EvmEvent - The structure of an EVM Event
An EVM event is a self-contained data structure, which can be manipulated
and accessed using EVM API functions. Application code can:
+ Create, duplicate and destroy an event
+ Set and retrieve the values of standard data items contained within
+ Add variable data items to the event, and set and retrieve their
+ Post the event to the EVM daemon for distribution to subscribers
+ Read events from an open file descriptor
+ Write events to an open file descriptor
Command line utilities are provided that allow users access to these capa-
The Contents of an Event
The event structure includes two types of data items:
1. Standard data items, with predefined names
2. Variable data items, with names and types defined at the time they are
added to the event
When you create an event you can include as many data items as you like.
When you post the event, the API functions automatically add the standard
items which pertain to the current environment, such as the host name and
Standard Data Items
Standard data items are those which are commonly required in an event, and
which are understood and may be acted upon by EVM. The following table is
a list of the standard data items that may be contained in an event. The
identifier is the keyword used to post, display, or format the item.
Data item/Id Description
Names the event. Must match a name
in the daemon's template database if
the event is to be posted.
UNIX system time when the first
occurrence of this event was gen-
Number of instances of the same
event that have been combined into a
single stored event. The Time
Posted and Last Timestamp items
indicate when the first and last
instances of the event were posted.
If Repeat Count is present and non-
zero, the system time when the
latest occurrence of this event was
Identifies the event. See the
description following this table.
HOST_NAME Name of the posting node.
Host IP Address
HOST_IP IP address of the posting node.
In a cluster environment, a value of
EvmTRUE indicates that the event was
posted on behalf of the cluster, not
the individual node, and will be
distributed to every node in the
In a cluster environment, the name
of the posting cluster.
Cluster IP Address
In a cluster environment, the IP
address of the posting cluster.
Cluster Member ID
In a cluster environment, the node's
If present and EvmTRUE for an event
generated in the kernel, the event
will not be propagated from the ker-
nel to user space.
PID of the process which posted the
Parent Process ID
PID of the parent of the process
which posted the event.
Name of the owner of the posting
Indicates the importance of the
event. Does not affect the order of
event distribution. See the
description following this table.
Name of I18N catalog file for inter-
I18N message set id
Identifies the message set within
the I18N message catalog.
I18N message id
I18N_MSG_ID I18N message id for the event.
Event format text. See the
EvmEventFormat(3) and evmtemplate(4)
reference pages for a description of
the format string.
REF Reference to event explanation text.
The event name is the primary means of identifying an event. It must be
present for an event to be posted. Although it can be any syntactically-
valid string, the name should generally identify the posting facility and
indicate what happened.
The event name is an ASCII character string, made up of a dot-separated
series of components, with the left-most component representing the top of
a notational hierarchy. Component substrings may include any combination of
letters, digits and underbar characters. There is no restriction on the
number of components that can be included in an event name. An event tem-
plate must contain at least two components. An event must contain at least
three components to be accepted for posting.
The naming scheme provides an open-ended way to identify events, letting
you provide detail to any level. Careful naming gives the system adminis-
trator an intuitive and precise way to select events for viewing and moni-
toring and facilitates the identification of the system components which
issue events and the recognition of patterns that warn of problems. The
more detail included in the event name, the more precise the specification
criteria can be.
The event identifier data item is a numeric quantity, assigned to an event
by the EVM daemon as the event is posted. In combination with the host and
timestamp data items, the value can be used to produce a unique identity
for an event.
The daemon assigns identifiers according to the following rules:
+ Each posted event receives an unsigned integer event identification
number, with a value greater by one than that of the previous event
posted through the same EVM daemon.
+ The event identifier of the first event posted after the daemon is
started or restarted is zero.
+ The event identifier wraps back to zero after it has reached its max-
+ If a daemon receives an event that already contains an identifier, it
does not generate a new identifier for the event. This may happen if
the event is a cluster event posted in another node.
+ New event identifiers are assigned only to events which the daemon
validates and accepts for distribution.
+ If an event is accepted and does not already contain an identifier, a
new identifier is assigned to it even if there are no subscribers for
EVM uses an event's priority value solely for filtering, sorting and
presentation purposes - it does not use it to prioritize the distribution
sequence. The priority is an integer value in the range 0-700, with zero
being the least significant priority. This table indicates the event
priority, the default action taken by evmlogger for that priority, and a
description of the priority.
