Without paying attention, I restored wallet.dat from a backup with poor metadata preservation and left it root:root, effectively doing:
chown root:root ~/.bitcoin/wallet.dat
Starting bitcoind yielded the somewhat misleading:
Error: Error initializing database environment /home/zak/.bitcoin! To recover, BACKUP THAT DIRECTORY, then remove everything from it except for wallet.dat
Not the end of the world suggesting the user re-download the blockchain, but it won't actually help here.