Proper location for plugins

I can’t believe this topic does not already exist, but I can’t find it. Anyway, the plugin page in the manual suggests that plugs ought to live in dedicated folders inside usr. Makes sense, except I notice that my lv2 folder with lv2 plugins is inside the Ardour installation. In other words, it is [root]/opt/Ardour-6.9.0/lib/LV2
I am certainly able to create new directories inside usr, but could someone just confirm for me this is correct? If I install a new LV2 type .so plugin, should that be put into usr/lib/lv2 or [root]/opt/Ardour-6.9.0/lib/LV2 ? Does Ardour care? Do you? Should I?

For LV2 plugins see the LV2 Filesystem Hierarchy Standard.

Except after scanning the standard paths ($HOME/.lv2/ /usr/lib/lv2/, or whatever is given as LV2_PATH), Ardour asks liblilv to also index bundled LV2 plugins from /opt/Ardour-6.9.0/lib/LV2/.

Usually $HOME/.lv2/ or /usr/local/lib/lv2/

If you save it in /opt/Ardour-6.9/... it will be lost once you update ardour to 7.0.
Likewise /usr/lib/ is usually reserved for distribution packaged content. It may get overwritten or cause conflicts once you update the system.

Thank you so much, Robin. I hadn’t thought about migration. I certainly don’t want to reinstall my plugins again.

I keep all my plugins on a separate partition.
I know more paths to scan, but peace of mind is worth something.
All my home folders are linked there with the exception of the .config folders.
And those are backed up on another drive.
But what Robin posted are the “proper paths” that Ardour scans automatically.
I do this with reaper also. Just a thought.

I usually compile most of the plugins from source and install to /opt/NameOfPlugin-Version, say /opt/dragonfly-3.2.0, and then I run stow -d /opt -t /usr/local dragonfly-3.2.0 to create symlinks in /usr/local/

That way I can easily replace it with 3.2.1, when that’s released, by installing to /opt/dragonfly-3.2.1, adding a -D flag to the stow command to delete the links, and then running stow again with dragonfly-3.2.1 as the last argument.

That makes it easy to switch between the old and new versions, if there’s any regression, and it’s easy to uninstall the old version when I’m satisfied that the new version works fine ; rm -rf /opt/dragonfly-3.2.0