How to stress test a server

Siege is an http/https regression testing and benchmarking utility. It was designed to let web developers measure the performance of their code under duress, to see how it will stand up to load on the internet.
Install seige

apt-get install siege

Run the following command to seige a server. -t is the time to run, -c is the number of concurrent connections.

siege -b -t300S -c100 -d0 -v -u http://domain_name.com

You can also write stats into file

siege -b -t30S -c100 -d0 -v -i -f /<directoy>/<file_name>.txt

You can read further on website