Just to add a later note: I'm going to try Sigil because the Calibre Editor is increasingly slow/messy on Linux and full of useless tidbits. And window positioning no longer works.
Running Sigil 2.0.1 on Pop!_OS 22.04
Found Sigil in the Pop!_Shop. What it loads is a flatpak, though they don't tell you that going in...but it is the latest version and seems to work fine.
So I downloaded the epubcheck plugin and got the python thing working without much problem (do the "auto" and restart Sigil).
Then it couldn't find the epubcheck.jar file. Had to download the epubcheck zip file as a stand-alone and copy the files into the preferences location. That worked.
But then it couldn't find the java executable, so I tried the command:
Code:
flatpak install flathub org.freedesktop.Sdk.Extension.openjdk17//22.08
as above - thank you philja! Good old flatpak downloaded some 800 megabytes to put java into itself! Holy cow.
But it worked, the epubcheck now works inside Sigil. (It also works fine from the command line after having to download it separately, so I may just dump the plugin.)
But what a great waste of space! One day if I feel very bored, I'll try the build instructions and get rid of all the flatpak crap...but that looks like a real big job.