This is the TCP server-client suit to help you test if your OS supports c1000k(1 million connections).

wget --no-check-certificate https://github.com/ideawu/c1000k/archive/master.zip
unzip master.zip
cd c1000k-master
make

./server 7000

./client 127.0.0.1 7000

The server will ouput message like this and quit:

connections: 153
error: Too many open files

It says the server can only accept 153 connections, it reaches the max-open-files limitation so it quit.

The client will output message like this:

connections: 154
error: Connection refused