UBOS state


State diagram

A UBOS Device can be thought of as always being in a particular state. The following diagram shows these as a state chart:

UBOS state chart

A UBOS Device can either be in one of the following two major states:

  • “Powered Off”, or
  • “Powered On”.

When “Powered On”, initially it is:

  • “Booting”, until the boot process is complete and it is in state
  • “Operational”.
  • While ubos-admin is running, the device is in “In Maintenance”.

Once ubos-admin completes, the device goes back to being “Operational”. The device can further be:

  • “Shutting Down”, going back to “Powered Off”, or
  • “Rebooting”, going back to “Operational”.

While it hopefully never happens, the device can also be in state:

  • “Error”.

If the device enters one of the states shown with a gray background, a state transition callback is performed as described next.

State transitions

When UBOS transitions from one state to another, it invokes callbacks defined in /etc/state-callbacks. Callbacks are defined as follows:

  • Each file in /etc/state-callbacks defines one callback
  • Each callback file consists of a single line with the fully-qualified name of a Perl module with optional arguments that are passed-on verbatim, e.g. Some::Where::Callback a 17.
  • The Perl class must have a subroutine called stateChanged, which will be invoked when the device state changes. Arguments to the subroutine are:
    • the name of the new state
    • the remaining arguments from the callback file So in this example, the invocation may be Some::Where::Callback::stateChanged( 'Operational', 'a', 17 );

The values for the states are the same as the gray-shaded states shown in the diagram, except that blanks are removed: Operational, InMaintenance, ShuttingDown, Rebooting and Error.