systemd unit "Before=" with timer
In my system I have b.service activated by b.timer. I want another service (a.service) that start before b.service. I cant change b.service or b.timer because are not mine. I’ve putte Before=b.service in a.service but the timer start b.service without starting a.service.
You can mark a.service as RequiredBy b.service.
Make a.service look like:
[Unit]
Before=b.service
[Service]
Type=exec
ExecStart=...
[Install]
RequiredBy=b.service
And then:
systemctl enable a.service
Now whenever b.service starts — either via a timer or via systemctl start — your new a.service will start first.
The Before directive is only used during startup. It’s only used for to determine the orders of the services.
In order to achieve what you need, add the following section to to your a.service:
[Install]
WantedBy=b.service
Then run:
systemctl enable a.service
This will ensure that when b.service is supposed to get started, a.service will be started before.