# Extras Hooks The `extras.d` directory contains project dispatch scripts that are called at specific times by `stack.sh`, `unstack.sh` and `clean.sh`. These hooks are used to install, configure and start additional projects during a DevStack run without any modifications to the base DevStack scripts. When `stack.sh` reaches one of the hook points it sources the scripts in `extras.d` that end with `.sh`. To control the order that the scripts are sourced their names start with a two digit sequence number. DevStack reserves the sequence numbers 00 through 09 and 90 through 99 for its own use. The scripts are sourced at the beginning of each script that calls them. The entire `stack.sh` variable space is available. The scripts are sourced with one or more arguments, the first of which defines the hook phase: override_defaults | source | stack | unstack | clean override_defaults: always called first in any of the scripts, used to override defaults (if need be) that are otherwise set in lib/* scripts source: called by stack.sh. Used to set the initial defaults in a lib/* script or similar stack: called by stack.sh. There are four possible values for the second arg to distinguish the phase stack.sh is in: arg 2: pre-install | install | post-config | extra unstack: called by unstack.sh clean: called by clean.sh. Remember, clean.sh also calls unstack.sh so that work need not be repeated. The `stack` phase sub-phases are called from `stack.sh` in the following places: pre-install - After all system prerequisites have been installed but before any DevStack-specific services are installed (including database and rpc). install - After all OpenStack services have been installed and configured but before any OpenStack services have been started. Changes to OpenStack service configurations should be done here. post-config - After OpenStack services have been initialized but still before they have been started. (This is probably mis-named, think of it as post-init.) extra - After everything is started.