datasette publish uses hard links to avoid copying the db into a tmp directory. This can fail if /tmp is on another device, because hardlinks can't cross devices. You'll see something like this:

$ datasette publish heroku whatever.db
...
OSError: [Errno 18] Invalid cross-device link: '/mnt/c/Users/jacob/c/datasette/whatever.db' -> '/tmp/tmpvxq2yof6/whatever.db'

[In my case this is failing because I'm on a Windows machine, using WSL, so my code's on a different virtual filesystem from the Linux subsystem, Because Reasons.]

I'm not sure if it's possible to detect this (can you figure out which device /tmp is on?), or what the fallback should be (soft link? copy?).