I like to use the cheatcode tohd to put the knoppix dvd onto the hard drive. However, I didn't use mkimage when I ran it initially. (I don't know if that would make a difference)
For some reason, using the cheatcode "mkimage" later was ignored.
My boot command line was something like this:
knoppix64 tohd=/dev/sda1
and it dutifully created the KNOPPIX directory on /dev/sda1 but I didn't get a persistent storage file.
One thing that's interesting is that when knoppix boots it automagically scans the drives and finds that KNOPPIX directory even if I don't specify the cheatcode "fromhd=/dev/sda1".
So if you want to create that knoppix-data.img by hand just launch a terminal after booting into your KNOPPIX and
dd if=/dev/zero of=/mnt-system/KNOPPIX/knoppix-data.img bs=1024K count=4000
This will make a 4000MB persistent file (you can make larger if you like) The hard drive that I'm using is formatted FAT32 so my limit is 4GB. Using other formats will have no such restriction.
(And as always, exercise care with dd since you can easily clobber your drives if you enter the wrong parameters. They don't call it disk destroyer for nothing. I've done it once or twice by entering parameters without thinking.)
Then you need to format it
mkfs.ext2 /mnt-system/KNOPPIX/knoppix-data.img
(You may need to use a -F parameter to "force" it to use a regular file, since it normally expects block devices)
(For some reason I thought it had to be reiserfs, but ext2 seems to work. I kept formatting it as reiser and it wouldn't use it)
Also, if you don't like the messages about KNOPPIX-DATA when you boot, there's a file called "knoppix-data.inf" that you can rename. It will mount a persistent PARTITION, and since we're using a persistent FILE, we don't really need it. The error messages don't hurt anything, but if you rename that file, you won't see them anymore. You can always rename it back to the original name.
mv /mnt-system/KNOPPIX/knoppix-data.inf /mnt-system/KNOPPIX/was-knoppix-data.inf
ALLEN BRADLEY 281G-F12S-10B-RRG-CBG /C AMORSTART MODULE 280G-FS-10-RG STK 2911
$332.50
AMD Ryzen 9 5950X 16-core 32-thread Desktop Processor
$319.99
Intel Core i5-8500 Six Core Desktop PC CPU Processor 3.00GHz LGA1151 SR3XE
$49.99
(1) Intel Core i7-4790 3.60GHz - SR1QF - Processor - CPU
$33.00
Intel Core i9-12900KF - 12th Gen Alder Lake 16-Core (8P+8E) 3.2GHz LGA CPU
$262.99
Intel Core i7-4790 3.60GHz Quad Core CPU Processor SR1QF LGA 1150 Socket
$32.99
Intel Core i5-13600KF - 13th Gen Raptor Lake 14-Core (6P+8E) 3.5GHz LGA CPU
$220.99
Intel Core i7-14700KF Unlocked Desktop Processor
$420.22
Intel Core i5-8500 3.00GHz SR3XE Socket 1151 6 Core CPU Processor
$55.00
Intel Xeon E3-1285 V3 3.6 GHz 8M Quad-Core SR14W CPU Processor
$49.50