How to recive more than 65000 bytes in C++ socket using recv()

Question

I am developing a client server application (TCP) in Linux using C++. I want to send more than 65,000 bytes at the same time. In TCP, the maximum packet size is

Answer 1

It is possible that your problem is related to kernel socket buffer sizes. Try adding the following to your code:

int buffsize = 1024*1024;
setsockopt(s, SOL_SOCKET, SO_RCVBUF, &buffsize, sizeof(buffsize));

You might need to increase some sysctl variables too:

sysctl -w net.core.rmem_max=8388608
sysctl -w net.core.wmem_max=8388608

Note however, that relying on TCP to fill your whole buffer is generally a bad idea. You should rather call recv() multiple times. The only good reason why you would want to receive more than 64K is for improved performance. However, Linux should already have auto-tuning that will progressively increase the buffer sizes as required.