On Thu, 14.04.11 16:15, "Jóhann B. Guðmundsson" (johannbg@xxxxxxxxx) wrote: > > On 04/14/2011 03:36 PM, Lennart Poettering wrote: > >> In man systemd.unit > >> > > >> > BindTo= > >> > Configures requirement dependencies, very similar in style > >> > to Requires=, however in addition to this behaviour it also > >> > declares that this unit is stopped when any of the units > >> > listed suddenly disappears. Units can suddenly, unexpectedly > >> > disappear if a service terminates on its own choice, a > >> > device is unplugged or a mount point unmounted without involvement of > >> > systemd. > >> > > >> > ExecStop=-/bin/systemctl stop upsd-device.service > >> > ExecStop=-/bin/systemctl stop upsd-monitor.service > > Why ExecStop= here? > > It was meant as an either or. > > The BindTo= reference in the man page does not mention that it will take > down with it any service bound to it when the service is stop. Requires= and BindTo= both do that. The difference between the two switches is mostly an ordering issue: Let's say you have a unit A and a unit B. B requires A, and should be started after A is up. So in B you say: Requires=A After=A now, if you shut down A with "systemctl stop A", this will also stop B, and it will do so in the inverse starting order. i.e. stop B first, stop A second. BindTo= would do exactly the same here. The difference now comes if for some reason A dies independently of anybody running "systemctl stop A": should we then shut down B retroactviely? The ordering would normally suggest that B goes down before A, but if A just goes away on its own, then should we still shut down B? If you use BindTo= that's what would happen. If you use Requires= it wouldn't. So where is this interesting? If A is a device and B is a service, then normally B should start after A is plugged in and be killed before A is unplugged. By using BindTo= you can also make it be killed if A is unplugged with B still running. Lennart -- Lennart Poettering - Red Hat, Inc. -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