EVM Priority/Name Notification Description
Emergency Log, mail to root
A dangerous situation
has been detected and
immediate action either
is required or has been
600 - 699
Alert Log, mail to root
A dangerous situation
is imminent and immedi-
ate action either is
required or has been
500 - 599
Critical Log, mail to root
A failure has been
detected that renders
some part of the system
400 - 499
A non-critical failure
has been detected in or
by some component of
the system or applica-
300 - 399
Some aspect of the sys-
tem or application
200 - 299
Notification of an
event that the com-
ponent is designed to
100 - 199
A normal operational
event - for example, an
application has started
or terminated normally.
Events in this range
typically will not be
saved in the system EVM
1 - 99
Program debug informa-
tion. Events in this
range may be monitored
for informational pur-
poses, but typically
will not be saved in
the system EVM log
Priority 0 should be
used for events that
intended to be sub-
scribed to by programs,
and are not expected to
be interesting to
Catalog Name and Message Set Id
If you plan to internationalize your events, you will need to supply an
I18N catalog file containing the format strings for all of the events, and
include the name of the file in the event. You also can break the file into
multiple message sets, and give the message set id in the event - but note
that all messages pertaining to a particular event must belong to the same
set. If all events described in a single template file use messages from
the same catalog or message set or both, you will probably want to supply
these items as global values, so that you need only to specify them once.
You should set the cluster event data item only if your application is
cluster-aware, and is posting the event on behalf of the cluster, rather
than an individual node. Cluster events are distributed to all nodes in
Formatting an Event for Display
Although an event is an opaque binary structure, it can be formatted into a
human-readable string by using the evmshow(1) command or by calling the
EvmEventFormat(3) function. Formatting is essential for human-oriented
output, but may not be necessary for an application program that will sim-
ply extract any variable data the event contains, and take the necessary
The starting point for formatting an event is the format data item. A for-
mat is a text string that may contain a simple piece of text, the names of
standard data items, or the names of variables whose values are to be sub-
stituted into the text, or any combination of these.
You include variable names for substitution by preceding them with a $
character - for example $temp. You include standard data items by preced-
ing their names with @ - for example, @timestamp.
The EvmEventFormat(3) routine automatically converts data items or vari-
ables into displayable form, regardless of their types.
You can escape the special meaning of a $ or @ characters in the format
text by preceding it with a backslash (\). To include a literal backslash
in the text, use a double backslash.
If an event does not include a format data item, formatting it will result
in a default text string that includes the event name and any variables the
event may contain.
If the event includes a repeat count, then the repeat count is prepended to
the output in the form [repeat_counttimes].
Variable Data Items
You can use variable data items in your events to provide data that may be
different each time the event is posted.
You can give the variable any name you like - the name is a string that is
carried with the event, and can be used by a subscriber to extract the data
in its original form. A variable name can be made up of any combination of
upper or lower case alphanumeric characters and the underscore character.
By convention, names beginning with an underscore are reserved for system
EVM's variable data items have these properties:
+ A name
+ A type
+ A value
+ A size (implicit for most types)
+ An I18N message id (for string variables only)
The following table shows the variable types that EVM supports:
Type Identification Remarks
EvmTYPE_BOOLEAN 8-bit integer
EvmTYPE_CHAR 8-bit character
EvmTYPE_INT16 16-bit signed integer
EvmTYPE_INT32 32-bit signed integer
EvmTYPE_INT64 64-bit signed integer
EvmTYPE_UINT8 8-bit unsigned integer
EvmTYPE_UINT16 16-bit unsigned integer
EvmTYPE_UINT32 32-bit unsigned integer
EvmTYPE_UINT64 64-bit unsigned integer
EvmTYPE_FLOAT 32-bit floating point value
EvmTYPE_DOUBLE 64-bit floating point value
EvmTYPE_STRING Null-terminated character string
Binary data - cannot be interpreted
directly. The size must be specified
Data types EvmTYPE_FLOAT and EvmTYPE_DOUBLE cannot be used for events
posted within the kernel.
Event Management: EVM(5)