Your appliance needs to respond when alarms or other critical events occur. Whether it's CPU temperature, battery level, low disk space, or paper level, something is going to occur that requires action from your appliance.

The idea of having a general purpose event-handling system is, surprisingly, not common in Linux. Too often the need for event handling is not apparent until near the end of system testing of the appliance, so it is usually addressed as an afterthought—with ad hoc and poorly integrated code.

The authors have built enough Linux appliances to know that we should build event handling into the core of our design for Laddie. As part of the Laddie project, we built our own event-handling system that ...

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