Chapter 8: Tru64 UNIX Cluster Hooks - Event Manager

Overview

The Event Manager (EVM) is a new component added to Tru64 UNIX in the version 5.0 release of the operating system in response to customer requests to have common access to all system (and cluster) event information.

In previous releases, events that occurred on the system would likely be logged to one of two main loggers: the System Message Logger (syslogd) and the Binary Error Logger (binlogd) – although other logging methods could also be used. EVM works in cooperation with these other event loggers to consolidate information. Figure 8-1 illustrates the event path to EVM.

1. An application or kernel subsystem generates an event.

2. That event may be sent to one of the legacy Tru64 UNIX loggers, another logger or a log file, or posted directly to EVM.

3. Once the EVM daemon (evmd) receives the event, it sends the event to any program or kernel component that takes out an EVM subscription to that event.

Figure 8-1: EVM Event Path

Think of EVM as a publishing company or a favorite bookstore, events as magazines, and applications as subscribers. You (or your application in this case) subscribe to only those magazines (or events) that are of interest. Every time there is a new issue (or event), it is delivered to you. The same thing happens here. EVM receives the event and sends it to the subscribers. On occasion, you may go to the bookstore to pick up some magazines. You can get events from EVM in much the same way, using the evmget(1) program.

You can even wait for events to occur using the evmwatch(1) program (kind of like waiting in line all night to get concert tickets – except without the lawn chair).