/usr/lib/python2.7/dist-packages/charmtools/templates/bash/files/hooks/start is in charm-tools 2.1.2-0ubuntu4.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/bash
# Here put anything that is needed to start the service.
# Note that currently this is run directly after install
# i.e. 'service apache2 start'
|