Disabling DNS change in openvpn client

Question

I am having trouble using fcntl() and fileno. I am having trouble implementing a lock mechanism. However when I try to close a file I get the following error fcntl: Bad file descriptor. I am using fileno to get the file description and I am getting -1.

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

//args ==path to the file
int main(int argc, char *argv[])
{
    struct flock lock = {F_WRLCK, SEEK_SET,   0,      0,     0 };
    int fd;
    FILE* fp;

    lock.l_pid = getpid();

    if (argc > 1) 
        lock.l_type = F_RDLCK;

    printf("%s\n", argv[1]);

    fp = fopen(argv[1], "w");

    if(fp==NULL)
    {
        perror("fopen");
        exit(1);
    }

    fd=fileno(fp);

    getchar();

    if (fcntl(fd, F_SETLKW, &lock) == -1) {
        perror("fcntl");
        exit(1);
    }

    lock.l_type = F_UNLCK; 


    if (fcntl(fd, F_SETLK, &lock) == -1) {
        perror("fcntl");
        exit(1);
    }

    close(fd);

    return 0;
}

Solution

Gnome's network manager with OpenVPN lets you only get Addresses from the VPN server and have your own DNS server and search domains be configured. Not sure if your requirement is for a Desktop System or a server and what desktop environment you are using.

But, there exists a case where you might not be able to access your own DNS service (from the one provided by your service provider) because all your traffic including DNS'es would be routed from the VPN server. In this case you can manually set google's free DNS server addresses there.

Not sure if you are using network-manager's OpenVPN module to configure VPNs. But that would be a better way.

Also this script/tutorial might be of help to you.

Comments

[asio_guy]

you should have handled argc <= 1

[julian joseph]

I don't have access to the server.

[Boban P.]

After connecting your linux box to the vpn, try to manualy set dns servers that belong to a vpn routed network, and see if it's working.

[julian joseph]

Thanks! What I did was dissect the openvpn configuration file (save keys into their own files etc.) and configure the gnome network manager by hand (instead of executing openvpn on the command line). Now it works as intended.

[atkawa7]

The problem is because of if (argc > 1) lock.l_type = F_RDLCK; which does not work with "w". I am putting a read lock but trying to write which do not work together well