How can I launch a systemd service at startup before another systemd service starts?

 

There are 3 main properties for managing dependencies. I'll try to briefly explain the difference but you can find more details at [Unit] Section Options | freedesktop.org

1. After=

   This option only sets the order of the units, it doesn't guarantee that the service has finished starting up.

2. Wants=

   This option allows your unit to start only after another unit has finished starting up. (Doesn't matter if it started successfully or not)

3. Requires=

   Just like Wants=, however, this will make your unit start only after the dependencies have successfully started.

You can also use the inverse of each of those options.

1. After= is inversed by Before=
2. Wants= is inversed by WantedBy=
3. Requires= is inversed by RequiredBy=

To fix your problem, you need to change your mount service to:

[Unit]
Description=MountSmokeScreen
After=network.target
Before=sonarr.service radarr.service

[Service]
Type=oneshot
ExecStart=/home/samsepioldoloresh4ze/bin/check.mount
TimeoutStopSec=20
KillMode=process
Restart=on-failure

[Install]
WantedBy=multi-user.target sonarr.service radarr.service

Or you can add Wants=mountgdrive.service to the sonarr.service and radarr.service units.

You can do that without modifying the default files by running the following (You need to do the same for radarr.service):

systemctl edit sonarr.service

And insert the following:

[Unit]
Wants=mountgdrive.service

Note: You can replace Wants= with Requires or WantedBy= with RequiredBy= if you don't want the two services to start at all if mountgdrive.service fails (Though Wants= is usually enough and even recommended in the docs).

EDIT: The WantedBy and RequiredBy options can only be used under the [Install] section. (Thanks @Yankee)

 

[Source:  https://askubuntu.com/questions/1024916/how-can-i-launch-a-systemd-service-at-startup-before-another-systemd-service-sta ]