3.4 Triggers

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A trigger says when a service starts by itself. Triggers are independent of service type: a Simple service can have a timer, and a Oneshot can start at boot.

Triggers is a multi_string, each entry either type or type:argument.

A service with no triggers is demand-only: it starts only when something asks for it, whether an administrator, a dependency, or an OnFailure handler.

Multiple triggers of the same type are allowed. A service with ["timer:*-*-* 02:00:00", "timer:*-*-* 14:00:00"] runs at 2am and 2pm, and each trigger is independent — its own timerfd, its own next-firing computation, its own history.

3.4.1 Arity is enforced #

boot takes no argument. boot:<something> accepts only the sub-triggers in the table above, and any other value is malformed rather than an unknown trigger type to be ignored. timer with no schedule is malformed, as is timer: with an empty one.

That strictness is the point. Unknown values on a service key are ignored for forward compatibility, and if unknown trigger types were ignored too, boot:setled would be silently accepted and the service would simply never start. Instead it fails to decode, loudly.

3.4.2 Disabled #

Disabled=1 suppresses automatic activation and nothing else. No trigger fires: not boot, not boot:settled, not a timer, and not any trigger type added later. A disabled service's timers are neither armed nor serviced.

The definition is still loaded into the in-memory model, and an explicit start still works. To stop a service being started at all, deny SERVICE_START in its ServiceSecurity descriptor — that is an access control question, not a trigger question, and answering it with the Disabled flag would mean a flag that anyone who can write the key can clear.

Enabling and disabling are registry writes performed by administrative tools, not peinit commands. peinit picks the change up through a registry change notification, or on the next reload-config.

3.4.3 Extensibility #

The type:argument shape is designed to grow. Path, device and event triggers slot into the same array with no schema change, because a trigger is a string in a list rather than a field of its own.

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