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How to get the local listening ports in real time by C programming?

I want to write a LINUX C application that can monitor the system TCP listening ports which provide web service. Whenever a new port is listened, or one port is released, I can detect it in real time.
Does Linux provide system call to provide this feature? Or Should I hook the Kernel function?

netstat

1 Answer
1

The code below will help you check if a port is open, if you need real time processing; you may continuously run the program in a separate thread.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

int main(int argc, char *argv)

int portno = 22;
char *hostname = "localhost;

int sockfd;
struct sockaddr_in serv_addr;
struct hostent *server;

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


server = gethostbyname(hostname);

if (server == NULL)
fprintf(stderr,"ERROR, no such hostn");
exit(0);


bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);

serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
printf("Port is closed");
else
printf("Port is active");


close(sockfd);
return 0;



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