
	 * main loop: wait for a datagram, then echo it
	 */
	clientlen = sizeof(clientaddr);
	while (1) {

		/*
		 * recvfrom: receive a UDP datagram from a client
		 */
		bzero(buf, BUFSIZE);
		n = recvfrom(sockfd, buf, BUFSIZE, 0,
				(struct sockaddr *) &clientaddr, &clientlen);
		if (n < 0)
			error("ERROR in recvfrom");

		hostaddrp = inet_ntoa(clientaddr.sin_addr);
		if (hostaddrp == NULL)
			error("ERROR on inet_ntoa\n");
		printf("server received datagram from (%s), data:%s\n",
				hostaddrp, buf);
	}
}