.. _daemon_ticker:

#26: Daemon Services
====================

Technical Background
++++++++++++++++++++

The Karabo control system uses **daemon tools encore**, which is a widely used
collection of tools for managing UNIX services.
In more detail, karabo *device-servers* are managed by daemon tools and they are typically
restarted by the daemon supervisor if shutdown.

The daemon services that run Karabo device servers can be managed through web interfaces independent
of the Karabo communication.

The `KaraboDaemonManager` is a device that interfaces this service management with Karabo and the KaraboGUI.


Daemon Control - Karabo GUI
+++++++++++++++++++++++++++

If the `KaraboDaemonManager` is online, an extra button *Service Manager* will appear in the `System Topology` panel.

.. figure:: images/daemon_button.png
   :align: center
   :alt: Daemon Service Button
   :figclass: align-center

   Retrieve the scene of the `KaraboDaemonManager` by clicking the *Service Manager* button

Clicking on the button will request an overview scene of the `KaraboDaemonManager` device.

.. figure:: images/daemon_scene.png
   :align: center
   :alt: Daemon Service Scene
   :figclass: align-center

   The scene of the `KaraboDaemonManager` providing operator control of the services

The retrieved scene will be shown in an undocked view and provides a table element with all
karabo device servers found in the Karabo Topic.

The status of the device servers is highlighted with **green** and **red** colors and the following
actions can be requested.

- **Start**: Start a device server. If a device server is already started, nothing happens.
- **Stop**: Stop a device server. The server is asked gently to stop. It will not restart, but remain offline. Press *Start* to start the server again.
- **Kill**: This will force the server to be killed, even if it does not react on *Stop* anymore. The device server will commonly **restart** and come back online.
  If the server does not restart on its own, you may use the *Start* button.

Requesting a command multiple times does not hurt the system and killing (restarting) multiple times after each other
is fine as well, don't hesitate to try this.