phpseclib of how to get PID and kill

Question

Normally i restart tomcat by entering the command on the putty.My problem tomcat always hang.Below is the step 1. ps aux | grep tomcat 2. Get PID 3. Kill PID cd /usr/local/tomcat/bin 4../startup.sh

and now plan to make it auto but then how to add in the script below.

 $ssh = new Net_SSH2('172.16.2.96');
 if (!$ssh->login('root', 'password')) {
    exit('Login Failed');
}
//Line here
echo $ssh->exec('service tomcat start');

really appreciate your help.thank you