Alarm lifecycle & modes

An alarm's current severity describes the condition now. Its unacknowledged severity records what the operator still needs to acknowledge. Keeping these separate preserves visibility of short-lived alarms.

A typical local alarm

1. The PV connects and reports NO_ALARM.
2. Its severity rises to MAJOR. QtALH updates the row, parent summaries, and eligible alarm actions.
3. The condition clears. Current severity returns to NO_ALARM.
4. With the default transient mask, the outstanding MAJOR acknowledgement remains.
5. The operator acknowledges it. The outstanding indication clears.

An acknowledgement can also occur while the alarm is still active. It does not change the alarmed PV or correct the equipment condition. In global active mode it does write: QtALH writes the IOC ACKS field (Channel Access channels) and, when the channel sets $ACKPV, the configured value to that acknowledgement PV, which can drive IOC logic. The automatic acknowledgement of a latched transient when a channel is re-enabled or its NoAck mask is removed makes the same writes. Runtime Overrides Retry ACKPV can also write a previously refused $ACKPV value later, independent of the channel's current alarm. Local and passive modes write neither. NoAck and NoAckT masks change acknowledgement requirements and transient retention.

Choose who owns acknowledgement

Mode	Acknowledgement	Configured output PVs
Local (default)	Maintained in this QtALH runtime.	Heartbeat, severity, and acknowledgement PVs are not written.
Global (-global)	Uses IOC ACKS/ACKT fields for Channel Access channels. pva:// channels keep acknowledgement in this runtime.	Active mode can write configured outputs when permitted.
Passive (-S, with either local or global)	Operator acknowledgement is disabled; no CA or pvAccess writes.	Writes are suppressed.

In global active mode, -caputackt writes each record's configured ACKT setting once, when a configured channel first becomes writable after startup or reload, including when its IOC connects or grants write access later. PVA alarms have no ACKS/ACKT fields, so pva:// channels apply the same acknowledgement rules locally. Access-right failures remain visible; severity-output and automatic Force PV ACKT retries have specific behavior described in Compatibility.

Separate the controls

• Silence (-s) controls sound.
• Disable file logging (-D) controls alarm and operation file writes; configured helper queues retain their behavior.
• Passive (-S) controls CA/pvAccess writes and operator acknowledgement.
• Display filters control which rows appear.

These controls do not disable configured shell commands. Commands can run for configured severity/status transitions, and related-process actions run on request. MASTER_ONLY and stop-logging broadcasts impose additional command restrictions.

What a group represents

Groups aggregate eligible descendant channel severity, acknowledgement, and mask counts. Cancel and Disable exclude channels from active summaries; NoAck removes their acknowledgement requirements. A parent's alarm can remain elevated because a different descendant still has an alarm or outstanding acknowledgement.

Before the first usable event, an unconnected channel uses ERROR as a placeholder. Connection and access changes can also produce ERROR. Value-only updates refresh the displayed value without creating another alarm record.