Ask Klaus

UEFI Boot Problems

I just bought a new Lenovo Notebook, and I'm trying to start Knoppix from USB flash disk. Knoppix seems to start to a certain point, but then I get no graphics, just a black screen. None of the cheatcodes seem to help. What happens, how to fix?

With the recent versions, Knoppix supports booting on UEFI-enabled computers. However, the graphics card in UEFI boot mode is set to a VESA graphics mode by the firmware, not to "text mode" as known for non-UEFI systems. A visible indication of this is the missing boot logo and the fact that after the kernel has loaded, the usual text messages that indicate progress during the Knoppix boot are missing until the mode setting kicks in and resets the screen resolution. Because the graphics chipset had been in a VESA mode previously, the X server can fail to set the native resolution; hence, the "black screen" or system freeze effect that you observed.

The only workaround I found so far is disabling UEFI and reverting to Legacy or CSM (compatibility support module) boot mode, which re-enables text mode for the bootloader and puts the graphics card in a default mode that lets Xorg start normally. Some notebooks, especially MacBooks with DVD drives, do not boot in UEFI mode automatically when selecting to boot from CD or DVD. For this purpose, the Knoppix "boot-only" CD is useful. An ISO for the CD resides in the KNOPPIX folder. The boot-only CD starts the bootloader and kernel from the CD, then searches for other drives that contain the KNOPPIX folder (e.g., a USB flash disk), and continues booting from there.

Joining PDFs

Is there a simple way to concatenate several hundred PDF files into a single, continuous PDF under Linux?

The easiest way that requires no special program is using the PostScript/PDF interpreter Ghostscript directly. The original command line is somewhat lengthy, so I usually put this in a script (e.g., pdfcat.sh):

#!/bin/bash
gs -q -sPAPERSIZE=a4 -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=- "$@"

If you need a different paper size than A4 (e.g., letter), change the PAPERSIZE option accordingly.

The syntax for concatenating all files in a directory is:

pdfcat.sh directory/*.pdf > all.pdf