I set up a new umbrel with knots, syncing nicely. But on another umbrel that already had core, it doesn't look like its a drop in replacement, as a test I tried to run knots in parallel, but it started syncing from 0, so I guess umbrel assignes a different datadir. I have to test this a bit more, but it looks like if I uninstall the Bitcoin (core) app it will also delete the blockchain and knots will then just start syncing from scratch...
Discussion
I am getting old and forgetful. i forgot that Knots required a new install. I ran them both at the same time so I thought that you could just upgrade. Thanks for letting me know. That's valuable info.
Actually there is a way: https://docs.mempool.guide/page/migrationumbrel.html
You just have to stop both, copy the data, and then run knots. Since its basically the same software, the structure in the datadir is compatible..
Now this is the way that it should be done!
Before Umbrel 1.0 it used to be a little more complicated if you weren’t used to command line (and I wasn’t)
Bitcoin apps just keeps getting better and better.