Match systemd socket Accept mode to the service design

One shared listener and one service instance per connection require different unit arrangements.

Source facts

The Debian systemd.socket manual describes Accept=no using a corresponding service unit and Accept=yes instantiating a service template for incoming connections. The daemon must support receiving sockets through the documented activation interface. The socket does not automatically add a requirement preventing its service from being started independently.

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

Applicability

Review systemd socket activation and the cooperating service design in the Debian trixie systemd.socket manual.

DSE recommendation

DSE recommends confirming the program’s supported activation model before writing socket units. Decide whether a connection needs its own process or a shared long-running daemon, then review the matching unit names and instance lifecycle. Document listener ownership so the application does not compete with systemd to bind the same address. Review direct service startup as a separate path and add an explicit dependency only when the design requires it. Keep connection limits and cleanup responsibilities with the operational owner rather than assuming activation alone handles capacity safely.

Verification

In an isolated service pair, inspect which unit owns the listener and observe the number of service instances created by test connections. Confirm the application receives the expected socket and shuts down cleanly. Test direct service startup only if the supported design permits it, then review the resulting state. Retain the socket unit, service or template unit and observed instance names with the test. Ask the service owner to explain listener ownership during both activation and any allowed direct-start path before accepting the design.

Official reference

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