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

I'm running Ubuntu 16.04 on an old HP Laptop

I've installed some software on it to create a small homemade plex server. I've installed sonarr, radarr, deluge, jackett, etc etc and they all automatically launch at startup!

A couple of days ago I decided to install rclone too and I've created (thanks to a GitHub project) a couple of folders that have to be mounted at each startup by launching a script (I launch it via terminal writing sudo ~/bin/check.mount). Sonarr and Radarr are set up to download stuff via deluge to a temp folder and then export it to one of these two mounted folders.

The problem is, by the time I manually launch the script Sonarr/Radarr are already up and running and can't find their root folders, so they give me an error.

What I'd like to do is create a mountgdrive.service (service, or whatever is necessary) to automatically launch the check.mount script and, if that's not enough, insert a delay in sonarr.service and radarr.service! Is that possible?

I wrote this with sudo nano /etc/systemd/system/mountgdrive.service

[Unit]
Description=MountSmokeScreen
After=network.target

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

[Install]
WantedBy=multi-user.target

and added to sonarr.service and radarr.service mountgdrive.service in the After= bit, like this

[Unit]
Description=Sonarr
After=syslog.target network.target mountgdrive.service

[Service]
User=samsepioldoresh4ze
etcetc
....

But it's not working! Sonarr and Radarr start normally, but the drives are not mounted! What am I doing wrong?

Also, rtcwake doesn't work on my laptop - I think it's a kernel issue?! Is there a way to fix that?

The reason you are having this problem is because you are using After= while you also need Requires= or Wants=.

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)