bootfrom=/.//iso/ADRIANE-KNOPPIX_....
This cannot work. Did you try
bootfrom=/dev/sdb1/mnt-iso/iso/ADRIANE-KNOPPIX_...
bootfrom=/.//iso/ADRIANE-KNOPPIX_....
This cannot work. Did you try
bootfrom=/dev/sdb1/mnt-iso/iso/ADRIANE-KNOPPIX_...
Thank you, Werner, but I not always boot from sdb1. The line that I posted works fine, but I want to share with you all what I found out. The speed of the search for the iso is notably increased (and thus the boot time is greatly decreased) if I press the [CONTROL] key when it is performed. I don't know whay, but it works for me. So, this is an important update about this issue. Best regards.

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