EMS Manual

EMS Components and Architecture
EMS Manual—426909-005
2-2
Event Messages
Event Messages
Event messages are based on tokens that convey information about events, which are
significant occurrences in the subsystem environment.
Because of their token structure, event messages are much more convenient and
efficient for applications to process than text messages. Information is easier to find
and in a more convenient form. Character-by-character scans or conversions to
internal form—typically required by text messages—are not required by event
messages. In addition, EMS provides facilities that derive display text from message
tokens. Therefore, with EMS, event information can be presented both to operators
and to applications in the format most appropriate to each.
Another advantage of event messages is that they are subsystem specific, so the
information they contain can be tailored to provide an exact and complete specification
of the event circumstances.
Before EMS, the NonStop Kernel supported only text messages (numbered and
unnumbered console messages). These messages are still supported for the benefit of
subsystems and applications that have not yet migrated to EMS. These messages
have the subsystem ID of EMS and have event numbers in the range 1 through 512.
Information Contained in Event Messages
A subsystem generates an event message whenever it detects a significant
occurrence. The subsystem sends the event message to EMS, which stores the event
message indefinitely (depending on how long the log files are kept).
An event message includes many kinds of information besides what happened, such
as:

Information about the message itself
For example, the message contains a value identifying it as an event message (as
opposed to a command or response message), a count of how long the message
is, and a time stamp indicating when the message was generated.

Information about the subsystem reporting the message
All event messages include a subsystem identifier, process identifiers, and other
relevant information about the creator of the message.

Information specifying how the message should be handled
EMS includes some conventions that determine how each message is interpreted
after it is reported. These conventions, triggered by certain token values, include
whether the message is critical and whether operator action is required. (For
details, see Special Kinds of Event Messages
on page 2-3.)

Information about the actual event (occurrence)