Basic monit example

unicorn.conf

check process unicorn
  with pidfile /path/to/pid/unicorn.pid
  start program = "/sbin/service unicorn start" with timeout 120 seconds
  stop program = "/sbin/service unicorn stop"
  if totalmem is greater than 500 MB for 2 cycles then restart

1. Define the process you want monit to monitor, in this case we'll call the process unicorn. This will let you run:

sudo monit start unicorn
sudo monit restart unicorn
sudo monit stop unicorn

1. Next tell monit where to find the process id to know a process is running.
2. Next, feed unicorn the command to run to start the service. You can add options like "with timeout 120 seconds" or "as uid unprivileged_user"
3. Tell monit how to stop the program.
4. You can add other conditionals like this one to restart the process if it starts eating too much memory.

This file lives in /etc/monit.d/ by default.