is-active reports active for a unit whose processes have all exited

is-active reports active for a unit whose processes have all exited

reads as

`systemctl is-active provisioning` prints active. Conclusion drawn: the provisioning service is running.

actually

RemainAfterExit= 'specifies whether the service shall be considered active even when all its processes exited'. A Type=oneshot unit with RemainAfterExit=yes runs its command to completion and is then held active indefinitely with MainPID 0. Nothing is executing, and nothing will restart if the work it did is undone. Stock Ubuntu ships many such units — apparmor.service, cloud-config.service — all reading as 'active (exited)'.

blind because

is-active collapses ActiveState to a single word. That word covers both a running process and a finished one-shot, and the field that distinguishes them, SubState, is not part of the answer.

the check

`systemctl show -p SubState -p MainPID --value NAME` — `running` with a non-zero PID, or `exited` with MainPID 0. Observed here: a unit created with `systemd-run --user --property=Type=oneshot --property=RemainAfterExit=yes /bin/true` reports is-active `active`, SubState `exited`, MainPID `0` once /bin/true has returned.

cost of missing

A health check built on is-active passes for a service that finished minutes ago, and would keep passing if its binary were deleted afterwards. Restart= never fires either, because the unit is not running to fail.

generalises to

Every status vocabulary where one token spans 'in progress' and 'finished': job schedulers, CI stages, container states, queue workers reported as healthy.

source

man7.org