incomplete systemd setup instructions in dist-install.sh

[gschintgen]

Hi, I installed btrfsmaintenance as outlined in README.md and followed the instructions given by dist-install.sh, specifically this one:

• copy *.timer files to the systemd.unit path (eg. /usr/lib/systemd/system/ or /etc/systemd/system)

However it's also necessary to copy the .service files to the same location, else systemd gives somewhat cryptic error output and the maintenance scripts won't be executed. So I'd like to suggest a slight change to the displayed instructions: "- copy .timer and *.service files [...]".

[mfeif]

Related. I also copied the *.service files, and when I tried to enable them, I got another somewhat cryptic message:

# systemctl enable btrfs-scrub.timer
Created symlink /etc/systemd/system/timers.target.wants/btrfs-scrub.timer → /etc/systemd/system/btrfs-scrub.timer.
# systemctl enable btrfs-scrub.service
The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
settings in the [Install] section, and DefaultInstance for template units).
This means they are not meant to be enabled using systemctl.
Possible reasons for having this kind of units are:
1) A unit may be statically enabled by being symlinked from another unit's
   .wants/ or .requires/ directory.
2) A unit's purpose may be to act as a helper for some other unit which has
   a requirement dependency on it.
3) A unit may be started when needed via activation (socket, path, timer,
   D-Bus, udev, scripted systemctl call, ...).
4) In case of template units, the unit is meant to be enabled with some
   instance name specified.

It's a good bet that I don't know what I'm doing; I'm still new to systemd vs older methods.

[gschintgen]

Related. I also copied the *.service files, and when I tried to enable them, I got another somewhat cryptic message:

# systemctl enable btrfs-scrub.service
...
3) A unit may be started when needed via activation (socket, path, timer,
   D-Bus, udev, scripted systemctl call, ...).
```> # systemctl enable btrfs-scrub.timer
Created symlink /etc/systemd/system/timers.target.wants/btrfs-scrub.timer → /etc/systemd/system/btrfs-scrub.timer.

This was new for me, too: those .service files are not intended to be enabled, they're activated/executed whenever the .timer unit fires. That's why I only proposed to add the step about copying the .service files, so that they're accessible, not trying to enable them.

It actually makes sense: some service units are statically enabled and configured with all their dependencies, while others are dynamically called upon via other means, timers in this case.

Anyway, the documentation should be amended. (Otherwise I'm quite happy with btrfsmaintenance! Thanks!)

[kdave]

Thanks for the suggestion, dist-install and README have been updated.