Comment 4 for bug 1781540

Continued testing:

I installed the 'original' shellprocess.conf

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$ cat /etc/calamares/modules/shellprocess.conf
dontChroot: true
timeout: 300
script:
  - "cp /cdrom/casper/vmlinuz @@ROOT@@/boot/vmlinuz-$(uname -r)"
  - "[ -d /sys/firmware/efi ] && chroot @@ROOT@@ apt-cdrom add || exit 0"
  - "[ -d /sys/firmware/efi ] && chroot @@ROOT@@ sed -e '/deb http/ s/^#*/#/' -i /etc/apt/sources.list || exit 0"
  - "[ -d /sys/firmware/efi ] && chroot @@ROOT@@ apt update || exit 0"
  - "[ -d /sys/firmware/efi ] && chroot @@ROOT@@ apt -y install grub-efi-amd64-bin || exit 0"
  - "[ -d /sys/firmware/efi ] && chroot @@ROOT@@ sed -i 's/#deb/deb/' /etc/apt/sources.list || exit 0"
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and got the following result (at 78%),

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Error

Installation failed

External command failed to finish.
Command [ -d /sys/firmware/efi ] && chroot /tmp/calamares-root-v75xv4du apt-cdrom add || exit 0 failed to finish in 300 seconds. There was no output from the command.
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