Ah… the sheer fun of linux. Found a recommended command to back up the header in my luks encrypted boot disk. All well and good.
[cryptsetup luksHeaderBackup UUID=xyz –header-backup-file /mnt/backup/file.img is what finally worked if you’re interested. Must be root!]
But the original id in the command was by /dev/device. Good, as far as it goes if you already know the device, but my distro doesn’t boot by device. Took a while to find it boots by UUID. If you know how to look you can find that in grub.cfg. Only took me seven hours. I’m old and slow I guess.
Wonder how long it will take to do a restore if I need it?