I have a service foo.service which depends on service bar.service. I need to make sure that bar.service is started before foo.service and that bar.service launched successfully.
From this source it says that Requires:
This directive lists any units upon which this unit essentially depends. If the current unit is activated, the units listed here must successfully activate as well, else this unit will fail. These units are started in parallel with the current unit by default.
and that After:
The units listed in this directive will be started before starting the current unit. This does not imply a dependency relationship and one must be established through the above directives if this is required.
Is it correct to have both the Requires and After sections in the same unit file? Requires says that the service will be launched in parallel, but After says it will be launched before. If bar.service fails to start during the After condition, will it attempt to launch it again during the Requires section? If so I need to find another way to launch foo.service
foo.service
[Unit]
After=bar.service
Requires=bar.service
It is perfectly fine to use both After= and Requires=. They have different purposes. Requires= sets up a start dependency. systemd makes sure that if any body is trying to start foo.service, it should start bar.service too. Should bar.service fails at some point, then foo.service is taken down too.
After= is putting a start order between services. If both of the services are scheduled to start, then After= makes sure the start order is set.
You can look at systemd's own service file as an example.
/lib/systemd/system/basic.target
[Unit]
...
Requires=sysinit.target
After=sysinit.target
...