Wait to start Transmission daemon until after USB drive has mounted?

Question

I'm running transmission-daemon as a systemd service on OSMC. When opening its remote control web interface after a reboot all transfers are almost always halted with the message "Error: No data found! Ensure your drives are connected [...]".

I'm assuming this is because Transmission starts before the download path exists -- in this case on an USB drive that gets automatically mounted by the system to /media/Elements/[...] without any manual configuration made from me. I have not edited fstab.

After trying this answer without success, I'm wondering if there's some other way to solve this? What I did according to that answer was to add the following in an override.conf:

cat /etc/systemd/system/transmission.service.d/override.conf

[Unit]
After=media-Elements.mount
After=media-Vault\x2013.mount
After=media-Black\x20Mesa.mount

The service file:

$ cat /lib/systemd/system/transmission.service

[Unit]
Description=Transmission BitTorrent Daemon
After=udisks-glue.service

[Service]
User=osmc
Group=osmc
Type=notify
ExecStartPre=/bin/sleep 10
ExecStart=/usr/bin/transmission-daemon -f --log-error --allowed *.*.*.*

[Install]
WantedBy=multi-user.target

Systemd status:

$ systemctl status transmission

● transmission.service - Transmission BitTorrent Daemon
   Loaded: loaded (/lib/systemd/system/transmission.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/transmission.service.d
           └─override.conf
[...]

Worth mentioning is that I get Warning: transmission.service changed on disk. Run 'systemctl daemon-reload' to reload units. when checking the status of transmission after every reboot. daemon-reload silences it until the next reboot.

This question is related, but has to do with fstab mounts. I would prefer to solve it without fstab if possible, since I don't want to treat the USB drive as permanently attached.

---

After trying the initial answer:

$ systemctl cat --no-pager transmission.service
# Warning: transmission.service changed on disk, the version systemd has loaded is outdated.
# This output shows the current version of the unit's original fragment and drop-in files.
# If fragments or drop-ins were added or removed, they are not properly reflected in this output.
# Run 'systemctl daemon-reload' to reload units.
# /lib/systemd/system/transmission.service
[Unit]
Description=Transmission BitTorrent Daemon
After=udisks-glue.service

[Service]
User=osmc
Group=osmc
Type=notify
ExecStartPre=/bin/sleep 10
ExecStart=/usr/bin/transmission-daemon -f --log-error --allowed *.*.*.*

[Install]
WantedBy=multi-user.target

# /etc/systemd/system/transmission.service.d/override.conf

[Unit]
RequiresMountsFor=/media/Elements

[Install]
WantedBy=media-Elements.mount

Answer 1

EDIT: It turns out my first approach didn't work as expected. An [Install] section on an overrides file doesn't really work and RequiresMountsFor= seems to only work for mounts which are declared in fstab. Therefore, I'm proposing an alternative that will accomplish the same effects, but using different directives.

In order to prevent the unit from starting unless the /media/Elements volume is mounted, use the ConditionPathIsMountPoint= directive which will check that and prevent the unit from starting unless that directory is mounted.

# /etc/systemd/system/transmission.service.d/override.conf

[Unit]
ConditionPathIsMountPoint=/media/Elements

(NOTE: You can use the systemctl edit transmission.service command to open an editor on this overrides file.)

In order to trigger the start of transmission.service whenever the USB gets mounted, you need to add a symlink to it to a .wants/ directory for the mount unit. (Ideally, this would be taken care by an [Install] section, but it doesn't seem to work from an overrides file.)

Create it manually with these two commands:

$ sudo mkdir -p /etc/systemd/system/media-Elements.mount.wants/
$ sudo ln -sf /lib/systemd/system/transmission.service /etc/systemd/system/media-Elements.mount.wants/

After that's in place, mount /media/Elements and see Transmission get started...

---

Original answer below...

So, the After= directive only afects ordering, if both units are queued to be started, then this one will be started after the other one completes, but it doesn't trigger the start of the other one. You need Requires= for that.

But for mounts, there's a nice shortcut in RequiresMountsFor=, which can take the mounts as paths.

You also probably want to set this up so that this unit is started when the USB drive is mounted. You can trigger that by using WantedBy= (in the [Install] section) and referring to the .mount unit from here. After setting that up and using systemctl enable to create the "Wanted" relationship, the start of this unit will be (also) triggered when the USB drive is mounted (if that is done later and not during boot up.)

Putting it all together:

# /etc/systemd/system/transmission.service.d/override.conf

[Unit]
RequiresMountsFor=/media/Elements "/media/Vault 13" "/media/Black Mesa"

[Install]
WantedBy=media-Elements.mount
WantedBy=media-Vault\x2013.mount
WantedBy=media-Black\x20Mesa.mount

And then enable this unit, which will create symlinks under the *.mount.wants/ directories (the exact symlink names will be printed in systemctl enable output):

# systemctl enable transmission.service

This should take care of it.

It's unclear to me why you're listing the three mounts, since in the text of the question you suggest only /media/Elements is used to store Transmission downloads... If that's indeed the case, you could probably remove the other two and keep only the references to the "Elements" one.

(NOTE: I haven't tested this all before posting, but I'm fairly confident this will work. If for some reason it doesn't, leave me a comment with more details, I'm happy to work with you to figure this out.)