/usr/lib/python2.7/dist-packages/charmtools/templates/bash/files/hooks/upgrade-charm 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 5 6 | #!/bin/bash
# This hook is executed each time a charm is upgraded after the new charm
# contents have been unpacked
#
# Best practice suggests you execute the hooks/install and
# hooks/config-changed to ensure all updates are processed
|