“No key available with this passphrase” whenever I try to boot. (please take on faith that I am typing in the correct passphrase)
Also got a “volume group “luks” not found” message after trying one of the other boot test/options.
What do I do to access the hard drive again?
Do you do backups? If so, you might see whether you can unlock a backup using that passphrase. NB: Not suggesting you restore from backup.
Just putting it out there but if you had any non-ASCII characters (i.e. Unicode characters) in your passphrase then even the correct passphrase might magically suddenly cease working. So is your passphrase pure ASCII?
Thanks.
My passphrase is generated by by typing as usual - it has a couple of numbers and characters using the shift key on the numbers row. If that makes them Unicode then I’ve learned something new.
I’ll try the backup idea and let ou know what happens.
If you mean like !@#$%^&*() then, no, those are pure ASCII, not Unicode. If you have a regular US/UK keyboard then what you can see on the keycaps are pure ASCII and safe for use in a LUKS passphrase. And that particular problem won’t apply.
Non-ASCII is like: any character from a non-Latin script (such as Greek, Cyrillic, Hebrew, Indian, Chinese, Japanese, Korean, Thai, …) and a whole lot of unusual symbols and accented characters (such as ™ © ö ø ½) and a whole lot of other unusual symbols (such as ⇒ → 
) and all the emojis and other random icons (such as 
). (That rebus translates as: Google is a pile of poo I think. 
)