You should start Tomcat as a batch job instead of manually starting it from QSH. Schedule it to start automatically when your IBM i starts up.
Use the following command (adjust the parameters as required):
SBMJOB CMD(QSH CMD('/home/tony/java-interop-tutorial/tomcat/bin/startup.sh')) JOB(CATALINA) JOBQ(QBATCH) CPYENVVAR(*YES) ALWMLTTHD(*YES)
Check the log file to see if it starts up successfully.
Run Qshell. Use the cat command to dump the content of <tomcat-root>/logs/catalina.out.