bash: ab: command not found

[nguyendn]

I run hbench on Ubuntu server and ab is installed

ab -c 100 -n 10000 http://simplewsgi.herokuapp.com/ 
This is ApacheBench, Version 2.3 <$Revision: 1528965 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking simplewsgi.herokuapp.com (be patient)
Completed 1000 requests
Completed 2000 requests

But hbench throws this error:

hbench -c 100 -n 10000 http://simplewsgi.herokuapp.com/
Benching: |=================================================================================================================================|
Herokubench ran into an error while executing ApacheBench. It is likely there was a syntax error in your command. Please see output below.
Running ab -c 100 -n 10000 http://simplewsgi.herokuapp.com/  attached to terminal... up, run.6806
bash: ab: command not found