Error adding effect, could I know which

Hello. I just made an LV2 plugin working well on my computer (even with mod-app). I’ve built it with the mod-plugin-builder, I arrived to deploy it correctly in the mod duo via modsdk.

When I try to add the effect to the current pedalboard, a notification says “Error adding effect”, and… I can’t know why…

Is there a method to be able to know what happens ?

I arrived to see what happened using mod-host -i via ssh.
My plugin is now deployed, and I am happy.
So, that’s closed.


I am having this issue as well “Error Adding Effect” (And found another similar post with no soutions: Developing a plugin - Error Adding Effect? )

Does anyone have docs on using mod-host to debug this @falkTX ? I will keep looking through the code of the mod-host but I wonder if you have any pointers?

Just running “mod-host -i” enters an interactive mode I can enter commands which I don’t understand yet. I need some more time to look into this, but I didn’t see anything about debugging/logs etc.

Ideally I could get some debug logs from normal running but it looks like from what I see I need to manually find out how to load my lv2 plugin using the mod-host interactive commands.

If I find something else out when I get more time to look into this I will report back.


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So I have found the bug in my plugin. The ttl files had one URL for the plugin and the .so file reported something else in its descriptor. It would be great to have a wiki or something for debugging tips. I am wondering if I may be better off working in a DAW on my host to do dev instead of working directly on mod first. It may be easier debugging.

I did try the following on the mod host that made me consider reviewing the code in these and find the bug (in case it helps anyone):

mod-host -iv
mod-host> add 2
lilv_plugin_instantiate(): error: No plugin in <file:///root/.lv2/bauto-level.lv2/>
can’t get lilv instance
resp -102

I looked and the .so file existed at the given path, so I checked the ttl file and it was fine. So I reviewed the C code and found the URL was wrong in the descriptor. I hope my experience reported here might help someone else if they encounter a similar issue.


If you are running any recent dwarf or duox build, you can use journalctl -u jack2 to get logs from the host process.


I got the same error when publishing a freshly built plugin. After some sleuthing on the forums, I discovered that there was no modgui.ttl file in the output directory of the plugin after the build. I copied that file into the new plugin’s directory and republished and was able to add it to a board in the MOD GUI.