HP OpenVMS Systems Documentation

You can set alarms on absolute values (such as the current integer value of the sampled variable) or on delta values (such as the difference between the current or last value). Alarms can be Greater Than exception alarms, Less Than exception alarms, Equal To alarms, and so on. (See the svrThrAlarmType object description.)

Hysteresis (the tendency of certain binary devices to show different threshold values when changing from 0 to 1 than when changing from 1 to 0) is introduced by providing thresholds both for setting and resetting of the alarm state, thereby limiting the number of traps that are sent on alarm triggering.

You can create alarms to persist across agent reboots; however, this is not recommended for dynamic table variables.

The triggering of an alarm changes a state variable in the conceptual row and can also trigger the sending of a trap, or the local logging of an event.

An alarm entry is created by the management console using the current value of svrAlarmNextThrIndex to name the instances of the row variables, setting the svrThrStatus to underCreation. When you create a threshold entry for the first time, issue a set request on svrThrStatus.

You can set the remaining row variables in the same operation or in subsequent operations. Those not set retain their default values as described. You must set variable values for the following objects in the Alarms group before you enable the alarm:

• svrThrStatus (set to underCreation)
• svrThrVariableName through svrThrSeverity (set appropriately; see the object descriptions)

When the row is created with the initial set, you must set svrThrStatus to underCreation. When the management console has completed the row setup, it sets this variable to rowEnabled. Variables in the row can only be written if svrThrStatus is in the initial underCreation state or has been set to rowDisabled.

To delete the row, set the status to rowInvalid. Be aware that errors in variable polling and threshold checking that cannot be corrected cause a row status change to rowError. Once the status is set to rowError by the agent, the agent does not reset the status. Instead, the management console must reset the status based on information returned with svrThrErrorValue or for other reasons.

Greater Than or Greater Than or Equal To thresholds for absolute values occur when the sample value equals or exceeds the svrThrThresholdValue and svrThrAlarmState was reset. This condition causes svrThrAlarmState to be set and, if svrAlarmEnableTraps is true, a svrThrExceptTrap is sent. SvrThrAlarmState is reset when the sample value falls below or equals svrThrResetValue.

Less Than or Less Than or Equal To thresholds for absolute values occur when the sample value falls below or equals the svrThrThresholdValue, and svrThrAlarmState was reset. This condition causes the svrThrAlarmState to be set and, if svrAlarmEnableTraps is true, a svrThrExceptTrap is sent. SvrThrAlarmState is reset when the sample value exceeds or equals svrThrResetValue.

Equal To thresholds for absolute values occur when the sample value equals svrThrThresholdValue and svrThrAlarmState was reset. This condition causes the svrThrAlarmState to be set and, if svrAlarmEnableTraps is true, a svrThrExceptTrap is sent. SvrThrAlarmState is reset when the sample value does not equal svrThrResetValue.

The same conditions apply for delta values as for absolute values except the difference between the sample value and the svrThrLastValue is used for comparison with both the svrThrThresholdValue and the svrThrResetValue. Note that it is possible to have negative delta values since the difference is computed as the current value minus the svrThrLastValue.

By default, the files used to store persistent data are SYS$SYSTEM:TCPIP$MGT_THRESHOLDS.DAT and SYS$SYSTEM:TCPIP$MGT_THRESHOLDS.BAK. To move the files off the system disk or rename them, the system manager can define the logical names TCPIP$MGT_PERSISTENCE_DAT and TCPIP$MGT_PERSISTENCE_BAK in the SYS$MANAGER:SYLOGICALS.COM file as appropriate. For example, to point to files in a different location, add the following definitions to SYS$MANAGER:SYLOGICALS.COM. (The examples are formatted to fit the table column.)

$ DEFINE/SYS -

_$ TCPIP$MGT_PERSISTENCE_DAT -

_$ DISK2:[SNMP.MIB]PERSIST.DAT;

$ DEFINE/SYS -

_$ TCPIP$MGT_PERSISTENCE_BAK -

_$ DISK2:[SNMP.MIB]PERSIST.BAK;

The value is reset if svrThrStatus changes to rowDisabled or rowInvalid. For guidelines on state changes, see the description for svrThrAlarmType.

On agent restarts, the value is retrieved and compared to the svrThrComparisonValue. If not equal, the OID instancing for svrThrVariableName might be incorrect. If this situation occurs, svrThrStatus is set to rowError and svrThrErrorValue to badValue.