Upstart Overview

Upstart is a legacy event-based init and service-management system developed by Canonical. Older Ubuntu and several other distributions used it, but current Ubuntu releases use systemd. Study Upstart when maintaining a confirmed legacy host, not as the default assumption for a modern installation.

Confirming a Legacy Upstart Host

Inspect PID 1 and the active control interface:

$ ps -p 1 -o pid,comm,args=
$ readlink /proc/1/exe
$ initctl version

The last command succeeds meaningfully only where the Upstart control service and client are present. A directory such as /usr/share/upstart or leftover files under /etc/init is weak evidence because packages and migration remnants can remain after another init system takes over.

CheckWhat is the strongest evidence that a host actually uses Upstart?

Jobs and Events

An Upstart job describes a service or task, including its process commands and lifecycle conditions. An event is a named notification with optional environment variables. Job configuration can express when its goal should become start or stop.

System job files commonly live under /etc/init/ with a .conf suffix. For example:

description "Example worker"
start on runlevel [2345]
stop on runlevel [016]
exec /usr/local/sbin/example-worker

This uses runlevel events as compatibility inputs. Upstart can also react to filesystem, device, network, or application-defined events depending on what the system emits.

CheckWhat does an Upstart start on stanza define?

Event-Driven Startup

During startup, Upstart loads job definitions and receives events. Matching start on or stop on expressions update job goals; job transitions can emit additional events that unlock other work. Independent jobs can progress concurrently.

This model avoids one hard-coded global script sequence, but it can be difficult to diagnose when event names, ordering, and conditions are implicit. Events are not a durable message queue by default, so a job added or condition changed later should not assume every past event will be replayed.

CheckHow can one Upstart job lead to another job starting?

Migration and Compatibility

Systemd can provide limited compatibility for some legacy service scripts, but it does not execute Upstart job syntax as native systemd units. When migrating, translate lifecycle conditions, environment, respawn policy, logging, dependencies, and readiness semantics rather than mechanically renaming files.

CheckWhich init system is used by current standard Ubuntu releases?

Summary

You can now read Upstart as a legacy event-and-job model.

Confirm the live PID 1 and control interface.
Distinguish job definitions from event notifications.
Interpret start on and stop on as lifecycle expressions.
Migrate semantics explicitly rather than renaming configuration files.

Practice

In the practice terminal, run: ps -p 1 -o pid,comm,args= Then run: ls /etc/init/ Upstart job files live there as .conf files; on a modern system the directory is usually missing.

Inspect PID 1, then look inside /etc/init.