Inspecting logs in DevStack with the GNU Screen

Debugging OpenStack components on DevStack
==========================================

By default, DevStack [0] uses GNU Screen [1] to display all the execution traces of the different components in the deployment.
Learning how to use the screen is crucial for the development process given that you will be able to have a better
understanding of what is going on under the hood.

This gist aims to be a cheatsheet for all the people getting started with OpenStack development using DevStack.

Connect to the screen session
-----------------------------

screen -x stack

Navigate the log screens
------------------------

- Get a full list of all the services

ctrl+a then "

This command will output a list of all the services running with the format "num name", being num the screen number
and name the name of the service.

e.g. 20 c-vol 21 h-eng 22 h-api 23 h-api-cfn 24 h-api-cw 25 tr-api 26 tr-tmgr 27 tr-cond (full list ommited)

c stands for Cinder, h for Heat, tr for Trove, etc.

- Go directly to a specific screen window

ctrl+a then '

Then enter a number (like 25) or name (like tr-api)

- Go to the next screen

ctrl+a n

- Go to the previous screen

ctrl+a p

Take control of the screen
--------------------------

ctrl+a esc

This will allow you to use the keyboard arrows to inspect the logs, to stop the process (ctrl+c) or
to rerun a process (running the last command). Once you have control of that screen, you can do whatever you want
as it was a regular terminal.

Detach from the screen
----------------------

ctrl+a d

Finish the screen session.

Notes
-----

- You cannot perform any action with your mouse. Not even the scroll. It's a CLI after all.
- Different components in OpenStack are built from different running services. Hence you will see various
services for the same component. You will need to dig more into the OpenStack component architecture to get
a better understanding of what is this about. E.g. Trove has tr-api, tr-cond, tr-tmgr, this is, API, Conductor
and Task Manager.

[0] http://docs.openstack.org/developer/devstack/
[1] http://www.gnu.org/software/screen/