Originally posted by jonr
But I've re-read the manual and GNU website pages several times and can't see where I'm going wrong.
OK, I got the date format to work, and the incremental backup to be just that.
What I needed was a backslash to put a literal space in the date. The manual probably assumes every reader knows that and doesn't mention it. (This kind of assumption is REALLY common...)
So it turns out the date-file creation that works, in the form I wanted it, goes:
LASTFULL=`date +%F\ %T`
Unfortunately (or not), in the process of getting to this point, I also read that it's not recommended to make incremental backups this way! Sometimes certain files are not detected etc.
Back to the drawing board. At least I know how to specify dates for tar now.