From: Henrik.Carlqvist@deadspam.com   
      
   On Fri, 07 Mar 2025 20:54:21 +0100, Marco Moock wrote:   
   > Does anybody have an idea what is going wrong and if that is an issue in   
   > VirtualBox or in Slackware/GRUB?   
      
   No, I have never booted Slackware 15.0 with GRUB and I have never used   
   VirtualBox.   
      
   However, if it would be to any use for you I have successfully booted   
   Slackware 15.0 in EFI mode both on pysical hardware and on virtual   
   machines run in qemu. Instead of GRUB I use syslinux/extlinux but I do   
   not use syslinux 4.07 which is shipped with Slackware, instead I use   
   Syslinux version 6.03. I have used the same method also on earlier   
   version 14.2 of Slackware.   
      
   Unfortunately my Slackware installation is heavily customized, I have   
   modified the installation initrd startup and installation scripts to   
   automagically create all partitions needed before starting an   
   installation with a minimal number of questions.   
      
   On the first version of Slackware where I applied this boot method I did   
   not have the automated custimization of the partitioning, then I simply   
   manually created a GPT partition table with all the partitions I wanted   
   including an EFI partition which I mounted below /boot/efi. I then had a   
   package containing an installation script and the needed syslinux files:   
      
   drwxr-xr-x root/root         0 2021-01-14 12:45 ./   
   drwxr-xr-x root/root         0 2020-09-30 22:45 boot/   
   drwxr-xr-x root/root         0 1970-01-01 01:00 boot/efi/   
   drwxr-xr-x root/root         0 2021-01-14 12:35 boot/efi/EFI/   
   drwxr-xr-x root/root         0 2023-03-29 12:23 boot/efi/EFI/Boot/   
   -rwxr-xr-x root/root    199952 2020-09-30 21:31 boot/efi/EFI/Boot/   
   bootx64.efi   
   -rwxr-xr-x root/root    139968 2020-09-30 21:31 boot/efi/EFI/Boot/   
   ldlinux.e64   
   -rwxr-xr-x root/root       256 2023-03-29 12:23 boot/efi/EFI/Boot/   
   syslinux.cfg   
   drwxr-xr-x root/root         0 2023-03-29 12:22 install/   
   -rw-r--r-- root/root       494 2023-03-29 12:21 install/doinst.sh   
      
   The files bootx64.efi and ldlinux.e64 are from Syslinux 6.03.   
      
   The installation script doinst.sh contains the following:   
      
   -8<----------------------------------------------------------   
   #!/bin/sh   
      
   if [ -f /var/log/setup/tmp/SeTrootdev ]; then   
     rootpart=`cat /var/log/setup/tmp/SeTrootdev`   
   else   
     rootpart=`grep "/ " etc/fstab | awk '{print $1}'`   
   fi   
   bootdev=`grep boot etc/lilo.conf | grep dev | awk '{print $NF}'`   
   echo "  APPEND root=$rootpart rdinit=ro intel_pstate=disable" >>  boot/   
   efi/EFI/Boot/syslinux.cfg   
   ./usr/sbin/efibootmgr -c -d $bootdev -p 3 -l \\EFI\\Boot\\bootx64.efi -L   
   "Syslinux"   
   # Make sure that kernel is up-to-date   
   cp -p boot/vmlinuz boot/efi/EFI/Boot/vmlinuz   
   -8<----------------------------------------------------------   
      
   The above script assumes that my custom installation has made an attempt   
   to configure a lilo.conf which will not be used. This is to find the boot   
   disk which typically is called something like /dev/sda or /dev/nvme0n1.   
   The script adds a line pointing to the right root partition to   
   syslinux.cfg before calling efibootmgr to point the UEFI BIOS to the boot   
   disk and syslinux bootx64.efi file.   
      
   Before being modified the syslinux.cfg file looks like this:   
      
   -8<----------------------------------------------------------   
   PROMPT 0   
   TIMEOut 100   
   DEFAULT Slackware 15.0   
      
   LABEL Slackware 15.0   
     MENU LABEL Slackware 15.0   
     LINUX vmlinuz   
   # example of what needs to get added to this file:   
   #  APPEND root=/dev/nvme0n1p2 rdinit=ro pci=nommconf   
   # Such a line will be added by doinst.sh   
   -8<----------------------------------------------------------   
      
   So this did not answer your question upon how to install GRUB which I   
   have avoided myself. I am aware that syslinux is considered abandonware,   
   but it still works for me and I find the synax of syslinux rather   
   familiar. I have during the years used configuration files with such   
   syntax not only to boot UEFI systems but also to boot optical media and   
   PXE network booting.   
      
   regards Henrik   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)