Why changing value of SO_RCVBUF doesn't work?

Question

I\'m making a program which create a RAW socket in order to read all traffic. Between the call of socket() and recvfrom() (last one is in a loop to get out all packets from

Answer 1

The level argument to setsockopt should be SOL_SOCKET, not 0:

int a = 65535;
if (setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &a, sizeof(int)) == -1) {
    fprintf(stderr, "Error setting socket opts: %s\n", strerror(errno));
}

Answer 2

You may also be limited by the OS, if it still doesn't seem to be working. Check the values in:

/proc/sys/net/core/rmem_default
/proc/sys/net/core/rmem_max

If it's TCP as you say in your example, and not actually a raw socket, you can also check the values in:

/proc/sys/net/ipv4/tcp_mem

If you run cat on these files they'll show you the current settings. To change them permanently, use sysctl. It's a good idea to write these settings down before you start changing things. Here's a great tutorial on making those changes: http://fasterdata.es.net/fasterdata/host-tuning/linux/.