If a cgroup fails to be destroyed (most likely because there are still
processes running as part of a service after the main pid exits), don't
free and remove the cgroup unit from the manager. This fixes a
regression introduced by the cgroup rework in v205 where systemd would
forget about processes still running after the unit becomes inactive.
(This can happen when the main pid exits and KillMode=process or none).
Before, "systemctl reenable getty@tty1.service" would fail with:
Failed to issue method call: File exists
To fix this, reimplement "reenable" explicitly as a disable followed by
an enable.
This is shorter and is how the man page documents its behavior.
Otherwise, when a network device is renamed, systemd-sysctl is run twice
with the same network device name: once for ACTION="add" and once for
ACTION="move".
When a sigchld is received from an alien child, main_pid is set to
0 then service_enter_running calls main_pid_good to check if the
child is running. This incorrectly returned true because
kill(main_pid, 0) would return >= 0.
This fixes an error where a service would die and the cgroup would
become empty but the service would still report as active (running).
Ross Lagerwall