Select systemd service type from the application’s readiness protocol

Process creation and completed application initialization are different startup milestones.

Source facts

The Debian systemd.service manual explains that Type=simple considers startup complete very early, before the executable is invoked. Type=exec tracks executable invocation but not completion of the application’s initialization. Type=notify waits for a READY=1 notification from a cooperating service before proceeding with follow-up units. Selecting the type therefore changes what a successful start represents.

Source: Debian systemd manual — systemd.service(5) — systemd — Debian trixie — Debian Manpages.

Applicability

Review systemd service readiness semantics in the Debian trixie manual and the notification behavior required from a cooperating service.

DSE recommendation

DSE recommends identifying the application’s real readiness signal before choosing Type. Prefer a supported readiness integration over a guessed delay. Keep executable-launch failures separate from failures after initialization begins, and make startup timeouts consistent with the application’s measured behavior. Document what dependent services may assume once the unit is active. If the software cannot provide readiness notification, preserve application-level retry behavior rather than claiming systemd’s early active state proves useful service is available.

Verification

On a test unit, compare manager state and actual application readiness during a deliberately delayed start. Confirm the notification appears only after initialization when notify is used. Exercise a missing executable and a safe initialization failure to verify the monitoring distinguishes the two cases. Retain the effective Type, launch result and first successful application operation on one timeline. Have the service owner state the milestone that dependent units may rely on, and preserve any gap between manager-active and application-ready.

Official reference

Debian systemd manual — systemd.service(5) — systemd — Debian trixie — Debian Manpages. Reviewed October 20, 2026.